{
  "bibcode": "2019GCN.25443....1R",
  "body": "J. Ruan (McGill U.), N. Vieira (McGill U.), D. Haggard (McGill U.), M. R.\nDrout (U. of Toronto), N. Asfari (U. of Toronto), R. Carlberg (U. of\nToronto), R. Doyon (U. de Montreal), R. Fernandez (U. of Alberta), B.\nGaensler (U. of Toronto), V. Kaspi (McGill U.), D. Lafreniere (U. de\nMontreal), C. Matzner (U. of Toronto), D-S. Moon (U. of Toronto), C. Ni (U.\nof Toronto), M. Nynka (MIT), A. L. Piro (Carnegie Obs.), S. Safi-Harb (U.\nof Manitoba), K. Spekkens (RMC/Queen���s U.)\n\nWe report on optical imaging obtained on the MegaPrime/MegaCam instrument\n(1x1 deg FOV) at the Canada-France-Hawaii Telescope, to search for a\ncounterpart to the candidate gravitational wave source S190814bv. We\nobtained deep images for the entire updated 50% confidence localization\nregion (GCN 25333) in g-band on UTC 2019-08-16 (1.7 days post-merger), in\ni-band on UTC 2019-08-18 (3.6 days post-merger), in i-band on UTC\n2019-08-19 (4.6 days post-merger), and in both i- and z-band on 2019-08-21\n(6.6 days post-merger). In each of those nights, we also obtained images of\na few additional galaxies in the larger 90% confidence localization region.\nWe stacked the images from each night and calibrated based on the\nPan-STARRS 3pi Survey. For an initial search, we visually inspected the\ngalaxies in our stacked images from the GLADE catalog (Dayla et al., 2018),\nbased on a candidate host-galaxy prioritization scheme.\n\nWe find one potential faint counterpart lying near the possible host-galaxy\n2MASX J00472894-2526263, which is located at (RA, Dec = 11.870618,\n-25.440655) and a distance of 267 Mpc. This galaxy was the 5th\nhighest-ranked candidate host-galaxy in the LIGO/Virgo localization region\nfrom the GLADE catalog based on our prioritization scheme. The potential\ncounterpart is at ~17��� away from the center of this galaxy, and is located\nat (RA, Dec = 11.866781, -25.437264). The potential counterpart was not\ndetected in our g-band imaging at 1.7 days post-merger, but was\nsubsequently detected in i-band at 3.6, 4.6, and 6.6 days post-merger, and\nin z-band at 6.6 days post-merger. A table of our aperture photometry\nmeasurements is provided below:\n\nUTC, days post-merger, band, mag\n2019-08-16, 1.7, g, >22.8\n2019-08-18, 3.6, i, 22.86+/-0.19\n2019-08-19, 4.6, i, 22.80+/-0.23\n2019-08-21, 6.6, i, 22.93+/-0.12\n2019-08-21, 6.6, z, 22.24+/-0.30\n\nCutouts of our images can be found at this link:\nhttp://www.physics.mcgill.ca/~jruan/S190814bv/cutouts_rank4.png\n\nWe also visually examined deeper reference images from DECam taken as part\nof the DECaLS/DESI Legacy Imaging Surveys, in g-, r- and z-bands. Our\ncandidate counterpart from CFHT is also not detected in these DECam\nreference images. We note that these deep DECam reference images reveal\nanother source (which we label T1 in our cutouts below) that is ~4.5��� away\nfrom our possible counterpart. This T1 source is also clearly detected in\nour i-band images at 6.6 days post-merger, and is not the same object as\nour potential counterpart. Cutouts showing the clear positional offsets\nbetween T1 and the potential counterpart can be found at this link:\nhttp://www.physics.mcgill.ca/~jruan/S190814bv/cutouts_rank4_DECam.png\n\nFurther follow-up of this potential counterpart is encouraged. We are\ncontinuing observations, and analysis will be reported.\n\nWe thank the CFHT queued service observing team and the telescope staff for\ntheir help in obtaining these observations.",
  "circularId": 25443,
  "createdOn": 1566448996000,
  "email": "mdrout@carnegiescience.edu",
  "subject": "LIGO/Virgo S190814bv: a potential faint optical counterpart in CFHT imaging",
  "submitter": "Maria R Drout at Carnegie Observatories  <mdrout@carnegiescience.edu>",
  "eventId": "LIGO/Virgo S190814bv"
}