SRG/ART-XC and NuSTAR observations of the X-ray pulsar GRO J1008-57 in the lowest luminosity state

Lutovinov, A.; Tsygankov, S.; Molkov, S.; Doroshenko, V.; Mushtukov, A.; Arefiev, V.; Lapshov, I.; Tkachenko, A.; Pavlinsky, M.

doi:10.48550/arxiv.2103.05728

Cited by 4 publications

(4 citation statements)

References 38 publications

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“…The evolution of the shape of the pulse profile followed the pattern typical for transient accreting X-ray pulsars, with complex evolution of pulse profiles in time as described below. Such behaviour has been reported in several pulsars Koliopanos & Gilfanov 2016;Tsygankov et al 2018;Wilson-Hodge et al 2018;Lutovinov et al 2021) and predicted theoretically as a result of the switch of the emission diagram from a pencil beam to fan-shaped beam due to the changes in accretion regime (Gnedin & Sunyaev 1973;Basko & Sunyaev 1976;Mushtukov et al 2015a), although the detailed picture is still debated (e.g. Mushtukov et al 2018).…”

Section: Evolution Of the Pulse Profilementioning

confidence: 63%

Pulsating iron spectral features in the emission of X-ray pulsar V0332+53

Bykov,

Filippova,

Gilfanov

et al. 2021

Preprint

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We present results of phase-and time-resolved study of iron spectral features in the emission of the Be/X-ray transient pulsar V 0332+53 during its type II outburst in 2004 using archival RXTE/PCA data. Coherent pulsations of both fluorescent iron line at ≈ 6.4 keV and neutral iron K-edge at ≈ 7.1 keV have been detected throughout the entire outburst. The pulsating iron K-edge is reported for the first time for this object. Near the peak of the outburst, the 3-12 keV pulse profile shows two deep, 𝐹 max /𝐹 min ∼ 2, and narrow dips of nearly identical shape, separated by exactly Δ𝜙 = 0.5 in phase. The dip spectra are nearly identical to each other and very similar in shape to the spectra outside the dips. The iron K-edge peaks at the phase intervals corresponding to the dips, although its optical depth 𝜏 𝐾 ∼ 0.05 is by far insufficient to explain the dips. The iron line shows pulsations with a complex pulse profile without any obvious correlation with the total flux or optical depth of the K-edge. Accounting for the component associated with reprocessing of the pulsar emission by the surface of the donor star and circumstellar material, we find a very high pulsation amplitude of the iron line flux, 𝐹 max /𝐹 min ∼ 10. We demonstrate that these properties of V 0332+53 can not be explained by contemporary emission models for accreting X-ray pulsars and speculate about the origin of the observed iron spectral features.

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Section: Evolution Of the Pulse Profilementioning

confidence: 63%

Pulsating iron spectral features in the emission of X-ray pulsar V0332+53

Bykov,

Filippova,

Gilfanov

et al. 2021

Preprint

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“…The analysis of the spectrum of A 0535+262 by Tsygankov et al (2019a) also showed a possible cyclotron line at 47.7 keV. The persistent low-luminosity HMXB X Persei and the transient HMXB GRO J1008−57, which has recently been observed at ∼10 35 erg s −1 (Lutovinov et al 2021), are the other examples of a similar peculiar twocomponent continuum. Tsygankov et al (2019b) suggested that the high-energy component can be explained by the production of the cyclotron photons due to collisional excitations of the Landau levels and their subsequent reprocessing in the heated atmosphere.…”

Section: Introductionmentioning

confidence: 74%

X-ray emission from magnetized neutron star atmospheres at low mass accretion rates. I. Phase-averaged spectrum

Sokolova-Lapa,

Gornostaev,

Wilms

et al. 2021

Preprint

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Recent observations of X-ray pulsars at low luminosities allow, for the first time, to compare theoretical models for the emission from highly magnetized neutron star atmospheres at low mass accretion rates ( Ṁ 10 15 g s −1 ) with the broadband X-ray data. The purpose of this paper is to investigate the spectral formation in the neutron star atmosphere at low Ṁ and to conduct a parameter study of physical properties of the emitting region. We obtain the structure of the static atmosphere, assuming that Coulomb collisions are the dominant deceleration process. The upper part of the atmosphere is strongly heated by the braking plasma, reaching temperatures of 30-40 keV, while its denser isothermal interior is much cooler (∼2 keV). We numerically solve the polarized radiative transfer in the atmosphere with magnetic Compton scattering, free-free processes, and non-thermal cyclotron emission due to possible collisional excitations of electrons. The strongly polarized emitted spectrum has a double-hump shape that is observed in low-luminosity X-ray pulsars. A low-energy "thermal" component is dominated by extraordinary photons that can leave the atmosphere from deeper layers due to their long mean free path at soft energies. We find that a high-energy component is formed due to resonant Comptonization in the heated non-isothermal part of the atmosphere even in the absence of collisional excitations. The latter, however, affect the ratio of the two components. A strong cyclotron line originates from the optically thin, uppermost zone. A fit of the model to NuSTAR and Swift/XRT observations of GX 304−1 provides an accurate description of the data with reasonable parameters. The model can thus reproduce the characteristic double-hump spectrum observed in low-luminosity X-ray pulsars and provides insights into spectral formation.

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“…All in-flight ART-XC characteristics measured in these observations have proved to be close to those expected before launch (see details below). Moreover, ART-XC revealed the transient X-ray pulsar GRO J1008-57 in the state with the lowest observed luminosity and significantly detected pulsations during this state for the first time (Lutovinov et al 2021).…”

Section: Calibration and Performance Verification Phasementioning

confidence: 92%

The ART-XC telescope on board the SRG observatory

Pavlinsky,

Tkachenko,

Levin

et al. 2021

Preprint

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ART-XC (Astronomical Roentgen Telescope -X-ray Concentrator) is the hard X-ray instrument with grazing incidence imaging optics on board the Spektr-Roentgen-Gamma (SRG) observatory. The SRG observatory is the flagship astrophysical mission of the Russian Federal Space Program, which was successively launched into orbit around the second Lagrangian point (L2) of the Earth-Sun system with a Proton rocket from the Baikonur cosmodrome on 13 July 2019. The ART-XC telescope will provide the first ever true imaging all-sky survey performed with grazing incidence optics in the 4-30 keV energy band and will obtain the deepest and sharpest map of the sky in the energy range of 4-12 keV. Observations performed during the early calibration and performance verification phase as well as during the on-going all-sky survey that started on 12 Dec. 2019 have demonstrated that the in-flight characteristics of the ART-XC telescope are very close to expectations based on the results of ground calibrations. Upon completion of its 4-year all-sky survey, ART-XC is expected to detect ∼ 5000 sources (∼ 3000 active galactic nuclei, including heavily obscured ones, several hundred clusters of galaxies, ∼ 1000 cataclysmic variables and other Galactic sources), and to provide a high-quality map of the Galactic background emission in the 4-12 keV energy band. ART-XC is also well suited for discovering transient X-ray sources. In this paper, we describe the telescope, results of its ground calibrations, major aspects of the mission, the in-flight performance of ART-XC and first scientific results.

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SRG/ART-XC and NuSTAR observations of the X-ray pulsar GRO J1008-57 in the lowest luminosity state

Cited by 4 publications

References 38 publications

Pulsating iron spectral features in the emission of X-ray pulsar V0332+53

Pulsating iron spectral features in the emission of X-ray pulsar V0332+53

X-ray emission from magnetized neutron star atmospheres at low mass accretion rates. I. Phase-averaged spectrum

The ART-XC telescope on board the SRG observatory

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