Gamma-ray Burst 210427A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Apr 21 04:57:46 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      59
TRIGGER_NUM:     641192237
GRB_RA:          168.183d {+11h 12m 44s} (J2000),
                 168.424d {+11h 13m 42s} (current),
                 167.621d {+11h 10m 29s} (1950)
GRB_DEC:         -53.250d {-53d 15' 00"} (J2000),
                 -53.366d {-53d 21' 57"} (current),
                 -52.978d {-52d 58' 39"} (1950)
GRB_ERROR:       5.83 [deg radius, statistical plus systematic]
GRB_INTEN:       338 [cnts/sec]
DATA_SIGNIF:     15.60 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19331 TJD;   117 DOY;   21/04/27
GRB_TIME:        17832.99 SOD {04:57:12.99} UT
GRB_PHI:         170.00 [deg]
GRB_THETA:       150.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.30
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   3%  Generic Transient
DETECTORS:       0,1,0, 0,0,0, 1,0,0, 0,0,1, 0,0,
SUN_POSTN:        34.82d {+02h 19m 17s}  +13.90d {+13d 54' 12"}
SUN_DIST:        126.32 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      216.67d {+14h 26m 41s}  -11.54d {-11d 32' 08"}
MOON_DIST:        56.65 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      288.36,  6.81 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      199.41,-51.62 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 329.58,18.38 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Apr 21 04:57:37 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     641192237
GRB_RA:          168.167d {+11h 12m 40s} (J2000),
                 168.407d {+11h 13m 38s} (current),
                 167.604d {+11h 10m 25s} (1950)
GRB_DEC:         -53.383d {-53d 22' 59"} (J2000),
                 -53.500d {-53d 29' 57"} (current),
                 -53.111d {-53d 06' 39"} (1950)
GRB_ERROR:       6.98 [deg radius, statistical plus systematic]
GRB_INTEN:       409 [cnts/sec]
DATA_SIGNIF:     9.30 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        19331 TJD;   117 DOY;   21/04/27
GRB_TIME:        17832.99 SOD {04:57:12.99} UT
GRB_PHI:         170.00 [deg]
GRB_THETA:       150.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.40
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      93%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,1,0, 0,0,0, 1,0,0, 0,0,1, 0,0,
SUN_POSTN:        34.82d {+02h 19m 17s}  +13.90d {+13d 54' 11"}
SUN_DIST:        126.24 [deg]   Sun_angle= -8.9 [hr] (East of Sun)
MOON_POSTN:      216.67d {+14h 26m 40s}  -11.54d {-11d 32' 06"}
MOON_DIST:        56.72 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      288.40,  6.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      199.53,-51.73 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 329.58,18.38 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Apr 21 04:57:56 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     641192237
GRB_RA:          172.990d {+11h 31m 58s} (J2000),
                 173.244d {+11h 32m 59s} (current),
                 172.397d {+11h 29m 35s} (1950)
GRB_DEC:         -53.520d {-53d 31' 11"} (J2000),
                 -53.638d {-53d 38' 15"} (current),
                 -53.244d {-53d 14' 37"} (1950)
GRB_ERROR:       1.90 [deg radius, statistical only]
DATA_SIGNIF:     13.90 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        19331 TJD;   117 DOY;   21/04/27
GRB_TIME:        17832.99 SOD {04:57:12.99} UT
GRB_PHI:         174.00 [deg]
GRB_THETA:       148.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        34.82d {+02h 19m 17s}  +13.90d {+13d 54' 12"}
SUN_DIST:        128.61 [deg]   Sun_angle= -9.2 [hr] (East of Sun)
MOON_POSTN:      216.67d {+14h 26m 41s}  -11.54d {-11d 32' 11"}
MOON_DIST:        54.34 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      291.17,  7.53 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      203.23,-50.05 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_641192237.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Apr 21 04:58:31 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     641192237
GRB_RA:          171.800d {+11h 27m 12s} (J2000),
                 172.051d {+11h 28m 12s} (current),
                 171.213d {+11h 24m 51s} (1950)
GRB_DEC:         -52.810d {-52d 48' 35"} (J2000),
                 -52.928d {-52d 55' 38"} (current),
                 -52.535d {-52d 32' 04"} (1950)
GRB_ERROR:       1.13 [deg radius, statistical only]
DATA_SIGNIF:     17.70 [sigma]
DATA_INTERVAL:   5.120 [sec]
GRB_DATE:        19331 TJD;   117 DOY;   21/04/27
GRB_TIME:        17832.99 SOD {04:57:12.99} UT
GRB_PHI:         172.00 [deg]
GRB_THETA:       148.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        34.82d {+02h 19m 17s}  +13.90d {+13d 54' 12"}
SUN_DIST:        128.41 [deg]   Sun_angle= -9.1 [hr] (East of Sun)
MOON_POSTN:      216.68d {+14h 26m 42s}  -11.54d {-11d 32' 19"}
