{
  "bibcode": "2019GCN.25406....1L",
  "body": "The LIGO Scientific Collaboration, the Virgo Collaboration and the Fermi\nGBM team report:\n\nIn routine Fermi GBM follow-up analysis of subthreshold GW triggers from\nLIGO/Virgo, a potential short gamma-ray burst counterpart GBM-190816 was\nidentified.\n\nOffline analysis of data from LIGO Livingston Observatory (L1) and Virgo\nObservatory (V1) identified a possible compact binary merger candidate at\n2019-08-16 21:22:13.027 UTC (GPS time: 1250025751.027). The LIGO Hanford\nObservatory was not collecting low-noise data at the time. The candidate\nwas found by the PyCBC Live [1], MBTAOnline [2], and GstLAL [3] analysis\npipelines.\n\nThe GBM Targeted Search [4,5,6], a sensitive and coherent search for\nsubthreshold GRB-like signals, was run from +/-30 s around the GW candidate\nand identified a candidate gamma-ray signal starting at 21:22:14.563 UTC,\n1.5 s after the GW trigger time. GBM-190816 is approximately 0.1 s in\nduration and was identified with the hard spectral template [6]. The\noffset, duration, and spectral properties are consistent with a short GRB\norigin, while the observed properties are inconsistent with other\nastrophysical or terrestrial transients that GBM observes. The False Alarm\nRate (FAR) for the GBM Targeted Search detection statistic is 1.2E-4 Hz.\n\nNeither the GW trigger nor the potential short GRB are significant enough\nto report on their own merit. However, these events are of interest because\nof their potential association. Investigation on the data quality of the\ngravitational-wave event is ongoing. At this time we cannot reliably\nestimate the FAR of the gravitational-wave event. Analysis is ongoing in\nestablishing the FAR, data-quality and overall potential astrophysical\nnature of the event.\n\nThe skymap available at this moment is obtained primarily by combining the\nlocalization from L1-V1 using BAYESTAR [7] with the Fermi-GBM localization;\nthe 90% error area corresponds to 5855 sq. deg. while the 50% error area is\n1257 sq. deg. This skymap is available through the OpenLVEM wiki page at\n\nhttps://wiki.gw-astronomy.org/OpenLVEM/FermiGBM-LVC\n\nFrom a preliminary inspection of the GW analysis, if the signal is\nastrophysical, the lighter compact object may have a mass < 3 solar masses.\n\n [1] Nitz et al. PRD 98, 024050 (2018)\n\n [2] Adams et al. CQG 33, 175012 (2016)\n\n [3] Messick et al. PRD 95, 042001 (2017)\n\n [4] Blackburn et al. 2015, ApJS 217, 8\n\n [5] Goldstein et al. arXiv:1612.02395\n\n [6] Goldstein et al. arXiv:1903.12597\n\n [7] Singer & Price PRD 93, 024013 (2016)",
  "circularId": 25406,
  "createdOn": 1566278605000,
  "email": "adam.michael.goldstein@gmail.com",
  "subject": "Fermi GBM-190816: A subthreshold GRB candidate potentially associated with a subthreshold LIGO/Virgo compact binary merger candidate",
  "submitter": "Adam Goldstein at Fermi-GBM, USRA  <adam.michael.goldstein@gmail.com>"
}