SRG/ART-XC and NuSTAR Observations of the X-Ray pulsar GRO J1008-57 in the Lowest Luminosity State
Lapshov I; Doroshenko V; Lutovinov A; Tsygankov S; Arefiev V; Molkov S; Pavlinsky M; Tkachenko A; Mushtukov A
https://urn.fi/URN:NBN:fi-fe2021093048197
Tiivistelmä
We report results of the first broadband observation of the transient X-ray pulsar GRO J1008-57 performed in the quiescent state. Observations were conducted quasi-simultaneously with NuSTAR and the Mikhail Pavlinsky ART-XC telescope on board SRG right before the beginning of a Type I outburst. GRO J1008-57 was detected in the state with the lowest observed luminosity around several x1034 erg s-1 and consequently accreting from the cold disk. Timing analysis allowed us to detect pulsations during this state for the first time. The observed pulsed fraction of about 20% is, however, almost three times lower than in brighter states when the accretion proceeds through the standard disk. We traced the evolution of the broadband spectrum of the source on a scale of three orders of magnitude in luminosity and found that at the lowest luminosities the spectrum transforms into the double-hump structure similarly to other X-ray pulsars accreting at low luminosities (X Persei, GX 304-1, and A 0535+262) reinforcing the conclusion that this spectral shape is typical for these objects.
Kokoelmat
- Rinnakkaistallenteet [19207]