//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29981 SUBJECT: GRB 210510A: Fermi GBM Final Real-time Localization DATE: 21/05/10 19:30:27 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely SHORT GRB At 19:20:00 UT on 10 May 2021, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 210510A (trigger 642367205.830352 / 210510806). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 192.3, Dec = 44.9 (J2000 degrees, equivalent to J2000 12h 49m, 44d 53'), with a statistical uncertainty of 21.7 degrees. The angle from the Fermi LAT boresight is 20.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210510806/quicklook/glg_skymap_all_bn210510806.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/bn210510806/quicklook/glg_healpix_all_bn210510806.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2021/bn210510806/quicklook/glg_lc_medres34_bn210510806.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29986 SUBJECT: Fermi GRB 210510A: Global MASTER-Net observations report DATE: 21/05/10 21:17:39 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 210510A ( Fermi GBM team, GCN 29981) errorbox 195 sec after notice time and 624 sec after trigger time at 2021-05-10 19:30:25 UT, with upper limit up to 19.4 mag. The observations began at zenith distance = 9 deg. The sun altitude is -21.6 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 210510A errorbox 266 sec after notice time and 695 sec after trigger time at 2021-05-10 19:31:35 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 71 deg. The sun altitude is -46.4 deg. The galactic latitude b = 73 deg., longitude l = 123 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1610677 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 655 | 2021-05-10 19:30:25 | MASTER-Tavrida | (12h 43m 26.49s , +35d 16m 46.0s) | C | 60 | 18.8 | 725 | 2021-05-10 19:31:35 | MASTER-SAAO | (12h 47m 18.36s , +38d 00m 12.5s) | C | 60 | 18.6 | 734 | 2021-05-10 19:31:45 | MASTER-Tavrida | (12h 53m 14.67s , +35d 15m 53.1s) | C | 60 | 18.8 | 805 | 2021-05-10 19:32:55 | MASTER-SAAO | (12h 57m 28.18s , +38d 00m 18.3s) | C | 60 | 18.6 | 885 | 2021-05-10 19:34:15 | MASTER-SAAO | (13h 06m 45.94s , +36d 00m 19.6s) | C | 60 | 18.9 | 964 | 2021-05-10 19:35:35 | MASTER-SAAO | (13h 16m 36.57s , +36d 01m 37.0s) | C | 60 | 19.3 | 1016 | 2021-05-10 19:36:26 | MASTER-Tavrida | (12h 53m 48.53s , +33d 17m 50.4s) | C | 60 | 18.9 | 1044 | 2021-05-10 19:36:54 | MASTER-SAAO | (12h 48m 34.07s , +40d 02m 32.9s) | C | 60 | 18.7 | 1095 | 2021-05-10 19:37:46 | MASTER-Tavrida | (13h 03m 42.88s , +37d 15m 57.1s) | C | 60 | 19.0 | 1124 | 2021-05-10 19:38:14 | MASTER-SAAO | (12h 59m 01.24s , +40d 01m 19.0s) | C | 60 | 18.7 | 1203 | 2021-05-10 19:39:34 | MASTER-SAAO | (13h 07m 07.94s , +34d 00m 18.1s) | C | 60 | 19.2 | 1264 | 2021-05-10 19:40:34 | MASTER-Tavrida | (13h 13m 58.18s , +37d 17m 