GRB 220401A

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

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
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 .

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/"

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
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 , 31816
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 ).

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
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 ), 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
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 ).

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/