GCN Circular 17505
Subject
GRB 150220A: Fermi GBM observation
Date
2015-02-24T17:40:09Z (10 years ago)
From
Oliver Roberts at UCD/Fermi <oliver.roberts@ucd.ie>
O.J. Roberts (UCD) and C. Meegan (UAH) report on behalf of
the Fermi GBM Team:
"At 14:21:35.60 UT on the 20th of February 2015, the Fermi
Gamma-Ray Burst Monitor triggered and located GRB 150220A
(trigger 446134898 / 150220598), which was also detected by
IPN (Hurley et al. 2015, GCN 17502) and Konus-Wind
(Golenetskii et al. 2015, GCN 17503 ). The GBM on-ground
location is consistent with the IPN triangulated position.
The angle from the Fermi LAT boresight is 78 degrees.
The GBM light curve shows three pulses occurring over two
main emission episodes. These episodes begin at about
T0-9.5s and T0+105s respectively. The duration (T90) of the
entire light curve is about 145s (50-300 keV).
The time-averaged spectrum of both emission episodes, from
T0-9.5s to T0+37.6s and from T0+104.7s to T0+162.6s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.02 +/- 0.03
and the cutoff energy, parameterised as Epeak, is
192.3 +/- 9.5 keV.
The event fluence (10-1000 keV) in this time interval is
(2.72 +/- 0.07)E-05 erg/cm^2. The 1.024-sec peak photon
flux measured starting from T0+17.9 s in the 10-1000 keV
band is 15.7 +/- 0.4 ph/s/cm^2.
A Band function fits the spectrum equally well with
Epeak = 170.8 +/- 12.8 keV, alpha = -0.97 +/- 0.05
and beta = -2.41 +/- 0.21.
The spectral analysis results presented above are
preliminary; final results will be published in the GBM
GRB Catalog."