Gamma-ray Burst 210618A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 18 Jun 21 01:43:54 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     1056426,   Seg_Num: 0
GRB_RA:          235.820d {+15h 43m 17s} (J2000),
                 235.993d {+15h 43m 58s} (current),
                 235.419d {+15h 41m 40s} (1950)
GRB_DEC:         +46.043d {+46d 02' 36"} (J2000),
                 +45.976d {+45d 58' 35"} (current),
                 +46.201d {+46d 12' 02"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       2596 [cnts]    Image_Peak=130 [image_cnts]
TRIGGER_DUR:     0.512 [sec] 
TRIGGER_INDEX:   204     E_range: 25-100 keV
BKG_INTEN:       32031 [cnts]
BKG_TIME:        6204.78 SOD {01:43:24.78} UT
BKG_DUR:         8 [sec]
GRB_DATE:        19383 TJD;   169 DOY;   21/06/18
GRB_TIME:        6217.00 SOD {01:43:37.00} UT
GRB_PHI:         -156.63 [deg]
GRB_THETA:        13.09 [deg]
SOLN_STATUS:     0x20000003
RATE_SIGNIF:     12.36 [sigma]
IMAGE_SIGNIF:    7.01 [sigma]
MERIT_PARAMS:     +1  +0  +0  -1  +2  -3  +0  +0 +26  +0 
SUN_POSTN:        86.81d {+05h 47m 14s}  +23.40d {+23d 24' 12"}
SUN_DIST:        105.20 [deg]   Sun_angle= -9.9 [hr] (East of Sun)
MOON_POSTN:      178.25d {+11h 52m 59s}   +6.30d {+06d 17' 53"}
MOON_DIST:        63.42 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:       73.78, 51.29 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      211.66, 62.73 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 352.39,-17.94 [deg].  
COMMENTS:           
COMMENTS:        NOTE: This BAT event is temporally(1.0<100sec) coincident with the FERMI_GBM event (trignum=645673421).

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 18 Jun 21 01:44:00 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     645673421
GRB_RA:          226.800d {+15h 07m 12s} (J2000),
                 226.997d {+15h 07m 59s} (current),
                 226.342d {+15h 05m 22s} (1950)
GRB_DEC:         +41.933d {+41d 55' 60"} (J2000),
                 +41.852d {+41d 51' 06"} (current),
                 +42.125d {+42d 07' 29"} (1950)
GRB_ERROR:       13.40 [deg radius, statistical plus systematic]
GRB_INTEN:       128 [cnts/sec]
DATA_SIGNIF:     6.40 [sigma]
INTEG_TIME:      2.048 [sec]
GRB_DATE:        19383 TJD;   169 DOY;   21/06/18
GRB_TIME:        6216.14 SOD {01:43:36.14} UT
GRB_PHI:         255.98 [deg]
GRB_THETA:       105.00 [deg]
DATA_TIME_SCALE: 2.0480 [sec]
HARD_RATIO:      0.42
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      94%  GRB
2nd_MOST_LIKELY:   4%  Generic Transient
DETECTORS:       0,0,0, 0,1,0, 0,0,1, 0,0,0, 0,0,
SUN_POSTN:        86.81d {+05h 47m 14s}  +23.40d {+23d 24' 12"}
SUN_DIST:        105.08 [deg]   Sun_angle= -9.3 [hr] (East of Sun)
MOON_POSTN:      178.25d {+11h 52m 59s}   +6.30d {+06d 17' 52"}
MOON_DIST:        55.85 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:       69.96, 58.65 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      204.47, 55.98 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_lc_medres34_bn210618072.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 196.65,-0.32 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1056426).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 18 Jun 21 01:44:17 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      57
TRIGGER_NUM:     645673421
GRB_RA:          231.310d {+15h 25m 14s} (J2000),
                 231.494d {+15h 25m 59s} (current),
                 230.881d {+15h 23m 31s} (1950)
GRB_DEC:         +44.230d {+44d 13' 48"} (J2000),
                 +44.155d {+44d 09' 20"} (current),
                 +44.405d {+44d 24' 17"} (1950)
GRB_ERROR:       9.78 [deg radius, statistical only]
DATA_SIGNIF:     10.40 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        19383 TJD;   169 DOY;   21/06/18
GRB_TIME:        6216.14 SOD {01:43:36.14} UT
GRB_PHI:         256.00 [deg]
GRB_THETA:       109.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        86.81d {+05h 47m 14s}  +23.40d {+23d 24' 12"}
SUN_DIST:        105.10 [deg]   Sun_angle= -9.6 [hr] (East of Sun)
MOON_POSTN:      178.25d {+11h 53m 00s}   +6.30d {+06d 17' 47"}
MOON_DIST:        59.79 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:       72.25, 54.83 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      207.75, 59.59 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_lc_medres34_bn210618072.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_645673421.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
