GRB210820A

This page lists all entries on GRB210820A in GRBweb

Summary IPN Swift GCN 30664 GCN 30666 GCN 30667 GCN 30668 GCN 30669 GCN 30670 GCN 30672 GCN 30673 GCN 30674 GCN 30675 GCN 30686 GCN 30688 GCN 30695 GCN 30731 GCN 30757

Summary table
Variable Value Source
T0 17:38:00 UTC GCN_circulars,Swift Det
ra 20.6395° Swift
decl 4.6079° Swift
pos_error 5.82e-05° Swift
T90 196.8 s Swift
T90_start 17:38:00 UTC Swift
fluence 1.50e-06 erg/cm² Swift
T100 196.8 s
GBM_located False
mjd 59446.73472222222 GCN_circulars,Swift Det
IPN table
GRB_name GRB210820A
ra 20.6292°
decl 4.6333°
pos_error 5.00e-02°
Swift table
GRB_name GRB210820A
t_trigger 17:38:00 UTC
ra 20.6395°
decl 4.6079°
pos_error 5.82e-05°
T90 196.8 s
fluence 1.50e-06 erg/cm²
GCN 30664 table
GRB_name GRB210820A
GCN_number 30664
Detection_method Swift Det
t_trigger 17:38:00 UTC
ra 20.6290°
decl 4.6320°
Circular_text TITLE: GCN CIRCULAR NUMBER: 30664 SUBJECT: GRB 210820A: Swift detection of a burst with an optical counterpart DATE: 21/08/20 17:52:12 GMT FROM: David Palmer at LANL A. P. Beardmore (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU), N. J. Klingler (GSFC/UMBC/CRESSTII), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 17:38:00 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 210820A (trigger=1069551). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 20.629, +4.632 which is RA(J2000) = 01h 22m 31s Dec(J2000) = +04d 37' 55" 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 30 sec. The peak count rate was ~500 counts/sec (15-350 keV), at ~8 sec after the trigger. The XRT began observing the field at 17:40:05.7 UT, 125.0 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 20.6376, 4.6071 which is equivalent to: RA(J2000) = 01h 22m 33.02s Dec(J2000) = +04d 36' 25.6" with an uncertainty of 11.1 arcseconds (radius, 90% containment). This location is 94 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 3.75e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 130 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 01:22:33.48 = 20.63952 DEC(J2000) = +04:36:28.2 = 4.60783 with a 90%-confidence error radius of about 0.76 arc sec. This position is 7.4 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.53 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.031. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 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 30666 table
GRB_name GRB210820A
GCN_number 30666
Detection_method Swift Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 30666 SUBJECT: Swift GRB 210820A: Global MASTER-Net observations report DATE: 21/08/20 19:03:39 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the Swift GRB 210820A ( A. P. Beardmore et al., GCN 30664) errorbox 4451 sec after notice time and 4532 sec after trigger time at 2021-08-20 18:53:33 UT, with upper limit up to 15.2 mag. The observations began at zenith distance = 84 deg. The sun altitude is -26.1 deg. The galactic latitude b = -57 deg., longitude l = 138 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1695760 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 4622 | MASTER-Kislovodsk | C | 180 | 14.5 | 4622 | MASTER-Kislovodsk | C | 180 | 15.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.
GCN 30667 table
GRB_name GRB210820A
GCN_number 30667
Detection_method Swift-XRT Det
ra 20.6396°
decl 4.6076°
Circular_text TITLE: GCN CIRCULAR NUMBER: 30667 SUBJECT: GRB 210820A: Enhanced Swift-XRT position DATE: 21/08/21 02:29:36 GMT FROM: Phil Evans at U of Leicester A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 2824 s of XRT Photon Counting mode data and 3 UVOT images for GRB 210820A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 20.63963, +4.60764 which is equivalent to: RA (J2000): 01h 22m 33.51s Dec (J2000): +04d 36' 27.5" with an uncertainty of 2.5 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team.
GCN 30668 table
GRB_name GRB210820A
GCN_number 30668
Detection_method Swift-XRT Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 30668 SUBJECT: GRB 210820A: Swift-XRT refined Analysis DATE: 21/08/21 02:38:02 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), K.L. Page (U. Leicester) and A.P. Beardmore report on behalf of the Swift-XRT team: We have analysed 6.5 ks of XRT data for GRB 210820A (Beardmore et al. GCN Circ. 30664), from 131 s to 18.2 ks after the BAT trigger. The data comprise 339 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 30667). The late-time light curve (from T0+5.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.9 (+0.6, -0.5). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.77 (+/-0.03). The best-fitting absorption column is 1.20 (+/-0.11) x 10^21 cm^-2, in excess of the Galactic value of 3.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.28 (+0.25, -0.13) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.9 x 10^-11 (3.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.6 (+4.3, -0.0) x 10^20 cm^-2 Galactic foreground: 3.6 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.28 (+0.25, -0.13) If the light curve continues to decay with a power-law decay index of 1.9, the count rate at T+24 hours will be 2.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x 10^-15 (9.6 x 10^-15) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01069551. This circular is an official product of the Swift-XRT team.
