Gamma-ray Burst 210520A

(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:     Thu 20 May 21 19:07:27 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      45
TRIGGER_NUM:     643230427
GRB_RA:          149.917d {+09h 59m 40s} (J2000),
                 150.057d {+10h 00m 14s} (current),
                 149.588d {+09h 58m 21s} (1950)
GRB_DEC:         -65.900d {-65d 54' 00"} (J2000),
                 -66.003d {-66d 00' 10"} (current),
                 -65.659d {-65d 39' 33"} (1950)
GRB_ERROR:       16.80 [deg radius, statistical plus systematic]
GRB_INTEN:       171 [cnts/sec]
DATA_SIGNIF:     8.10 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.94 SOD {19:07:02.94} UT
GRB_PHI:         320.00 [deg]
GRB_THETA:        15.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.42
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      85%  GRB
2nd_MOST_LIKELY:  10%  Distant Particles
DETECTORS:       1,1,0, 1,0,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:        57.80d {+03h 51m 13s}  +20.14d {+20d 08' 39"}
SUN_DIST:        109.25 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      165.76d {+11h 03m 02s}  +11.82d {+11d 49' 21"}
MOON_DIST:        78.69 [deg]
MOON_ILLUM:      61 [%]
GAL_COORDS:      286.59, -8.64 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      206.39,-66.77 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 45.98,-23.95 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 20 May 21 19:07:36 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      58
TRIGGER_NUM:     643230427
GRB_RA:          107.183d {+07h 08m 44s} (J2000),
                 107.237d {+07h 08m 57s} (current),
                 107.057d {+07h 08m 14s} (1950)
GRB_DEC:         -62.683d {-62d 40' 59"} (J2000),
                 -62.719d {-62d 43' 06"} (current),
                 -62.601d {-62d 36' 04"} (1950)
GRB_ERROR:       12.85 [deg radius, statistical plus systematic]
GRB_INTEN:       132 [cnts/sec]
DATA_SIGNIF:     12.70 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.94 SOD {19:07:02.94} UT
GRB_PHI:         350.00 [deg]
GRB_THETA:        30.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.40
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      74%  GRB
2nd_MOST_LIKELY:  24%  Distant Particles
DETECTORS:       1,1,0, 1,0,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:        57.80d {+03h 51m 13s}  +20.14d {+20d 08' 39"}
SUN_DIST:         91.50 [deg]   Sun_angle= -3.3 [hr] (East of Sun)
MOON_POSTN:      165.76d {+11h 03m 02s}  +11.82d {+11d 49' 19"}
MOON_DIST:        87.01 [deg]
MOON_ILLUM:      61 [%]
GAL_COORDS:      273.36,-21.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      160.19,-81.71 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 45.98,-23.95 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 20 May 21 19:07:46 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     643230427
GRB_RA:          137.450d {+09h 09m 48s} (J2000),
                 137.516d {+09h 10m 04s} (current),
                 137.293d {+09h 09m 10s} (1950)
GRB_DEC:         -68.810d {-68d 48' 35"} (J2000),
                 -68.898d {-68d 53' 51"} (current),
                 -68.605d {-68d 36' 18"} (1950)
GRB_ERROR:       5.62 [deg radius, statistical only]
DATA_SIGNIF:     13.40 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.94 SOD {19:07:02.94} UT
GRB_PHI:         339.00 [deg]
GRB_THETA:        17.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        57.80d {+03h 51m 13s}  +20.14d {+20d 08' 39"}
SUN_DIST:        105.13 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      165.76d {+11h 03m 02s}  +11.82d {+11d 49' 16"}
MOON_DIST:        83.15 [deg]
MOON_ILLUM:      61 [%]
GAL_COORDS:      285.07,-14.04 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      208.84,-72.30 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_643230427.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
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:     Thu 20 May 21 19:08:45 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      1
TRIGGER_NUM:     643230427
GRB_RA:          149.210d {+09h 56m 50s} (J2000),
                 149.333d {+09h 57m 20s} (current),
                 148.923d {+09h 55m 41s} (1950)
GRB_DEC:         -68.060d {-68d 03' 35"} (J2000),
                 -68.162d {-68d 09' 43"} (current),
                 -67.821d {-67d 49' 15"} (1950)
GRB_ERROR:       2.29 [deg radius, statistical only]
DATA_SIGNIF:     14.50 [sigma]
DATA_INTERVAL:   11.264 [sec]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.94 SOD {19:07:02.94} UT
GRB_PHI:         327.00 [deg]
GRB_THETA:        14.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        57.80d {+03h 51m 13s}  +20.14d {+20d 08' 39"}
SUN_DIST:        109.21 [deg]   Sun_angle= -6.1 [hr] (East of Sun)
MOON_POSTN:      165.77d {+11h 03m 04s}  +11.82d {+11d 49' 03"}
MOON_DIST:        80.84 [deg]
MOON_ILLUM:      61 [%]
GAL_COORDS:      287.73,-10.51 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      211.08,-67.99 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_643230427.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
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.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9218).

