GRB 231025A

J.Mangan (CNRS/IJCLab) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 06:46:59.59 UT on 25 October 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 231025A (trigger 719909224/231025283).
which was also detected by Swift/BAT-GUANO (Ronchini et al. 2023, GCN 34884
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 ).
The Fermi GBM Final Real-time Localization is reported in GCN 34883
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 .

The GBM light curve consists of a single emission episode with a duration (T90)
of about 6 s (50-300 keV). The time-averaged spectrum
from T0-2.0 to T0+4.1 s is best fit by a simple power law function with index -1.4 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(1.2 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-3.1 s in the 10-1000 keV band is 1.3 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"

Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), James DeLaunay (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:

Swift/BAT did not localize GRB 231025A onboard (T0: 22023-10-25T06:46:59.59 UTC,Fermi GCN 34883
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 ). 

The Fermi 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.

The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst with a sqrt(TS) of 10.1 in a 4.096 s analysis time bin, starting at T0 -4.0961 s.

NITRATES results are consistent with a burst detected inside the BAT coded FOV, with a DeltaLLHOut of 13.17, and are consistent with Fermi GBM's localization (GCN 34883
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 ).

See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.

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/

The Fermi GBM team reports the detection of a likely SHORT GRB

"At 06:46:59.59 UT on 25 October 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 231025A (trigger 719909224/231025283).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 190.96, Dec = -53.08 (J2000 degrees, equivalent to J2000 12h 44m, -53d 05'),
with a statistical uncertainty of 16.32 degrees.

The angle from the Fermi LAT boresight is 113 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231025283/quicklook/glg_skymap_all_bn231025283.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231025283/quicklook/glg_healpix_all_bn231025283.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231025283/quicklook/glg_lc_medres34_bn231025283.gif"