MNRAS 504, 4907–4922 (2021) doi:10.1093/mnras/stab1009
Advance Access publication 2021 April 13
The double-peaked Type Ic supernova 2019cad: another SN 2005bf-like
object
C. P. Gutie´rrez ,1,2,3‹ M. C. Bersten,4,5,6 M. Orellana,7,8 A. Pastorello,9 K. Ertini,4,5 G. Folatelli,4,5,6
G. Pignata,10,11 J. P. Anderson,12,11 S. Smartt,13 M. Sullivan ,3 M. Pursiainen ,3,14 C. Inserra ,15
N. Elias-Rosa,9,16 M. Fraser ,17 E. Kankare,2 S. Moran,2 A. Reguitti,10,11,9 T. M. Reynolds,2
M. Stritzinger,18 J. Burke,19,20 C. Frohmaier ,21 L. Galbany ,22 D. Hiramatsu,19,20 D. A. Howell,19,20
H. Kuncarayakti,1,2 S. Mattila,2 T. Mu¨ller-Bravo ,3 C. Pellegrino19,20 and M. Smith 23
Affiliations are listed at the end of the paper
Accepted 2021 April 6. Received 2021 April 6; in original form 2021 February 6
ABSTRACT
We present the photometric and spectroscopic evolution of supernova (SN) 2019cad during the first ∼100 d from explosion.
Based on the light-curve morphology, we find that SN 2019cad resembles the double-peaked Type Ib/c SN 2005bf and the Type
Ic PTF11mnb. Unlike those two objects, SN 2019cad also shows the initial peak in the redder bands. Inspection of the g-band
light curve indicates the initial peak is reached in ∼8 d, while the r-band peak occurred ∼15 d post-explosion. A second and
more prominent peak is reached in all bands at ∼45 d past explosion, followed by a fast decline from ∼60 d. During the first
30 d, the spectra of SN 2019cad show the typical features of a Type Ic SN, however, after 40 d, a blue continuum with prominent
lines of Si II λ6355 and C II λ6580 is observed again. Comparing the bolometric light curve to hydrodynamical models, we
find that SN 2019cad is consistent with a pre-SN mass of 11 M, and an explosion energy of 3.5 × 1051 erg. The light-curve
morphology can be reproduced either by a double-peaked 56Ni distribution with an external component of 0.041 M, and an
internal component of 0.3 M or a double-peaked 56Ni distribution plus magnetar model (P ∼ 11 ms and B ∼ 26 × 1014 G). If
SN 2019cad were to suffer from significant host reddening (which cannot be ruled out), the 56Ni model would require extreme
values, while the magnetar model would still be feasible.
Key words: supernovae: general – supernovae: individual: SN 2019cad.
1 IN T RO D U C T I O N
Core-collapse supernovae (SNe) are produced by the explosion of
massive stars (MZAMS > 8–10 M). They are traditionally classified
into different classes depending on the presence or absence of certain
lines. SNe from collapsing stars that do not show hydrogen but show
helium in their spectra are classified as Type Ib SNe (SNe Ib), while
those with no hydrogen or helium are classified as Ic SNe (SNe Ic; e.g.
Filippenko 1997; Gal-Yam 2017; Modjaz, Gutie´rrez & Arcavi 2019).
The absence of these spectral lines implies their progenitor stars
shed their hydrogen- and helium-rich envelops over their lifetimes,
mainly due to strong stellar winds (Heger et al. 2003; Georgy et al.
2009) or binary interaction (e.g. Podsiadlowski, Joss & Hsu 1992;
Nomoto, Iwamoto & Suzuki 1995; Eldridge, Izzard & Tout 2008).
While both mechanisms are successful in explaining the absence of
the hydrogen layer, removing the helium layer is still a challenge as
it is found in denser parts of the star. Given these complications, it
has been proposed that some helium is possibly present in SNe Ic
but it is not seen in the spectrum because it is not excited (Dessart
et al. 2012, but see Williamson, Kerzendorf & Modjaz 2021). On the
other hand, recent observational evidence, such as the low progenitor
 E-mail: claudia.gutierrez@utu.fi
masses inferred for SNe Ic from their light curves (Drout et al. 2011;
Lyman et al. 2016; Taddia et al. 2018b) and the relative SN Ic rate
(Smith et al. 2011), favours the binary scenario.
The direct identification of stars in pre-explosion images can give
more insights about the nature of the SN progenitor (e.g. Van Dyk
et al. 2002; Van Dyk, Li & Filippenko 2003; Mattila et al. 2008;
Smartt et al. 2009; Van Dyk 2017). However, for hydrogen-free
objects only a couple of cases exist: a confirmed progenitor for the
SN Ib iPFT13bvn (Cao et al. 2013; Folatelli et al. 2016) and two
progenitor candidates, one for the Type Ic SN 2017ein (Kilpatrick
et al. 2018; Van Dyk et al. 2018; Xiang et al. 2019) and another one
for the Type Ib SN 2019yvr (Kilpatrick et al. 2021). If post-explosion
images confirm the progenitor association, then it would represent
the first progenitor detection for an SN Ic and the second for an SN Ib.
SNe Ic are the most intriguing objects among core-collapse events.
They represent a heterogeneous class showing a large range in
luminosity and light-curve shapes (e.g. Bianco et al. 2014; Lyman
et al. 2016; Prentice et al. 2016; Taddia et al. 2018b), as well as diverse
spectra (e.g. Matheson et al. 2001; Modjaz et al. 2014; Shivvers
et al. 2019). A small fraction of SNe Ic have been observed with
broad absorption lines that have been associated with long-duration
gamma-ray bursts (GRBs; Woosley & Bloom 2006; Cano et al.
2017). These objects, usually labelled as broad-line SNe Ic (SNe Ic-
C© 2021 The Author(s)
Published by Oxford University Press on behalf of Royal Astronomical Society
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BL), represent a challenge in our understanding of the explosion
mechanism and final steps of massive-star evolution. Fortunately,
high-cadence surveys are detecting and following up more objects of
this type allowing their characterization and physical understanding.
Stripped-envelope SNe, considered as hydrogen-deficient objects,
usually present bell-shaped light curves, with a single peak reached
a couple of weeks after explosion. These light curves are powered by
the decay of 56Ni to 56Co, and then to 56Fe. Some stripped-envelope
SNe with a well-constrained explosion date and good photometric
cadence have shown early emission prior to the usual nickel peak.
When it is observed, this initial peak lasts a few days and has been
attributed to the cooling of the ejecta after the shock breakout (e.g.
Woosley et al. 1994; Bersten et al. 2012; Nakar & Piro 2014), while
the second peak has a duration of a couple of weeks and is mainly
powered by the decay of 56Ni. There are now many cases where the
SN was observed before the nickel peak (see Modjaz et al. 2019,
and references therein), but most of them were classified as SN IIb
(transitional objects between SNe II and SNe Ib) and the emission
can be well explained as due to the cooling of a thin but extended
hydrogen envelope. In the other known cases, they showed some
peculiarities, as was the case of the Type Ib SN 2008D associated
with an X-ray flash (Mazzali et al. 2008; Soderberg et al. 2008), or
the cases of the SNe Ic SN 2006aj (Campana et al. 2006) and more
recently SN 2017iuk (Izzo et al. 2019) associated with long-duration
GRBs (i.e. SN Ic-BL). In these cases, the early emission is harder to
explain due to the cooling of an envelope and because of the compact
nature of their progenitor. Some alternatives, such as the presence of
circumstellar material, the cooling of a cocoon jet or some external
nickel seem to be required (Soderberg et al. 2008; Bersten et al. 2013).
Unlike the early emission discussed above, which lasts for a
few days, there are two objects in the literature where the early
emission is longer in duration, appearing as a peak at around 20 d
from the explosion, followed by a main peak occurring at ∼40 d
from the explosion. These objects are SN 2005bf (Anupama et al.
2005; Tominaga et al. 2005; Folatelli et al. 2006) and PTF11mnb
(Taddia et al. 2018a). SN 2005bf was classified as a transitional object
between SNe Ic and SNe Ib (Folatelli et al. 2006), while PTF11mnb
was catalogued as a typical SN Ic. Anupama et al. (2005) claimed
that SN 2005bf was the explosion of a massive He star with some
H left. Tominaga et al. (2005) concluded that the progenitor was
a Wolf–Rayet WN star and the morphology of the light curve can
be reproduced by a double-peaked 56Ni distribution. Folatelli et al.
(2006) found that the most favoured model is consistent with an
energetic and asymmetric explosion of a massive WN star, where an
unobserved relativistic jet was launched producing a two-component
explosion. Finally, through analysing late-phase spectroscopy and
photometry of SN 2005bf, Maeda et al. (2007) suggested that the
power source of this SN is a magnetar. On the other hand, for
PTF11mnb, Taddia et al. (2018a) suggested that the progenitor was a
massive single star with a double-peaked 56Ni distribution powering
the SN light curve.
In this paper, we present photometry and spectra of a peculiar
event, the Type Ic SN 2019cad. We discuss its observed properties
and compare it with SN 2005bf and PTF11mnb. The paper is
organized as follows. A description of the observations and data
reduction are presented in Section 2. In Section 3, we describe the
photometric and spectral properties of SN 2019cad and a comparison
with similar events. The progenitor properties are analysed through
hydrodynamic modelling in Section 4, while in Section 5 we present
the discussion and conclusions. Throughout, we assume a flat CDM
universe, with a Hubble constant of H0 = 70 km s−1 Mpc−1, and
m = 0.3.
2 O B S E RVAT I O N S O F S N 2 0 1 9 C A D
SN 2019cad (also known as ZTF19aamsetj and ATLAS19ecc) was
discovered by the Zwicky Transient Facility (ZTF; Bellm et al. 2019;
Graham et al. 2019) on 2019 March 17 (MJD = 58559.24) at a
magnitude of mr = 19.02 ± 0.11 mag (Nordin et al. 2019). The last
non-detection obtained by ZTF occurred on 2019 March 16 (MJD
= 58558.19) with a detection limit of mr ∼ 19.183 mag. A deeper
early detection and a non-detection were obtained by the Asteroid
Terrestrial-impact Last Alert System (ATLAS; Tonry et al. 2018;
Smith et al. 2020) on 2019 March 12 (MJD = 58554.42; mo =
19.91 ± 0.11 mag) and 2019 March 4 (MJD = 58546.46; mo =
20.50 mag), respectively. These new constraints allow us to adopt
the mid-point between the last non-detection and first detection as
the explosion epoch (MJD = 58550.44 ± 4 (2019 March 8).
