A1 Refereed original research article in a scientific journal

SRG/ART-XC and NuSTAR Observations of the X-Ray pulsar GRO J1008-57 in the Lowest Luminosity State




AuthorsLutovinov A, Tsygankov S, Molkov S, Doroshenko V, Mushtukov A, Arefiev V, Lapshov I, Tkachenko A, Pavlinsky M

PublisherIOP PUBLISHING LTD

Publication year2021

JournalAstrophysical Journal

Journal name in sourceASTROPHYSICAL JOURNAL

Journal acronymASTROPHYS J

Article numberARTN 17

Volume912

Issue1

Number of pages6

ISSN0004-637X

DOIhttps://doi.org/10.3847/1538-4357/abec43

Self-archived copy’s web addresshttps://research.utu.fi/converis/portal/detail/Publication/56008252


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 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.


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