MOON_DIST:        54.55 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      290.26,  7.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      201.68,-49.92 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_641192237.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Apr 21 04:59:08 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      3
TRIGGER_NUM:     641192237
GRB_RA:          174.240d {+11h 36m 58s} (J2000),
                 174.498d {+11h 37m 59s} (current),
                 173.638d {+11h 34m 33s} (1950)
GRB_DEC:         -52.690d {-52d 41' 23"} (J2000),
                 -52.808d {-52d 48' 28"} (current),
                 -52.413d {-52d 24' 46"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
DATA_SIGNIF:     26.60 [sigma]
DATA_INTERVAL:   18.432 [sec]
GRB_DATE:        19331 TJD;   117 DOY;   21/04/27
GRB_TIME:        17832.99 SOD {04:57:12.99} UT
GRB_PHI:         174.00 [deg]
GRB_THETA:       147.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        34.82d {+02h 19m 17s}  +13.90d {+13d 54' 13"}
SUN_DIST:        129.70 [deg]   Sun_angle= -9.3 [hr] (East of Sun)
MOON_POSTN:      216.68d {+14h 26m 44s}  -11.54d {-11d 32' 28"}
MOON_DIST:        53.26 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      291.65,  8.54 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      203.37,-48.93 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_641192237.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 27 Apr 21 05:06:40 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     641192237
GRB_RA:          177.320d {+11h 49m 17s} (J2000),
                 177.586d {+11h 50m 21s} (current),
                 176.699d {+11h 46m 48s} (1950)
GRB_DEC:         -53.360d {-53d 21' 35"} (J2000),
                 -53.479d {-53d 28' 42"} (current),
                 -53.082d {-53d 04' 54"} (1950)
GRB_ERROR:       1.14 [deg radius, statistical only]
GRB_DATE:        19331 TJD;   117 DOY;   21/04/27
GRB_TIME:        17832.99 SOD {04:57:12.99} UT
GRB_PHI:         177.00 [deg]
GRB_THETA:       146.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        34.83d {+02h 19m 19s}  +13.91d {+13d 54' 19"}
SUN_DIST:        130.77 [deg]   Sun_angle= -9.5 [hr] (East of Sun)
MOON_POSTN:      216.76d {+14h 27m 02s}  -11.57d {-11d 34' 19"}
MOON_DIST:        52.18 [deg]
MOON_ILLUM:      100 [%]
GAL_COORDS:      293.63,  8.39 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      206.22,-48.36 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_locplot_all_bn210427206.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 was generated completely by automated pipeline processing.  
COMMENTS:        This is likely a Long GRB.

GCN Circular #29903
The Fermi GBM team reports the detection of a likely LONG GRB
At 04:57:12 UT on 27 Apr 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210427A (trigger 641192237.991858 / 210427206).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 177.3, Dec = -53.4 (J2000 degrees, equivalent to J2000 11h 49m, -53d 23'), with a statistical uncertainty of 1.1 degrees.
The angle from the Fermi LAT boresight is 146.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_skymap_all_bn210427206.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/bn210427206/quicklook/glg_healpix_all_bn210427206.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210427206/quicklook/glg_lc_medres34_bn210427206.gif
GCN Circular #29904
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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 210427A ( Fermi GBM team, GCN 29903) errorbox 83 sec after trigger time at 2021-04-27 04:58:36 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 41 deg. The sun altitude is -71.8 deg.
The galactic latitude b = 8 deg., longitude l = 294 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1602343
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

      93 | 2021-04-27 04:58:36 |         MASTER-OAFA | (11h 30m 41.80s , -52d 41m 19.0s) |   C |    20 | 16.8 |        
     149 | 2021-04-27 04:59:26 |         MASTER-OAFA | (11h 35m 39.45s , -51d 53m 30.7s) |   C |    30 | 17.0 |        
     203 | 2021-04-27 05:00:15 |         MASTER-OAFA | (11h 35m 46.94s , -51d 53m 27.2s) |   C |    40 | 17.1 |        
     267 | 2021-04-27 05:01:15 |         MASTER-OAFA | (11h 35m 42.92s , -51d 51m 45.2s) |   C |    50 | 17.2 |        
     342 | 2021-04-27 05:02:25 |         MASTER-OAFA | (11h 35m 42.91s , -51d 53m 27.9s) |   C |    60 | 17.3 |        
     432 | 2021-04-27 05:03:45 |         MASTER-OAFA | (11h 35m 45.38s , -51d 51m 52.5s) |   C |    80 | 17.4 |        
     542 | 2021-04-27 05:05:24 |         MASTER-OAFA | (11h 35m 40.74s , -51d 52m 31.1s) |   C |   100 | 17.5 |        
     671 | 2021-04-27 05:07:24 |         MASTER-OAFA | (11h 47m 58.15s , -52d 31m 41.5s) |   C |   120 | 17.3 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.