GCN 30669 table
GRB_name GRB210820A
GCN_number 30669
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 30669 SUBJECT: GRB 210820A: Nanshan/NEXT optical upper limit DATE: 21/08/21 04:01:10 GMT FROM: Dong Xu at NAOC/CAS S.Y. Fu (NAOC), Z.P. Zhu (NAOC,HUST), X. Liu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of GRB 210820A (Beardmore et al., GCN 30664) using the NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We obtained 10x200 s frames in the Sloan r-band, starting at 21:17:58 UT on 2021-08-20, i.e., 3.67 hr after the BAT trigger. No optical source is detected in our stacked image at the Swift/UVOT position (Beardmore et al., GCN 30664), down to a limiting magnitude of r~21.3, calibrated with the nearby PanSTARRS field.
GCN 30670 table
GRB_name GRB210820A
GCN_number 30670
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 30670 SUBJECT: GRB 210820A: NOT optical upper limit DATE: 21/08/21 07:30:12 GMT FROM: Dong Xu at NAOC/CAS Z.P. Zhu (NAOC, HUST), D. B. Malesani (DTU space), L. Izzo (DARK/NBI), J.P.U. Fynbo (DAWN/NBI), D. Xu (NAOC), R. Clavero (NOT) report on behalf of a larger collaboration: We observed the field of GRB210820A (Beardmore et al., GCN30664) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. We obtained 3x200s frames in the Sloan r- filter, starting at 00:49:56 UT on 2021-08-21 (i.e., ~ 7.29 hr after the BAT trigger). No optical source is detected in our stacked image at the Swift/UVOT position (Beardmore et al., GCN 30664), down to a limiting magnitude of r~22.2, calibrated with the nearby PanSTARRS field.
GCN 30672 table
GRB_name GRB210820A
GCN_number 30672
Detection_method Swift-BAT Det
ra 20.6395°
decl 4.6078°
Circular_text TITLE: GCN CIRCULAR NUMBER: 30672 SUBJECT: GRB 210820A: RATIR Optical Detections DATE: 21/08/21 15:52:28 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Eleonora Troja (GSFC), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Enrico Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), Rosa L. Becerra (UNAM), Simone Dichiara (UMD), and Océlotl López (UNAM) report: We observed the field of GRB 210820A (Beardmore, et al., GCN 30664) with the Reionization and Transients Infrared Camera (RATIR) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2021/08 21.27 to 2021/08 21.50 UTC (12.47 to 17.96 hours after the BAT trigger), obtaining a total of 3.70 hours exposure in the r and i bands. We detect one source within the Swift-XRT error circle (Beardmore, et al., GCN 30667). In comparison with the SDSS DR9 and 2MASS catalogs, we obtain: r = 22.84 +/- 0.22 i = 22.66 +/- 0.18 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. The source is located at RA, Dec = 1:22:33.47, +4:36:28.1 (J2000, +/-0.5"). This is 0.2 arcsec away from the UVOT OT (GCN 30664). We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.
GCN 30673 table
GRB_name GRB210820A
GCN_number 30673
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 30673 SUBJECT: GRB 210820A: LCO Optical Upper Limit DATE: 21/08/21 16:05:02 GMT FROM: Robert Strausbaugh at U. of the Virgin Islands R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration: We observed Swift GRB 210820A (Beardmore, et al., GCN 30664) with the LCO 1-m Sinistro instrument at the Teide Observatory, Tenerife site, on August 21, from 01:20 to 01:51 UT (corresponding to 7.7 to 8.5 hours from the GRB trigger time) with the Bessel R and I filters. We performed a series of 5x120s exposures in R and I. In the UVOT detection region (Beardmore, et al., GCN 30664) no optical counterpart could be detected down to the following upper limits, calculated using the USNO-B.1 catalog as reference: R>20.16 I>19.17 These magnitudes are not corrected for galactic extinction. R.S. is funded by NSF AST grant #1831682
GCN 30674 table
GRB_name GRB210820A
GCN_number 30674
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 30674 SUBJECT: GRB 210820A: LT optical upper limit DATE: 21/08/21 17:30:40 GMT FROM: Martin Blazek at HETH/IAA-CSIC M. Blazek, D. A. Kann (both HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/ IAA-CSIC, DARK/NBI), C. C. Thoene, J. F. Agui Fernandez (both HETH/IAA-CSIC) report: We observed the location of the Swift GRB 210820A (Beardmore et al., GCN #30664) with 2-m Liverpool Telescope located in La Palma, Canary Isands, Spain. We obtained 15 x 60 s images beginning 2021-08-21 03:29:30 UT. In a stack of all images, centered at 0.4175 days after the GRB, no source is detected at the UVOT position. Measured against three nearby SDSS stars, we derive an upper limit of r' > 21.1 mag. This agrees with the non-detections reported by Lipunov et al. (GCN #30666), Fu et al. (GCN #30669)., and Zhu et al. (GCN #30670).
