TITLE:   GCN CIRCULAR
NUMBER:  43634
SUBJECT: GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
DATE:    26/02/08 04:24:37 GMT
FROM:    Rushikesh Sonawane  at IISER, TVM <rushikesh23@iisertvm.ac.in>

R. Sonawane (IISER, TVM) and S. Bala (USRA) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 13:12:10.83 UT on 07 February 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260207B (trigger 792162735/260207550).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 292.87, Dec = 50.03 (J2000 degrees, equivalent to
J2000 19h 31m, +50d 1'), with a statistical uncertainty of 2.81 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 45 degrees.

The GBM light curve consists of a short spike (Main Emission, ME) 
followed by an extended emission (EE) with a total duration (T90) of about 56 s (50-300 keV).

The ME from T0-1 to T0+5 s is best fit by a power law function with an 
exponential high-energy cutoff. The power law index is -1.18 +/- 0.07 and the
cutoff energy, parameterized as Epeak, is 350 +/- 65 keV. The total fluence (10-1000 keV) 
in this time interval is (2.7 +/- 0.1)E-06 erg/cm^2.

The EE from T0+10 to T0+89 s, is best fit by a Band function with 
Epeak= 32 +/- 4 keV, alpha = -1.7 +/- 0.1 and beta = -2.4 +/- 0.1. 
The total fluence (10-1000 keV) during this time interval is (7.5 +/- 0.4)E-06 erg/cm^2. 


The time-averaged (ME+EE) spectrum from T0-2 to T0+89 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.83 +/- 0.05 and the cutoff energy,
parameterized as Epeak, is 67 +/- 9 keV. A Band function fits this interval equally
well with Epeak= 52 +/- 10 keV,  alpha = -1.7 +/- 0.1 and beta = -2.2 +/- 0.1. 
The event fluence (10-1000 keV) in this time interval is (9.6 +/- 0.5)E-06 erg/cm^2. 
The 1-sec peak photon flux measured starting from T0+0.0024 s in the 10-1000 keV band
is 16.6 +/- 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/"