//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 31811 SUBJECT: GRB 220401A: Fermi GBM Final Localization DATE: 22/04/01 17:40:40 GMT FROM: Peter Veres at UAH The Fermi GBM team reports the detection of a likely LONG GRB. At 10:17:40.89 UT on 1 April 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 220401A (trigger 670501065/ 220401429). The trigger was initially classified as a Solar flare but it is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 8.0, Dec = 50.0 (J2000 degrees, equivalent to J2000 0h 3m, 50d 00'), with a statistical uncertainty of 4.2 degrees. The angle from the Fermi LAT boresight is 82.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220401429/quicklook/glg_skymap_all_bn220401429.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/bn220401429/quicklook/glg_healpix_all_bn220401429.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220401429/quicklook/glg_lc_medres34_bn220401429.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 31816 SUBJECT: GRB 220401A: Fermi GBM observation DATE: 22/04/02 13:25:43 GMT FROM: Peter Veres at UAH P. Veres (UAH), E. Bissaldi (Politecnico and INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 10:17:40.89 UT on 1 April 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 220401A (trigger 670501065 / 220401429). The localization was reported in GCN 31811. The GBM lightcurve consists of two emission episodes with a duration (T90) of about 39.2 s (50-300 keV). The time-averaged spectrum from T0-8.2 s to T0+38.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.37 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 46 +/- 2 keV. The event fluence (10-1000 keV) in this time interval is (2.42 +/- 0.06)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+7.0 s in the 10-1000 keV band is 7.8 +/- 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/" //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 31817 SUBJECT: GRB 220401A: Swift/BAT-GUANO detection outside the coded FOV DATE: 22/04/02 22:50:45 GMT FROM: Aaron Tohuvavohu at U Toronto Gayathri Raman (PSU), Aaron Tohuvavohu (U Toronto), James DeLaunay (UAlabama), Jamie A. Kennea (PSU), report: Swift/BAT did not localize GRB 220401A onboard (T0: 2022-04-01T10:17:40 UTC, Fermi/GBM GCN 31811, 31816). The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu, arXiv:2111.01769), detects the burst with a sqrt(TS) of 10.1 in a 1.024 s analysis time bin. Only the peak of the second emission episode (at ~T0+35s) is clearly detected in BAT. NITRATES results are consistent with a burst coming from outside the coded FoV, as indicated by the Fermi/GBM localization (GCN 31816). See Section 9.1 and Figure 20 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/