On 2019 March 22 (MJD = 58564.36), SN 2019cad was observed
spectroscopically by the Global SN Project (GSP) and classified as
an SN Ic around maximum light at a redshift z = 0.0267 (Burke
et al. 2019). In the classification report, Burke et al. (2019) noted
the object was slightly faint (i.e. Mr ∼ −16.6 mag) compared what
is typically observed in SNe Ic. 20 d after the classification, the r-
band ZTF light curve showed a rebrightening, which was confirmed
5 d later in the g band. Because of this rebrightening, we started a
follow-up campaign the details of which are now described.
2.1 Photometry
Photometric coverage of SN 2019cad was acquired using different
facilities and instruments over a period of 14 weeks as follows:
(i) ATLAS: Photometry in the orange (o) filter (a red filter that
covers a wavelength range of 5600 to 8200 Å) and cyan (c) filter
(wavelength range 4200 to 6500 Å) was obtained by the twin 0.5 m
ATLAS telescope system (Tonry et al. 2018), spanning from 2019
March 11 to 2019 May 30. The data were reduced and calibrated
automatically as described in Tonry et al. (2018) and Smith et al.
(2020). Table A1 lists the mean magnitudes.
(ii) Gran Telescopio Canarias: One epoch of r-band photometry
was obtained with the 10.4-m Gran Telescopio Canarias (GTC) using
OSIRIS. The r-image was reduced with IRAF following standard
procedures. The photometry was performed using the PYTHON
package PHOTUTILS (Bradley et al. 2019) of ASTROPY (Astropy
Collaboration 2018). The r magnitude was calibrated using Pan-
STARRS (Chambers et al. 2016; Magnier et al. 2020).
(iii) Las Cumbres Observatory: Multiband photometry was
obtained with the 1.0-m telescopes of Las Cumbres Observatory
(Brown et al. 2013) at three different epochs through the Global
Supernova Project (GSP). The data reduction and SN photometry
measurements were performed following the prescriptions described
in Firth et al. (2015).
(iv) Liverpool Telescope: Five epochs of ugriz were obtained with
the 2-m Liverpool Telescope (LT; Steele et al. 2004) using the IO:O
imager. LT data were reduced using the standard IO:O pipeline. The
photometry was performed using PHOTUTILS. The ugriz magnitudes
were calibrated using Pan-STARRS sequences.
(v) Nordic Optical Telescope: Using the 2.56-m Nordic Optical
Telescope (NOT) at Roque de los Muchachos Observatory, we
obtained six epochs of ugriz photometry from April 23 to June 19,
and three epochs of JHK photometry from April 30 to June 13. The
optical observations were performed with ALFOSC, and the near-
infrared (NIR) observations with NOTCam. All NOT observations
were obtained through the NOT Unbiased Transient Survey (NUTS)
allocated time. Optical and NIR data reduction and SN photometry
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SN 2019cad: another SN 2005bf-like object 4909
measurements were performed using the PYTHON/PYRAF SNOOPY
pipeline (Cappellaro 2014). The ugriz magnitudes were calibrated
using observations of local Sloan and Pan-STARRS sequences, while
the JHK magnitudes were calibrated using 2MASS (Skrutskie et al.
2006).
(vi) Neil Gehrels Swift Observatory: One epoch of UltraVio-
let (UV) Optical observations were obtained with the UltraVio-
let/Optical Telescope (UVOT) on board the Swift spacecraft. Imaging
observations were processed with aperture photometry following
Brown et al. (2009). No template subtractions were achieved.
(vii) William Herschel Telescope: One epoch of gr photometry
was obtained with ACAM in the William Herschel Telescope (WHT)
on 2019 June 20. The images were reduced with IRAF following
standard procedures, while the photometry was performed using
PHOTUTILS. The gr magnitudes were calibrated using Pan-STARRS.
Optical, NIR, and UVOT photometry are presented in Tables A2,
A3, and A4, respectively. Additional photometry in the gr bands
was obtained from the ZTF public stream through the Lasair1 broker
(Smith et al. 2019) and presented in Table A5.
2.2 Spectroscopy
SN 2019cad was observed spectroscopically at 12 epochs spanning
phases between 13.6 to 88.1 d past explosion. These observations
were acquired with five different instruments: ALFOSC at the NOT,
SPRAT (Piascik et al. 2014) at the LT, the FLOYDS spectrograph
(Brown et al. 2013) on the Faulkes Telescope South (FTS), OSIRIS
at the GTC, and with the Spectral Energy Distribution Machine
(SEDM; Blagorodnova et al. 2018) on the automated 60-in telescope
at Palomar Observatory (P60; Cenko et al. 2006).2 The log of
spectroscopic observations of SN 2019cad is presented in Table A6.
Data reductions for ALFOSC and OSIRIS were performed follow-
ing standard routines in IRAF. The SPRAT data were reduced using the
Fast and Dark Side of Transient experiment Fast extraction pipeline
(FDSTfast).3 FLOYDS spectra were reduced using the PYRAF-based
FLOYDS PIPELINE4 (Valenti et al. 2014), while the public SEDM
spectrum was automatically reduced by the IFU data reduction
pipeline (Rigault et al. 2019). All spectra are available via the
WISeREP5 repository (Yaron & Gal-Yam 2012).
3 C H A R AC T E R I Z I N G SN 2 0 1 9 C A D
3.1 Host galaxy
The host galaxy of SN 2019cad was identified as UGC 4798, a spiral
galaxy at a redshift of 0.0267 (de Vaucouleurs et al. 1991).6 Adopting
the recessional velocity corrected for Local Group infall into Virgo
reported by HyperLEDA7 (Makarov et al. 2014; vvir = 8152 ± 3 km
s−1), we obtain a distance modulus μ = 35.38 ± 0.13 mag, which is
equivalent to a distance of 119.2 ± 8.4 Mpc.
SN 2019cad was located 3.′′6 east and 7.′′6 north from the galaxy
centre. Its host has been classified as a H I-rich galaxy (Wang et al.
1https://lasair.roe.ac.uk/
2Public spectrum obtained from the TNS webpage: https://wis-tns.weizma
nn.ac.il/object/2019cad.
3https://github.com/cinserra/FDST
4https://github.com/LCOGT/floyds pipeline
5https://wiserep.weizmann.ac.il/
6http://ned.ipac.caltech.edu/
7http://leda.univ-lyon1.fr
Figure 1. NOT r-band image of SN 2019cad and its host galaxy. SN 2019cad
is marked with a red crosshair. The locations of SN 2005mf (Ic), SN 2013V
(Ia), and SNHunt263 (Ia) are marked in blue, green, and magenta circles,
respectively. The orientation of the image is indicated in the bottom-right
corner.
2013) with a stellar mass of log10(M∗) = 10.59 M (Chen et al. 2012)
and a star formation rate (SFR) of 1.97 ± 0.01 Myr−1 (Cormier
et al. 2016). SN 2019cad is the fourth SN reported in UGC 4798.
SN 2005mf was detected at 5.′′9 west and 13.′′3 north from the galaxy
centre (Bian et al. 2005), SN 2013V was found at 11.′′5 west and
11.′′1 north of the centre of the galaxy (Crowley et al. 2013), while
SNHunt263 was detected at 1.′′ west and 25.′′ south of the centre of
the galaxy (Drake et al. 2009). SN 2005mf was classified as an SN Ic
(Modjaz et al. 2005), while SN 2013V and SNHunt263 as SNe Ia
(Tomasella et al. 2013; Elias-Rosa et al. 2014). All these SNe have
been located at projected distances larger than 4.5 kpc from the centre
of the galaxy, see Fig. 1. The substantial number of SNe detected in
UGC 4798 in the last 15 yr is not rare. Previous studies (e.g. Tho¨ne
et al. 2009; Anderson & Soto 2013) have shown that several galaxies
have been hosted multiple SNe. Most of these galaxies have a high
SFR. However, for NGC 2770, the high number of SNe Ib was found
by Tho¨ne et al. (2009) to be a coincidence.
To estimate the oxygen abundance of UGC 4798, we use the public
spectrum of the central region of the galaxy obtained from the Sloan
Digital Sky Survey (SDSS; Ahumada et al. 2020). Applying the
O3N2 diagnostic method from Pettini & Pagel (2004), we obtain an
oxygen abundance of 12 + log (O/H) = 8.72 ± 0.08. Employing the
same method, Modjaz et al. (2011) reported an oxygen abundance at
the position of SN 2005mf of 12 + log (O/H) = 8.66 ± 0.09, which
is around the solar abundance (e.g. Pettini & Pagel 2004). Based on
the small differences in these two estimations, we suggest the oxygen
abundance near SN 2019cad to be around solar.
3.2 Extinction estimation
To determine the intrinsic properties of SN 2019cad, an estimation
of the total reddening (from both the Milky Way and the host galaxy)
along the line of sight to the object is needed. The galactic reddening
was found to be E(B − V)MW = 0.015 mag (Schlafly & Finkbeiner
2011). To calculate the host galaxy extinction, we searched for the
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Na I D absorption lines in the SN spectra. A narrow Na I D line at
the host galaxy rest wavelength is clearly detected in the NOT
spectra, with an equivalent width (EW) of ∼1.32 Å. This strong
absorption suggests a significant reddening from the host galaxy.
Using the relations of E(B − V) and EW(Na I D) found by Turatto,
Benetti & Cappellaro (2003) from low and heavily reddened SNe Ia,
we obtain two values: E(B − V)Host = 0.21 and 0.63 mag. Applying
the empirical relation from Poznanski, Prochaska & Bloom (2012),
we find an E(B − V)Host = 0.49 ± 0.08 mag. Unfortunately, there
are large discrepancies in these estimations, which is likely caused
by the fact that the lines have saturated (Munari & Zwitter 1997;
Poznanski et al. 2011). Therefore, we explored alternative methods
to determine the host extinction.
