GRB 230518A
GCN Circular 33822
Subject
GRB 230518A: Fermi GBM Final Real-time Localization
Date
2023-05-18T22:59:56Z (2 years ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
The Fermi GBM team reports the detection of a likely SHORT GRB
At 22:49:27 UT on 18 May 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230518A (trigger 706142972.60896 / 230518951).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 256.4, Dec = -49.6 (J2000 degrees, equivalent to J2000 17h 05m, -49d 36'), with a statistical uncertainty of 19.0 degrees.
The angle from the Fermi LAT boresight is 23.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230518951/quicklook/glg_skymap_all_bn230518951.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/bn230518951/quicklook/glg_healpix_all_bn230518951.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230518951/quicklook/glg_lc_medres34_bn230518951.gif
GCN Circular 33825
Subject
GRB 230518A: Swift/BAT-GUANO detection
Date
2023-05-19T11:34:53Z (2 years ago)
From
Aaron Tohuvavohu at University of Toronto <aaron.tohu@gmail.com>
Samuele Ronchini (PSU), Gayathri Raman (PSU), James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 230518A onboard (T0: 2023-05-18T22:49:27.61 UTC, Fermi/GBM GCN 33822).
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 11 in a 0.128 s analysis time bin.
The burst duration is ~0.256 seconds.
NITRATES results, independently, are ambiguous with respect to whether this burst originates from in or outside the BAT coded FOV, with a borderline DeltaLLHOut of 6.5.
The majority of the Fermi/GBM localization lies outside the 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/
GCN Circular 33828
Subject
GRB 230518A: Fermi GBM Observation
Date
2023-05-19T17:07:45Z (2 years ago)
From
sumanbala2210@gmail.com
S. Bala (USRA), C. Fletcher (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 22:49:27.61 UT on 18 May 2023, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 230518A (trigger 706142972/230518951).
which was also detected by Swift/BAT-GUANO (S. Ronchini et al. 2023, GCN
33825).
The Fermi GBM Final Real-time Localization was reported in GCN 33822.
The angle from the Fermi LAT boresight is 23 degrees.
The GBM light curve consists of one short peak with a duration (T90)
of about 0.9 s (50-300 keV). The time-averaged spectrum
from T0-0.7 to T0+0.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is 0.6 +/- 0.7 and the cutoff energy,
parameterized as Epeak, is 503 +/- 138 keV.
The event fluence (10-1000 keV) in this time interval is
(5.5 +/- 0.9)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.0 s in the 10-1000 keV band is 4 +/- 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/"
GCN Circular 33843
Subject
IPN triangulation of GRB 230518A (short)
Date
2023-05-21T13:50:51Z (2 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko,
on behalf of the IPN,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
and
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team, report:
The short-duration GRB 230518A
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 33822;
Swift-BAT/GUANO detection: Ronchini, GCN Circ. 33825)
has been detected by Fermi (GBM trigger 706142972), Swift (BAT),
and INTEGRAL (SPI-ACS), so far, at about 82168 s UT (22:49:28).
The burst was outside the coded field of view of the BAT.
We have triangulated it to a GBM-SPI-ACS annulus centered at
RA(2000)=19.521 deg (01h 18m 05s) Dec(2000)=-66.594 deg (-66d 35' 40")
whose radius is 88.662 +/- 2.786 deg (3 sigma).
The annulus combined with the Fermi-GBM final position (GCN 33822;
glg_healpix_all_bn230518951_v00) gives 480 sq. deg (3 sigma) localization region.
The localization is inconsistent with the localization of the NSBH merger event candidate S230518h (LVK Collaborations, GCN Circ. 33813, 33816).
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB230518_T82167/IPN/