GCN Circular 39060
Samuele Ronchini (PSU), James DeLaunay (PSU), Tyler Parsotan (NASA GSFC), Jamie A. Kennea (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU) report:
Swift/BAT did not detect EP250125a onboard (T0: 2025-01-25T02:37:31.749 UTC, EP GCN 39028).
The EP notice distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
Using the NITRATES analysis (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), we searched for emission on 8 timescales from 0.128s to 16.384s in the interval [-20,+20] seconds around the trigger time. We find no evidence for a signal, and derive the following upper limits.
We quote the 5-sigma flux upper limits in the 15-350 keV band, computed at the EP250125a position RA = 175.36337 deg , Dec = -21.71347 deg provided in GCN 39029, for three spectral templates (soft, normal, and hard GRB-like templates described in [arXiv:1612.02395]) and for four time bins. In units of 10^-7 erg/s/cm^2:
| time_bin (s) | soft | normal | hard |
|---|---|---|---|
| 0.256 | 7.23 | 5.47 | 5.08 |
| 1.024 | 3.68 | 2.79 | 2.59 |
| 4.096 | 1.98 | 1.50 | 1.39 |
| 16.384 | 1.21 | 0.92 | 0.85 |
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/