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(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1056426).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 18 Jun 21 01:45:28 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      0
TRIGGER_NUM:     645673421
GRB_RA:          272.340d {+18h 09m 22s} (J2000),
                 272.463d {+18h 09m 51s} (current),
                 272.053d {+18h 08m 13s} (1950)
GRB_DEC:         +51.780d {+51d 46' 48"} (J2000),
                 +51.785d {+51d 47' 06"} (current),
                 +51.769d {+51d 46' 10"} (1950)
GRB_ERROR:       7.93 [deg radius, statistical only]
DATA_SIGNIF:     9.40 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        19383 TJD;   169 DOY;   21/06/18
GRB_TIME:        6216.14 SOD {01:43:36.14} UT
GRB_PHI:         254.00 [deg]
GRB_THETA:       137.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        86.81d {+05h 47m 14s}  +23.40d {+23d 24' 12"}
SUN_DIST:        104.65 [deg]   Sun_angle= 11.6 [hr] (West of Sun)
MOON_POSTN:      178.26d {+11h 53m 02s}   +6.29d {+06d 17' 30"}
MOON_DIST:        87.65 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:       79.73, 27.31 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      275.67, 75.17 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_lc_medres34_bn210618072.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_645673421.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.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1056426).

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Fri 18 Jun 21 01:52:56 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     645673421
GRB_RA:          227.770d {+15h 11m 05s} (J2000),
                 227.964d {+15h 11m 51s} (current),
                 227.318d {+15h 09m 16s} (1950)
GRB_DEC:         +42.470d {+42d 28' 12"} (J2000),
                 +42.390d {+42d 23' 23"} (current),
                 +42.658d {+42d 39' 29"} (1950)
GRB_ERROR:       7.60 [deg radius, statistical only]
GRB_DATE:        19383 TJD;   169 DOY;   21/06/18
GRB_TIME:        6216.14 SOD {01:43:36.14} UT
GRB_PHI:         256.00 [deg]
GRB_THETA:       106.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   41731 (Gnd S/W Version number)
SUN_POSTN:        86.81d {+05h 47m 15s}  +23.40d {+23d 24' 13"}
SUN_DIST:        105.08 [deg]   Sun_angle= -9.4 [hr] (East of Sun)
MOON_POSTN:      178.32d {+11h 53m 17s}   +6.26d {+06d 15' 43"}
MOON_DIST:        56.70 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:       70.53, 57.80 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      205.13, 56.80 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_lc_medres34_bn210618072.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_locplot_all_bn210618072.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 Short GRB.  
COMMENTS:           
COMMENTS:        NOTE: This GBM event is temporally(1.0<100sec) coincident with the SWIFT_BAT event (trignum=1056426).

GCN Circular #30248
The Fermi GBM team reports the detection of a likely SHORT GRB
At 01:43:36 UT on 18 Jun 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210618A (trigger 645673421.140258 / 210618072).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 227.8, Dec = 42.5 (J2000 degrees, equivalent to J2000 15h 11m, 42d 30'), with a statistical uncertainty of 7.6 degrees.
The angle from the Fermi LAT boresight is 106.0 degrees.
The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_skymap_all_bn210618072.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/bn210618072/quicklook/glg_healpix_all_bn210618072.fit
The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210618072/quicklook/glg_lc_medres34_bn210618072.gif
GCN Circular #30249
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-IAC robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Spain (IAC Teide Observatory) was pointed to the Swift GRB210618.07 (trigger No 1056426,15h 43m 16.80s , +46d 02m 34.8s, R=0.05) errorbox 14 sec after notice time and 41 sec after trigger time at 2021-06-18 01:44:18 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 37 deg. The sun altitude is -37.7 deg.
MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB210618.07 errorbox 28 sec after notice time and 56 sec after trigger time at 2021-06-18 01:44:33 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 77 deg. The sun altitude is -51.4 deg.
The galactic latitude b = 51 deg., longitude l = 73 deg.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1639424
We obtain a following upper limits.
