Sensitivity of the HAWC Observatory to Gamma-ray Bursts

Author: Tilan Ukwatta

Abstract: We present the sensitivity of the HAWC (High Altitude Water Cherenkov) observatory to Gamma-ray Bursts (GRBs). HAWC is a very-high-energy observatory under construction at Sierra Negra, Mexico at an altitude of 4100m. It will consist of 300 water tanks with 4 photomultiplier tubes (PMT) each and will detect Cherenkov light from secondary particles created in extensive air showers induced by very-high-energy gamma rays in the energy range from ∼30 GeV to 100 TeV. HAWC has two data acquisition (DAQ) systems: the main DAQ and scaler DAQ. The main DAQ system measures the arrival direction and energy of the high-energy gamma rays by timing the arrival of particles on the ground. The direction of the original primary particle may be resolved with an error between 2 and 0.1 degrees depending on energy and location in the sky. The scaler DAQ counts the hits in each PMT and searches for statistical excess over the background noise. HAWC complements existing Imaging Atmospheric Cherenkov Telescopes and the space-based gamma-ray telescopes with its very-high-energy reach, high duty cycle and large field-of-view. HAWC should be able to observe high-energy power-law components of GRBs that extend beyond 30 GeV. HAWC is also sensitive to primordial black hole bursts that may be progenitors of some GRBs. Based on the standard model, final seconds of a black hole will be explosive and will emit copious amount of gamma rays in the energy range which HAWC can observe. Thus, HAWC will be able to either detect a PBH burst or set stringent limits on the PBH burst rate. The first stage of the instrument with 10% of the channels deployed has been completed and is performing as expected, with 30% of the channels anticipated by the summer of 2013.