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Abstract

We present the development of a real-time flare monitor for the High Altitude
Water Cherenkov (HAWC) observatory. The flare monitor has been fully
operational since 2017 January and is designed to detect very high energy (VHE;
$E\gtrsim100$ GeV) transient events from blazars on time scales lasting from 2
minutes to 10 hours in order to facilitate multiwavelength and multimessenger
studies. These flares provide information for investigations into the
mechanisms that power the blazars' relativistic jets and accelerate particles
within them, and they may also serve as probes of the populations of particles
and fields in intergalactic space. To date, the detection of blazar flares in
the VHE range has relied primarily on pointed observations by imaging
atmospheric Cherenkov telescopes. The recently completed HAWC observatory
offers the opportunity to study VHE flares in survey mode, scanning 2/3 of the
entire sky every day with a field of view of $\sim$1.8 steradians. In this
work, we report on the sensitivity of the HAWC real-time flare monitor and
demonstrate its capabilities via the detection of three high-confidence VHE
events in the blazars Markarian 421 and Markarian 501.