Hae
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A kilonova as the electromagnetic counterpart to a gravitational-wave source
Gravitational waves were discovered with the detection of binary black-hole mergers(1) and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive ...
The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor
Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae(1). However, while such stars are observed with masses > 25 M-circle dot (ref. (2)), detections of > 18 M-circle ...
Extreme variability in an active galactic nucleus: Gaia16aax
We present the results of a multiwavelength follow-up campaign for the luminous nuclear transient Gaia16aax, which was first identified in 2016 January. The transient is spatially consistent with the nucleus of an active ...
The evolution of superluminous supernova LSQ14mo and its interacting host galaxy system
We present and analyse an extensive dataset of the superluminous supernova (SLSN) LSQ14mo (z = 0.256), consisting of a multi-colour light curve from -30 d to +70 d in the rest-frame (relative to maximum light) and a series ...
SN 2017gci: a nearby Type I Superluminous Supernova with a bumpy tail
We present and discuss the optical spectrophotometric observations of the nearby (z = 0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches M-g = -21.5 mag. Its ...
Evidence for rapid disc formation and reprocessing in the X-ray bright tidal disruption event candidate AT 2018fyk
We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) candidate AT 2018fyk/ASASSN-18ul discovered by ASAS-SN. The Swift light curve is atypical for ...
Observations of the GRB Afterglow ATLAS17aeu and Its Possible Association with GW170104
We report the discovery and multiwavelength data analysis of the peculiar optical transient, ATLAS17aeu. This transient was identified in the sky map of the LIGO gravitational wave event GW 170104 by our ATLAS and Pan-STARRS ...
Forbidden hugs in pandemic times: I. Luminous red nova AT 2019zhd, a new merger in M 31
<p>We present the follow-up campaign of the luminous red nova (LRN) AT 2019zhd, the third event of this class observed in M 31. The object was followed by several sky surveys for about five months before the outburst, during which it showed a slow luminosity rise. In this phase, the absolute magnitude ranged from M<sub>r</sub>=-2.8 +/- 0.2 mag to M<sub>r</sub>=-5.6 +/- 0.1 mag. Then, over a four to five day period, AT 2019zhd experienced a major brightening, reaching a peak of M<sub>r</sub>=-9.61 +/- 0.08 mag and an optical luminosity of 1.4x10<sup>39</sup> erg s<sup>-1</sup>. After a fast decline, the light curve settled onto a short-duration plateau in the red bands. Although less pronounced, this feature is reminiscent of the second red maximum observed in other LRNe. This phase was followed by a rapid linear decline in all bands. At maximum, the spectra show a blue continuum with prominent Balmer emission lines. The post-maximum spectra show a much redder continuum, resembling that of an intermediate-type star. In this phase, Hα becomes very weak, Hβ is no longer detectable, and a forest of narrow absorption metal lines now dominate the spectrum. The latest spectra, obtained during the post-plateau decline, show a very red continuum (T<sub>eff</sub> ≈ 3000 K) with broad molecular bands of TiO, similar to those of M-type stars. The long-lasting, slow photometric rise observed before the peak resembles that of LRN V1309 Sco, which was interpreted as the signature of the common-envelope ejection. The subsequent outburst is likely due to the gas outflow following a stellar merging event. The inspection of archival HST images taken 22 years before the LRN discovery reveals a faint red source (M<sub>F555W</sub>=0.21 +/- 0.14 mag, with F555W-F814W = 2.96 +/- 0.12 mag) at the position of AT 2019zhd, which is the most likely quiescent precursor. The source is consistent with expectations for a binary system including a predominant M5-type star.</p>...
PS15cey and PS17cke: prospective candidates from the Pan-STARRS Search for kilonovae
Time domain astronomy was revolutionized with the discovery of the first kilonova, AT2017gfo, in August 2017, which was associated with the gravitational wave signal GW170817. Since this event, numerous wide-field surveys ...
Forbidden hugs in pandemic times II. The luminous red nova variety: AT 2020hat and AT 2020kog
We present the results of our monitoring campaigns of the luminous red novae (LRNe) AT 2020hat in NGC 5068 and AT 2020kog in NGC 6106. The two objects were imaged (and detected) before their discovery by routine survey ...