GRB 220823A

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

Swift/BAT did not localize GRB 220823A onboard (T0: 2022-08-23T03:28:52
 UTC, Fermi/GBM trig #682918137).

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, GUANO sent a command to the Swift Burst Alert Telescope (BAT)
to save 200 seconds of BAT event-mode data from [-45,+45] 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 13.4 in a 1.024 s
analysis time bin.

The duration of the burst as seen by BAT is T90~1.4 s.

NITRATES results, independently, are ambiguous with respect to whether this
burst originates from in or outside the BAT FOV, with a borderline
DeltaLLHOut of 9.9 and no specific location in the FOV significantly
preferred.
Effort to localize this burst will continue.

Independent spectral and/or fluence measurements of this burst from other
instruments could help determine the preferred spatial origin.

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/

B. Hirstov (UAH) and C. Fletcher (USRA)
report on behalf of the Fermi GBM Team:

"At 03:28:52.39 UT on 23 August 2022, the Fermi Gamma-Ray
Burst Monitor (GBM) triggered and located GRB 220823A
(trigger 682918137 / 220823145),which was also detected by
Swift/BAT-GUANO (A. Tohuvavohu et al. 2022, GCN 32476
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 ).

The on-ground calculated location, using the GBM trigger
data, is RA = 82.94, DEC = +2.44 (J2000 degrees, equivalent
to 05h, 31m, 2d 26'), with a statistical uncertainty of 3
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] ).

The angle from the Fermi LAT boresight at the GBM trigger
time is 15 degrees.

The GBM light curve consists of single peak with a duration
(T90) of 1.1 +/- 0.7 s (50-300 keV).

The time-averaged spectrum from T0-1.024 s to T0+0.256 s is
best fit by a power law with an exponential cutoff with
Epeak = 1189 +/- 608 keV and alpha = -0.52 +/- 0.26.

The event fluence (10-1000 keV) in this time interval is
(1.1 +/- 0.1)E-6 erg/cm^2. The 0.064-sec peak photon flux
measured starting from T0-0.064 s in the 10-1000 keV band
is 5 +/- 1 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/"