GCN 30675 table
GRB_name GRB210820A
GCN_number 30675
Detection_method Swift-BAT Det
ra 20.6220°
decl 4.6420°
Circular_text TITLE: GCN CIRCULAR NUMBER: 30675 SUBJECT: GRB 210820A: Swift-BAT refined analysis DATE: 21/08/21 18:36:42 GMT FROM: Amy Lien at GSFC S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), H. A. Krimm (NSF), A. Y. Lien (U Tampa), 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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 210820A (trigger #1069551) (Beardmore et al., GCN Circ. 30664). The BAT ground-calculated position is RA, Dec = 20.622, 4.642 deg which is RA(J2000) = 01h 22m 29.4s Dec(J2000) = +04d 38' 30.6" with an uncertainty of 3.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve shows many weak overlapping pulses that start at ~T0 and end at ~T+260 s. T90 (15-350 keV) is 196.8 +- 51.4 sec (estimated error including systematics). The time-averaged spectrum from T+0.78 to T+258.97 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.26 +- 0.22. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+10.92 sec in the 15-150 keV band is 0.8 +- 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/1069551/BA/
GCN 30686 table
GRB_name GRB210820A
GCN_number 30686
Detection_method Swift-UVOT Det
ra 20.6395°
decl 4.6079°
Circular_text TITLE: GCN CIRCULAR NUMBER: 30686 SUBJECT: GRB 210820A: Swift/UVOT Detection DATE: 21/08/22 19:54:45 GMT FROM: Sam LaPorte at PSU GRB 210820A: Swift/UVOT Detection S. J. LaPorte (PSU) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 210820A 131 s after the BAT trigger (Beardmore et al., GCN Circ. 30664). A source consistent with the XRT position (Beardmore et al., GCN Circ. 30664) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 01:22:33.48 = 20.63952 (deg.) Dec (J2000) = +04:36:28.3 = 4.60786 (deg.) with an estimated uncertainty of 0.45 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag v 437 1684 156 18.86 +/- 0.24 b 387 555 39 18.57 +/- 0.19 u 131 381 246 17.60 +/- 0.06 w1 784 1733 58 >19.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.030 in the direction of the burst (Schlegel et al. 1998).
GCN 30688 table
GRB_name GRB210820A
GCN_number 30688
Detection_method correction
Circular_text TITLE: GCN CIRCULAR NUMBER: 30688 SUBJECT: GRB 210820A: NUTTelA-TAO / BSTI Early Optical Limits (Preliminary) DATE: 21/08/23 00:07:17 GMT FROM: Bruce Grossan at LBNL/UCB SSL T. Komesh (NU), B. Grossan (UCB, NU), Z. Maksut (NU), A. Kim (NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), E. Linder (UCB, NU), E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory: The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) observed the field of GRB 210820A on receipt of an automated GCN / BAT position alert, observing in Sloan g', r' and i' bands, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14). We received the alert at 17:39:26 UT (85 seconds between GRB time and notification time) and started observations at 17:39:32 UT on 2021-08-20, 6.5 s after receipt, 91 s after the BAT trigger. Observations were made under 95+% moon illumination and cloudy conditions starting at only about 20 deg. target altitude. No source consistent with the XRT or UVOT position was detected. The observations fully cover the UVOT U detection observation time (Palmer 2021, GCN 30664) and some additional UVOT observations (LaPorte 2021, GCN 30686). Note that these observations provide essentially full-time coverage, simultaneous in all three bands. We report the following results: start time end time UL g' UL r' ULi' exposure_time (s) ------------ ----------- ------ ------ ------ -------------------- 17:39:32 17:40:32 17.0 15.1 16.4 60 17:40:57 17:56:42 17.9 15.9 16.8 135 UL g', r', i', gives the 5 sigma upper limit sensitivity in magnitudes in the respective filter, for images co-added to the given exposure time. The first row in the table corresponds to co-adds of an initial short exposure image sequence of 7.5 s each, the second row corresponds to co-adds from a continuing series of 15 s exposures, uninterrupted for the entire interval. No uncatalogued sources near the XRT location were found up to the co-add times indicated. Calibration was done with the few bright Pan-STARRS catalog stars on our images. We caution the reader that these are preliminary results, without color or other corrections, and will likely change in small measure. Please also note that times are approximate. We anticipate improved analysis in 15-30 days posted at http://ecl.nu.edu.kz/gamma-ray-burst/grb210820a. ---------------------------------- NU = Nazarbayev University, Nur-Sultan, Kazakhstan UCB = University of California, Berkeley, USA HKUST = Hong Kong University of Science and Technology FAI = Fesenkov Astrophysical Institute, Kazakhstan The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
