The optical transient AT2019qiz started a decay as seen with Swift
ATel #13193; Wenda Zhang (Astronomical Institute, Czech Academy of Sciences), Wenfei Yu, Zhen Yan and Stefano Rapisarda (Shanghai Astronomical Observatory)
on 15 Oct 2019; 04:34 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)
Subjects: Optical, Ultra-Violet, X-ray, Transient, Tidal Disruption Event
AT2019qiz is a tidal disruption event (TDE) candidate initially discovered in the optical wavelength on the rise (Atel #13131, #13143, #13146, #13170). Neil Gehrel Swift has monitored the source in the past two weeks in the UV and optical bands as well as in the soft X-ray band simultaneously.
A recent Swift observation on 2019-10-13 07:42:07 (UT, obsid: 00012012011) of AT2019qiz indicated that the source is probably entering its decay phase, as compared with the observation taken three days earlier on 2019-10-10 01:41:48 (UT, obsid: 00012012010). The magnitudes in the W1, M2, and W2 bands increased from 14.28 +/- 0.05, 14.18 +/- 0.05, and 14.31 +/- 0.07 to 14.45 +/- 0.06, 14.38 +/- 0.05, and 14.54 +/- 0.07, respectively. In the meantime, the fluxes in the U and B bands are consistent with remaining constant, with the U magnitude evolved from 14.87 +/- 0.06 to 14.94 +/- 0.06 and the B magnitude evolved from 15.77 +/- 0.06 to 15.85 +/- 0.06. The V magnitude increased from 15.52 +/- 0.07 to 15.70 +/- 0.08. The trend suggests that the source is under a flux decay.
The source was also observed simultaneously by Neil Gehrel Swift/XRT with a net exposure of 1.00 ks. We performed source detection using Ximage/sosta and concluded that no X-ray source is detected at the position of AT2019qiz. The 3-sigma upper limit on the 0.3-10 keV count rate is 1.15e-2 c/s, corresponding to an upper limit of 4.16e-13 erg/s/cm^{-2} on the 0.3-10 keV flux if assuming a spectrum of absorbed power-law with a photon index of 2 and a Galactic neutral hydrogen column density of 6.5e20 cm^{-2}.
We encourage multi-wavelength follow-up observations of the source which is probably under a decay. We would like to thank the Swift team for approving and scheduling these observations.
