A Comprehensive X-ray Report on AT2019wey
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2020-11-30
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Yao, Yuhan; Kulkarni, S. R.; Gendreau, K. C.; Jaisawal, Gaurava K.; Enoto, Teruaki; Grefenstette, Brian W.; Marshall, Herman L.; Garcia, Javier A.; Ludlam, R. M.; Pike, Sean N.; Ng, Mason; Zhang, Liang; Altamirano, Diego; Jaodand, Amruta; Cenko, S. Bradley; Remillard, Ronald A.; Steiner, James F.; Negoro, Hitoshi; Brightman, Murray; Lien, Amy; Wolff, Michael T.; Ray, Paul S.; Mukai, Koji; Wadiasingh, Zorawar; Arzoumanian, Zaven; Kawai, Nobuyki; Mihara, Tatehiro; Strohmayer, Tod E.; A Comprehensive X-ray Report on AT2019wey; High Energy Astrophysical Phenomena (2020); https://arxiv.org/abs/2012.00160
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0
This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
The Galactic low-mass X-ray binary AT2019wey (ATLAS19bcxp, SRGA J043520.9+552226, SRGE J043523.3+552234, ZTF19acwrvzk) was discovered as a new optical transient in Dec 2019, and independently as an X-ray transient in Mar 2020. In this paper, we present comprehensive NICER, NuSTAR, Chandra, Swift, and MAXI observations of AT2019wey from ~1 year prior to the discovery to the end of September 2020. AT2019wey appeared as a ~1 mCrab source and stayed at this flux density for several months, displaying a hard X-ray spectrum that can be modeled as a power-law with photon index Gamma~1.8. In June 2020 it started to brighten, and reached ~20 mCrab in ~2 months. The inclination of this system can be constrained to i<~30 deg by modeling the reflection spectrum. Starting from late-August (~59082 MJD), AT2019wey entered into the hard-intermediate state (HIMS), and underwent a few week-long timescale outbursts, where the brightening in soft X-rays is correlated with the enhancement of a thermal component. Low-frequency quasi-periodic oscillation (QPO) was observed in the HIMS. We detect no pulsation and in timing analysis of the NICER and NuSTAR data. The X-ray states and power spectra of AT2019wey are discussed against the landscape of low-mass X-ray binaries.