GRB 230808A

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

At 10:49:12 UT on 8 Aug 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230808A (trigger 713184557.782692 / 230808451).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 81.6, Dec = 58.5 (J2000 degrees, equivalent to J2000 05h 26m, 58d 30'), with a statistical uncertainty of 2.2 degrees.

The angle from the Fermi LAT boresight is 36.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230808451/quicklook/glg_skymap_all_bn230808451.png

The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230808451/quicklook/glg_healpix_all_bn230808451.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230808451/quicklook/glg_lc_medres34_bn230808451.gif

James DeLaunay (UAlabama), Gayathri Raman (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:

Swift/BAT did not localize GRB 230808A onboard (T0: 2023-08-08T10:49:12.78 UTC, Fermi GBM Trig 713184557, GCN 34369
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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 2022, ApJ, 941, 169), detects the burst with a sqrt(TS) of 9.6 in a 16.384 s analysis time bin, starting at T0 + 16.384 s.

NITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a DeltaLLHOut of 12.1.
The Fermi GBM localization (GCN 34369
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 ) has this burst significantly outside of the BAT coded FOV

See Section 9.1 and Figures 10 and 17 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/

A. Myers (NPP/GSFC) and S. Lesage (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

“At 10:49:12.78 UT on 08 August 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230808A (trigger 713184557/230808451, which was also detected by Swift/BAT-GUANO (B. Person et al. 2020; GCN 34375
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  reported by James Delaunay). The Fermi GBM Final Real-time Localization was reported at GCN 34369
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 .

The angle from the Fermi LAT boresight is 36 degrees.

The GBM light curve consists of a multiple-emission episode with a duration (T90) of about 62 s (50-300 keV). The time-averaged spectrum from T0-4.6 to T0+69.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 430 +/- 60 keV.

The event fluence (10-1000 keV) in this time interval is (1.31 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+18 s in the 10-1000 keV band is 6.4 +/- 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/"