TITLE:   GCN CIRCULAR
NUMBER:  33297
SUBJECT: ZTF23aabmzlp/AT2023azs: Neil Gehrels Swift Observatory X-ray observations
DATE:    23/02/07 15:14:32 GMT
FROM:    Igor Andreoni at JSI  <igor.andreoni@gmail.com>

Igor Andreoni (JSI/UMD/NASA-GSFC) reports on behalf of a larger
collaboration


Follow-up observations of the optical fast transient ZTF23aabmzlp/AT2023azs
(Andreoni et al., GCN #33229, AstroNote 2023-21) were carried out with the
Neil Gehrels Swift Observatory starting on 2023-01-29 09:54 UT. The total
exposure time on target was 1.9ks.

A faint source is tentatively detected in Swift XRT data at the location of
ZTF23aabmzlp/AT2023azs in the 0.3-10 keV energy range. The source has a
background-subtracted count rate of (2.5 +- 1.1) * 10^(-3) ct/s, which was
obtained using an aperture with a radius of 18 arcsec.

Using WebPIMMS [1], we converted the count rate to flux assuming a
powerlaw model with a photon index of 2 and Galactic NH of 9.85E19 cm^(-2)
[2]. The resulting flux in the 0.3-10 keV band is (8.6 +- 3.8) * 10^(-14)
erg/s/cm^2.

The possible detection of an X-ray counterpart and the detection of a radio
counterpart with VLA (Perley et al., GCN #33253) further suggest that the
fast optical transient ZTF23aabmzlp/AT2023azs is a cosmological afterglow.


We thank the Swift team for approving and scheduling ToO observations of
this source (target ID 15860).

[1] https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/w3pimms/w3pimms.pl
[2] HI4PI Collaboration, N. Ben Bekhti, L. Floer, et al., 2016, Astronomy &
Astrophysics, 594, A116 (HI4PI Map).