```
Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      47 |          MASTER-IAC |  P| |    10 | 16.6 |        
      61 |         MASTER-OAFA |   C |    10 | 16.5 |        
      76 |         MASTER-OAFA |   C |    40 | 17.4 |  Coadd 
      67 |          MASTER-IAC |  P| |    10 | 16.6 |        
      92 |          MASTER-IAC |  P| |    20 | 17.3 |        
      91 |         MASTER-OAFA |   C |    10 | 16.6 |        
     122 |          MASTER-IAC |  P| |    20 | 17.3 |        
     133 |         MASTER-OAFA |   C |    20 | 17.0 |        
     159 |          MASTER-IAC |  P| |    30 | 17.6 |        
     178 |         MASTER-OAFA |   C |    30 | 17.3 |        
     205 |          MASTER-IAC |  P| |    40 | 18.0 |        
     233 |         MASTER-OAFA |   C |    40 | 17.4 |        
     260 |          MASTER-IAC |  P| |    50 | 18.2 |        
     297 |         MASTER-OAFA |   C |    50 | 17.5 |        
```
Filter C is a clear (unfiltred) band.
The observation and reduction will continue. The message may be cited.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 18 Jun 21 02:00:28 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     1056426,   Seg_Num: 0
GRB_RA:          235.820d {+15h 43m 17s} (J2000),
                 235.993d {+15h 43m 58s} (current),
                 235.419d {+15h 41m 40s} (1950)
GRB_DEC:         +46.043d {+46d 02' 36"} (J2000),
                 +45.976d {+45d 58' 35"} (current),
                 +46.201d {+46d 12' 02"} (1950)
GRB_DATE:        19383 TJD;   169 DOY;   21/06/18
GRB_TIME:        6217.00 SOD {01:43:37.00} UT
TRIGGER_INDEX:   204
GRB_PHI:         -156.63 [deg]
GRB_THETA:        13.09 [deg]
DELTA_TIME:      27931.00 [sec]
TRIGGER_DUR:     0.512 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     12.36 [sigma]
IMAGE_SIGNIF:    7.01 [sigma]
LC_URL:          sw01056426000msb.lc
SUN_POSTN:        86.82d {+05h 47m 17s}  +23.40d {+23d 24' 13"}
SUN_DIST:        105.19 [deg]   Sun_angle= -9.9 [hr] (East of Sun)
MOON_POSTN:      178.39d {+11h 53m 33s}   +6.23d {+06d 13' 54"}
MOON_DIST:        63.37 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:       73.78, 51.29 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      211.66, 62.73 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 352.39,-17.94 [deg].  
COMMENTS:        The 3rd packet (of 3) was missing in the lightcurve data stream.

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 18 Jun 21 02:00:35 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1056426,   Seg_Num: 0
POINT_RA:        235.827d {+15h 43m 18s} (J2000)
POINT_DEC:       +46.038d {+46d 02' 16"} (J2000)
IMG_START_DATE:  19383 TJD;   169 DOY;   21/06/18
IMG_START_TIME:  6282.29 SOD {01:44:42.29} UT,   65.3 [sec] since BAT Trigger Time
COUNTS:          34    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many iterations.

GCN Circular #30250
M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
At 01:43:37 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210618A (trigger=1056426). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 235.820, +46.043 which is
```
   RA(J2000) = 15h 43m 17s
   Dec(J2000) = +46d 02' 36"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 3 sec. The peak count rate was ~3600 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 01:44:42.2 UT, 65.3 seconds after the BAT trigger. No source was detected in the 2.5-s promptly available image. Due to a short visibility interval, no further data were immediately collected. We are waiting for the full dataset to detect and localise the XRT counterpart.
Due to the short visibility window, UVOT data are not available at this time.
Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.inaf.it). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/)

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Fri 18 Jun 21 02:45:55 UT
NOTICE_TYPE:     Swift-XRT Nack-Position
TRIGGER_NUM:     1056426,   Seg_Num: 0
POINT_RA:        235.782d {+15h 43m 08s} (J2000)
POINT_DEC:       +46.032d {+46d 01' 55"} (J2000)
IMG_START_DATE:  19383 TJD;   169 DOY;   21/06/18
IMG_START_TIME:  9940.86 SOD {02:45:40.86} UT,   3723.9 [sec] since BAT Trigger Time
COUNTS:          40    Min_needed= 20
STD_DEV:         0.00   Max_StdDev_for_Good=28.44 [arcsec]
PH2_ITER:        4    Max_iter_allowed= 4
ERROR_CODE:      2
COMMENTS:        SWIFT-XRT Nack Position.  
COMMENTS:        Algorithm did not converge; too many iterations.

