GRB 221027A

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

At 04:09:34 UT on 27 Oct 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221027A (trigger 688536579.352978 / 221027173).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 189.4, Dec = -10.0 (J2000 degrees, equivalent to J2000 12h 37m, -10d 00'), with a statistical uncertainty of 1.9 degrees.

The angle from the Fermi LAT boresight is 52.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221027173/quicklook/glg_skymap_all_bn221027173.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/bn221027173/quicklook/glg_healpix_all_bn221027173.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn221027173/quicklook/glg_lc_medres34_bn221027173.gif

Arimoto M. (Kanazawa University), Bissaldi E. (Politecnico and INFN Bari),
Longo F. (University and INFN Trieste), Scotton L. (CNRS/IN2P3/LUPM)
and Maheso D. (Johannesburg Univ.) report on behalf of the Fermi-LAT
team:

On October, 27, 2022 Fermi-LAT detected high-energy emission from GRB 221027A,
which was also detected by Fermi-GBM (trigger 221027173 / 688536579,
GCN 32861
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 ) at 04:09:34.35 UT .

The best LAT on-ground location is found to be

RA, Dec =  185.3, -5.7 (J2000)

with an error radius of 0.4 deg (90 % containment, statistical error only).
This was 51 deg from the LAT boresight at the time of the trigger.

The data from the Fermi-LAT show a significant increase in the event
rate that is spatially
and temporally correlated with the trigger with high significance.


The 100 MeV - 1 GeV photon flux in the time interval 0-500 s after
the GBM trigger is (9.1 +/- 2.6)E-06 ph/cm2/s.
The estimated integrated photon index above 100 MeV is -2.2 +/- 0.3.
The highest-energy photon is a 1.1 GeV event with 96% probability
which is observed 26 seconds after the GBM trigger.

A Swift ToO has been requested for this burst.


The Fermi-LAT point of contact for this burst is
Dimakatso Jeannett Maheso (d.j.maheso@gmail.com).

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.

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

"At 04:09:34.35 UT on 27 October 2022, the Fermi
Gamma-Ray Burst Monitor (GBM) triggered and located
GRB 221027A (trigger 688536579 / 221027173), which was
also detected by Fermi-LAT (M. Arimoto et al. 2022, GCN 32862
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 ).

The Fermi GBM Final Real-time Localization (GCN 32861
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 ) is
consistent with the LAT position.

The angle from the Fermi LAT boresight at the GBM trigger
time is 51 degrees.

The GBM light curve consists of a bright pulse
with a duration (T90) of about 7 s (50-300 keV).
The time-averaged spectrum from T0-1.5s to T0+9.7 s is
best fit by a Band function with Epeak = 341 +/- 37 keV,
alpha = -0.75 +/- 0.06, and beta = -2.09 +/- 0.14.

The event fluence (10-1000 keV) in this time interval is
(9.2 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux
measured starting from T0+1.2 s in the 10-1000 keV band
is 8.5 +/- 0.3 ph/s/cm^2.

A power law function with an exponential high-energy cutoff
fits the spectrum equally well. The power law index
is -0.81 +/- 0.04 and the cutoff energy, parameterized as
Epeak, is 411 +/- 29 keV

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/"

A. Ursi, F. Longo (Univ. Trieste and INFN Trieste), C. Pittori, F.
Verrecchia (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS, and Univ. Roma Tor
Vergata), A. Argancc, M. Cardillo, C. Casentini, Y. Evangelista, L.
Foffano, E. Menegoni, G. Piano (INAF/IAPS), A. Bulgarelli, A. Di Piano, V.
Fioretti, G. Panebianco, N. Parmiggiani (INAF/OAS-Bologna), F. Lucarelli
(SSDC, and INAF/OAR), M. Romani (INAF/OA-Brera), M. Marisaldi
(INAF/OAS-Bologna, and Bergen University), M. Pilia, A. Trois
(INAF/OA-Cagliari), I. Donnarumma (ASI), A. Giuliani (INAF/IASF-Mi), and P.
Tempesta (TeleSpazio), report on behalf of the AGILE Team:

The AGILE satellite detected the GRB 221027A at T0 = 2022-10-27 04:09:34 s
(UTC), reported by Fermi GBM (GCNs #32861
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 , #32866
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 ) and Fermi LAT (GCN
#32862
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 ). The burst is clearly visible in the AGILE scientific ratemeters of
the MiniCALorimeter (MCAL; 0.4-100 MeV) and AntiCoincidence (AC; 50-200
keV) detectors. The event lasted about 10 s and it released a total number
of 11040 counts in the MCAL detector (above a background rate of 1180 Hz),
and 30890 counts in the AC detector (above a background rate of 3250 Hz).
The AGILE ratemeters light curves can be found at
http://www.agilescienceapp.it/notices/GRB221027A_AGILE_RM.png .

The event also triggered a high time resolution MCAL data acquisition, from
T0-22.42 s to T0+7.94 s (UTC), and released 5086 counts in the detector,
above a background rate of 472 Hz. The MCAL light curve can be found at
http://www.agilescienceapp.it/notices/GRB221027A_080667_593928574.000000.png
. The time-integrated spectrum of the burst between T0 and T0+3s be fitted
in the energy range 0.4-10 MeV with a power-law with ph. ind. = -2.31
(-0.69/+1.26), resulting in a reduced chi-squared of 1.44 (48 d.o.f.) and a
fluence of 1.8e-06 ergs/cm^2 (90% confidence level), in the same energy
range. At the T0, the event was 67 deg off-axis.

Additional analysis of AGILE data is in progress. Automatic MCAL GRB alert
Notices can be found at: https://gcn.gsfc.nasa.gov/agile_mcal.html.