SRG/ART-XC and NuSTAR Observations of the X-Ray pulsar GRO J1008-57 in the Lowest Luminosity State
Abstract
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 ×1034 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2021
- DOI:
- 10.3847/1538-4357/abec43
- arXiv:
- arXiv:2103.05728
- Bibcode:
- 2021ApJ...912...17L
- Keywords:
-
- Pulsars;
- Neutron stars;
- High mass x-ray binary stars;
- 1306;
- 1108;
- 733;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 5 figures, accepted to ApJ