44.8s) | C | 60 | 19.0 | 1283 | 2021-05-10 19:40:53 | MASTER-SAAO | (13h 16m 39.04s , +34d 01m 47.2s) | C | 60 | 19.2 | 1343 | 2021-05-10 19:41:54 | MASTER-Tavrida | (12h 45m 55.92s , +31d 17m 02.9s) | C | 60 | 18.9 | 1363 | 2021-05-10 19:42:13 | MASTER-SAAO | (13h 09m 23.60s , +40d 02m 05.4s) | C | 60 | 18.6 | 1442 | 2021-05-10 19:43:33 | MASTER-SAAO | (13h 19m 36.73s , +40d 00m 54.1s) | C | 60 | 18.6 | 1522 | 2021-05-10 19:44:52 | MASTER-SAAO | (12h 27m 44.76s , +36d 02m 15.7s) | C | 60 | 19.3 | 1602 | 2021-05-10 19:46:12 | MASTER-SAAO | (12h 37m 29.23s , +36d 01m 02.4s) | C | 60 | 19.1 | 1681 | 2021-05-10 19:47:32 | MASTER-SAAO | (12h 47m 36.34s , +38d 01m 14.7s) | C | 60 | 19.0 | 1712 | 2021-05-10 19:48:02 | MASTER-Tavrida | (12h 55m 27.65s , +31d 16m 34.4s) | C | 60 | 18.5 | 1761 | 2021-05-10 19:48:51 | MASTER-SAAO | (12h 57m 37.99s , +38d 02m 36.3s) | C | 60 | 18.8 | 1841 | 2021-05-10 19:50:11 | MASTER-SAAO | (13h 06m 57.68s , +36d 00m 30.6s) | C | 60 | 19.1 | 1884 | 2021-05-10 19:50:54 | MASTER-Tavrida | (12h 43m 26.25s , +35d 15m 30.1s) | C | 60 | 18.6 | 1921 | 2021-05-10 19:51:31 | MASTER-SAAO | (13h 16m 49.60s , +36d 01m 41.1s) | C | 60 | 19.3 | 1963 | 2021-05-10 19:52:14 | MASTER-Tavrida | (12h 53m 15.75s , +35d 17m 03.0s) | C | 60 | 18.6 | 2001 | 2021-05-10 19:52:51 | MASTER-SAAO | (12h 48m 46.44s , +40d 01m 58.7s) | C | 60 | 19.0 | 2043 | 2021-05-10 19:53:33 | MASTER-Tavrida | (12h 44m 11.06s , +33d 15m 16.8s) | C | 60 | 18.6 | 2080 | 2021-05-10 19:54:11 | MASTER-SAAO | (12h 59m 07.35s , +40d 02m 43.5s) | C | 60 | 18.9 | 2122 | 2021-05-10 19:54:52 | MASTER-Tavrida | (12h 53m 54.03s , +33d 16m 51.5s) | C | 60 | 18.7 | 2160 | 2021-05-10 19:55:30 | MASTER-SAAO | (13h 07m 18.49s , +34d 01m 23.8s) | C | 60 | 19.4 | 2240 | 2021-05-10 19:56:50 | MASTER-SAAO | (13h 16m 47.58s , +34d 00m 09.2s) | C | 60 | 19.3 | 2319 | 2021-05-10 19:58:10 | MASTER-SAAO | (13h 09m 35.11s , +40d 00m 34.7s) | C | 60 | 18.8 | 2399 | 2021-05-10 19:59:30 | MASTER-SAAO | (13h 19m 52.79s , +40d 02m 10.9s) | C | 60 | 18.9 | 2451 | 2021-05-10 20:00:21 | MASTER-Tavrida | (13h 07m 43.98s , +39d 06m 51.0s) | C | 60 | 19.2 | 2479 | 2021-05-10 20:00:49 | MASTER-SAAO | (12h 27m 49.38s , +36d 01m 47.5s) | C | 60 | 19.4 | 2560 | 2021-05-10 20:02:10 | MASTER-SAAO | (12h 37m 43.47s , +36d 03m 21.7s) | C | 60 | 19.1 | 2639 | 2021-05-10 20:03:30 | MASTER-SAAO | (12h 27m 28.23s , +38d 03m 48.9s) | C | 60 | 19.4 | 2719 | 2021-05-10 20:04:49 | MASTER-SAAO | (12h 47m 46.61s , +38d 02m 16.7s) | C | 60 | 19.4 | 2798 | 2021-05-10 20:06:09 | MASTER-SAAO | (12h 37m 35.89s , +38d 01m 36.0s) | C | 60 | 19.2 | 2822 | 2021-05-10 20:06:32 | MASTER-Tavrida | (13h 13m 54.97s , +37d 17m 13.2s) | C | 60 | 19.0 | 2878 | 2021-05-10 20:07:28 | MASTER-SAAO | (12h 57m 52.50s , +38d 01m 10.9s) | C | 60 | 19.3 | 2901 | 2021-05-10 20:07:51 | MASTER-Tavrida | (12h 45m 56.80s , +31d 15m 37.7s) | C | 60 | 19.1 | 2958 | 2021-05-10 20:08:48 | MASTER-SAAO | (13h 07m 09.82s , +36d 02m 38.8s) | C | 60 | 19.2 | 3037 | 2021-05-10 20:10:08 | MASTER-SAAO | (13h 16m 58.47s , +36d 00m 45.7s) | C | 60 | 19.3 | 3073 | 2021-05-10 20:10:43 | MASTER-Tavrida | (12h 55m 21.49s , +31d 15m 21.2s) | C | 60 | 18.7 | 3117 | 2021-05-10 20:11:27 | MASTER-SAAO | (12h 49m 02.96s , +40d 03m 10.9s) | C | 60 | 19.3 | 3153 | 2021-05-10 20:12:03 | MASTER-Tavrida | (12h 34m 28.11s , +33d 16m 18.8s) | C | 60 | 19.0 | 3197 | 2021-05-10 20:12:47 | MASTER-SAAO | (12h 59m 17.74s , +40d 02m 10.5s) | C | 60 | 18.8 | 3323 | 2021-05-10 20:14:54 | MASTER-Tavrida | (12h 43m 20.26s , +35d 16m 17.4s) | C | 60 | 18.9 | 3403 | 2021-05-10 20:16:13 | MASTER-Tavrida | (12h 53m 09.24s , +35d 15m 41.6s) | C | 60 | 19.0 | 3482 | 2021-05-10 20:17:33 | MASTER-Tavrida | (12h 44m 04.78s , +33d 16m 26.5s) | C | 60 | 19.0 | 3516 | 2021-05-10 20:18:07 | MASTER-SAAO | (13h 07m 32.69s , +34d 01m 38.5s) | C | 60 | 19.2 | 3562 | 2021-05-10 20:18:52 | MASTER-Tavrida | (12h 53m 50.63s , +33d 15m 35.1s) | C | 60 | 18.9 | 3596 | 2021-05-10 20:19:26 | MASTER-SAAO | (13h 17m 01.23s , +34d 00m 27.0s) | C | 60 | 19.3 | 3641 | 2021-05-10 20:20:11 | MASTER-Tavrida | (13h 03m 39.09s , +37d 14m 44.9s) | C | 60 | 19.2 | 3676 | 2021-05-10 20:20:46 | MASTER-SAAO | (13h 09m 50.95s , +40d 00m 53.9s) | C | 60 | 19.0 | 3756 | 2021-05-10 20:22:06 | MASTER-SAAO | (13h 20m 09.64s , +40d 02m 16.0s) | C | 60 | 18.9 | 3812 | 2021-05-10 20:23:02 | MASTER-Tavrida | (12h 24m 46.52s , +33d 15m 54.2s) | C | 60 | 18.8 | 3836 | 2021-05-10 20:23:26 | MASTER-SAAO | (12h 27m 56.26s , +36d 02m 20.8s) | C | 60 | 19.3 | 3891 | 2021-05-10 20:24:22 | MASTER-Tavrida | (13h 13m 51.39s , +37d 14m 55.6s) | C | 60 | 19.3 | 3915 | 2021-05-10 20:24:46 | MASTER-SAAO | (12h 37m 50.22s , +36d 03m 41.6s) | C | 60 | 19.2 | 3971 | 2021-05-10 20:25:41 | MASTER-Tavrida | (12h 45m 53.47s , +31d 15m 59.7s) | C | 60 | 19.1 | 3995 | 2021-05-10 20:26:05 | MASTER-SAAO | (12h 27m 35.56s , +38d 03m 23.6s) | C | 60 | 19.4 | 4050 | 2021-05-10 20:27:01 | MASTER-Tavrida | (12h 55m 13.37s , +31d 15m 24.8s) | C | 60 | 19.1 | 4075 | 2021-05-10 20:27:25 | MASTER-SAAO | (12h 37m 43.48s , +38d 04m 08.6s) | C | 60 | 19.4 | 4130 | 2021-05-10 20:28:20 | MASTER-Tavrida | (12h 34m 23.91s , +33d 15m 57.7s) | C | 60 | 19.0 | 4360 | 2021-05-10 20:32:10 | MASTER-Tavrida | (13h 14m 08.25s , +31d 16m 37.0s) | C | 60 | 19.4 | 4392 | 2021-05-10 20:32:42 | MASTER-SAAO | (12h 46m 37.46s , +36d 01m 45.7s) | C | 60 | 19.0 | 4439 | 2021-05-10 20:33:30 | MASTER-Tavrida | (12h 43m 13.89s , +37d 14m 06.1s) | C | 60 | 19.1 | 4472 | 2021-05-10 20:34:02 | MASTER-SAAO | (12h 56m 25.63s , +36d 03m 27.9s) | C | 60 | 19.2 | 4519 | 2021-05-10 20:34:49 | MASTER-Tavrida | (12h 53m 31.29s , +37d 14m 17.2s) | C | 60 | 19.0 | 4598 | 2021-05-10 20:36:09 | MASTER-Tavrida | (13h 03m 03.01s , +35d 14m 41.9s) | C | 60 | 19.4 | 4678 | 2021-05-10 20:37:28 | MASTER-Tavrida | (13h 13m 00.49s , +35d 16m 02.5s) | C | 60 | 17.8 | 4757 | 2021-05-10 20:38:48 | MASTER-Tavrida | (12h 24m 41.38s , +33d 14m 33.5s) | C | 60 | 18.2 | 4788 | 2021-05-10 20:39:19 | MASTER-SAAO | (12h 47m 14.67s , +34d 02m 45.3s) | C | 60 | 19.1 | 4837 | 2021-05-10 20:40:07 | MASTER-Tavrida | (12h 44m 22.41s , +39d 15m 04.4s) | C | 60 | 18.4 | 4868 | 2021-05-10 20:40:38 | MASTER-SAAO | (12h 56m 52.56s , +34d 03m 34.6s) | C | 60 | 19.2 | 4916 | 2021-05-10 20:41:26 | MASTER-Tavrida | (12h 54m 43.17s , +39d 14m 13.2s) | C | 60 | 17.7 | 4948 | 2021-05-10 20:41:58 | MASTER-SAAO | (12h 26m 33.47s , +38d 03m 43.1s) | C | 60 | 19.3 | 5028 | 2021-05-10 20:43:18 | MASTER-SAAO | (12h 36m 35.41s , +38d 02m 29.3s) | C | 60 | 19.2 | 5107 | 2021-05-10 20:44:38 | MASTER-SAAO | (12h 48m 57.58s , +32d 03m 46.0s) | C | 60 | 19.3 | 5134 | 2021-05-10 20:45:05 | MASTER-Tavrida | (13h 13m 03.10s , +33d 16m 20.5s) | C | 60 | 18.2 | 5187 | 2021-05-10 20:45:57 | MASTER-SAAO | (12h 50m 14.37s , +42d 04m 13.2s) | C | 60 | 19.3 | 5214 | 2021-05-10 20:46:24 | MASTER-Tavrida | (12h 34m 26.73s , +33d 14m 33.4s) | C | 60 | 18.7 | 5267 | 2021-05-10 20:47:17 | MASTER-SAAO | (12h 58m 19.35s , +32d 02m 48.6s) | C | 60 | 19.5 | 5294 | 2021-05-10 20:47:44 | MASTER-Tavrida | (13h 04m 38.97s , +31d 14m 04.4s) | C | 60 | 18.7 | 5346 | 2021-05-10 20:48:37 | MASTER-SAAO | (13h 00m 52.63s , +42d 03m 59.6s) | C | 60 | 19.3 | 5373 | 2021-05-10 20:49:03 | MASTER-Tavrida | (13h 14m 12.99s , +31d 14m 27.2s) | C | 60 | 19.1 | 5426 | 2021-05-10 20:49:56 | MASTER-SAAO | (12h 46m 39.77s , +36d 03m 23.4s) | C | 60 | 19.3 | 5452 | 2021-05-10 20:50:22 | MASTER-Tavrida | (12h 43m 16.29s , +37d 15m 37.9s) | C | 60 | 18.3 | 5505 | 2021-05-10 20:51:16 | MASTER-SAAO | (12h 56m 26.46s , +36d 02m 06.8s) | C | 60 | 19.4 | 5532 | 2021-05-10 20:51:42 | MASTER-Tavrida | (12h 53m 26.95s , +37d 14m 07.7s) | C | 60 | 18.7 | 5585 | 2021-05-10 20:52:35 | MASTER-SAAO | (12h 27m 06.57s , +40d 04m 48.3s) | C | 60 | 19.4 | 5611 | 2021-05-10 20:53:01 | MASTER-Tavrida | (13h 03m 05.20s , +35d 15m 46.0s) | C | 60 | 18.2 | 5665 | 2021-05-10 20:53:55 | MASTER-SAAO | (12h 37m 33.27s , +40d 02m 58.9s) | C | 60 | 19.2 | 5690 | 2021-05-10 20:54:21 | MASTER-Tavrida | (13h 12m 53.41s , +35d 15m 06.8s) | C | 60 | 18.2 | 5744 | 2021-05-10 20:55:14 | MASTER-SAAO | (12h 47m 26.03s , +34d 04m 23.3s) | C | 60 | 19.4 | 5770 | 2021-05-10 20:55:40 | MASTER-Tavrida | (12h 44m 13.37s , +39d 15m 41.7s) | C | 60 | 18.1 | 5824 | 2021-05-10 20:56:34 | MASTER-SAAO | (12h 56m 57.67s , +34d 03m 13.2s) | C | 60 | 19.3 | 5904 | 2021-05-10 20:57:54 | MASTER-SAAO | (12h 28m 44.20s , +42d 04m 20.3s) | C | 60 | 19.2 | 5922 | 2021-05-10 20:58:13 | MASTER-Tavrida | (13h 03m 21.98s , +33d 13m 49.1s) | C | 