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GCN Circular 32288

Subject
GRB 220627A: Fermi GBM Detection of a possible Lensed or Ultra-long GRB
Date
2022-06-28T20:22:56Z (2 years ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
O.J. Roberts (USRA/NASA), B. Hristov (UAH) and C. Meegan (UAH) report
on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 21:21:00.09 UT on 27 June 2022, the Fermi Gamma-ray Burst Monitor
(GBM) triggered and located GRB 220627A (trigger 678057665/220627890)
which was also detected by the LAT (N. Di Lalla, et al. 2022, GCN 32283)
and observed by Swift-BAT-GUANO (G. Raman, et al. 2022, GCN 32287).

The Fermi GBM Final Real-time Localization (GCN 32278) is consistent
with the LAT position.

The angle from the Fermi LAT boresight is 27 degrees.

The GBM light curve shows multiple bursts over a duration (T90) of
about 138 s (10-1000 keV).

The time-averaged spectrum for the this burst from T0-5 s to T0+289 s
is best fit by a power law function with an exponential high-energy
cutoff. The power law index is -0.83 +/- 0.02 and the cutoff energy,
parameterized as Epeak, is 410 +/- 16 keV. The event fluence (10-1000 keV)
in this time interval is (7.88 +/- 0.13)E-05 erg/cm^2.

A Band function fits the spectrum equally well with Epeak= 390 +/- 20 keV,
alpha = -0.81 +/- 0.03 and beta = -2.68 +/- 0.31.

The 1-sec peak photon flux measured starting from T0+171.1 s in the
10-1000 keV band is 5.1 +/- 0.2 ph/s/cm^2.

Separately, about 1000 s later at 21:36:56.39 UT, GBM triggered on
678058621/220627901, which localized to a similar location of
RA: 207.02 deg. Dec: -28.48 deg. (J2000 degrees, equivalent to
J2000 13h 48m, +/- 28d 28'), with a statistical uncertainty of 1.2 degrees
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a core-plus-tail model,
with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger
than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

We find the T90 of this multiple pulsed burst of similar shape, to be
127 s (10-1000 keV). The time-averaged spectrum for the this burst
from T0-47 s to T0+122 s is best fit by a power law function with an
exponential high-energy cutoff. The power law index is -1.12 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 227 +/- 15 keV. The event
fluence (10-1000 keV) in this time interval is (2.47 +/- 0.08)E-05 erg/cm^2.

The 1-sec peak photon flux measured starting from T0+113.2 s in the
10-1000 keV band is 3.5 +/- 0.2 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/"
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