{
  "bibcode": "2021GCN.30109....1A",
  "body": "Tomas Ahumada (UMD), Shreya Anand (Caltech), Harsh Kumar (IIT-B), Igor\nAndreoni (Caltech), Albert Kong (NTHU), Erik Kool (SU), Ana\nSagues-Carracedo (SU), Simeon Reusch (DESY), , Michael Coughlin (UMN),\nMansi Kasliwal (Caltech), Robert Stein (DESY), Leo Singer (NASA/GSFC), and\nMatthew Graham (Caltech) report on behalf of the ZTF collaboration:\n\nWe observed the localization region of the short GRB210529B (trigger\n644025222.097546) detected by the Gamma-Ray Burst Monitor (GBM) on the\nFermi satellite with the Palomar 48 inch telescope equipped with the 47\nsquare degree Zwicky Transient Facility (ZTF; Bellm et al., 2019; Graham et\nal., 2019) camera. We obtained a series of g- and r-band images covering\nabout 686 square degrees beginning at 05:06:36.18 UT on 2021-05-30 (~ 5.1\nhours after the burst trigger time). This corresponds to ~85% of the\nprobability enclosed in the region of the GRB localization that was\nunocculted by the Earth for Fermi GBM (GCN 30101). Exposures reached a\nmedian depth of 22.2 mag in the g-band and 22.3 mag in the r-band.\nOn 2021-05-31, we obtained another epoch of g- and r-band follow-up\nobservations, beginning at 05:07:50.96 UT with exposures reaching a median\ndepth of 22.2 mag and 22.2 mag respectively, and covering ~85% of the\nenclosed probability.\n\nThe images were processed in real-time through the ZTF reduction and image\nsubtraction pipelines at IPAC (Masci et al. 2019). We queried the ZTF alert\nstream using Kowalski (Duev et al. 2019). We required at least 2 detections\nseparated by at least 15 minutes to select against moving objects.\nFurthermore, we cross-matched our candidates with the Minor Planet Center\nto flag known asteroids, reject stellar sources (Tachibana and Miller\n2018), and apply machine learning algorithms (Duev et al. 2019, Mahabal et\nal. 2019). We require no spatially coincident ZTF alert to be issued before\nthe detection time of the GBM trigger.\n\nWe identified 146 transient candidates located within the 95% probability\ncontour of the skymap that passed automatic selection criteria. The\nmajority of the transients showed no evolution between the two nights. We\nperformed forced photometry (Masci et al. 2019) on the candidates reported\nbelow and found no previous history of variability.\n\n+--------------+-----------+-------------+--------------+--------+-------+-----------+\n|     Name     |  IAU Name |      RA     |     Dec      | disc. mag |\n notes     |\n+--------------+-----------+-------------+--------------+--------+-------+-----------+\n| ZTF21abcwmzx | AT2021nzo | 14:42:28.10 | +31:56:34.19 | g = 21.51 |\n(1)(e)  |\n| ZTF21abcwnbm | AT2021nzp | 14:43:43.24 | +33:44:52.20 | g = 21.54 |\n(1)(d)  |\n| ZTF21abcwuxv | AT2021nzq | 15:30:34.50 | +43:05:52.27 | r = 21.82 |\n(a)(b) |\n| ZTF21abcwvzr | AT2021nzr | 14:49:49.23 | +35:05:43.32 | r = 21.9  |\n(a)(e) |\n| ZTF21abcwwaj | AT2021nzs | 14:40:59.49 | +32:07:24.64 | r = 21.24 |\n(a)(c) |\n| ZTF21abcwyoe | AT2021nzt | 15:58:56.54 | +33:08:01.79 | r = 21.83 |\n(a)(d) |\n| ZTF21abcwyvi | AT2021nzu | 15:58:53.27 | +33:39:12.74 | r = 21.98 |\n(a)(b) |\n\nNotes:\n(1) shows rise and rapid decay\n(a) Non-detection during the second night (2021-05-31). These have two or\nmore detections separated by >50 min during the first night.\n(b) hostless\n(c) host at z=0.1\n(d) nuclear\n(e) likely offset from host\n\nBased on observations obtained with the Samuel Oschin Telescope 48-inch and\nthe 60-inch Telescope at the Palomar Observatory as part of the Zwicky\nTransient Facility project. ZTF is supported by the National Science\nFoundation under Grant No. AST-2034437 and a collaboration including\nCaltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center\nat Stockholm University, the University of Maryland, Deutsches\nElektronen-Synchrotron and Humboldt University, the TANGO Consortium of\nTaiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin,\nLawrence Livermore National Laboratories, and IN2P3, France. Operations are\nconducted by COO, IPAC, and UW.\n\n\n-- \nTomas Ahumada (he/him)\nPh.D. Candidate\nDepartment of Astronomy\nUniversity of Maryland, College Park\nNASA Goddard Space Flight Center, Code 661\nB.Sc. Astronomy, Pontificia Universidad Cat��lica de Chile",
  "circularId": 30109,
  "createdOn": 1622541848000,
  "email": "tahumada@astro.umd.edu",
  "subject": "GRB210529B: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 644025222)",
  "submitter": "Tomas Ahumada at U. of Maryland  <tahumada@astro.umd.edu>",
  "eventId": "GRB 210529B"
}