Constraints on the host extinction can be also found using the
colour of the SN around the maximum (Drout et al. 2011; Taddia
et al. 2015; Stritzinger et al. 2018). Drout et al. (2011) found that
in SNe Ibc the V − R colour at 10 d from the V-band maximum
shows very small scatter, varying between 0.18 and 0.34 mag. Later,
Stritzinger et al. (2018), following a similar approach, but using a
range of optical or optical/NIR colour combinations, built intrinsic
colour-curve templates, which we can use to measure the colour
excess. By comparing the SN 2019cad g − r and r − i colours with
the templates from Stritzinger et al. (2018), we found an excess in r
− i that corresponds to E(B − V) ∼ 0.22 mag, however, the g − r
colours were found to be bluer than the template (see Fig. 2, middle
panel). Because of the inconsistency in the colours (excess in r − i,
but deficit in g − r), this method is not applicable in this SN, which
could have been expected from its peculiar evolution.
Another method to estimate the host reddening is to derive the
Balmer decrement from an H II region that we assume is sharing
the same extinction of the SN along the line of sight. In the latest
spectrum of SN 2019cad, a weak emission from H α and H β is
detectable. To measure the flux of latter emission lines, we remove
the SN flux following the procedure presented in Pignata et al. (2011).
We stress the fact that due to the very low signal-to-noise ratio of
H β (∼2.0), the measurement of its flux is very uncertain, therefore
we consider its minimum and maximum flux to obtain an estimation
of the maximum (E(B − V) = 0.80 mag) and minimum (E(B −
V) = 0.28 mag) colour excess along the line of sight of SN 2019cad.
Even though with large uncertainties, such values provide additional
evidence that SN 2019cad is highly reddened.
The reddening estimation is one of the largest systematic uncer-
tainties in the SN field. As we have shown above, large differences
are found using different methods. The methods used were obtained
for normal core-collapse SNe, and even in these cases it is not
clear which methods are robust, if any. The situation is even worse
for peculiar events as SN 20019cad. Therefore, we decided not to
consider host galaxy extinction in the rest of this paper, but we
explore in Section 3.7 and Section 5 the implications of a larger host
galaxy reddening (E(B − V)Host = 0.49 mag, the median of these
estimations and the value obtained with the most recent empirical
relation of E(B − V) and EW(Na I D)).
3.3 Light curves
The multiband light curves of SN 2019cad are shown in Fig. 2
(top panel). SN 2019cad presents an unusual light-curve evolution
characterized by the presence of an initial peak between 10 and 20 d
from explosion, followed by the main peak at ∼45 d. This double-
peaked light curve resembles those of the peculiar Type Ic SN 2005bf
(Folatelli et al. 2006) and PTF11mnb (Taddia et al. 2018a).
Figure 2. Upper panel: Optical light curves of SN 2019cad. ATLAS
photometry is presented as circles, ZTF photometry as stars, NOT photometry
as crosses, LT photometry as pluses, Las Cumbres photometry as pentagons,
NOTCam photometry as up-facing triangles, GTC photometry as squares,
WHT photometry as hexagons, and Swift photometry as right-facing trian-
gles. Upper limits are presented as open symbols. The explosion estimation is
indicated as a vertical black arrow. The vertical lime-green arrows represent
epochs of optical spectroscopy. The photometry is corrected for Milky Way
extinction. The solid lines show the Gaussian process (GP) interpolation.
Middle panel: Colour curves of SN 2019cad. Only corrections for Milky
Way extinction have been made. Solid lines (purple and green) show the
intrinsic colour-curves templates (g − r and r − i) from Stritzinger et al.
(2018). Bottom panel: Bolometric light curve of SN 2019cad assuming an
E(B − V)Host = 0.0 mag (stars) and E(B − V)Host = 0.49 mag (dashed line).
To estimate the main parameters of the light curves, we use
Gaussian processes (GPs). Following Gutie´rrez et al. (2020), we
perform the light curve interpolation with the PYTHON package
GEORGE (Ambikasaran et al. 2015) using the Matern 3/2 kernel.
We find that SN 2019cad reaches an initial peak absolute g-band
magnitude of Mg = −16.35 mag in ∼8 d. In the r and o bands, the
initial peak is Mr = −16.68 mag and Mo = −16.86 mag at ∼15 and
∼18.9 d, respectively. After this peak, the light curves in the o and
r bands show a small decrease in brightness (between ∼0.2 and 0.4
mag in ∼10 d), while the g band decreases more than 1 mag in the
same period (∼13 d). Following this initial peak, a rise of 1.5–3
mag is observed in all bands. The peak in groi occurs at ∼43.9,
44.3, 41.5, and 44.9 d with magnitudes of Mmaxg = −17.83 mag,
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SN 2019cad: another SN 2005bf-like object 4911
Table 1. Light-curve parameters of SN 2019cad assuming an E(B − V)Host = 0 mag.
Band Initial peak Epoch Main peak Epoch Change in magnitude Decline rate
magnitude (d) magnitude (d) from the main peak to after 60 d
(mag) (mag) 20 d post-peak (mag) (mag per 100 d)
g −16.35 8 −17.83 43.9 2.20 7.10 ± 0.21
r −16.68 15 −18.10 44.3 1.71 5.91 ± 0.25
o −16.86 18.9 −18.07 41.5 1.50 5.33 ± 1.12
i – – −18.26 44.9 1.67 5.83 ± 0.10
Mmaxr = −18.10 mag, Mmaxo = −18.07 mag, and Mmaxi = −18.26
mag. Once SN 2019cad has reached the main peak, the light curves
decrease by 2.20 (g), 1.71 (r), 1.67 (i), 1.50 (o), and 1.45 (z) mag in
∼20 d. Table 1 shows a summary of the light-curve parameters.
From 60 to 100 d, the light curve shows a linear decline in griz. The
slope of the decline in all bands is faster than the expected from the
full trapping of gamma-ray photons and positrons from the decay of
56Co (0.98 mag per 100 d; Woosley, Hartmann & Pinto 1989). Fitting
a line to the tail, we measure a slope of 7.10 ± 0.21 mag (100d)−1 in
the g band and 5.91 ± 0.25 mag (100d)−1 in the r band. To guarantee
that we use luminosities when the light curve has entered the nebular
phase, we follow the prescriptions of Meza & Anderson (2020) and
we fit a line to the tail from 75 to 100 d. Thus, we derive a slope of
6.54 ± 0.31 mag (100d)−1 in g and 6.00 ± 0.21 mag (100d)−1 in
r. Taddia et al. (2018b) found that the linear decay slope for SNe Ic
is between 1.7 and 2.7 mag (100d)−1. These declines are faster than
the expected from the 56Co decay, but slower than those measured in
SN 2019cad. If the radioactive decay powers the light curve, then the
extremely fast decline suggests a significant leakage of gamma-ray
photons which can, for example, be achieved assuming a low-mass
ejecta.
The colour curves of SN 2019cad are presented in the middle panel
of Fig. 2. During the first 20 d, SN 2019cad becomes redder, going
from a colour of g − r = 0.27 mag at 8.6 d to g − r = 1.53 mag
at 20.1 d. At around 20 d, the g − r colour shows a maximum that
corresponds to the initial peak in the optical light curves. After this
peak, the SN evolves to bluer colours, reaching a minimum of g −
r = 0.24 mag at ∼44 d. This g − r minimum matches with the main
peak of the light curves. From 43 to 100 d, the SN slowly becomes
redder again. A similar but less intense colour evolution is observed
in r − i and i − z.
3.4 Bolometric luminosity
Using the groiz photometry, we build a pseudo-bolometric light curve
for SN 2019cad. First, we interpolated the observed magnitudes using
GPs to have the groiz light curves with similar coverage at the same
epochs. Then, extinction-corrected (only galactic extinction) groiz
magnitudes were converted into fluxes at the effective wavelength
of the corresponding filters. Next, we integrated a spectral energy
distribution (SED) over the wavelengths covered, assuming zero flux
beyond the integration limits. Fluxes were converted to luminosity
using the distance adopted in Section 1. To estimate the full
bolometric light curve, we extrapolated the SED constructed from
the groiz. In the UV, we did a linear extrapolation to zero flux at 3000
Å. On the NIR side, the fluxes were extrapolated using a blackbody
fit to the SED. This way to extrapolate to UV and NIR has been
extensively used in the literature (e.g. Folatelli et al. 2006). The full
bolometric light curve of SN 2019cad for E(B − V)Host = 0.0 mag (red
crosses) and E(B − V)Host = 0.49 mag (dashed line) is presented in
the bottom panel of Fig. 2. As seen, the limited photometric coverage
at early and late times gives us larger uncertainties during the initial
peak as well as a slightly increase in luminosity after 100 d.
To estimate the luminosity of the initial and main peak, together
with the slope of the tail, we use GPs. For the bolometric light curve
assuming E(B − V) = 0.0 mag, we find a main peak luminosity
of Lbol = 5.1 × 1042 erg s−1 occurring at 43.6 d. The initial peak
happens at 23 d at a luminosity of 1.7 × 1041 erg s−1. After ∼60 d, the
bolometric light curve declines at a rate of 5.75 mag per 100 d. These
values are much higher than that expected from the 56Co decay, but
they are comparable to those obtained for the redder filters in the
optical light curves.
3.5 Spectral evolution
Fig. 3 shows the optical spectra of SN 2019cad from 13.6 to 88.1 d
past explosion. The first four spectra obtained during the initial peak
(before 30 d) display the typical features of an SN Ic (identifications
confirmed by the SYNOW (Fisher 2000) fits; see below). At this early
phase, the spectra are dominated by strong O I λ7774, Ca II (H&K and
NIR triplet) and Fe II lines (around 5000 Å). Si II λ6355 and Na I D
are also visible, together with a weak absorption of C II λ6580 and
λ7235. From 13.6 to 22.3 d, the bluer part of the spectra diminishes
due to Fe II line-blanketing, Si II λ6355 becomes weak, and C II λ6580
completely disappears.
