GRB 220228A

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

At 10:30:05.92 UT on 28 Feb 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 220228A (trigger 667737010 / 220228438).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 321.0, Dec = -16.9 (J2000 degrees, equivalent to J2000 21h 24m, -16d 54'), with a statistical uncertainty of 8.5 degrees.

The angle from the Fermi LAT boresight is 28.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220228438/quicklook/glg_skymap_all_bn220228438.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220228438/quicklook/glg_healpix_all_bn220228438.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220228438/quicklook/glg_lc_medres34_bn220228438.gif

N. Omodei, N. Di Lalla (Stanford University), R. Pillera (INFN Bari) 
report on behalf of the Fermi-LAT team:

On February 28, 2022, Fermi-LAT detected high-energy emission from GRB 
220228A, which was also detected by**Fermi-GBM (trigger 667737010 / 
220228438, GCN 31658
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 ).

The best LAT on-ground location is found to be

RA, Dec = 311.2, -22.7 (degrees, J2000)

with an error radius of 0.7 deg (90 % containment, statistical error 
only). This was 23 deg from the LAT boresight at the time of the trigger:

T0 = 10:30:05.92 UT.

The data from the Fermi-LAT show a significant increase in the event 
rate that is spatially and temporally correlated with the GBM emission 
with high significance. The photon flux above 90 MeV in the time 
interval 0-1000s after the GBM trigger is 4E-6 �� 1E-6 ph/cm2/s.

The estimated photon index above 90 MeV is -2.9 �� 0.4.

The highest-energy photon is a 323 MeV**event which is observed 77 
seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is Roberta 
Pillera**(roberta.pillera@ba.infn.it).

The Fermi-LAT is a pair conversion telescope designed to cover the 
energy band from 20 MeV to greater than 300 GeV. It is the product of an 
international collaboration between NASA and DOE in the U.S. and many 
scientific institutions across France, Italy, Japan and Sweden.

J. Wood (NASA/MSFC) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 10:30:05.92 UT on 28 Feb 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220228A (trigger 667737010 / 220228438)
which was also detected by the Fermi LAT (N. Omodei et al. 2022, GCN 31659
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 ).
The GBM on-ground location (GCN 31658
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 ) is consistent with the LAT position.

The GBM light curve consists of a single pulse
with a duration (T90) of about 12.5 s (50-300 keV).
The time-averaged spectrum from T0-7 s to T0+6 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is 1.7 +/- 0.2 and
the cutoff energy, parameterized as Epeak, is 106 +/- 46 keV

The event fluence (10-1000 keV) in this time interval is
((1.1 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.5 s in the 10-1000 keV band
is 3.1 +/- 0.2 ph/s/cm^2.

A power law function fits the spectrum equally well
with index -1.9 +/- 0.1.

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/"