Gamma-ray Burst 210421B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Wed 21 Apr 21 19:05:14 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     640695289
GRB_RA:          272.080d {+18h 08m 19s} (J2000),
                 272.169d {+18h 08m 41s} (current),
                 271.870d {+18h 07m 29s} (1950)
GRB_DEC:         +57.150d {+57d 08' 60"} (J2000),
                 +57.154d {+57d 09' 16"} (current),
                 +57.140d {+57d 08' 25"} (1950)
GRB_ERROR:       2.13 [deg radius, statistical only]
GRB_DATE:        19325 TJD;   111 DOY;   21/04/21
GRB_TIME:        39284.81 SOD {10:54:44.81} UT
GRB_PHI:         255.18 [deg]
GRB_THETA:        20.04 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        29.73d {+01h 58m 54s}  +12.13d {+12d 07' 52"}
SUN_DIST:         93.94 [deg]   Sun_angle= 7.8 [hr] (West of Sun)
MOON_POSTN:      143.86d {+09h 35m 26s}  +19.48d {+19d 28' 37"}
MOON_DIST:        92.11 [deg]
MOON_ILLUM:      66 [%]
GAL_COORDS:       85.71, 28.25 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      276.88, 80.54 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_lc_medres34_bn210421455.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210421455/quicklook/glg_locplot_all_bn210421455.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice has human-in-the-loop processing.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(2.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9154).

GCN NOTICE

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Wed 21 Apr 21 10:55:37 UT
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    9154,   Sub_Num: 0
GRB_INTEN:      9.15 [sigma]
GRB_TIME:       39282.18 SOD {10:54:42.18} UT
GRB_DATE:       19325 TJD;   111 DOY;   21/04/21
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.  
COMMENTS:       Time_Scale=2.0000 and Time_Error=1.0000.  
COMMENTS:       The SPIACS lightcurve can be found at:  
COMMENTS:       ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2021-04/2021-04-21T10-54-42.0924-17824-15248-0.lc

GCN Circular #29869
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University)
MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB210421.45 (trigger No 640695289,18h 08m 19.20s , +57d 09m 00.0s, R=2.13) errorbox 63 sec after notice time and 29500 sec after trigger time at 2021-04-21 19:06:25 UT, with upper limit up to 19.2 mag. The observations began at zenith distance = 59 deg. The sun altitude is -23.8 deg.
The galactic latitude b = 28 deg., longitude l = 86 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1598312
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   29590 | 2021-04-21 19:06:25 |      MASTER-Tavrida | (18h 05m 57.66s , +57d 18m 06.1s) |   C |   180 | 18.5 |        
   29770 | 2021-04-21 19:06:25 |      MASTER-Tavrida | (18h 05m 57.68s , +57d 18m 05.9s) |   C |   540 | 19.2 |  Coadd 
   29790 | 2021-04-21 19:09:44 |      MASTER-Tavrida | (18h 06m 04.40s , +57d 18m 11.5s) |   C |   180 | 18.5 |        
   29989 | 2021-04-21 19:13:04 |      MASTER-Tavrida | (18h 06m 00.51s , +57d 19m 50.6s) |   C |   180 | 18.7 |        
   30189 | 2021-04-21 19:16:23 |      MASTER-Tavrida | (18h 06m 00.35s , +57d 18m 29.6s) |   C |   180 | 18.5 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #29870
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
Correction to GCN Circ. 29870 for GRB 210421B, GRB type originally reported as "likely short GRB", corrected to "likely long GRB".
GCN Circular #29877
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
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
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
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
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
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/

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Jochen Greiner, last update: 12-Jun-2021 [Disclaimer]