//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29688 SUBJECT: IceCube Astrotrack Bronze 135113_19489408.amon is likely background DATE: 21/03/22 03:42:56 GMT FROM: Marcos Santander at U. Alabama/IceCube The IceCube Collaboration (http://icecube.wisc.edu/ ) reports: On 2021-03-22 at 02:34:09.177018 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream (https://gcn.gsfc.nasa.gov/notices_amon_g_b/135113_19489408.amon ). The threshold astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 1.382 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. Upon further examination of the light deposition pattern of this event in the detector, and in particular due to the presence of light deposition in its veto region, it is likely that it was caused by a down-going muon (background) rather than by a high-energy neutrino. Studies of this event will continue over the coming days and, if the background hypothesis is rejected, we will issue further updates. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu //////////////////////////////////////////////////////////////////////// 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 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.