{
  "bibcode": "2013GCN.14549....1L",
  "body": "D. Lennarz, I. Taboada (Georgia Tech) report on behalf of the HAWC\ncollaboration (http://www.hawc-observatory.org/collaboration/):\n\nWe used data from the partially built HAWC detector to perform a search\nfor VHE emission in temporal coincidence with GRB 130427A (A. Maselli et\nal., GCN 14448). This search was conducted using the scaler data\nacquisition only, as the main data acquisition was not operational at\nthe time. At the time of the GBM trigger, the elevation of the burst in\nHAWC's field of view, was only 33.13 degrees and setting. The\nsensitivity of HAWC at this elevation is more than 2 orders of magnitude\npoorer than near the zenith. Furthermore, while near zenith the nominal\nthreshold of the scaler system is a few GeV, towards the horizon the\nnominal threshold is much higher.\n\nWe used six search windows with respect to the GBM trigger time: one in\nthe range 0 s to 20 s, which covers the bright structured peak seen by\nFermi-GBM that seems to be correlated with the Fermi-LAT emission (S.\nZhu et al., GCN 14508), an extended window from -5 s to 55 s and a\nwindow from -5 s to 145 s, which is slightly larger than the T90\nreported by GBM. We also searched around the second peak in the GBM\nlight curve (120 s to 300 s), -10 s to 10 s around the time of the\nhighest energy LAT photon and in an extended window from -10 s to 290 s.\nWe find a deviation of +38960 / -77884 / -337877 / -165991 / -519485 /\n-1036 of the global PMT count with respect to a moving average in the\nsix time windows mentioned above. The p-value for these deviations\nassuming background hypothesis are 17 % / 78 % / 95 % / 71 % / 90 % and\n50 % respectively. Our observations are consistent with background only.\n\nThe implications of this non-detection with respect to the VHE fluence\nof this GRB will be reported elsewhere.\n\nHAWC is a gamma-ray detector under construction in Central Mexico. It\ncurrently consists of 29 operational Water Cherenkov Detectors out of\n300 planned. A detailed description of the sensitivity of HAWC to GRBs\ncan be found in A.U. Abeysekara et al., Astroparticle Physics 35,\n641-��650 (2012).",
  "circularId": 14549,
  "createdOn": 1367630640000,
  "email": "dirk.lennarz@gatech.edu",
  "subject": "GRB 130427A: Non-observation of VHE emission with HAWC",
  "submitter": "Dirk Lennarz at HAWC  <dirk.lennarz@gatech.edu>",
  "eventId": "GRB 130427A"
}