X-ray Brightening of AT2019wey

ATel #13932; Y. Yao (Caltech), T. Enoto (RIKEN), D. Altamirano (Univ. of Southampton), P. S. Ray (NRL), M. Ng (MIT), Z. Arzoumanian, K. C. Gendreau, T. E. Strohmayer (NASA/GSFC), Z. Wadiasingh (NASA/GSFC/USRA), & S. R. Kulkarni (Caltech)
on 10 Aug 2020; 17:10 UT
Credential Certification: Yuhan Yao (yyao@astro.caltech.edu)

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AT2019wey (ATLAS19bcxp) rose to prominence with the discovery of strong X-ray emission by the Spectrum-Roentgen-Gamma (SRG) mission (ATel #13571). Our Keck/LRIS spectroscopy obtained in March 2020 shows hydrogen lines in absorption (z=0). Recent Palomar 200-inch spectroscopy shows H-alpha in emission, and separately we detected radio emission in the decimeter band (ATel #13921). These observations suggest an accreting binary and motivated us to pursue Swift/XRT and NICER monitoring of the source.
From 2020 Apr 12 to Aug 9, the XRT count rate in the 0.3-10 keV band has increased from 0.6 count/s (cps) to 3.7 cps. From 2020 Aug 4 to Aug 9, the NICER count rate in the 0.4-10 keV band has increased from 100 cps to 170 cps (110 cps is approximately 10 mCrab). The time-averaged NICER spectrum can be fitted with a combined black-body (kT = 0.13 keV) and power-law (photon index = 1.9) model with absorption column NH = 5.6e+21 cm-2. Timing analysis shows strong band-limited noise below 1 Hz but no clear evidence of coherent pulsations or quasiperiodic oscillations.
In view of the brightening, observations in other bands would be very useful.
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.