NICER Monitoring of the TDE AT2022lri Reveals Strong Day-timescale X-ray Flares
ATel #15751; Yuhan Yao (Caltech), Suvi Gezari (STScI)
on 10 Nov 2022; 22:44 UT
Credential Certification: Yuhan Yao (yyao@astro.caltech.edu)
Subjects: X-ray, Tidal Disruption Event
AT2022lri/ZTF22abajudi is a tidal disruption event (TDE) at z=0.032 (Yao et al. 2022, TNS Astronote, 223, 1). Soft 0.3-2 keV X-ray emission was detected by Swift/XRT on 2022 October 23.
High-cadence X-ray monitoring of this TDE is conducted with the NICER telescope (GO program 5035; PI Yao). From October 25 to November 10, NICER obtained 67 ks of observations. The minimum and maximum 0.3-1.2 keV fluxes are 4.1+/-0.3 count/s and 51.2+/-1.2 count/s, respectively. Hour-timescale X-ray variability is present. The average 0.3-1.2 keV flux on November 10 is 3.3+/-0.1 e-11 erg/s/cm^2 (=1.5 mCrab).
Defining X-ray flares to be flux variations by more than a multiplicative factor of five, we observed four flares that peaked on MJD 59880.6, 59883.2, 59887.0, and 59892.7. The flares are significant in both 0.3-0.5 keV and 0.5-1.2 keV, but are more extreme in the harder band. We computed the hardness ratio as HR=(H-S)/(H+S), where S and H are the counts in 0.3-0.5 keV and 0.5-1.2 keV, respectively. The variations of flux and HR are correlated, and the evolution roughly follows log(0.3-1.2 keV count rate) = 2.5 x HR + 1.9. For this preliminary analysis, background subtraction was not performed.
We note that similar strong day-timescale X-ray flares are rarely observed in TDEs. Further multi-wavelength observations and X-ray grating spectroscopy are strongly encouraged.