GCN Circular #30251
Oc�lotl Lopez (UNAM), Margarita Pereyra (UNAM), Rosa L. Becerra (UNAM), Nat Butler (ASU), Alan M. Watson (UNAM), Simone Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Diego Gonzalez (UNAM), Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report:
We observed the field of the GRB 210618A (Fermi GBM Team, GCN circ. 30248 and Bernardini et al., GCN circ. 30250) with the DDOTI wide-field imager at the Observatorio Astron�mico Nacional on Sierra San Pedro Martir ( http://ddoti.astroscu.unam.mx) from 2021-06-18 03:52:24 UTC to 2021-03-18 06:39:28 UTC (from 2.14 to 4.93 hours after the trigger).
We observed a field of approximately 3.4 degrees in RA and 3.4 degrees in declination (about 11.55 square degrees), centered on the Swift BAT ground position of RA 235.74010768 , Dec 46.14225361(J2000), covering the BAT error region. We obtained 7604.6 seconds of exposure in the w filter. We calibrated our images against the APASS catalog.
We find no new sources within the BAT error region. To our 10-sigma limit we obtain an upper limit of w = 20.47 mag for the optical afterglow.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro Martir.
GCN Circular #30252
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU) and M. G. Bernardini (INAF-OAB) report on behalf of the Swift-XRT team:
We have analysed 5.2 ks of Photon Counting (PC) mode XRT data for the Swift-BAT-detected burst GRB 210618A (Bernardini et al. GCN Circ. 30250), collected between T0+65 s and T0+22.6 ks.
Three uncatalogued X-ray sources have been detected consistent with being within 296 arcsec of the Swift-BAT position, however none of them is above the RASS limit or shows definitive signs of fading. Two sources (Source 1 and Source 4) are consistent within the XRT error circle with two spectroscopically identified quasars, and the third one (Source 2) is consistent with a SDSS galaxy with photo_z=0.59 and marginally consistent with a candidate quasar. Therefore, for the moment the most plausible afterglow candidate is Source 2. Swift will perform follow-up observations to confirm this candidate.
Details of these sources are given below:
Source 1:
```
  RA (J2000.0):  235.8870  =  15:43:32.87
  Dec (J2000.0): +46.0253  =  +46:01:31.0
  Error: 8.9 arcsec (radius, 90% conf.)
  Count-rate: (3.82 [+1.19, -1.00])e-3 ct s^-1	 
  Distance: 179 arcsec from Swift-BAT position.
  Flux: (1.17 [+0.36, -0.30])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
```
This source is consistent with SDSS J154332.15+460133.2, spectroscopically classified as a quasar at z = 0.657.
Source 2:
```
  RA (J2000.0):  235.7698  =  15:43:4.75
  Dec (J2000.0): +46.0691  =  +46:04:08.6
  Error: 9.3 arcsec (radius, 90% conf.)
  Count-rate: (4.0 +/- 1.0)e-3 ct s^-1	 
  Distance: 156 arcsec from Swift-BAT position.
  Flux: (1.35 +/- 0.35)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) 
```
This source is positionally consistent with SDSS J154305.56+460405.0, a galaxy with photo_z = 0.590 +/- 0.153 and 12.2 arcsec away from SDSS J154305.40+460418.7, a candidate quasar (Richards et al., 2015, ApJS, 219, 39).
Source 4:
```
  RA (J2000.0):  235.7183  =  15:42:52.39
  Dec (J2000.0): +46.0336  =  +46:02:01.0
  Error: 8.7 arcsec (radius, 90% conf.)
  Count-rate: (1.48 [+0.78, -0.60])e-3 ct s^-1	 
  Distance: 256 arcsec from Swift-BAT position.
  Flux: (7.2 [+3.8, -2.9])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)
```
This source is positionally consistent with SDSS J154251.96+460206.1, spectroscopically classified as a quasar at z = 2.130.
Six uncatalogued sources were also detected too far from the GRB position to be likely afterglow candidates.
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/01056426.
This circular is an official product of the Swift-XRT team.
GCN Circular #30253
J. Wood (NASA/MSFC) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 01:43:36.14 UT on 18 June 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210618A (trigger 645673421 / 210618072) which was also detected by the Swift/BAT (M. G. Bernardini et al. 2019, GCN 30250).
The Fermi GBM Final Real-time Localization (GCN 30248) is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 113 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 3.6 s (50-300 keV). The time-averaged spectrum from T0-1.6 s to T0+2.2 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.62 +/- 0.26 and the cutoff energy, parameterized as Epeak, is 440 +/- 140 keV
The event fluence (10-1000 keV) in this time interval is (1.2 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.3 s in the 10-1000 keV band is 2.1 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak= 400 +/- 190 keV, alpha = -0.60 +/- 0.32 and beta = -2.3 +/- 0.9.
