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GCN Circular 33120

Subject
ZTF22acaruqr/AT2022adzb: Neil Gehrels Swift Observatory X-ray detection
Date
2022-12-29T00:48:26Z (a year ago)
From
Igor Andreoni at JSI <igor.andreoni@gmail.com>
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.
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