From 40 d past explosion, the spectra of SN 2019cad show a
remarkable transformation, which coincides with the main light-
curve peak. At 45 d, the spectrum is anew characterized by a blue
continuum with weak features of Ca II (H&K and NIR triplet), Na I D,
and Fe II. O I λ7774 is now the strongest feature in the spectrum. Si II
λ6355, C II λ6580, and λ7235 are visible again after almost complete
disappearance at 22.3 d. At 50 d, C II λ6580 and λ7235 become
weaker and are undetectable at 53 d. In the same period, the bluer
part of the spectra shows three absorption features that correspond to
Fe II λλλ4924, 5018, and 5169 lines, together with a clear detection
of Sc II λ5531.
Later on, from day 62.8, the Ca II NIR triplet starts to show an
emission component, suggesting the start of the nebular phase. Sc II
λ5531 becomes stronger, while Sc II λ5663 is clearly detected. On the
other hand, Si II λ6355 vanishes. We observe a significant decrease
of the flux in the bluer part of the spectra, which is mainly produced
by the line-blanketing. In the last observation, at 88.1 d, the spectrum
shows a combination of absorption and emission lines. The redder
part of the spectrum starts to be dominated by forbidden emission
lines of [O I] λλ6300, 6364 and [Ca II] λλ7291, 7323, while the bluer
part is still dominated by the iron absorption lines. The Na I D line
presents a strong residual absorption component. At this stage, the
Ca II NIR triplet is the strongest feature in the spectrum.
To identify the lines in the spectra of SN 2019cad, we use the
SYNOW code (Fisher 2000). Fig. 4 shows the best fit obtained for the
SN spectra at 13.6 and 45.2 d. For the first spectrum, we assume a
blackbody temperature of Tbb = 5300 K and a photospheric velocity
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4912 Gutie´rrez et al.
Figure 3. Spectral sequence of SN 2019cad from 13.6 to 88.1 d from explosion. The phases are labelled on the right. Each spectrum has been corrected for
Milky Way reddening and shifted vertically by an arbitrary amount for presentation. The vertical dashed lines indicate the rest position of the strongest lines.
The colour of the spectra represents the different phases where they were observed: initial peak in blue, main peak in orange, and linear tail in green.
of vph = 8600 km s−1, while for the spectrum at 45.2 d, we use Tbb =
5600 K and vph = 5500 km s−1. The synthetic spectrum at 13.6 d
was obtained including Ca II, O I, Na I D, Si II, Fe II, and C II. Overall,
the synthetic spectrum reproduces very well the observed features of
SN 2019cad and helps us to confirm the two absorptions near ∼6000
Å as Si II and C II. For the second epoch, the synthetic spectrum
contains lines of Ca II, O I, Na I D, Si II, C II, and Ba II. Although we
can reproduce most of the lines observed in SN 2019cad, we do not
find a great match for the Ca II H & K neither for the continuum in the
region between 5500 and 7500 Å. The difficulty to reproduce this
second spectrum could be caused by the energy source powering
the main peak, which could break some of the assumptions of
SYNOW. One interesting characteristic of these two spectra and their
respective fits is the strength of the Si II and C II lines. Normally, these
lines become weaker over time due to a temperature dependence:
their strength decreases as the temperature decreases. However, for
SN 2019cad the temperature rises at ∼40 d, and thus the Si II and
C II are detected again. The presence of C II in the SN spectra could
indicate a significant amount of carbon in the progenitor star.
3.6 Expansion velocities
We measure the expansion velocities of the ejecta from the minimum
absorption flux of six spectral features. The velocity evolution of
Ca II λλ8498, 8542, 8662 triplet feature, Na I D λ5893 O I λ7774,
Fe II λ5169, Si II λ6355, and C II λ6580 is presented in Fig. 5. At
earlier phases (before 30 d), all lines have decreasing velocities, as
expected for a homologous expansion. After 40 d, the velocities of
Ca II and Na I D slightly increase, while for the rest of the lines, they
remain nearly constant. The change in the velocity evolution matches
with the remarkable transformation observed in the light curves and
suggests an additional source of energy. The Ca II NIR triplet has the
highest velocity, evolving from ∼13 000 to ∼10 200 km s−1, while
the Si II has the lowest one, decreasing from ∼7400 to ∼5200 km s−1.
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SN 2019cad: another SN 2005bf-like object 4913
Figure 4. Spectral comparison of SN 2019cad at 13.6 and 45.2 d and the
SYNOW fits. The SYNOW synthetic spectra (orange) are overplotted on the
observed spectra (black).
Figure 5. Evolution of expansion velocities of SN 2019cad derived from the
minimum of the absorption line. Epochs are with respect to the explosion.
For comparison, we also include the Fe II and Ca II velocities of SN 2005bf
(Folatelli et al. 2006) and Fe II λ5169 velocities of PTF11mnb (Taddia et al.
2018a).
This behaviour implies that the Ca II lines mainly form in the outer
part of the ejecta and Si II lines form in deeper layers. Na I D, Fe II, and
O I have intermediate velocities (between ∼11 000 and ∼6000 km
s−1). At early phases, Na I D expands faster, followed by O I and Fe II,
but after 40 d, all of them have similar velocities (∼7000 km s−1). In
general, the velocity range of SN 2019cad is comparable with other
normal SN Ic, however, the flat/rising velocity behaviour measured
after 40 d is similar to that observed in SN 2005bf (Tominaga et al.
2005; Folatelli et al. 2006) and PTF11mnb (Taddia et al. 2018a).
3.7 Comparison with other SNe
The photometric and spectroscopic evolution of SN 2019cad is
unprecedented, however, its double-peaked light curves resemble
the Type Ib/c SN 2005bf (Folatelli et al. 2006) and the Type Ic
Figure 6. Light curve and colour comparisons. Upper and middle panel:
Comparison of the g-band (upper) and r-band (middle) light curves of
SN 2019cad (blue stars) with the double-peaked light curves of SN 2005bf
(red pentagons) and PTF11mnb (yellow circles), and the normal Type Ic
SN 2004aw (green triangles). Please note that for SN 2004aw we use the B
and R bands. A light curve of SN 2019cad assuming an E(B − V) = 0.49
mag is also included for reference. Bottom panel: Colour (g − r) curves of
SN 2019cad and the comparison sample. Only corrections for Milky Way
extinction have been made.
PTF11mnb (Taddia et al. 2018a). From the spectral analysis, we find
that SN 2019cad has the characteristic lines of an SN Ic at early times,
but around the main peak, the spectra show an unexpected evolution,
characterized by a blue continuum and the presence of C II and Si II
lines, which had disappeared at ∼20 d (Section 3.5). Looking for
objects with similar characteristics, we use SNID (Blondin & Tonry
2007). At early phase (before 30 d), we find a good match with the
normal Type Ic SN 2004aw (Taubenberger et al. 2006), however, after
the main peak, good spectral matches were not obtained. Based on the
common features that SN 2019cad share with SN 2005bf, PTF11mnb
(photometrically), and SN 2004aw (spectroscopically), we compare
their light curves and spectra in Figs 6 and 7, respectively. Table 2
shows the main parameters measured for the double-peaked light
curve SNe and SN 2004aw.
To compare the photometric evolution of these objects in the g and
r bands, we present the light curves of SN 2019cad assuming an E(B
− V) = 0.0 mag, but we also correct the light curve for an E(B −
V) = 0.49 mag (clear blue stars). Additionally, we include the normal
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4914 Gutie´rrez et al.
Figure 7. Spectral comparison of SN 2019cad with SN 2005bf,
PTF11mnb, and SN 2004aw at three different epochs (13, 40, and 80 d).
Type Ic SN 2004aw (in B and R). From the light curve comparison
(Fig. 6, upper and middle panels), we find that SN 2019cad has a
very pronounced initial peak, both in the g and r bands. While in
SN 2005bf and PTF11mnb the initial peak decreases ∼0.5 mag in
the g, in SN 2019cad the brightness changes more than 1 mag. In the
r band, only SN 2019cad shows an initial peak. Instead, SN 2005bf
and PTF11mnb present a shoulder, which is more conspicuous in
PTF11mnb.
Followed by the first maximum, a rise to the main peak is observed
in all three objects. Although the brightness in SN 2005bf and
PTF11mnb increases ∼1 mag in g, in SN 2019cad the rise is around
3 mag in g and about 1.8 mag in r. For SN 2005bf, the main peak
occurs at ∼40 d in g and ∼42 d in r. PTF11mnb reaches it at ∼46 and
∼52 d, and SN 2019cad at 43.9 and 44.3 d, respectively. SN 2019cad
has a main peak that is the most narrow of those shown by these three
double-peaked objects. At around 100 d, SN 2005bf has declined by
more than 2 mag from peak in r band, PTF11mnb only ∼1 mag, and
SN 2019cad more than 4 mag.
On the other hand, SN 2004aw shows the typical light curve of an
SN Ic, with a main R-peak at ∼14 d from the explosion. In terms of
luminosity, SN 2004aw is brighter than the initial peak of SN 2019cad
(for E(B − V) = 0.0 mag), but it is similar in the r band when an
E(B − V) = 0.49 mag is assumed for SN 2019cad. Comparing the
luminosity of the double-peaked objects, we find that SN 2019cad
is always fainter than SN 2005bf and PTF11mnb in both the initial
and main peak for E(B − V) = 0.0 mag. However, if an E(B − V) =
0.49 mag is assumed, SN 2019cad is >1.5 mag brighter than these
two objects.
From the colour curves (Fig. 6, bottom panel), SN 2019cad and
SN 2004aw show a similar evolution during the first 20 d, SN 2004aw
being slightly redder. In the same period, SN 2005bf and PTF11mnb
show colours much bluer than SN 2019cad and SN 2004aw. This
behaviour suggests that at early phases SN 2019cad was comparable
to any other normal SN Ic, however, after 20 d, the evolution of
SN 2019cad changes radically: it becomes rapidly bluer reaching
a minimum at ∼44 d (corresponding to the main peak in the light
curve). From this epoch, the evolution and colours of SN 2019cad,
SN 2005bf, and PTF11mnb are similar.
