GRB 220418B
GCN Circular 31930
Subject
GRB 220418B: Swift-XRT observations
Date
2022-04-21T09:32:41Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
B. Sbarufatti (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato
(INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), J. D.
Gropp (PSU) and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Swift/BAT-GUANO-detected burst GRB 220418B, collecting 4.8 ks of Photon
Counting (PC) mode data between T0+113.8 ks and T0+148.8 ks. These
observations were delayed due to the Moon observing constraint.
Due to a high XRT temperature and consequent high background, the data
contain many low significance detections (ranked as "poor") which are
likely to be spurious, but no objects are detected within the BAT/GUANO
error region. We therefore conclude that no XRT afterglow to this
object has been found.
The 3-sigma upper limit is 2.3e-3 ct/sec, which, assuming a typical GRB
spectral, equates to an observed 0.3-10 keV flux of ~9e-14 erg/cm^2/s.
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
https://www.swift.ac.uk/ToO_GRBs/00021486.
This circular is an official product of the Swift-XRT team.
GCN Circular 31928
Subject
GRB 220418B Fermi GBM observation
Date
2022-04-21T01:25:04Z (3 years ago)
From
Cori Fletcher at USRA <cfletcher@usra.edu>
C. Fletcher (USRA), S. Dalessi (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 17:16:21.65 UT on 18 April 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220418B (trigger 671994986 / 220418720).
which was also detected by the Swift-BAT/GUANO (GCN 31919, 31921)
The Fermi GBM Final Real-time Localization (GCN 31915) is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 80 degrees.
The GBM light curve shows a single peak
with a duration (T90) of about 1.7 s (50-300 keV).
The time-averaged spectrum from T0-1.024 s to T0+1.024 s is
best fit a simple power law function with index -1.6 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is
(3.8 +/- 0.6)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.57 s in the 10-1000 keV band
is 121 +/- 76 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 31923
Subject
GRB 220418B: Swift ToO observations
Date
2022-04-20T00:54:19Z (3 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT-GUANO GRB 220418B.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021486
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 Swift/BAT-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 31921
Subject
GRB 220418B: Swift/BAT-GUANO refined location of a short burst
Date
2022-04-19T13:26:14Z (3 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:
Further analysis has improved the location of the short GRB reported
in GCN 31919, and its confidence.
This new position is fully consistent with the originally reported
position, with a smaller uncertainty region.
The BAT position is
RA, Dec = 224.344 -17.539 deg which is
RA(J2000) = 14h 57m 22.56s
Dec(J2000) = -17d 32��� 20.4���
with an estimated uncertainty of 3 arcmin.
We encourage followup from other instruments.
GCN Circular 31919
Subject
GRB 220418B: Swift/BAT-GUANO candidate arcminute localization of a short burst
Date
2022-04-19T05:52:20Z (3 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
Aaron Tohuvavohu (U Toronto), James DeLaunay (UAlabama), Gayathri
Raman (PSU), Jamie A. Kennea (PSU), report:
Swift/BAT did not localize GRB 220418B onboard (T0:
2022-04-18T17:16:21 UTC, Fermi/GBM trig #671994986).
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,
arXiv:2111.01769), detects the burst in a 2.048 s analysis time bin
with a sqrt(TS) of 10.4.
A candidate arcminute localization is found with DeltaLLHPeak of 11.8.
See Section 9.1 and Figure 20 in the NITRATES paper for brief
descriptions and interpretations of sqrt(TS), DeltaLLHPeak, and
DeltaLLHOut.
The BAT position is
RA, Dec = 224.329, -17.514 deg which is
RA(J2000) = 14h 57m 18.96s
Dec(J2000) = -17d 30��� 15.4���
with an estimated uncertainty of 5 arcmin.
This position is consistent with the Fermi/GBM localization (GCN 31915).
XRT and UVOT follow-up has been requested, but will be delayed due to
the position's proximity to the Moon.
We encourage prompt followup from other facilities.
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 31915
Subject
GRB 220418B: Fermi GBM Final Real-time Localization
Date
2022-04-18T17:26:38Z (3 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 17:16:21 UT on 18 Apr 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 220418B (trigger 671994986.650868 / 220418720).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 216.5, Dec = -26.6 (J2000 degrees, equivalent to J2000 14h 26m, -26d 36'), with a statistical uncertainty of 29.8 degrees.
The angle from the Fermi LAT boresight is 90.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_skymap_all_bn220418720.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_healpix_all_bn220418720.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2022/bn220418720/quicklook/glg_lc_medres34_bn220418720.gif