[vsnet-grb-info 27587] IceCube 135113_19489408.amon: Swift-XRT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29690
SUBJECT: IceCube 135113_19489408.amon: Swift-XRT observations
DATE:    21/03/22 16:29:13 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

J.P. Osborne (U. Leicester), F. Krauss (PSU), T. Gregoire (PSU), P.A. Evans (U.
Leicester), J.A. Kennea (PSU), H. A. Ayala Solares (PSU), D.F. Cowen (PSU), J.
DeLaunay (PSU) and D. B. Fox (PSU) report:

Swift has observed the field of the IceCube Astrotrack Bronze
135113_19489408.amon. 4ks of cleaned XRT data were gathered between 04:55 and
07:03 UT on 2021 March 22.

A point source is reliably detected at RA, Dec = (85.73812, -44.7522) which is
equivalent to:

  RA(J2000.0) = 05h 42m 57.15s
  Dec(J2000.0) = -44d 45’ 07.9”

with an uncertainty of 5.1” (radius, 90% confidence). This position is consistent
with the source 1RXS J054257.9-444452 in the RASS Faint Source Catalogue. Using
a spectrum fitted to the XRT data, we find that the current 0.3-10 keV flux is
9.7 (+3.4, -2.7) ×10^-13 erg cm^-2 s^-1, which is about 3.7-sigma above the
catalogued flux, suggesting variability or possibly an outburst: however, we
caution that the spectral fit is very uncertain, and this flux increase should
be viewed with caution.

The source has no counterpart in SIMBAD, although it is a few arcseconds from a
WISE object.

Given the low statistical quality of the XRT spectral information, the lack of
blazar classification for the RASS source, and the likelihood that the alert was
caused by a muon, not an astrophysical neutrino (GCN Circ. 29688), we cannot
claim this as a probable counterpart; however, should variability be detected at
other wavelengths the case for this source as an interesting object would be
strengthened.