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  • SRG/ART-XC and NuSTAR Obser...
    Lutovinov, A.; Tsygankov, S.; Molkov, S.; Doroshenko, V.; Mushtukov, A.; Arefiev, V.; Lapshov, I.; Tkachenko, A.; Pavlinsky, M.

    The Astrophysical journal, 05/2021, Letnik: 912, Številka: 1
    Journal Article

    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 ×10 34 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.