Fig. 7 presents the spectral comparison of SN 2019cad with
SN 2005bf, PTF11mnb, and SN 2004aw at three different epochs:
∼13, ∼40, and ∼80 d from explosion. At around 13 d, SN 2019cad is
very similar to the normal Type Ic SN 2004aw. They show strong lines
of Ca II, O I, and Fe II. The spectrum of SN 2005bf has a similar Ca II
absorption line to SN 2019cad, however, the rest of the spectrum has
significant differences, such as weak detection of He I lines, lack of
O I, and a strong line around ∼6265 Å, which has been identified as a
high-velocity feature of H α (Folatelli et al. 2006). These properties
could indicate that SN 2019cad is similar, but more stripped than
SN 2005bf. By ∼40 d, all objects in the comparison sample present
very different spectra. Both SN 2019cad and SN 2004aw have a
prominent O I line, however, the Ca II absorption feature is shallow
in SN 2019cad. For SN 2005bf, the He I lines are exposed, but they
are missing in the rest of the objects. SN 2005bf, PTF11mnb, and
SN 2019cad have blue spectra compared to SN 2004aw. At this phase,
SN 2019cad has prominent lines of C II and Si II, which are not clearly
seen in the other objects. At ∼80 d, most of the objects show some
signatures of emission lines, which indicate the beginning of the
nebular phase. Although SN 2019cad, SN 2005bf, and PTF11mnb
have similar light-curve morphology, and comparable colours after
40 d, their spectra are completely different. This spectral diversity
could suggest differences in their progenitor stars.
When we compared the evolution of the Fe II velocities of
SN 2019cad and those from the double-peaked SN 2005bf and
PTF11mnb, we notice that SN 2019cad lies between these two
objects (see Fig. 5). Before 15 d, SN 2019cad and SN 2005bf have
comparable velocities, but after that the velocity of SN 2019cad
continues to decrease, while the velocity of SN 2005bf increases
slightly, and then it is flat. PTF11mnb, the object with the lowest
velocities, has a flat evolution between 38 and 60 d. A flat evolution
is also observed in SN 2019cad later than 40 d.
4 L I G H T- C U RV E M O D E L L I N G
In order to understand the sources that could be responsible for
enhancing the light curve of SN 2019cad, we have explored the
main competing ideas that were presented in relation to peculiar
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SN 2019cad: another SN 2005bf-like object 4915
Table 2. Properties of SN 2019cad and the comparison sample.
Parameters SN 2019cad1 SN 2005bf2 PTF11mnb3 SN 2004aw4
Host Galaxy UGC 4798 MCG + 00-27-5 SDSS J003413.34+024832.9 NGC 3997
Explosion date (MJD) 58550.44 ± 4 53458.00 55804.34 ± 0.5 53080.9
Distance modulus 35.38 34.57 37.14 34.26
Spectroscopic classification Ic Ib/c Ic Ic
E(B − V)MW (mag) 0.015 0.045 0.016 0.20
E(B − V)Host (mag) 0.0 0.0 0.0 0.35
g band
Initial peak magnitude (mag) −16.35 −17.24 −17.39 –
Initial peak epoch (d) 8 16.2 21.3 –
Main peak magnitude (mag) −17.83a −18.25 −18.37 −17.63b
Main peak epoch (d) 43.9 40 46.3 7
r band
Initial peak magnitude (mag) −16.68a – – –
Initial peak epoch (d) 15 – – –
Main peak magnitude (mag) −18.10a −18.44 −18.45 −18.14b
Main peak epoch (d) 44.3 42 52.2 14
Notes. References: 1This work; 2Folatelli et al. (2006); 3Taddia et al. (2018a); 4Taubenberger et al. (2006).
aAbsolute magnitudes assuming E(B − V)Host = 0 mag.
bFor SN 2004aw, we report the B (instead g) and R magnitudes, respectively.
double-peaked SNe, SN 2005bf (Folatelli et al. 2006) and PTF11mnb
(Taddia et al. 2018a). Like SN 2019cad, these objects present a
rise and decline in luminosity prior to the main peak. Such early
behaviour cannot be reconciled with an extended envelope as used
to model cooling emission in SNe IIb or by assuming the presence
of a small amount of circumstellar material (Bersten et al. 2012;
Nakar & Piro 2014). We performed a brief exploration of these
possibilities with no success. The main reason was the duration of
the SN 2019cad first peak. Assuming the presence of a thin envelope,
we can only reproduce a first peak with a duration of less than 10 d
and a decreasing luminosity due to the cooling process. As a result
of this cooling process and the existence of an additional source
that heats the ejecta, usually radioactivity, the light curve shows a
minimum. Similar outcome can be obtained assuming the presence of
a local and low-mass CSM (see also Jin, Yoon & Blinnikov 2021 for
comparable results). Nevertheless, more extreme CSM conditions, as
expected to explain hydrogen-rich SNe with narrow emission lines
(SN IIn) or some superluminous SNe (SLSNe), could explain the
early and/or main peak in the SN light curve. However, we did not
explore these possibilities here. Instead, we analysed in detail the
following scenarios: (1) a double nickel distribution (Section 4.1)
and (2) the first peak powered by nickel but the second one by a
magnetar (Section 4.2). In this analysis, we have assumed a zero
host extinction (see discussion in Section 3.2).
4.1 Double 56Ni distribution
SN 2019cad is luminous enough to envisage that outflows were
involved in its explosion. Several studies (see e.g. MacFadyen,
Woosley & Heger 2001; Banerjee & Mukhopadhyay 2013) have
considered SNe with outflows or jets in relation to GRB. Jets can
induce nucleosynthesis of radioactive elements at the outer layers
of the ejecta before the shock front of the SN arrives (Nishimura,
Takiwaki & Thielemann 2015). The outer nickel produced in this
way could be responsible for the first peak observed in the light
curve of SN 2019cad as explored for SN 2005bf (Tominaga et al.
2005; Folatelli et al. 2006), PTF11mnb (Taddia et al. 2018a), and
SN 2008D (Bersten et al. 2013). The lack of high-energy emission
could be explained by the inability of the jets to breakout the SN
surface, or by geometric reasons. Although we did not find any high-
emission reported, we cannot rule out their possible existence.
To analyse the double 56Ni possibility, we performed hydrody-
namic calculations using different helium-rich progenitors as hy-
drostatic initial conditions. Specifically, we have tested models with
masses of 5 (He5) and 8 M (He8) at the pre-SNe stage. These models
were calculated by Nomoto & Hashimoto (1988) and correspond to
main-sequence stars of 18, and 25 M, respectively. A more massive
progenitor of 11 M (He11) corresponding to a main-sequence
star of 30 M computed with MESA code (Paxton et al. 2011)
was also used. We have artificially exploded these configurations
using the code presented in Bersten, Benvenuto & Hamuy (2011);
a one-dimensional radiation hydrodynamical code which assumed
flux-limited diffusion approximation and grey transfer for gamma
photons produced during the radioactive decay. The code assumes
that the positrons are fully trapped all times and fully deposit their
energy before annihilation following Sutherland & Wheeler (1984).
After several calculations, we found that the highest mass progenitor
(He11 in our case) is favoured to explain the double-peaked light
curve of SN 2019cad (see Fig. 8). This is because it allows the large
temporal departure between the light curve peaks as a consequence
of depositing the inner and outer nickel at a larger distance in
mass coordinate. For lower mass progenitors, even if the general
luminosity trend in the light curve can be reached, the resulting Lbol
between 20 and 40 d is far above that observed, with the morphology
of a minimum around 25 d poorly reproduced.
Our best case was produced by He11 assuming an explosion
energy of Eexp = 3.5 × 1051 erg, an ejected mass of Mej = 9.5 M,
and the formation of a neutron star of ≈1.5 M. Fig. 8 shows this
model compared with the observations of SN 2019cad. The double-
peaked morphology of the light curve was obtained assuming the
nickel distribution presented in Fig. 9. We have had to consider
a concentrated inner component close to the compact remnant
(1.5 M), similar to what was found for SN 2005bf (Folatelli et al.
2006), plus an external 56Ni component. In the model presented, the
external nickel needs to be close but below the surface to fit the time-
scale of the first peak of the light curve. We found that an external
56Ni mass of 0.041 M satisfied our requirements. This represents a
small fraction of the inner component, with a mass of 0.3 M.
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4916 Gutie´rrez et al.
Figure 8. Top panel: Comparison between our preferred double-peaked
56Ni model (black solid line) and the SN observations (orange stars). For
this model, we use a progenitor with a pre-SN mass of 11 M (He11),
corresponding to a zero-age main sequence mass of 30 M, an explosion
energy of 3.5 × 1051 erg, and ejected mass of 9.5 M. For comparison, we
also include the double 56Ni distribution models for lower pre-SN masses:
5 (He5; in blue dashed line) and 8 (He8; green dash–dotted line). In all
three cases, an enhancement of the gamma-ray leakage is assumed at around
the date of L-main peak. Models with lower mass produces an earlier main
peak and overestimate the rise time luminosity. The He11 model assuming a
constant κγ = 0.03 (dotted grey line) is also presented as reference. Bottom
panel: Evolution of the He11 (black solid line), He5 (in blue dashed line),
and He8 (green dash–dotted) line photospheric velocity compared with the
Fe II velocity of SN 2019cad.
Figure 9. The 56Ni abundance profile of our preferred model powered by
the double-peaked nickel distribution. The stellar surface is at 500 R for
∼11 M before explosion (i.e. the outer component is not extended up to
the surface). Note that the inner component shows a slightly decline due to
presence of other heavy elements such as Si, Ar, or Ca.
Table 3. SN 2019cad light-curve modelling parameters.
E(B − V)Host = 0.0 mag E(B − V)Host = 0.49 mag
Double 56Ni distribution model
Internal 56Ni component 0.300 M 0.904 M
External 56Ni component 0.041 M 0.132 M
Double 56Ni distribution plus magnetar model
Initial period (P) 11 ms 4 ms
Magnetic field (B) 26 × 1014 G 12 × 1014 G
External 56Ni component 0.041 M 0.132 M
Other 56Ni distributions have been also explored, in particular, we
analysed if a smoother transition between the inner and outer 56Ni
component could improve the light-curve modelling, but we did not
find substantial differences with the distribution showed in Fig. 9.
Therefore, we preferred to set a simplistic case with an inner 56Ni-
rich layer (the abundance mimics the one of Si-Ar-Ca, i.e. increasing
outward) and an outer component with constant nickel abundance.
These are well-departed zones, with no nickel in the middle (see
Fig. 9).
