GCN Circular 34128
Subject
LIGO/Virgo/KAGRA S230627c: Upper limits from Swift/BAT-GUANO
Date
2023-07-01T03:37:08Z (a year ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Gayathri Raman (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), James DeLaunay (U Alabama), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT was observing 99.2% of the GW localization probability (Bilby.multiorder.fits,0) at merger time.
The entirety of the GW 90% credible region is contained inside the coded FoV.
The LVK 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 merger 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, weighted over the GW localization, for four spectral templates (soft, normal, and hard GRB-like templates described in [arXiv:1612.02395], and spectral shape from GRB170817A [arXiv:1710.05446]) and for four time bins.
In units of 10^-8 erg/s/cm^2:
Bin duration (s) | hard normal soft GRB 170817A
----------------------------------------------------
0.256 | 7.0 7.7 4.9 8.3
1.024 | 3.6 4.0 2.5 4.2
4.096 | 1.9 2.2 1.4 2.3
16.384 | 1.2 1.3 0.8 1.4
For a median distance of 291 Mpc, we derive luminosity upper limits (in units of 10^47 erg/s) as follows:
Bin duration (s) | hard normal soft GRB 170817A
-----------------------------------------------------
0.256 | 7.1 7.8 5.0 8.4
1.024 | 3.6 4.0 2.5 4.3
4.096 | 2.0 2.2 1.4 2.3
16.384 | 1.2 1.3 0.8 1.4
The upper limits as function of sky position are plotted here, alongside the GW localization:
https://doi.org/10.5281/zenodo.8102958
The corresponding fits file can be found here:
https://doi.org/10.5281/zenodo.8102951
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/