GCN NOTICE

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Thu 20 May 21 19:08:21 UT
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    9218,   Sub_Num: 0
GRB_INTEN:      10.02 [sigma]
GRB_TIME:       68822.71 SOD {19:07:02.71} UT
GRB_DATE:       19354 TJD;   140 DOY;   21/05/20
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.  
COMMENTS:       Time_Scale=0.8000 and Time_Error=0.4000.  
COMMENTS:       
COMMENTS:       NOTE: This SPIACS event is temporally(0.0<100sec) coincident with the FERMI_GBM event (trignum=643230427).  
COMMENTS:          
COMMENTS:       The SPIACS lightcurve can be found at:  
COMMENTS:       ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2021-05/2021-05-20T19-07-02.6407-29699-19344-0.lc

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 20 May 21 19:16:27 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     643230427
GRB_RA:          147.870d {+09h 51m 29s} (J2000),
                 147.995d {+09h 51m 59s} (current),
                 147.577d {+09h 50m 18s} (1950)
GRB_DEC:         -66.960d {-66d 57' 35"} (J2000),
                 -67.061d {-67d 03' 38"} (current),
                 -66.725d {-66d 43' 28"} (1950)
GRB_ERROR:       3.66 [deg radius, statistical only]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.94 SOD {19:07:02.94} UT
GRB_PHI:         325.00 [deg]
GRB_THETA:        15.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        57.81d {+03h 51m 14s}  +20.15d {+20d 08' 43"}
SUN_DIST:        108.56 [deg]   Sun_angle= -6.0 [hr] (East of Sun)
MOON_POSTN:      165.84d {+11h 03m 21s}  +11.79d {+11d 47' 20"}
MOON_DIST:        79.92 [deg]
MOON_ILLUM:      61 [%]
GAL_COORDS:      286.62, -9.98 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      207.84,-67.99 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_locplot_all_bn210520797.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:        In the LAT Field-of-view.  
COMMENTS:        This is likely a Long GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9218).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Thu 20 May 21 20:35:20 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     643230427
GRB_RA:          136.550d {+09h 06m 12s} (J2000),
                 136.614d {+09h 06m 27s} (current),
                 136.397d {+09h 05m 35s} (1950)
GRB_DEC:         -68.630d {-68d 37' 47"} (J2000),
                 -68.716d {-68d 42' 58"} (current),
                 -68.428d {-68d 25' 40"} (1950)
GRB_ERROR:       2.29 [deg radius, statistical only]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.94 SOD {19:07:02.94} UT
GRB_PHI:         339.47 [deg]
GRB_THETA:        17.28 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        57.86d {+03h 51m 27s}  +20.16d {+20d 09' 24"}
SUN_DIST:        104.75 [deg]   Sun_angle= -5.3 [hr] (East of Sun)
MOON_POSTN:      166.54d {+11h 06m 09s}  +11.49d {+11d 29' 40"}
MOON_DIST:        82.96 [deg]
MOON_ILLUM:      61 [%]
GAL_COORDS:      284.71,-14.17 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      207.97,-72.57 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_locplot_all_bn210520797.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(0.0<100sec) coincident with the INTEGRAL_SPIACS event (trignum=9218).

