UV/optical brightening of the TDE candidate AT2019qiz as detected by Swift

ATel #13146; Wenda Zhang (Astronomical Institute, the Academy of the Czech Republic), Wenfei Yu, Zhen Yan, Stefano Rapisarda (Shanghai Astronomical Observatory)
on 30 Sep 2019; 03:01 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)

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AT2019qiz is a tidal disruption event (TDE) candidate probably young and in the rise (Atel #13131). An earlier Neil Gehrel Swift/XRT pointed observation taken on 2019-09-27 indicated that the source was not detected in the X-ray (Atel #13143). Swift observed the source for the third time on 2019-09-29UT09:14:47 (obsid: 00012012003), with all six filters of Swift/UVOT used as the previous observation. We perform aperture photometry on the images of all the six filters. By comparing the source fluxes between the most recent observation and the one taken on 2019-09-27UT01:18:16 (obsid: 00012012002), we find that the source appears to brighten in the U, UVW1, UVM2, and UVW2 bands. The filter magnitudes on 2019-09-27 were 15.68 +/- 0.06, 15.39 +/- 0.06, 15.30 +/- 0.06, and 15.07 +/- 0.07, respectively, while the magnitudes on 2019-09-29 were 15.53 +/- 0.07, 15.21 +/- 0.06, 15.20 +/- 0.06, and 14.96 +/- 0.07, although the brightening in the individual UVM1 and UVW2 band is not significant. In the meantime, the fluxes in the U and B bands are consistent with remaining constant, with the V magnitude evolved from 16.04+/-0.08 to 16.07+/-0.09, and the B magnitude evolved from 16.43+/-0.06 16.45+/-0.07. The flux comparison can be seen at 202.127.29.4/wenfei/AT2019qiz_uvotlc.png

The source was also observed simultaneously by Neil Gehrel Swift/XRT with a net exposure of 1.02 ks. We perform source detection using Ximage/sosta and find that no source was detected at the position of AT2019qiz. The 3-sigma upper limit on the 0.3-10 keV count rate is 1.13e-2 c/s, corresponding to an upper limit of 4.09e-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}.

The apparent brightening of AT2019qiz in the UV/optical bands is consistent with a TDE candidate in the rise. We encourage multi-wavelength follow-up observations of the source. We would like to thank the Swift team for approving and scheduling our ToO request.