//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 31658 SUBJECT: GRB 220228A: Fermi GBM Final Localization DATE: 22/02/28 21:52:12 GMT FROM: Joshua Wood at MSFC/Fermi-GBM 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 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 31659 SUBJECT: GRB 220228A: Fermi-LAT detection DATE: 22/02/28 22:06:43 GMT FROM: Niccolo Di Lalla at Stanford U 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). 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 31660 SUBJECT: GRB 220228A: Fermi GBM observation DATE: 22/02/28 22:26:02 GMT FROM: Joshua Wood at MSFC/Fermi-GBM 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). The GBM on-ground location (GCN 31658) 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/"