GCN Circular #30059
The Fermi GBM team reports the detection of a likely LONG GRB
At 19:07:02 UT on 20 May 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210520A (trigger 643230427.939988 / 210520797).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 147.9, Dec = -67.0 (J2000 degrees, equivalent to J2000 09h 51m, -67d 00'), with a statistical uncertainty of 3.7 degrees.
The angle from the Fermi LAT boresight is 15.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_skymap_all_bn210520797.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/bn210520797/quicklook/glg_healpix_all_bn210520797.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210520797/quicklook/glg_lc_medres34_bn210520797.gif
GCN Circular #30060
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 210520A ( Fermi GBM team, GCN 30059) errorbox 12138 sec after notice time and 12187 sec after trigger time at 2021-05-20 22:30:10 UT, with upper limit up to 17.0 mag. Observations started at twilight. The observations began at zenith distance = 39 deg. The sun altitude is -10.0 deg.
The galactic latitude b = -14 deg., longitude l = 285 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1617942
We obtain a following upper limits.
```
Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   12218 | 2021-05-20 22:30:10 |         MASTER-OAFA | (09h 02m 19.62s , -69d 42m 16.2s) |   C |    60 | 16.8 |        
   12297 | 2021-05-20 22:31:29 |         MASTER-OAFA | (09h 24m 33.57s , -69d 42m 48.7s) |   C |    60 | 17.0 |        
   12376 | 2021-05-20 22:32:49 |         MASTER-OAFA | (08h 58m 19.03s , -67d 47m 42.0s) |   C |    60 | 17.0 |        
Filter C is a clear (unfiltred) band. 
```
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 21 May 21 03:06:54 UT
NOTICE_TYPE:     Fermi-LAT Offline Position
TRIGGER_NUM:     210520797
GRB_RA:          123.000d {+08h 12m 00s} (J2000),
                 123.008d {+08h 12m 02s} (current),
                 122.978d {+08h 11m 55s} (1950)
GRB_DEC:         -69.400d {-69d 24' 00"} (J2000),
                 -69.465d {-69d 27' 52"} (current),
                 -69.248d {-69d 14' 53"} (1950)
GRB_ERROR:       44.39 [arcmin radius, 90% containment, statistical only]
GRB_DATE:        19354 TJD;   140 DOY;   21/05/20
GRB_TIME:        68822.00 SOD {19:07:02.00} UT
TRIGGER_ID:      0x20000000
MISC:            0x40000000
SUN_POSTN:        58.14d {+03h 52m 33s}  +20.21d {+20d 12' 42"}
SUN_DIST:        100.59 [deg]   Sun_angle= -4.3 [hr] (East of Sun)
MOON_POSTN:      170.01d {+11h 20m 03s}  +10.00d {+10d 00' 02"}
MOON_DIST:        85.82 [deg]
MOON_ILLUM:      64 [%]
GAL_COORDS:      282.53,-18.60 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      207.94,-77.47 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi LAT Offline position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        It is the result of human-in-the-loop processing.  
COMMENTS:        This is a human generated position of a LAT ground detection.
COMMENTS:        This source corresponds to GBM trigger 643230427.939988 / 210520797.

GCN Circular #30061
C. Zheng, Y. Q. Zhang, S. L. Xiong, S. L. Xie, Y. Huang, S. Xiao, Y. Zhao, J. C. Liu, C. Y. Li, W. C. Xue, C. Cai, 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 triggered a long burst, GRB 210520A, at 2021-05-20T19:07:03.550 UTC (denoted as T0), which was also observed by Fermi/GBM (GCN #30059) and INTEGRAL/SPI-ACS（TrigID 9218）.
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 50s.
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: 129.04 deg
dec: -72.01 deg
err: 5.55 deg (statistical only)
```
The current systematic error of location is estimated to be several degrees which could be minimized by the ongoing calibration.
GECAM location is consistent with the Fermi/GBM(GCN #30059) position within the error.