60 | 19.2 | 5983 | 2021-05-10 20:59:14 | MASTER-SAAO | (12h 39m 24.28s , +42d 03m 02.3s) | C | 60 | 19.2 | 6063 | 2021-05-10 21:00:34 | MASTER-SAAO | (12h 49m 04.18s , +32d 02m 40.5s) | C | 60 | 19.5 | 6145 | 2021-05-10 21:01:55 | MASTER-SAAO | (12h 50m 13.22s , +42d 04m 40.8s) | C | 60 | 19.3 | 6224 | 2021-05-10 21:03:15 | MASTER-SAAO | (12h 28m 10.66s , +34d 05m 14.3s) | C | 60 | 19.5 | 6304 | 2021-05-10 21:04:35 | MASTER-SAAO | (12h 58m 24.63s , +32d 03m 21.0s) | C | 60 | 19.5 | 6384 | 2021-05-10 21:05:54 | MASTER-SAAO | (12h 37m 43.23s , +34d 05m 09.6s) | C | 60 | 19.3 | 6464 | 2021-05-10 21:07:14 | MASTER-SAAO | (13h 01m 02.68s , +42d 03m 32.8s) | C | 60 | 19.3 | 6544 | 2021-05-10 21:08:34 | MASTER-SAAO | (12h 33m 07.87s , +30d 03m 39.9s) | C | 60 | 19.8 | 6623 | 2021-05-10 21:09:54 | MASTER-SAAO | (12h 46m 40.78s , +36d 04m 46.7s) | C | 60 | 19.4 | 6703 | 2021-05-10 21:11:13 | MASTER-SAAO | (12h 56m 33.82s , +36d 02m 43.7s) | C | 60 | 19.4 | 6783 | 2021-05-10 21:12:33 | MASTER-SAAO | (12h 27m 09.86s , +40d 05m 45.4s) | C | 60 | 19.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29993 SUBJECT: Fermi GRB 210510A: DDOTI Upper Limits on the Afterglow DATE: 21/05/11 19:55:18 GMT FROM: Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada Margarita Pereyra (UNAM), Nat Butler (ASU), Alan M. Watson (UNAM), Eleonora Troja (GSFC/UMD), Simone Dichiara (GSFC/UMD), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Océlotl López, Diego Gonzalez (UNAM), Alexander Kutyrev (GSFC/UMD), and Srihari Ravi (ASU), report: We observed the field of the likely short Fermi GRB 210510A (trigger 642367205, GCN #29981, Fermi GBM Team) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir ( http://ddoti.astroscu.unam.mx) on 2021-05-11 from 03:24 to 10:45 UTC (8.1 to 15.4 hours after the event). We observed a region of 20.4 degrees in RA by 20.4 degrees in declination, with a 3 x 2 grid, centered on the Fermi GBM Final Position RA = 192.330, Dec = +44.860 (J2000 degrees). This region contains 6 instrumental fields or about 400 square degrees. We obtained 2280 to 2400 seconds of exposure per instrumental field in the w filter. We obtained AB photometry by calibration against the APASS catalog. We detect no likely candidate for the afterglow to our 10-sigma upper limits of w = 20.20 to 20.42 (interquartile range). We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 30005 SUBJECT: GRB210510A: Optical afterglow candidate from the Zwicky Transient Facility DATE: 21/05/13 03:13:19 GMT FROM: Shreya Anand at GROWTH Caltech Shreya Anand (Caltech), Igor Andreoni (Caltech), Tomas Ahumada (UMD), Erik Kool (SU), Ana Sagues-Carracedo (SU), Simeon Reusch (DESY), Mansi Kasliwal (Caltech), Michael Coughlin (UMN), Harsh Kumar (IIT-B), Robert Stein (DESY), Leo Singer (NASA/GSFC), Matthew Graham (Caltech) on behalf of the ZTF collaboration