GCN 30695 table
GRB_name GRB210820A
GCN_number 30695
Detection_method Other
Circular_text TITLE: GCN CIRCULAR NUMBER: 30695 SUBJECT: GRB 210820A: GROND observations DATE: 21/08/23 13:50:31 GMT FROM: Ana Nicuesa at TLS Tautenburg A. Nicuesa Guelbenzu, S. Klose (both TLS Tautenburg) and A. Rau (MPE Garching) report: We observed the field of GRB 210820A (Swift trigger 1069551); Beardmore et al., GCN 30664) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2 m MPG/ESO telescope at La Silla Observatory (Chile). Observations were performed at 9:03 UT (midtime) on August 21, 2021, about 15.5 hours after the GRB trigger. They were executed at an average seeing of 1.3 arcsec and at an average airmass of 1.2. We detect a source within the XRT error circle (Beardmore, et al., GCN 30667) in the i' band with the following preliminary AB magnitude i'=22.46 +/- 0.28 in agreement with the RATIR detection (Butler et al., GCN 30672). We do not detect the source in the other bands down to the following limiting AB magnitudes: g' > 22.6, r' > 22.9, z' > 22.3, J > 20.9, H > 20.4, and K > 17.4. The given limits and magnitude are derived based on calibrating the images against SDSS in g'r'i'z' and 2MASS field stars in JHK. We thank Paul Eigenthaler for excellent support and for performing the observations.
GCN 30731 table
GRB_name GRB210820A
GCN_number 30731
Detection_method Swift Det
Circular_text TITLE: GCN CIRCULAR NUMBER: 30731 SUBJECT: GRB 210820A: CAHA 2.2m Optical Detection DATE: 21/08/27 18:03:36 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), A. Fernandez, and I. Hermelo (all CAHA) report: We observed GRB 210820A (Swift detection: Beardmore et al., GCN #30664) with CAFOS mounted on the 2.2m CAHA telescope at Calar Alto, Alemria, Spain, under inclement conditions (bright moonlight, passing clouds, low transparency). We obtained 10 x 90 s each in filters B, V, Rc. Stacks reveal no detection of the afterglow in B (very shallow because of moonlight) and Rc (shallow because of incoming clouds which also prevented further observations). However, the afterglow (Beardmore et al., GCN #30664; Butler et al., GCN #30672; LaPorte & Beardmore, GCN #30686; Nicuesa Guelbenzu et al., GCN #30695) is clearly detected in V, somewhat north of a source also seen in Pan-STARRS and in SDSS. We find the afterglow to be V = 22.43 +/- 0.15 mag (AB mag, derived from two SDSS field stars transformed to V via the equations of Lupton 2005) at 0.43868 days after the GRB.
GCN 30757 table
GRB_name GRB210820A
GCN_number 30757
Detection_method Optical
Circular_text TITLE: GCN CIRCULAR NUMBER: 30757 SUBJECT: GRB 210820A: TSHAO optical upper limit DATE: 21/09/03 17:11:38 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), I. Reva (FAP), A. Kusakin (FAP), A. Pozanenko (IKI), N.Pankov (HSE), V. Kim (FAP) report on behalf of GRB-IKI-FuN: We observed GRB 210820A (Beardmore et al., GCN 30664) with Zeiss-1000 telescope of Tien Shan Astronomical Observatory starting on Aug. 21 (UT) 21:32:02. The optical afterglow (Beardmore et al., GCN 30664; Lipunov et al., GCN 30666; Fu et al., GCN 30669; Zhu et al., GCN 30670; Butler et al., GCN 30672; Strausbaugh et al., GCN 30673; Blazek et al., GCN 30674; Laha et al., GCN 30675; LaPorte and Beardmore, GCN 30686; Komesh et al., GCN 30688; Guelbenzu et al., GCN 30695; Kann et al., GCN 30731) was not detected in the stacked image down to a limiting magnitude of 21.8 in R filter. Preliminary photometry of the field in a stacked image is following. Date UT start t-T0 Filter Exp. OT Err. UL(3 sigma) (mid, days) (s) 2021-08-21 21:32:02 1.17659 R 27*90 n/d n/d 21.8 The photometry is based on nearby USNO-B1.0 stars. USNO-B1.0 RA Dec R2 01:22:01.52088 +04:35:30.2028 17.48 01:22:14.95944 +04:43:31.2204 17.89