{
  "bibcode": "2019GCN.24337....1B",
  "body": "Joshua S. Bloom (UC Berkeley), Catherine Zucker (Harvard), Eddie Schlafly\n(LBNL), Doug Finkbeiner (Harvard), Jorge Mart��nez-Palomera (UC Berkeley),\nDaniel A. Goldstein (Caltech), and Igor Andreoni (Caltech) report:\n\n\"Starting at 2019-04-28 5:10 UTC, we observed the region of the UVOT\ntransient (Breeveld et al. GCN #24296) candidate counterpart of the\ngravitational wave event S190425z (LIGO/VIRGO Collaboration, GCN #24168)\nwith the Victor M. Blanco 4m Telescope at Cerro Tololo Inter-American\nObservatory, equipped with the Dark Energy Camera (DECam). We observed in\nfour bands (g for 6 minutes, r for 6 minutes, i for 8 minutes, z for 8\nminutes).\n\nConsistent with previous reports (Kong et al. GCN #24301, Arcavi et al. GCN\n#24307, Im et al. GCN #24318, Shappee et al. GCN #24313, Hu et al. GCN\n#24324, Chang et al. GCN #24325, Morihana et al. GCN #24328, Tanvir et al.\nGCN #24334, Troja et al. GCN #24335), in 1.2 arcsec seeing, we find no\nsource at the reported position of the UVOT source, placing the following\nupper limits, calibrated to PS1 photometry (Chambers et al. 2016,\narXiv:1612.05560C):\n\n  g > 24.0\n  r > 24.0\n  i > 23.7\n  z > 23.1\n\nThe nearby source noted in Palmese et al. (GCN #24312) at position\nra=17:02:19.19, dec=-12:29:07.3 is detected in r, i, z and not detected in\ng. We report the following magnitudes for this source:\n\n  z = 21.50\n  i = 22.04\n  r = 23.03\n  g > 24.0\n\nAll detection magnitudes inhere a ~0.1 mag uncertainty currently. The\nr-band detection is consistent with Palmese et al. (GCN #24312) and thus\ndoes not appear to be variable between the two observations. We find no\nevidence for any spatial extent beyond the stellar PSF. The photometric\nmeasurements (albeit not corrected for the Galactic extinction along the\nline of sight) suggest the source to be a M2-dwarf star (see West et al.,\n2011).\n\nThe currently reported astrometric location of the bright UV transient is\nnot precisely consistent with the location of the source discussed above.\nHowever, if they are indeed physically associated (through a refined\nastrometric study, especially since the UVOT source appears trailed) a\nconsistent picture emerges: the UVOT detection was due to a flare from an\nM2-dwarf star in our galaxy. We thus agree with the hypothesis advanced by\nLipunov et al. (GCN #24326) that the UVOT event is unrelated to GW\nS190425z.\"\n\nThis message may be cited.",
  "circularId": 24337,
  "createdOn": 1556514388000,
  "email": "jbloom@astron.berkeley.edu",
  "subject": "LIGO/Virgo S190425z: DECam Observations of the UVOT Candidate Region",
  "submitter": "Josh Bloom at UC Berkeley  <jbloom@astron.berkeley.edu>",
  "eventId": "LIGO/Virgo S190425z"
}