Discovery of a late-time X-ray brightening and spectral hardening in the TDE AT2019teq
ATel #15657; Yuhan Yao (Caltech), Muryel Guolo (JHU)
on 10 Oct 2022; 16:09 UT
Credential Certification: Yuhan Yao (yyao@astro.caltech.edu)
Subjects: X-ray, Tidal Disruption Event
AT2019teq/ZTF19accmaxo is a tidal disruption event (TDE) discovered by the Zwicky Transient Facility (ZTF) on 2019 October 20. It is one of the 30 TDEs selected by Phase I of ZTF (Hammerstein et al. 2022). Hereafter we use t to denote rest-frame days since its optical maximum (MJD 58794.3).
From 2019 December 14 to 2020 May 7 (t = 34--167 days), AT2019teq was observed by the Swift/XRT. The combined XRT spectrum (25ks) was soft, and only detected above background up to 4.0 keV. We modeled the spectrum with tbabs*ztbabs*zashift*powerlaw, with the Galactic column density fixed at nH(0)=5.3e+20 cm^-2 and the redshift fixed at 0.0878. The best-fit model indicates a power-law index of Gamma = 3.52 + 0.53 -0.45 and an absorption at the host redshift of nH(z)=0.14 +0.09 -0.07 e+22 cm^-2. The observed 0.3--10 keV flux is 3.6 +/- 0.2 e-13 erg s^-1 cm^-2, corresponding to an isotropic equivalent luminosity of 6.9 +/- 0.4 e+42 erg/s.
On 2022 September 8 (t = 952 days), AT2019teq was observed by XMM-Newton as part of GO (AO 21) program (P.I. Yao). The spectrum shows clear hardening, the source is detected above background up to 6.0 keV. We modeled the spectrum with tbabs*ztbabs*zashift*powerlaw, with the Galactic column density and the redshift fixed. The best-fit model indicates a power-law index of Gamma = 2.99 +/- 0.01 and an absorption at the host redshift of nH(z)=0.19 +/- 0.1 e+22 cm^-2. The observed 0.3--10 keV flux is 1.0 +/- 0.1 e-12 erg s^-1 cm^-2, corresponding to an isotropic equivalent luminosity of 1.92 +/- 0.02 e+43 erg/s.
A late-time spectral hardening in a TDE might be caused by the delayed formation of a magnetically dominated corona. Clear detections have recently been reported in AT2018fyk (Wevers et al. 2021) and AT2021ehb (Yao et al. 2022).
Given the X-ray spectral evolution and the brightening, we encourage multi-wavelength follow-up observations, particularly in the radio band to search for the presence of a jet/outflow.
Hammerstein et al. 2022, arxiv: 2203.01461
Wevers et al. 2021, ApJ, 912, 151
Yao et al. 2022, ApJ, 937, 8
