{
  "bibcode": "2019GCN.25643....1P",
  "body": "D. A. Perley (LJMU), A. Y. Q. Ho (Caltech), and C. M. Copperwheat (LJMU)\nreport on behalf of the GROWTH collaboration:\n\nWe obtained Liverpool Telescope IO:O imaging observations of\nZTF19abvizsw/AT2019pim (Kool et al., GCN 25616), initially reported as a\ncandidate counterpart to S190901ap but recently shown (Burdge et al.,\nGCN 25639) to be an unrelated luminous transient at high redshift. Three\nr-band images of 150 seconds each were acquired between UT 20:28 and\n20:35, followed by a griz sequence (3x150s per filter) between 22:33 and\n23:08.\n\nThe transient is well-detected in all four bands, but has faded\nsubstantially since the ZTF discovery epoch (see also Wei et al., GCN\n15640).  We report the following photometry (times given as UT midpoints):\n\nTime (UT)               filter  mag(AB) unc\n-------------------     ------  ------  ----\n2019-09-03 22:37:50     r       21.62   0.09\n2019-09-03 22:46:33     g       22.02   0.10\n2019-09-03 22:55:16     i       21.16   0.07\n2019-09-03 23:03:57     z       20.87   0.12\n\nAfter correcting for Galactic extinction (Schlafly et al. 2011, ApJ 737\n103) the SED is well-fit by to a power-law in frequency with spectral\nindex (F_nu ~ nu^beta) of beta ~ -1.4.\n\nAs noted in GCN 25616, this field was imaged by ZTF every night during\nthe 30 days prior to the ZTF discovery.  No source was detected in any\nof these observations, with the most recent nondetection corresponding\nto 2019-09-01 UT 07:35, 0.86 days prior to the ZTF discovery observation.\n\nThe fast rise, red power-law spectrum, and fast decline are consistent\nwith observations of known GRB optical afterglows.  However, we searched\nthe Fermi GBM subthreshold GRB catalog over the window between the last\nZTF detection and the discovery observation and found no GRB consistent\nwith the location of the transient over time window.\n\nFurther observations, including multiwavelength observations, have been\nrequested.\n\n________________________________\nImportant Notice: the information in this email and any attachments is for the sole use of the intended recipient(s). If you are not an intended recipient, or a person responsible for delivering it to an intended recipient, you should delete it from your system immediately without disclosing its contents elsewhere and advise the sender by returning the email or by telephoning a number contained in the body of the email. No responsibility is accepted for loss or damage arising from viruses or changes made to this message after it was sent. The views contained in this email are those of the author and not necessarily those of Liverpool John Moores University.",
  "circularId": 25643,
  "createdOn": 1567572636000,
  "email": "d.a.perley@ljmu.ac.uk",
  "subject": "Liverpool Telescope observations of ZTF19abvizsw, a candidate untriggered GRB afterglow",
  "submitter": "Daniel Perley at Liverpool JMU  <d.a.perley@ljmu.ac.uk>",
  "eventId": "ZTF19abvizsw"
}