GRB 210421B
GCN Circular 29870
Subject
GRB 210421B: Fermi GBM Final Localization
Date
2021-04-21T20:03:10Z (4 years ago)
From
Joe Mangan at UCD <joseph.mangan@ucdconnect.ie>
The Fermi GBM team reports the detection of a likely short GRB
At 10:54:44.812 UT on 21 Apr 2021, the Fermi Gamma-ray Burst Monitor
(GBM) triggered and located GRB 210421B (trigger 640695289 /
210421455).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 272.1, Dec = 57.2(J2000 degrees, equivalent to J2000 18h 08m,
57d 09'), with a statistical uncertainty of 2.1 degrees.
The angle from the Fermi LAT boresight is 20.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_skymap_all_bn210421455.png
The HEALPix FITS file, including the estimated localization
systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_healpix_all_bn210421455.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_lc_medres34_bn210421455.gif
GCN Circular 29874
Subject
GRB 210421B: Correction of GRB Type to "Likely Long GRB"
Date
2021-04-21T21:45:35Z (4 years ago)
From
Joe Mangan at UCD <joseph.mangan@ucdconnect.ie>
Correction to GCN Circ. 29870 for GRB 210421B, GRB type originally reported
as "likely short GRB", corrected to "likely long GRB".
GCN Circular 29877
Subject
GRB 210421B: Swift/BAT-GUANO detection and arcminute localization
Date
2021-04-21T22:47:22Z (4 years ago)
From
Aaron Tohuvavohu at U Toronto <aaron.tohu@gmail.com>
James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie A. Kennea
(PSU) report:
Swift/BAT did not trigger on GRB 210421B (T0: 2021-04-21 10:54:44 UTC,
Fermi/GBM GCN 29870, 29874; INTEGRAL/SPI-ACS trigger 9154).
The INTEGRAL/SPI-ACS 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 90 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 burst is strongly detected in BAT with a duration of ~15 seconds,
confirming the long classification correction of Fermi/GBM (GCN
29874).
The burst occurred during a Swift slew.
The position of the burst was found with SNR of 9.7 using a novel slew
image mosaicing procedure (DeLaunay et al. 2021, in prep.), and so the
positional uncertainty is not yet well characterized.
The BAT position is
RA, Dec = 270.817, 56.828 deg which is
RA(J2000) = 18h 03m 16.08s
Dec(J2000) = 56d 49��� 40.8���
with an estimated uncertainty of at least 5 arcmin.
This position is consistent with the Fermi GBM localization (GCN 29870).
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 29878
Subject
GRB 210421B: Swift ToO observations
Date
2021-04-22T01:26:20Z (4 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 GRB 210421B.
Automated analysis of the XRT data will be presented online at
https://www.swift.ac.uk/ToO_GRBs/00021429
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 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 29888
Subject
GRB 210421B: AstroSat CZTI detection
Date
2021-04-23T06:09:12Z (4 years ago)
From
Dipankar Bhattacharya at IUCAA <dipankar@iucaa.in>
P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al, 2020, arxiv:2011.07067) showed detection of a long GRB 210421B, which was also detected by Fermi-GBM (GCN #29870) and Swift-BAT (GCN #29877).
The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-04-21 10:54:43.5 UT. The measured peak count rate associated with the burst is 165 (+42, -33) cts/s above the background in the combined data of four quadrants, with a total of 905 (+230, -297) cts. The local mean background count rate was 504 (+4, -3) cts/s. Using cumulative rates, we measure a T90 of 16 (+3, -10) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-04-21 10:54:43.6 UT. The measured peak count rate is 320 (+72, -54) cts/s above the background in the combined Veto data of four quadrants, with a total of 1481 (+436, -479) cts. The local mean background count rate was 1629 (+5, -6) cts/s. We measure a T90 of 17 (+4, -11) s from the cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
GCN Circular 29891
Subject
GRB 210421B: AstroSat CZTI detection
Date
2021-04-23T12:44:05Z (4 years ago)
From
Varun Bhalerao at Indian Inst of Tech <varunb@iitb.ac.in>
P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (IITB), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al, 2020, arxiv:2011.07067) showed detection of a long GRB 210421B, which was also detected by Fermi-GBM (GCN #29870) and Swift (BAT - GCN #29877).
The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-04-21 10:54:43.5 UT. The measured peak count rate associated with the burst is 165 (+42, -33) cts/s above the background in the combined data of four quadrants, with a total of 905 (+230, -297) cts. The local mean background count rate was 504 (+4, -3) cts/s. Using cumulative rates, we measure a T90 of 16 (+3 -10) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2021-04-21 10:54:43.647 UT. The measured peak count rate is 320 (+72, -54) cts/s above the background in the combined Veto data of four quadrants, with a total of 1481 (+436, -479) cts. The local mean background count rate was 1629 (+5, -6) cts/s. We measure a T90 of 17 (+4, -11) s from the cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
Thanks,
Pallavi
GCN Circular 29892
Subject
GRB 210421B: Swift-XRT observations
Date
2021-04-23T15:32:05Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai
(INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B.
Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester) 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-detected burst GRB 210421B (James DeLaunay et al. GCN Circ.
29877), collecting 2.0 ks of Photon Counting (PC) mode data between
T0+45.1 ks and T0+85.2 ks.
No X-ray sources have been detected. The 3-sigma upper limit in the
field ranges from ~0.004 to ~0.008 ct s^-1, corresponding to a 0.3-10
keV observed flux of 1.6e-13 to 3.4e-13 erg cm^-2 s^-1 (assuming a
typical GRB spectrum).
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/00021429.
This circular is an official product of the Swift-XRT team.
GCN Circular 30225
Subject
GRB 210421B: Fermi GBM detection
Date
2021-06-12T17:55:20Z (4 years ago)
From
Joe Mangan at UCD <joseph.mangan@ucdconnect.ie>
J. Mangan (UCD), R. Dunwoody (UCD), C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
At 10:54:44.812 UT on 21 Apr 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210421B (trigger 640695289 / 210421455)
which was also detected by the Swift/BAT-GUANO (DeLaunay et al. 2021, GCN
29877)
The Fermi GBM Final Real-time Localization (GCN 29870) is consistent with
the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 20.1
degrees.
The GBM light curve consists of a single peak
with a duration (T90) of about 11 s (50-300 keV).
The time-averaged spectrum from T0-1.536 s to T0+9.728 is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.98 +/- 0.11 and
the cutoff energy, parameterized as Epeak, is 1253.00 +/- 500.00 keV
The event fluence (10-1000 keV) in this time interval is
(3.655 +/- 0.225)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.384 s in the 10-1000 keV band
is 2.74 +/- 0.26 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/