In addition to the early peculiar morphology, SN 2019cad shows
a steeper decline in the light curve after the main peak, similar
to that observed in SN 2005bf. Assuming that this peak was
powered by nickel, an artificial reduction in the gamma-ray trapping
was proposed to explain the post-peak behaviour of SN 2005bf
(Tominaga et al. 2005; Folatelli et al. 2006). An equivalent treatment,
as an ad hoc leakage factor used by Vreeswijk et al. (2017), also
resembles the incomplete trapping of gamma-rays in Drout et al.
(2013). Following this idea, we have modified the gamma-ray opacity
from κγ = 0.03 to κγ = 0.0005 cm2 g−1 around the mean light curve
peak of SN 2019cad. By default our code uses a fixed gamma-
ray opacity, however this can be changed as required. The values
mentioned above implies a decrease of the opacity by a factor of 60,
which in turn allows a much larger gamma-ray leakage. We cannot
provide a thorough physical justification for this assumption as it was
made to fit the rapid light curve post-maximum decline. However,
such a reduction of the gamma-ray opacity might be related to the
asymmetry of the explosion that produces extremely inhomogeneous
ejecta (see also e.g. Maeda et al. 2007).
The model presented reproduces the light-curve properties of
SN 2019cad reasonably well: the double-peaked morphology and
the fast decline after the peak. However, some discrepancies appear
around ≈ 25 d where the observations show a slightly higher
luminosity than the model. Finally, we note that, although we have
not considered the photospheric velocity evolution in the modelling
(which could lead to a possible degeneracy in the parameters found,
see discussion in Martinez et al. 2020 and references therein), the
model gives a relatively good representation of the Fe II λ5169
velocities as shown in the bottom panel of Fig. 8.
While we consider an E(B − V)Host = 0.0 mag for our analysis,
we also explore the effects of having an E(B − V)Host = 0.49 mag.
As shown in the bottom panel of Fig. 2, the main effect of assuming
non-negligible extinction is to increase the luminosity, and at first
order, we can consider that the shape of the light curve remains
similar. An increase in luminosity can be produced assuming a
larger nickel mass. To reproduce a brighter light curve, our model
requires an external nickel component of 0.132 M and an internal
component of 0.904 M. These values are ∼3 times higher than our
original model. Table 3 summarizes the values that better reproduce
the light curve of SN 2019cad assuming an E(B − V)Host = 0.0 and
0.49 mag, respectively.
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SN 2019cad: another SN 2005bf-like object 4917
4.2 Magnetar
The idea that a strongly magnetized neutron star or magnetar could
have been the powering source of the main peak in SN 2005bf was
proposed by Maeda et al. (2007). Late-time photometry of SN 2005bf
has provided further support to this idea.
The research on young magnetars into SNe has vastly grown
in last years, with suggestions for regular (see e.g. Sukhbold &
Thompson 2017), bright (Inserra et al. 2013; Dessart & Audit 2018;
Orellana, Bersten & Moriya 2018), and peculiar SNe (Bersten et al.
2016; Woosley 2018). Recent results provide new insights about the
magnetar properties. Detailed simulations have shown that magnetars
can accelerate iron-group elements deep in the ejecta, and explain the
high-velocity Fe lines observed in some core-collapse SNe (Chen,
Woosley & Whalen 2020). Another interesting characteristic is that
the magnetar creation might be accompanied by jets (e.g. Soker
2016). Based on this assumption, we propose that a magnetar and
a double nickel distribution can, in principle, be combined. To
explore this possibility for SN 2019cad, we applied a version of
the hydrodynamical code that incorporates the extra power source
of magnetar (Bersten et al. 2016) and assumes that this energy
is deposited at the inner layers of the ejecta. For the low-mass
progenitors we did not find a promising case, therefore the He11
configuration was again preferred. We performed a wide exploration
of the magnetar parameter space, for fixed standard properties of the
neutron star, and assuming the spin-down proceeds through vacuum
dipole radiation (braking index n = 3). We obtained an acceptable
match for the main peak for P ∼ 11 ms and B ∼ 26 × 1014 G
(see Fig. 10), with an explosion energy of Eexp = 3.5 × 1051 erg
and a conservative 56Ni mass (∼0.05 M) at the inner layers of the
progenitor. This inner nickel mass is constrained by the observations
at the tail of the light curve. We set the gamma-opacity to a usual
value, κγ = 0.03 cm2 g−1 during the complete evolution. Note that the
energy of the magnetar is assumed to be deposited at the inner layers
of the ejecta as internal energy. The magnetar model alone cannot
reproduce the two peaks observed in the light curve of SN 2019cad.
Therefore, we resume to the presence of some external nickel, and
turn on the same configuration of the outer ∼0.04 M 56Ni depicted
in Fig. 9.
In the hybrid model proposed for PTF11mnb (Taddia et al. 2018a),
the magnetar-powered light curve is explored through the semiana-
lytic prescription of Kasen & Bildsten (2010) in combination with the
diffusion one-zone model of Arnett (1982) for the 56Ni radioactive
decay. In order to obtain the maximum time-scale with that treatment,
the magnetar must ignite with a delay of several days from the
explosion. We note the physical difficulty to explain such delay.
The simulations of post-collapse are consistent with evolutionary
time-scales of seconds between the proto-neutron star birth and
the moment when the stable neutron star holds the high angular
momentum and strong magnetic field to initiates the spin-down
phase (Mezzacappa et al. 2001; Metzger, Thompson & Quataert
2007; Aloy & Obergaulinger 2021). However, in our hydrodynamical
implementation of the magnetar model assuming a massive (He11)
progenitor, such delay was not needed and the magnetar was turned-
on at the same time as the SN explosion, providing a more reliable
prescription. In addition, this model did not require a reduction of
the gamma-ray opacity.
Lastly, we explore the parameter space required to model a brighter
light curve (assuming an E(B − V)Host = 0.49 mag, see Fig. 2).
As shown in Fig. 10, in our double 56Ni distribution plus magnetar
model, the effect of the magnetar is more important for the main peak,
while the impact of the 56Ni mass is significant for the initial peak.
Figure 10. Top panel: The magnetar plus nickel model for a progenitor mass
of 11 M (see Section 4.2) compared with the light curve of SN 2019cad. For
the first maximum, an outer 56Ni mass of 0.041 M is assumed. The second,
main peak was modelled with an inner mass of 56Ni 0.05 M and a magnetar
with an initial period P = 11 ms and a magnetic field of B = 26 × 1014 G
(dashed line). The calculated light curve with both 56Ni components and
the magnetar is shown in black solid line. Bottom panel: Evolution of the
magnetar plus nickel model photospheric velocity compared with the Fe II
velocity of SN 2019cad.
It has been shown that in a magnetar, the peak luminosity is mostly
affected by the initial period (P) and the magnetic field (B) (e.g.
Kasen & Bildsten 2010; Dessart 2019). Taking these three parameters
(P, B, and 56Ni mass) into account, we can reproduce the new light
curve. To reach the main-peak luminosity, while preserving its time-
scale, a magnetar with P ∼ 4 ms and B ∼ 12 × 1014 G is necessary.
To reproduce the initial peak, we need to include an external nickel
component of 0.132 M. These parameters, summarized in Table 3,
are within the range of previously published values (e.g. Dessart
2019 for the magnetar and Anderson 2019, for the 56Ni mass).
5 D I SCUSSI ON AND C ONCLUSI ONS
We have presented the spectroscopic and photometric analysis of
the Type Ic SN 2019cad during the first 100 d from explosion.
Located at a projected distance of 4.6 kpc from the centre of H I-rich
galaxy UGC 4798, SN 2019cad presents an uncommon light-curve
evolution, which resembles the peculiar Type Ib/c SN 2005bf and
the Type Ic PTF11mnb. That is, an initial peak at about 10–15 d
from explosion followed by a main peak at ∼45 d from explosion.
While the luminosity of the first peak (Mr = −16.68 mag) is within
the ranges of normal hydrogen-free events (e.g. Taddia et al. 2018a),
the second one (Mmaxr = −18.10 mag) is brighter than normal, but
consistent with that observed in double-peaked SNe, if the extinction
is E(B − V) = 0 mag. From the spectroscopic point of view,
SN 2019cad shows important differences with respect to SN 2005bf
and PTF11mnb. During the first 30 d (first peak), the spectra of
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4918 Gutie´rrez et al.
SN 2019cad are comparable with typical SNe Ic, however, when the
light curve goes up to the main peak (at around 45 d), the spectra
display an unusual transformation, easily noticeable by the presence
of the Si II and C II lines. The presence of these lines were confirmed
by the SYNOW fits. At these later epochs, no spectral matches were
found, suggesting that SN 2019cad has a unique evolution.
To try to understand the peculiar photometric behaviour of
SN 2019cad, we have explored two possible scenarios, both assuming
a progenitor with a pre-SN mass of 11 M, corresponding to a zero-
age main sequence mass of 30 M, an explosion energy of 3.5 × 1051
erg, and ejected mass of 9.5 M, assuming the formation of a compact
object with a 1.5 M and a double-peaked 56Ni distribution, with an
outer, though below the surface, low-mass component of 0.04 M.
For the main peak we obtained (1) an inner nickel component of
0.3 M (Section 4.1); or (2) a 56Ni plus magnetar model (Section 4.2).
Specifically, the magnetar properties found are an initial rotation
period P ∼ 11ms and magnetic field strength of B ∼ 26 × 1014 G.
A discussion of how the neutron star properties can affect the values
of P and B can be found in Bersten et al. (2016). With this in mind,
as well as other simplifications of the 1D model, the parameters
obtained here for the magnetar should be considered approximate
values.
While either model can reproduce the overall morphology ob-
served in SN 2019cad, the double 56Ni distribution model provided a
bit better representation of the double-peaked light curve. However,
to reproduce the late (t > 60 d) behaviour of fast decline post-
maximum, we artificially reduced the gamma-ray trapping. Similar
approaches were explored by Tominaga et al. (2005) and Folatelli
et al. (2006) to fit the decline observed in SN 2005bf, but this was not
necessary in the case of SN PTF11mnb. For the magnetar model, an
internal component of 56Ni can be present, involving at most some
0.05 M. The gamma opacity was not needed to be reduced. The
drawback in this case is the worse fit of the bolometric light curve at
the transition (around t = 25 d) and up to the main peak.