We observed the localization region of the short GRB210510A (trigger 642367205) detected by the Gamma-Ray Burst Monitor (GBM) on the Fermi satellite with the Palomar 48 inch telescope equipped with the 47 square degree Zwicky Transient Facility (ZTF; Bellm et al., 2019; Graham et al., 2019) camera. We obtained a series of g- and r-band images covering about 1105 square degrees beginning at 05:02:53.10 UT on 2021-05-11 (~ 10 hours after the burst trigger time). This corresponds to ~84% of the probability enclosed in the region of the GRB localization map that was unocculted by the Earth for the Fermi GBM (GCN 28965). Exposures reached a median depth of 22.1 mag in the g-band and 22.0 mag in the r-band.  On 2021-05-12, we obtained another epoch of r-band follow-up observations, beginning at 05:01:58.00 UT with exposures reaching a median depth of 22.1 mag and and covering ~81% of the enclosed probability. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC (Masci et al. 2019). We queried the ZTF alert stream using Kowalski (Duev et al. 2019). We required at least 2 detections separated by at least 15 minutes to select against moving objects. Furthermore, we cross-matched our candidates with the Minor Planet Center to flag known asteroids, reject stellar sources (Tachibana and Miller 2018), and apply machine learning algorithms (Duev et al. 2019, Mahabal et al. 2019). We require no spatially coincident ZTF alert to be issued before the detection time of the GBM trigger. We identified 186 transient candidates located within the 95% probability contour of the skymap that passed automatic selection criteria and human vetting from two nights of follow-up. Amongst these candidates, only one candidate (ZTF21abaytuk, shown below) passes these criteria and evolves faster than 0.3 mag/day. +--------------+-----------+-------------+--------------+--------+-------+-----------+ |     Name     |  IAU Name |      RA     |     Dec      | filter | mag   |   MJD     | +--------------+-----------+-------------+--------------+--------+-------+-----------+ | ZTF21abaytuk | AT2021meo | 13:48:49.89 | +35:32:13.05 |   g    | 21.76 | 59345.224 | +--------------+-----------+-------------+--------------+--------+-------+-----------+ ZTF21abaytuk has a decay rate of 0.36 mag/day in the r-band from ZTF IPAC Forced photometry (Masci et al. 2018), and a color of g-r~0.5 mag, consistent with the expected red colors of an afterglow. This transient was discovered in a galaxy host with an SDSS photometric redshift of 0.221 ± 0.0742, whose WISE colors indicate that it may be an AGN. ZTF21abaytuk was found to be significantly variable by the ZTF Realtime Search and Triggering (ZTFReST) pipeline (Andreoni & Coughlin et al. 2021). We encourage further photometric and spectroscopic observations. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.