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NuSTAR Observations of the Transient Galactic Black Hole Binary Candidate Swift J1858.6–0814: A New Sibling of V404 Cyg and V4641 Sgr?

Hare, Jeremy and Tomsick, John A. and Buisson, Douglas J. K. and Clavel, Maïca and Gandhi, Poshak and García, Javier A. and Grefenstette, Brian W. and Walton, Dominic J. and Xu, Yanjun (2020) NuSTAR Observations of the Transient Galactic Black Hole Binary Candidate Swift J1858.6–0814: A New Sibling of V404 Cyg and V4641 Sgr? Astrophysical Journal, 890 (1). Art. No. 57. ISSN 1538-4357.

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Swift J1858.6−0814 was discovered by the Burst Alert Telescope on Swift on 2018 October 25. Here we report on the first follow-up Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the source, which shows variability spanning two orders of magnitude in count rate on timescales of ~10–100 s. The power spectrum of the source does not show any quasi-periodic oscillations or periodicity, but has a large fractional rms amplitude of 147% ± 3%, exhibiting a number of large flares throughout the observation. The hardness ratio (defined as R_(10–79keV)/R_(3–10keV)) of the flares tends to be soft, while the source spans a range of hardness ratios during nonflaring periods. The X-ray spectrum of the source shows strong reflection features, which become more narrow and peaked during the nonflaring intervals. We fit an absorbed relativistic reflection model to the source spectra to place physical constraints on the system. Most notably, we find that the source exhibits a large and varying intrinsic absorbing column density (N_H = (1.4–4.2) × 10²³ cm⁻²). This large intrinsic absorption is further supported by the energy spectra extracted from two flares observed simultaneously by NuSTAR and the Neutron Star Interior Composition Explorer. We find that the inner accretion disk of the source has a low inclination, I < 29∘ (3σ upper limit), while the iron abundance in the disk is close to solar, A_(Fe) = 1.0 ± 0.3. We set a 90% confidence upper limit on the inner radius of the accretion disk of r_(in) < 8r_(ISCO) and, by fixing r_(in) to be at r_(ISCO), a 90% confidence lower limit on the spin of the black hole of a∗ > 0.0. Finally, we compare the properties of Swift J1858.6−0814 to those of V404 Cygni and V4641 Sgr, which both show rapid flaring and a strong and variable absorption.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hare, Jeremy0000-0002-8548-482X
Tomsick, John A.0000-0001-5506-9855
Clavel, Maïca0000-0003-0724-2742
Gandhi, Poshak0000-0003-3105-2615
García, Javier A.0000-0003-3828-2448
Grefenstette, Brian W.0000-0002-1984-2932
Walton, Dominic J.0000-0001-5819-3552
Xu, Yanjun0000-0003-2443-3698
Additional Information:© 2020 The American Astronomical Society. Received 2019 November 4; revised 2019 December 27; accepted 2020 January 8; published 2020 February 12. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). J.H. and J.A.T. acknowledge partial support from NuSTAR Guest Observer grant 80NSSC19K0404. J.H. acknowledges support from an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by the USRA through a contract with NASA. D.J.W. acknowledges support from STFC in the form of an Ernest Rutherford Fellowship. M.C. acknowledges support from the Centre National d'Etudes Spatiales (CNES). J.A.G. acknowledges support from NASA grant 80NSSC19K1020 and from the Alexander von Humboldt Foundation. We thank the anonymous referee for providing useful comments which have improved the quality of this paper. Software: XSPEC (v12.10.1; Arnaud 1996), NUSTARDAS (v1.8.0), NICERDAS (V005), Stingray (Huppenkothen et al. 2017), Xselect (v2.4e), Matplotlib (Hunter 2007), HEASOFT (v6.25), MWDust (Bovy et al. 2016), XILLVER (García & Kallman 2010; García et al. 2013), RELXILL (v1.2.0; Dauser et al. 2014; García et al. 2014).
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
NASA Postdoctoral ProgramUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
Subject Keywords:Stellar mass black holes; X-ray transient sources; Lowmass X-ray binary stars
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Stellar mass black holes (1611); X-ray transient sources (1852); Lowmass X-ray binary stars (939)
Record Number:CaltechAUTHORS:20200212-140525387
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Official Citation:Jeremy Hare et al 2020 ApJ 890 57
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101248
Deposited By: Tony Diaz
Deposited On:12 Feb 2020 22:15
Last Modified:12 Feb 2020 22:15

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