The amount of nickel found for the double 56Ni distribution model
is larger than the expected for hydrogen-free SNe (see e.g. Prentice
et al. 2016; Taddia et al. 2018b; Anderson 2019), while for the model
including the magnetar is within the range of these objects. The
progenitor mass (pre-SN mass of 11 M, corresponding to a zero-
age main sequence mass of 30 M) is also large, but comparable
with that of SN 2005bf (Tominaga et al. 2005; Folatelli et al. 2006;
Maeda et al. 2007). The outer 56Ni component in the stellar interior
that we assumed to be related with jets could be hinted by high-
energy emission as in GRB-SNe explosions. Although, as this SN is
quite peculiar, it may be a failed GRB (Huang, Dai & Lu 2002) i.e.
having jet-like outflows without sufficient Lorentz factor, or even a
GRB with collimated jets that do not point in the direction of the
observer. Archival searches for detections of SN2019cad at other
wavelengths are therefore encouraged.
As discussed in Section 3.2, considerable discrepancies in the
reddening estimation for SN 2019cad were found with different
methods, and an E(B − V)Host = 0.0 mag was adopted for our
analysis. However, based on the strong narrow Na I D absorption
feature detected in the spectra, we deduce that SN 2019cad may suffer
a significant reddening. In Section 3.7, we compared SN 2019cad
with similar objects and briefly discussed the implications of a higher
reddening. By adopting an E(B − V)Host = 0.49 mag, we found that
the light curve has a significant increase in brightness. To reach
the new luminosity by using the double 56Ni distribution model, an
external nickel component of 0.132 M and a value of 0.904 M
for the internal component were needed. We note that a 56Ni mass
of 0.904 M is huge compared with the values measured in normal
stripped-envelope SNe (mean value of 0.293 M; Anderson 2019),
and is beyond those estimated for even extreme objects such as
GRB-SNe (∼0.3–0.6 M; e.g. Cano et al. 2017). These gigantic
values disfavour this model. On the other hand, assuming a magnetar
model, the luminosity could be easily reach by changing the initial
period and the magnetic field. However, as our model requires nickel
to reproduce the initial peak, an increase in the nickel mass is
essential. In our preferred case, the external nickel component is,
again, 0.132 M, but P ∼ 4 ms, which is a few times larger than the
theoretical limit for break-up (P ∼ 2 ms; Dessart 2019). In order to
maintain the time of the maximum in the light curve, the magnetic
field should be B ∼ 12 × 1014 G. These values favour the double
56Ni plus magnetar scenario.
Summarizing, SN 2019cad is within a rare type of event, with
only two previous examples, SN 2005bf and PTF11mnb. Despite
showing some similar features, these three SNe do show key
differences. The similarities in the light curve could suggest a similar
explosion mechanism, while the diversity in the spectra could imply
different progenitor evolution, e.g. distinctive grades of mass-loss.
Although we have found two models that can explain the main
photometric properties of SN 2019cad, there are still many issues
in our understanding of these objects and the ultimate source of
energy to power them is still a mystery.
AC K N OW L E D G E M E N T S
We thank the anonymous referee for the comments and suggestions
that have helped to improve the paper.
We are grateful to Peter Jonker who enabled the WHT observation
of this target during his program W19AN003. We thank Peter Brown
its contribution with data from the Neil Gehrels Swift Observatory.
CPG and MS acknowledge support from EU/FP7-ERC grant No.
(615929). MO acknowledges support from UNRN PI2018 40B696
grant. GP acknowledges support by ANID - Millennium Science
Initiative - ICN12 009. NER acknowledges support from MIUR,
PRIN 2017 (grant 20179ZF5KS). MF is supported by a Royal Society
- Science Foundation Ireland University Research Fellowship. SM
acknowledges support from the Magnus Ehrnrooth foundation. AR
acknowledges support from ANID BECAS/DOCTORADO NA-
CIONAL 21202412. TMR acknowledges the financial support of
the Jenny and Antti Wihuri foundation and the Vilho, Yrjo¨ and Kalle
Va¨isa¨la¨ Foundation of the Finnish academy of Science and Letters.
MS is supported by generous grants from VILLUM FONDEN
(13261, 28021) and by a project grant (8021-00170B) from the
Independent Research Fund Denmark. LG was funded by the
European Union’s Horizon 2020 research and innovation programme
under the Marie Skłodowska-Curie grant agreement No. 839090.
JB, DH, DAH, and CP were supported by NSF grant AST-1911225.
TMB was funded by the CONICYT PFCHA/DOCTORADOBECAS
CHILE/2017-72180113.
This work has been partially supported by the Spanish grant
PGC2018-095317-B-C21 within the European Funds for Regional
Development (FEDER).
Based on observations made with the Nordic Optical Telescope,
owned in collaboration by the University of Turku and Aarhus
University, and operated jointly by Aarhus University, the University
of Turku and the University of Oslo, representing Denmark, Finland
and Norway, the University of Iceland and Stockholm University at
the Observatorio del Roque de los Muchachos, La Palma, Spain, of
the Instituto de Astrofisica de Canarias.
Observations from the NOT were obtained through the NUTS and
NUTS2 collaboration which are supported in part by the Instrument
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SN 2019cad: another SN 2005bf-like object 4919
Centre for Danish Astrophysics (IDA). The data presented here were
obtained in part with ALFOSC, which is provided by the Instituto
de Astrofisica de Andalucia (IAA) under a joint agreement with the
University of Copenhagen and NOTSA.
Based on observations made with the GTC telescope, in the
Spanish Observatorio del Roque de los Muchachos of the Instituto
de Astrofı´sica de Canarias, under Director’s Discretionary Time.
This work has made use of data from the Asteroid Terrestrial-
impact Last Alert System (ATLAS) project. ATLAS is primarily
funded to search for near-earth asteroids through NASA grants
NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; by prod-
ucts of the NEO search include images and catalogues from
the survey area. The ATLAS science products have been made
possible through the contributions of the University of Hawaii
Institute for Astronomy, the Queen’s University Belfast, the Space
Telescope Science Institute, and the South African Astronomical
Observatory.
The Liverpool Telescope is operated on the island of La Palma by
Liverpool John Moores University in the Spanish Observatorio del
Roque de los Muchachos of the Instituto de Astrofisica de Canarias
with financial support from the UK Science and Technology Facilities
Council. This work makes use of data from the Las Cumbres
Observatory network.
Facilities: ATLAS; GTC; Las Cumbres Observatory; LT; NOT;
Swift, WHT, ZTF.
Software: PYTHON from https://www.python.org/, PHOTUTILS
(Bradley et al. 2019), ASTROPY (Astropy Collaboration 2018), IRAF,
SNOOPY (Cappellaro 2014), FDSTFAST, FLOYDS PIPELINE (Valenti
et al. 2014), GEORGE (Ambikasaran et al. 2015), SYNOW (Fisher
2000), MESA (Paxton et al. 2011), SNID (Blondin & Tonry 2007).
DATA AVAILA BILITY
The data underlying this article are available in the Appendix A
(Tables A1–A5) and through the WISeREP (https://wiserep.weizma
nn.ac.il/home) archive (Yaron & Gal-Yam 2012).
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APPENDI X: TA BLES
Photometry and spectroscopic observations of SN 2019cad.
Table A1. ATLAS AB optical photometry.
UT date MJD Phase Band Magnitude
(d)∗ (mag)
20190227 58542.48 – o >20.50
20190303 58546.46 – o >20.50
20190307 58550.44 – o >20.70
20190311 58554.42 3.88 o 19.91 ± 0.11
20190315 58558.43 7.78 o 19.45 ± 0.20
20190319 58562.39 11.64 o 18.43 ± 0.13
20190323 58566.41 15.55 o 18.44 ± 0.11
20190325 58568.41 17.50 o 18.63 ± 0.06
20190329 58572.39 21.38 o 18.54 ± 0.04
20190402 58576.43 25.31 c 19.45 ± 0.05
20190404 58578.40 27.23 o 18.74 ± 0.08
20190406 58580.40 29.18 c 19.43 ± 0.10
20190408 58582.37 31.10 o 18.63 ± 0.07
20190414 58588.39 36.96 o 17.64 ± 0.09
20190416 58590.36 38.88 o 17.35 ± 0.02
20190420 58594.34 42.76 o 17.33 ± 0.03
20190422 58596.34 44.71 o 17.41 ± 0.01
20190424 58598.32 46.63 o 17.46 ± 0.02
20190426 58600.33 48.59 o 17.47 ± 0.02
20190430 58604.34 52.50 c 18.04 ± 0.03
20190506 58610.30 58.30 o 18.65 ± 0.06
20190508 58612.27 60.22 c 18.76 ± 0.05
20190510 58614.27 62.17 o 18.77 ± 0.08
20190512 58616.27 64.12 o 18.71 ± 0.08
20190514 58618.29 66.09 o 19.16 ± 0.26
20190516 58620.31 68.05 o 19.34 ± 0.15
20190518 58622.26 69.95 o 19.47 ± 0.30
20190522 58626.24 73.83 o 19.40 ± 0.13
20190524 58628.25 75.79 o 19.32 ± 0.28
20190530 58634.25 81.63 o 19.57 ± 0.23
20190601 58636.25 83.58 c 22.28 ± 0.42
Note. ∗Rest-frame phase in days from explosion, MJD = 58550.44 ± 4.
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SN 2019cad: another SN 2005bf-like object 4921
Table A2. Optical photometry of SN 2019cad.