The GECAM light curve could be found here: http://twiki.ihep.ac.cn/pub/GECAM/GRBList/gecamb_lc_grd_all_combine_75236823.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 #30062
N. Di Lalla (Stanford Univ.), M. Arimoto (Kanazawa Univ.), M. Axelsson (KTH & Stockholm Univ.), D. Kocevski (NASA/MSFC), N. Omodei (Stanford Univ.) report on behalf of the Fermi-LAT Collaboration:
On May 20, 2021 Fermi-LAT detected high-energy emission from GRB 210520A, which was also detected by Fermi-GBM (trigger 643230427.939988 / 210520797, GCN 30059).
The best LAT on-ground location is found to be
(RA, Dec) = 123.0, -69.4 (degrees, J2000)
with an error radius of 0.7 deg (90% containment, statistical error only). This was 21 deg from the LAT boresight at the time of the GBM trigger:
T0 = 19:07:02 UT.
The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is spatially and temporally correlated with the GBM emission (9 degrees from the GBM location) with high significance.
The photon flux above 100 MeV in the time interval 0-100s after the GBM trigger is (2.5 +/- 0.7) e-05 ph/cm2/s.
The estimated photon index above 100 MeV is -2.6 +/- 0.4.
A Swift ToO has been approved for this burst.
The Fermi-LAT point of contact for this burst is Niccolo' Di Lalla (niccolo.dilalla@stanford.edu).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular #30063
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a series of observations, tiled on the sky, of the Fermi/LAT GRB 210520A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00099
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the Fermi/LAT event is high: 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 #30065
P. Veres, B. Hristov and C. Meegan (all UAH) report on behalf of the Fermi GBM Team:
"At 19:07:02.00 UT on 20 May 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210520A (trigger 643230427 / 210520797) which was also detected by the Fermi LAT (Di Lalla et al., GCN 30062) and GECAM (Zheng et al GCN 30061). The GBM on-ground location (reported in GCN 30059) is consistent with the LAT position.
The angle from the Fermi LAT boresight at the GBM trigger time is 21 degrees.
The GBM light curve consists of a large number of pulses with a duration (T90) of about 56 s (50-300 keV). The time-averaged spectrum from T0-1.3 s to T0+58 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.18 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 4.4 +/- 1.8 MeV.
The event fluence (10-1000 keV) in this time interval is (1.02 +/- 0.04)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.58 s in the 10-1000 keV band is 2.6 +/- 0.2 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 #30069
M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), A.P. Beardmore (U. Leicester), J.P. Osborne (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 Fermi/LAT-detected burst GRB 210520A (Di Lalla et al. GCN Circ. 30062) in a series of observations tiled on the sky. The total exposure time is 5.6 ks, distributed over 19 tiles; the maximum exposure at a single sky location was 649 s. The data were collected between T0+43.1 ks and T0+62 ks, and are entirely in Photon Counting (PC) mode.
Two uncatalogued X-ray sources are detected above the RASS 3-sigma upper limit at this position, matching the afterglow criteria. However, none of them shows definitive signs of fading, and both of them are consistent with 2MASS objects within the XRT error circle. Therefore, none of them is likely the afterglow.
Details of these sources are given below:
Source 2:
```
  RA (J2000.0):  122.12040 = 08:08:28.90
  Dec (J2000.0): -69.7668 = -69:46:00.5
  Error: 7.7 arcsec (radius, 90% conf.)
  Count-rate: (1.95 [+1.19, -0.85])e-2 ct s^-1	 
  Distance: 28.7' from Fermi/LAT position.
```
Source 3:
```
  RA (J2000.0):  124.47176 =  08:17:53.22
  Dec (J2000.0): -69.2963  =  -69:17:46.8
  Error: 8.6 arcsec (radius, 90% conf.)
  Count-rate: (3.0 [+1.6, -1.1])e-2 ct s^-1	 
  Distance: 31.8' from Fermi/LAT position.
```
The results of the full analysis of the tiled XRT observations are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00099.
This circular is an official product of the Swift-XRT team.

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Jochen Greiner, last update: 22-May-2021 [Disclaimer]