TITLE:   GCN CIRCULAR
NUMBER:  46120
SUBJECT: GRB 261030A: Fermi GBM Detection
DATE:    26/10/30 22:22:02 GMT
FROM:    Angus Jameson <abj0023@uah.edu>

A. Jameson (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 16:27:22.28 UT on 30 October 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 261030A (trigger 815070447/261030686).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 340.59, Dec = 7.07 (J2000 degrees, equivalent to
J2000 22h 42m, +7d 4'), with a statistical uncertainty of 1.00 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 74 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 37 s (50-300 keV). The time-averaged spectrum
from T0-2.2 to T0+48.7 s is best fit by
a Band function with Epeak = 117.9 +/- 0.8 keV,
alpha = -1.080 +/- 0.002, and beta = -2 +/- 0.01.

The event fluence (10-1000 keV) in this time interval is
(2.29 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+18 s in the 10-1000 keV band is 11.7 +/- 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/"