UT date MJD Phase u B V g r i z Telescope‡
(d)∗ (mag) (mag) (mag) (mag) (mag) (mag) (mag)
20190322 58565.32 14.49 20.10 ± 0.10 20.05 ± 0.09 19.25 ± 0.06 19.43 ± 0.04 18.77 ± 0.03 18.73 ± 0.03 – LCOGT
20190328 58571.11 20.13 – 21.24 ± 0.07 19.27 ± 0.03 20.39 ± 0.03 18.84 ± 0.03 18.58 ± 0.04 – LCOGT
20190329 58572.17 21.16 – 21.49 ± 0.07 19.58 ± 0.03 20.51 ± 0.05 19.01 ± 0.03 18.77 ± 0.03 – LCOGT
20190421 58594.85 43.26 18.44 ± 0.02 – – 17.58 ± 0.03 17.32 ± 0.02 17.19 ± 0.02 17.05 ± 0.02 LT
20190423 58596.86 45.21 – – – – 17.31 ± 0.02 – – NOT
20190424 58597.85 46.18 18.66 ± 0.02 – – 17.63 ± 0.02 17.33 ± 0.01 17.14 ± 0.01 17.07 ± 0.02 LT
20190427 58600.85 49.10 18.69 ± 0.02 – – 17.86 ± 0.03 17.46 ± 0.01 17.26 ± 0.01 17.16 ± 0.02 LT
20190428 58601.90 50.12 – – – – 17.55 ± 0.03 – – NOT
20190429 58602.95 51.14 – – – 18.22 ± 0.01 17.72 ± 0.01 17.56 ± 0.01 17.37 ± 0.01 NOT
20190430 58603.85 52.02 19.61 ± 0.02 – – 18.16 ± 0.02 17.69 ± 0.02 17.48 ± 0.02 17.30 ± 0.02 LT
20190501 58604.92 53.06 – – – – 17.98 ± 0.08 – – NOT
20190503 58606.85 54.94 – – – 18.57 ± 0.06 17.93 ± 0.03 17.73 ± 0.03 17.55 ± 0.03 LT
20190511 58614.88 62.76 – – – – 19.11 ± 0.10 – – NOT
20190513 58616.89 64.72 21.99 ± 0.24 – – 20.03 ± 0.03 19.26 ± 0.03 18.84 ± 0.03 18.47 ± 0.02 NOT
20190516 58619.85 67.60 >21.71 – – 20.19 ± 0.09 19.43 ± 0.04 19.05 ± 0.03 18.55 ± 0.03 NOT
20190603 58637.90 85.19 – 22.23 ± 0.10 – 21.50 ± 0.06 20.48 ± 0.02 20.06 ± 0.04 19.41 ± 0.05 NOT
20190606 58640.85 88.06 – – – – 20.45 ± 0.15 – – GTC
20190611 58645.89 92.97 – – – 22.01 ± 0.07 20.97 ± 0.03 20.51 ± 0.06 19.90 ± 0.10 NOT
20190619 58653.89 100.76 – – – >21.86 21.40 ± 0.04 20.92 ± 0.10 20.160.10 NOT
20190622 58656.89 103.68 – – – >21.68 20.95 ± 0.10 – – WHT
Notes. ∗Rest-frame phase in days from explosion, MJD = 58550.44 ± 4.
‡Telescope code: LCOGT: Las Cumbres Observatory; LT: 2.0-m Liverpool Telescope: NOT: Nordic Optical Telescope; GTC: Gran Telescopio Canarias; WHT:
William Herschel Telescope.
Observation performed in the U band.
UBV photometry is in the Vega system, while ugriz photometry is in the AB system.
Table A3. JHK Vega photometry of SN 2019cad obtained with NOTCam.
UT date MJD Phase J H K
(d)∗ (mag) (mag) (mag)
20190430 58603.95 52.12 17.29 ± 0.08 16.20 ± 0.10 16.35 ± 0.22
20190521 58624.89 72.51 18.00 ± 0.11 17.26 ± 0.24 17.74 ± 0.32
20190613 58647.89 94.92 20.09 ± 0.13 18.40 ± 0.15 18.24 ± 0.36
Notes. ∗Rest-frame phase in days from explosion, MJD = 58550.44 ± 4.
Table A4. UV photometry obtained with Swift in the AB system.
UT date MJD Phase UVW2 UVM2 UVW1 U B V
(d)∗ (mag) (mag) (mag) (mag) (mag) (mag)
20190507 58611.14 59.12 >18.72 >18.84 >18.93 >18.54 >18.50 >17.78
Note. ∗Rest-frame phase in days from explosion, MJD = 58550.44 ± 4.
1Finnish Centre for Astronomy with ESO (FINCA), University of Turku, FI-
20014 Turku, Finland
2Tuorla Observatory, Department of Physics and Astronomy, University of
Turku, FI-20014 Turku, Finland
3Department of Physics and Astronomy, University of Southampton,
Southampton SO17 1BJ, UK
4Facultad de Ciencias Astrono´micas y Geofı´sicas, Universidad Nacional de
La Plata, Paseo del Bosque S/N, B1900FWA La Plata, Argentina
5Instituto de Astrofı´sica de La Plata (IALP), CCT-CONICET-UNLP. Paseo
del Bosque S/N, B1900FWA La Plata, Argentina
6Kavli Institute for the Physics and Mathematics of the Universe (WPI), The
University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
7Universidad Nacional de Rı´o Negro. Sede Andina, Mitre 630 (8400),
Bariloche, Argentina
8Consejo Nacional de Investigaciones Cientı´ficas y Tecnicas (CONICET),
Argentina
9INAF - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5,
I-35122 Padova, Italy
10Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda.
Republica 252, Santiago, Chile
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4922 Gutie´rrez et al.
Table A5. ZTF AB optical photometry.
UT date MJD Phase Band Magnitude
(d)∗ (mag)
20190314 58556.20 5.61 r >19.61
20190316 58558.20 7.56 r >19.18
20190317 58559.24 8.57 r 19.02 ± 0.11
20190317 58559.30 8.63 g 19.31 ± 0.24
20190320 58562.15 11.41 r 18.75 ± 0.14
20190320 58562.24 11.49 g >18.54
20190325 58567.20 16.32 g 19.73 ± 0.18
20190325 58567.22 16.34 r 18.67 ± 0.09
20190330 58572.20 21.19 g 20.16 ± 0.24
20190330 58572.22 21.21 r 18.83 ± 0.15
20190402 58575.21 24.13 r 18.95 ± 0.13
20190402 58575.26 24.17 g 20.09 ± 0.23
20190407 58580.21 29.00 r 19.08 ± 0.11
20190409 58582.20 30.93 r 18.76 ± 0.08
20190411 58584.22 32.90 g 19.09 ± 0.12
20190414 58587.21 35.81 g 18.21 ± 0.06
20190416 58589.22 37.77 r 17.50 ± 0.05
20190418 58591.34 39.84 r 17.39 ± 0.05
20190420 58593.33 41.77 r 17.37 ± 0.06
20190421 58594.16 42.58 r 17.41 ± 0.03
20190421 58594.18 42.60 g 17.68 ± 0.05
20190425 58598.20 46.52 g 17.79 ± 0.05
20190426 58599.15 47.44 r 17.49 ± 0.05
20190428 58601.26 49.50 r 17.65 ± 0.05
20190502 58605.22 53.36 g 18.58 ± 0.08
20190505 58608.19 56.25 g 18.94 ± 0.10
20190514 58617.19 65.01 g 19.79 ± 0.17
20190514 58617.22 65.04 r 18.99 ± 0.11
20190515 58618.26 66.06 r 19.30 ± 0.20
Note. ∗Rest-frame phase in days from explosion, MJD = 58550.44 ± 4.
11Millennium Institute of Astrophysics (MAS), Nuncio Monsen˜or Sotero Sanz
100, Providencia, Santiago, Chile
12European Southern Observatory, Alonso de Co´rdova 3107, Casilla 19,
Santiago, Chile
13Astrophysics Research Centre, School of Mathematics and Physics, Queens
University Belfast, Belfast BT7 1NN, UK
14DTU Space, National Space Institute, Technical University of Denmark,
Elektrovej 327, DK-2800 Kgs. Lyngby, Denmark
15School of Physics & Astronomy, Cardiff University, Queens Buildings, The
Parade, Cardiff CF243AA, UK
16Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can
Magrans s/n, E-08193 Barcelona, Spain
17School of Physics, O’Brien Centre for Science North, University College
Dublin, Belfield, Dublin 4, Dublin, Ireland
18Department of Physics and Astronomy, Aarhus University, Ny Munkegade,
DK-8000 Aarhus C, Denmark
19Department of Physics, University of California, Santa Barbara, CA 93106-
9530, USA
20Las Cumbres Observatory, 6740 Cortona Dr, Suite 102, Goleta, CA 93117-
5575, USA
21Institute of Cosmology and Gravitation, University of Portsmouth,
Portsmouth PO1 3FX, UK
22Departamento de Fı´sica Teo´rica y del Cosmos, Universidad de Granada,
E-18071 Granada, Spain
23Universite´ de Lyon, Lyon, France; Universite´ de Lyon 1, Villeurbanne;
CNRS/IN2P3, Institut de Physique des Deux Infinis, F-69622 Lyon, France
Table A6. Spectroscopic observations of SN 2019cad.
UT date MJD Phase Range Telescope Grism/Grating
(d)∗ (Å) + Instrument
20190322 58564.36 13.56 3500–10 000 LCOGT + FLOYDS red/blue
20190325 58567.95 17.51 3780–9200 P60 + SEDM
20190327 58569.32 18.39 3500–9250 LCOGT + FLOYDS red/blue
20190401 58573.38 22.34 3500–10 000 LCOGT + FLOYDS red/blue
20190419 58592.02 40.50 4020–7990 LT + SPRAT VPH
20190420 58593.95 42.38 4020–7990 LT + SPRAT VPH
20190423 58596.87 45.22 3600–9180 NOT + ALFOSC Grism#4
20190428 58601.91 50.13 3420–9690 NOT + ALFOSC Grism#4
20190501 58604.94 53.08 3500–9590 NOT + ALFOSC Grism#4
20190511 58614.90 62.78 3500–9690 NOT + ALFOSC Grism#4
20190516 58619.92 67.67 3500–9650 NOT + ALFOSC Grism#4
20190606 58640.93 88.14 4000–10 235 GTC + OSIRIS R1000B + R1000R
Note. ∗Rest-frame phase in days from explosion, MJD = 58550.44 ± 4. Telescope code: LCOGT: Las Cumbres Observatory; P60:
60-in Telescope; LT: 2.0-m Liverpool Telescope; NOT: Nordic Optical Telescope; GTC: Gran Telescopio Canarias.
This paper has been typeset from a TEX/LATEX file prepared by the author.
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