{
  "bibcode": "2019GCN.24391....1L",
  "body": "A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (NASA/GSFC),\nD. M. Palmer (LANL), T. Sakamoto (AGU),\nA. A. Breeveld (MSSL-UCL), A. P. Beardmore (U. Leicester),\nD. N. Burrows (PSU), S. 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(ASDC), 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), F. E. Marshall (NASA/GSFC),\nA. Melandri (INAF-OAB), B. Mingo (U. Leicester), 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. 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 event S190503bf (LIGO/VIRGO Collaboration GCN Circ. 24377),\nwhere T0 is the LVC trigger time (2019-05-03T18:54:04.294 UTC).\n\nThe center of the BAT field of view at T0 is\nRA = 94.035 deg,\nDEC = -21.368 deg,\nROLL = 293.102 deg.\nThe BAT FOV (>10% partial coding) covers 99.75% of the integrated\nLVC localization probability, and 99.82% of the galaxy convolved\nprobability (Evans et al. 2016).\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. Note that the short spike around ~T-400s is due to\ndetector noise. Assuming an on-axis (100% coded) short GRB with a typical\nspectrum in the BAT energy range (i.e., a simple power-law model with a\npower-law index of -1.32, Lien & Sakamoto et al. 2016), the 5-sigma upper\nlimit in the 1-s binned light curve corresponds to a flux upper limit\n(15-350 keV) of ~ 6.74 x 10^-8 erg/s/cm^2.\n\nEvent data are available from T0+17.837 to T0+21.002. Image analysis from\nthe entire event data range and in 15-350 keV shows a marginal detection\nof 6.049 sigma at (RA, DEC) = (42.0339,-20.9022) deg (following the BAT\nonboard image trigger threshold, we consider detections below ~ 7 sigma\nin the image domain to be sub-threshold.). The location is at the edge of\nthe BAT FOV and well outside of the 90% LVC containment region. Also, no\nsignificant structure is seen in the mask-weighted light curve at this\nposition. Therefore, we believe that this marginal detection is unlikely\nto be related to the LVC event, and possibly not astrophysical.\nWithin the LVC 99.5% containment region, the highest significance detection\nin this image is 4.7 sigma, which is consistent with noise fluctuation that\nwe have seen in BAT images.\n\nBAT retains decreased, but significant, sensitivity to rate increases for\ngamma-ray events outside of its FOV. About 0.25% 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/S190503bf/web/source.html",
  "circularId": 24391,
  "createdOn": 1556992839000,
  "email": "amy.y.lien@nasa.gov",
  "subject": "LIGO/Virgo S190503bf: Swift/BAT Counterpart Search",
  "submitter": "Amy Lien at GSFC  <amy.y.lien@nasa.gov>",
  "eventId": "LIGO/Virgo S190503bf"
}