GCN Circular #29905
B. Biltzinger, F. Kunzweiler, F. Berlato, J. Burgess & J. Greiner (all MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger at 04:57:12 on 27 April 2021 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60).
The best-fit position (1 sigma statistical errors) is:
```
RA(2000.0) = 172.6+/-2.5 deg
Decl.(2000.0) = -54.4+/-1.7 deg
```
We estimate an additional systematic error of 1 deg.
Further details are available at: https://grb.mpe.mpg.de/grb/GRB210427206/
The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB210427206/healpix
The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB210427206/json
GCN Circular #29906
S. L. Xie,Y. Huang, S. L. Xiong, S. Xiao, C. Cai, Y. Zhao, J. C. Liu, C. Y. Li, Y. Q. Zhang, W. C. Xue, C. Zheng, Z. W. Guo, X. Y. Zhao, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, J. J. He, B. Li, C. Li, J. H. Li, Q. X. Li, X. B. Li, X. Q. Li, Y. G. Li, X. H. Liang, J. Y. Liao, J. C. Liu, X. J. Liu, Y. Q. Liu, F. J. Lu, Q. Luo, X. Ma, G. Ou, W. X. Peng, R. Qiao, D. L. Shi, J. Y. Shi, L. M. Song, X. Y. Song, G. X. Sun, X. L. Sun, Y. L. Tuo, C. W. Wang, J. Z. Wang, P. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, S. Yang, M. Yao, Q. B. Yi, B. X. Zhang, C. Y. Zhang, D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, S. N. Zhang, Z. Zhang, S. Y. Zhao, S. J. Zheng, X. Zhou (IHEP), report on behalf of GECAM team:
During the commissioning phase, GECAM-B was triggered by a long GRB 210427A at 2021-04-27T04:57:13.100 UTC (denoted as T0), which was also observed by Fermi/GBM (GCN #29903).
GECAM alert data was promptly downlinked to the ground through the short message service of BeiDou Navigation Satellite System (BDS). The time latency of the first BeiDou message relative to the trigger time is about 1 minute.
According to the BDS alert data, this burst mainly consists of multiple pulses with a duration of about 20s.
An automatic on-ground localization was calculated using the light curves and spectrum. Although the in-flight calibration of energy response and localization has not been finalized yet, GECAM-B localized this burst to the following position (J2000):
```
ra: 175.26 deg
dec: -59.87 deg
err: 5.75 deg (statistical only)
```
The current systematic error of location is estimated to be several degrees which could be minimized by the ongoing calibration.
The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_all_combine_73198633.png
As the detailed science data are downloaded, all analyses would be improved.
Please note that all GECAM results here are preliminary. The final analysis will be published in journal papers or GECAM online catalog.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time), which was funded by the Chinese Academy of Sciences (CAS).
GCN Circular #29997
K. Hurley, on behalf of the IPN,
I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,
D. Svinkin, S. Golenetskii, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, and C. Wilson-Hodge on behalf of the Fermi GBM team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu on behalf of the Swift-BAT team, and
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team, report:
The long-duration GRB 210427A (Fermi-GBM detection: The Fermi GBM team, GCN Circ. 29903; BALROG localization: Biltzinger et al., GCN Circ. 29905; GECAM detection: Xie et al., GCN Circ. 29906) was detected by Fermi (GBM trigger 641192237), Konus-Wind, Swift (BAT), outside the coded FoV, Mars-Odyssey (HEND), and GECAM-B at about 17832 s UT (04:57:12).
We have triangulated it to a preliminary, 3 sigma error box whose coordinates are:
```
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   177.792 (11h 51m 10s) -52.866 (-52d 51' 57")
  Corners:
   176.862 (11h 47m 27s) -54.591 (-54d 35' 28")
   176.750 (11h 47m 00s) -54.533 (-54d 31' 59")
   178.678 (11h 54m 43s) -51.138 (-51d 08' 18")
   178.782 (11h 55m 08s) -51.196 (-51d 11' 46")
  ---------------------------------------------
```
The error box area is 1036 sq. arcmin, and its maximum dimension is 3.6 deg (the minimum one is 4.8 arcmin). The Sun distance was 93 deg.
This box may be improved.
The IPN localization is consistent with, but reduces the area of, the Fermi RoboBA and BALROG localizations (GCN Circ. 29903 and 29905). It was inside the Transiting Exoplanet Survey Satellite (TESS) field of view.
We thank Robert Wilson for pointing out the TESS/IPN coincidence.
A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB210427_T17835/IPN/
The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.

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