GRB 221215A

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

At 04:14:27 UT on 15 Dec 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221215A (trigger 692770472.974848 / 221215177).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 156.1, Dec = 38.6 (J2000 degrees, equivalent to J2000 10h 24m, 38d 36'), with a statistical uncertainty of 13.6 degrees.

The angle from the Fermi LAT boresight is 45.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221215177/quicklook/glg_skymap_all_bn221215177.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/bn221215177/quicklook/glg_healpix_all_bn221215177.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221215177/quicklook/glg_lc_medres34_bn221215177.gif

James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Gayathri
Raman (PSU), Jamie A. Kennea (PSU) report:

Swift/BAT did not localize GRB 221215A onboard (T0:
2022-12-15T04:14:27 UTC, Fermi/GBM GCN 33054
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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 in a 4.096 s analysis time bin
with a sqrt(TS) of 11.8.

An arcminute localization is found with DeltaLLHOut of 19.7 and a
DeltaLLHPeak of 7.3.
Cross-correlation imaging also finds this source with SNR 5.5.

See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief
descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.

The BAT position is
RA, Dec = 155.056, +46.873 deg which is
   RA(J2000)  = 10h 20m 13.34s
   Dec(J2000) = +46d 52��� 21.7���
with an estimated uncertainty of 3 arcmin radius.

XRT and UVOT follow-up has been requested.
Results of follow-up observations will be reported in future circulars.

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/

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a ToO observation of the Swift/BAT-GUANO GRB 221215A. 
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021533

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Swift/BAT-GUANO event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

This circular is an official product of the Swift-XRT team.

K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi 
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J. D. Gropp (PSU), S.
Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and
P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Swift/BAT-GUANO-detected burst GRB 221215A, collecting 2.8 ks of Photon
Counting (PC) mode data between T0+97.3 ks and T0+113.8 ks. 

No X-ray sources have been detected consistent with being within 296
arcsec of the Swift/BAT-GUANO position. The 3-sigma upper limit in the
field is 0.005 ct  s^-1, corresponding to a 0.3-10 keV observed flux of
1.9e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum).

An uncatalogued was detected, however this was too far from the GRB
position to be the afterglow.

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021533.

This circular is an official product of the Swift-XRT team.

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

"At 04:14:27.97 UT on 15 December 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 221215A (trigger 692770472 / 221215177)
which was also detected by the Swift/BAT GUANO (DeLaunay et al. 2022, GCN 33062
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 )
The Fermi GBM Final Real-time Localization (GCN 33054
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 ) is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 53 degrees.

The GBM light curve shows a FRED-like pulse
with a duration (T90) of about 14 s (50-300 keV).
The time-averaged spectrum from T0-2 s to T0+12 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is 1.6 +/- 1.3 and
the cutoff energy, parameterized as Epeak, is 165 +/- 26 keV

The event fluence (10-1000 keV) in this time interval is
(6.8 +/- 1.2)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.7 s in the 10-1000 keV band
is 29.8 +/- 9.4 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/"