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 #30254
S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-70 to T+960 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210618A (trigger #1056426) (Bernardini, et al., GCN Circ. 30250). The BAT ground-calculated position is RA, Dec = 235.763, 46.072 deg which is
```
  RA(J2000)  =  15h 43m 03.2s 
  Dec(J2000) = +46d 04' 17.5" 
```
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%.
The mask-weighted light curve shows a fairly complex structure between roughly T-1.5 and T+0.5 seconds. The spacecraft slewed away from the burst location starting at around T+320 seconds. T90 (15-350 keV) is 2.13 +- 0.44 sec (estimated error including systematics).
The time-averaged spectrum from T-1.42 to T+0.96 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.18 +- 0.28. The fluence in the 15-150 keV band is 1.8 +- 0.3 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.50 sec in the 15-150 keV band is 1.1 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/1056426/BA/
GCN Circular #30255
Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), R. Fernandez-Munoz (IHSM/UMA-CSIC) and M. Jelinek (ASU-CAS), on behalf of a larger collaboration, report:
The 60cm BOOTES-2/TELMA robotic telescope at IHSM La Mayora (UMA-CSIC) in Algarrobo Costa (Malaga, Spain) automatically responded to the Swift and Fermi trigger of GRB 210618A (Fermi GBM team GCNC 30248, Bernardini et al. GCNC 30250). Images were taken starting at 01:54 UT, but due to poor weather conditions, only images taken after 02:17 UT (~34 min after trigger) could be used. In the co-added 10 x 60 s exposure image (clear filter), no optical afterglow is neither detected within the BAT/Swift error box (Bernardini et al. GCNC 30250) nor associated with the reported XRT/Swift sources (Osborne et al. GCNC 30252) down to 19.6 mag. This non-detection is consistent with the report from Lipunov et al. (GCNC 30249) and Lopez et al. (GCNC 30251).
We thank the staff at La Mayora for its excellent support.
GCN Circular #30256
N. P. M. Kuin (UCL-MSSL) and M. G. Bernardini (INAF-OAB) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 210618A 3728 s after the BAT trigger (Bernardini et al., GCN Circ. 30250). No optical afterglow consistent with the XRT candidates source 1, 2 or 4 (Osborne et al. , GCN Circ. 30252) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC          3728         3878          147         >20.4
white             3728         4496          344         >21.1
v                 4707         4843          133         >19.2
b                 4092         4291          197         >20.5
u                 3886         4086          197         >20.0
w2                4502         4702          197         >20.1
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.015 in the direction of the burst (Schlegel et al. 1998).
Since this is a short GRB, further Swift search for late time optical emission is being planned.
GCN Circular #30312
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA), M. Capalbi (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the Swift-BAT-detected burst GRB 210618A (Bernardini et al. GCN Circ. 30250). The observations now extend from T0+3.7 ks to T0+424.9 ks.
Of the sources reported by Osborne et al. (GCN Circ. 30252), "Source 2" is believed to be the afterglow. The position of this source is RA, Dec=235.7698, +46.0691 which is equivalent to:
```
RA (J2000): 15:43:04.75
Dec(J2000): +46:04:08.6
```
with an uncertainty of 9.3 arcsec (radius, 90% confidence). This position is 2.6 arcmin from the Swift-BAT position. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01056426. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/01056426.
This circular is an official product of the Swift-XRT team.
GCN Circular #30322
Y.-D. Hu, F. J. Aceituno, T.-R. Sun, A. J. Castro-Tirado, M. D. Caballero-Garcia, M. A. Castro Tirado and E. Fernandez-Garcia (IAA-CSIC) on behalf of a larger collaboration, report:
Following the detection of GRB210618A by Swift (Bernardini et al. GCNC 30250) and Fermi (Fermi GBM team. GCNC 30248), we triggered the 1.5m OSN telescope in Granada (Spain) for the possible X-ray afterglow detection, "Source 2" reported in Osborne et al. GCNC 30252. Optical images in the I-band were obtained starting on Jun 24, 21:11 UT (~6.8 d after trigger). No-optical afterglow is detected in the co-added image (300s x 3) within the Swift/XRT error box (Osborne et al. GCNC 30312) which down to I=20.9.
We thank the staff at OSN for their excellent support.

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Jochen Greiner, last update: 26-Jun-2021 [Disclaimer]