GCN Circular 33120
I. Andreoni (JSI/UMD/NASA-GSFC), N. Klingler (NASA-GSFC), D. Pasham (MIT), M. Coughlin (UMN) Follow-up observations of the optical fast transient ZTF22acaruqr/AT2022adzb (Coughlin et al., AstroNote 2022-270) were carried out with the Neil Gehrels Swift Observatory starting on 2022-12-25 02:19:02 UT until 2022-12-25 14:58:25 UT. The total exposure time on source was 3.27ks. A faint source is detected in Swift X-ray Telescope data in the 0.3-10 keV energy range. The source is spatially consistent with ZTF22acaruqr/AT2022adzb and has a background-subtracted count rate of (4.3 +- 1.3) * 10^(-3) ct/s. We fit the 0.3-10.0 keV X-ray spectrum containing 15 counts with a powerlaw model (tbabs * powlaw in XSPEC) which resulted in a c-stat/degrees of freedom of 8.5/11. The best-fit powerlaw index was constrained to be <1.8 while the observed 0.3-10 keV flux was 5(+2.5,-2.2)e-13 erg/s/cm^2 (68% confidence). No source is detected at the location of ZTF22acaruqr/AT2022adzb with the UVOT instrument using the uvm2 filter with a limiting magnitude of > 23.1 mag (AB). The source with the smallest separation from ZTF22acaruqr/AT2022adzb is located at RA, Dec = 124.51569 deg, 55.32129 deg and is likely a galaxy (Duncan et al., 2022) at a photometric redshift of zph = 0.6881 +- 0.1994 (Legacy Survey). If this source is the host, the projected separation from ZTF22acaruqr/AT2022adzb would be 29.4 kpc at the median redshift of z=0.6881. This galaxy is not cataloged as a possible AGN. The nature of the transient remains unclear. Follow-up observations are encouraged especially to measure the redshift and assess if the detected X-ray source is variable. We have planned NICER exposures in the coming days.