{
  "bibcode": "2019GCN.25415....1S",
  "body": "T. Sakamoto (AGU), S. D. Barthelmy (NASA/GSFC),\nA. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL),\nA. P. Beardmore (U. Leicester), M. G. Bernardini (INAF-OAB),\nA. A. Breeveld (MSSL-UCL), D. N. Burrows (PSU),\nS. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC),\nG. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA),\nP. D'Avanzo (INAF-OAB), V. D'Elia (ASI-SSDC), S. Emery (UCL-MSSL),\nP. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU),\nD. Hartmann (Clemson U.), J. A. Kennea (PSU), H. A. Krimm (NSF),\nN. P. M. Kuin (UCL-MSSL), D. B. Malesani (DTU),\nF. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J. A. Nousek (PSU),\nS. R. Oates (Uni. of Warwick), P. T. O'Brien (U. Leicester),\nJ. P. Osborne (U. Leicester), C. Pagani (U. Leicester),\nK. L. Page (U.Leicester), M. J. Page (UCL-MSSL), M. Perri (ASDC),\nJ. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),\nM. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU),\nE. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team:\n\nWe report the search results in the BAT data within T0 +/- 100 s of the\nLVC-Fermi event GBM-190816 (LIGO/VIRGO Collaboration and Fermi eam,\nGCN Circ. 25406), where T0 is the LVC trigger time\n(2019-08-16T21:22:13.027 UTC).\n\nThe center of the BAT Field of View at T0 is\nRA = 53.486 deg,\nDEC = -18.672 deg,\nand the roll angle is 85.896 deg.\nThe BAT FOV (>10% partial coding) covers 22.46% of the joint integrated\nLVC-Fermi localization probability. Note that Swift was slewing\nfrom ~T0-64.453 s to ~T0+140.547 s. Thus, the pointing direction is\nconstantly changing. However, the fraction of the joint integrated\nLVC-Fermi localization probability in the BAT FOV remains around 22%\nwithin T0 +/- 10 s. The sensitivity in the BAT FOV changes with the\npartial coding fraction. Please see the BAT FOV figure in the summary\npage (link below) for the specific location of the LVC region relative\nto the BAT FOV.\n\nWithin T0 +/- 100 s, no significant detections (signal-to-noise ratio\n>~ 5 sigma) are found in the BAT raw light curves with time bins of 64 ms,\n1 s, and 1.6 s. The large bump from ~T0 to ~T+100 s is likely due to\nthe background changes during slew.\n\nAssuming an on-axis (100% coded) short GRB with a typical spectrum in the\nBAT energy range (i.e., a simple power-law model with a power-law index\nof -1.32, Lien & Sakamoto et al. 2016), the 5-sigma upper limit in\nthe 1-s binned light curve corresponds to a flux upper limit (15-350 keV)\nof ~ 2.12 x 10^-7 erg/s/cm^2. Assuming a luminosity of ~ 2 x 10^47 erg/s\n(similar to GW170817) and an average Epeak of ~ 400 keV for short GRBs\n(Bhat et al. 2016), this flux upper limit corresponds to a distance\nof ~ 49.38 Mpc.\n\nEvent data captured during slew are available from T0-65.454 s to\nT0+150.361.\nNo significant detections are found in images created within ~T0 +/- 2 s in\n15-350 keV. A summary of the image search can be found in the link below\n(under the \"Event data image search\" section).\n\nBAT retains decreased, but significant, sensitivity to rate increases for\ngamma-ray events outside of its FOV. About 62.85% of the integrated LVC\nlocalization probability was outside of the BAT FOV but above the\nEarth's limb from Swift's location, and the corresponding flux upper limits\nfor this region are within roughly an order of magnitude higher than those\nwithin the FOV.\n\nThe results of the BAT analysis are available at\nhttps://swift.gsfc.nasa.gov/results/BATbursts/team_web/GBM-190816/web/source_public.html",
  "circularId": 25415,
  "createdOn": 1566335613000,
  "email": "amy.y.lien@nasa.gov",
  "subject": "LIGO/Virgo GBM-190816: no counterpart candidates in the Swift/BAT Observations",
  "submitter": "Amy Lien at GSFC  <amy.y.lien@nasa.gov>"
}