AstroNote 2021-258

The nuclear transient ZTF21abqhkjd/AT2021uqv was first detected by the Zwicky Transient Facility (ZTF; Bellm et al. 2019; Graham et al. 2019) on 2021 July 29 with g=20.4 mag, and first reported to TNS as a ZTF transient by ALeRCE on August 2. The source rose to peak in ~25 days, exhibited a persistent blue color of g-r ~ = -0.2 mag, and was selected by us as a TDE candidate (van Velzen et al. 2019).

On August 13, we obtained a Keck-I LRIS spectrum, which displays host galaxy lines at the redshift z=0.106, a blue continuum, and broad features around Halpha and the He II 4868A complex. The spectral features are characteristic of optically selected TDEs (van Velzen et al. 2021).

We triggered the Swift X-ray telescope. The first two Swift observations were obtained on August 28 (1.61 ks) and September 15 (1.73 ks). On Aug 28, an X-ray source in coincidence with the optical position of ZTF21abqhkjd was detected at 3.04-sigma with a count rate of 0.00735 +/- 0.0024 count/s. On Sep 15, we did not detect any X-ray sources at >3-sigma. In the stacked image (Aug 28 + Sep 15), ZTF21abqhkjd was detected at 3.30-sigma with a count rate of 0.00439 +/- 0.0013 count/s. 

The third Swift observation was obtained on October 2 (3.11 ks), where ZTF21abqhkjd was detected at 4.33-sigma with a count rate of 0.00787 +- 0.0018 count/s. An absorbed blackbody model fit to the Oct 2 XRT spectrum suggests a blackbody temperature of ~60 eV, and a 0.3--1 keV flux of 2e-13 erg/cm^2/s, corresponding to a luminosity of 6e+42 erg/s.

Swift/UVOT observations show that ZTF21abqhkjd is bright in the UV with uvw2-r ~ -0.5 mag. 

Further follow-up observations for this X-ray bright TDE are encouraged.

We thank the Swift team for the prompt approval and execution of our TOO observations. This report is based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.