GRB 231220A
GCN Circular 35407
Subject
GRB 231220A: Fermi GBM Final Real-time Localization
Date
2023-12-20T16:20:38Z (a year ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 16:10:17 UT on 20 Dec 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 231220A (trigger 724781422.403544 / 231220674).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 73.4, Dec = 82.3 (J2000 degrees, equivalent to J2000 04h 53m, 82d 17'), with a statistical uncertainty of 5.0 degrees.
The angle from the Fermi LAT boresight is 136.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_skymap_all_bn231220674.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/bn231220674/quicklook/glg_healpix_all_bn231220674.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn231220674/quicklook/glg_lc_medres34_bn231220674.gif
GCN Circular 35409
Subject
GRB 231220A: Swift/BAT-GUANO arcminute localization of a long burst
Date
2023-12-20T22:09:23Z (a year ago)
From
Samuele Ronchini at PSU <sjs8171@psu.edu>
Via
Web form
Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report:
Swift/BAT did not localize GRB 231220A onboard (T0: 2023-12-20T16:10:17.4 UTC, Fermi/GBM GCN 35407).
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 in a 4.096 s analysis time bin with a sqrt(TS) of 28.32, starting at T0 - 1.02 s.
An arcminute localization is found with DeltaLLHOut of 48.29 and a DeltaLLHPeak of 49.13.
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
The BAT position is
RA, Dec = 27.321, 77.897 deg which is
RA(J2000) = 01h 49m 17.04s
Dec(J2000) = +77d 53′ 49.2″
with an estimated uncertainty of 5 arcmin radius.
XRT and UVOT follow-up has been requested.
Results of follow-up observations will be reported in future circulars.
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 35410
Subject
GRB 231220A: Swift ToO observations
Date
2023-12-20T23:38:36Z (a year ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the GUANO GRB 231220A.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021638
Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the GUANO event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a
GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular 35411
Subject
GRB 231220A: Swift-XRT follow-up observations
Date
2023-12-21T15:25:45Z (a year ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A.
Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), R. Brivio (INAF-OAB) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the GUANO-detected
burst GRB 231220A, collecting 3.6 ks of Photon Counting (PC) mode data
between T0+27.0 ks and T0+39.5 ks.
No candidate counterpart was detected, with an upper limit of
2.2×10-3 ct s-1 at the best BAT position (GCN 35409).
One uncatalogued X-ray source was flagged as spurious
after manual inspection.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/00021638.
This circular is an official product of the Swift-XRT team.
GCN Circular 35477
Subject
GRB 231220A: Swift-UVOT upper limit
Date
2024-01-04T03:26:25Z (a year ago)
From
noelklin@umbc.edu
Via
Web form
N. Klingler (UMBC/NASA-GSFC/CRESST II) reports on behalf of the Swift-UVOT team:
Swift-UVOT has performed follow-up observations of the Swift-BAT/GUANO-detected and Fermi-GBM-detected GRB 231220A, collecting 2.6 ks of data between T0+35.2 ks and T0+47.8 ks. No candidate counterpart was detected. The 3 sigma limiting (AB) magnitude in the White filter near the center of the BAT/GUANO localization (GCN 35409) is >23.20.