Blazar Alerts with the HAWC Online Flare Monitor

Abstract

The High Altitude Water Cherenkov (HAWC) Observatory monitors the gamma-ray sky in the 100 GeV to 100 TeV energy range with > 95% uptime and unprecedented sensitivity for a survey instrument. The HAWC Collaboration has implemented an online flare monitor that detects episodes of rapid flaring activity from extragalactic very high energy (VHE) sources in the declination band from -26 to 64 degrees. This allows timely alerts to be sent to multiwavelength instruments without human intervention. The preliminary configuration of the online flare monitor achieves sensitivity to flares of at least 1 hour duration that attain an average flux of 10 times that of the Crab Nebula. While flares of this magnitude are not common, several flares reaching the level of 10 Crab have been observed in the VHE band within the past decade. With its survey capabilities and high duty cycle, HAWC will expand the observational data set on these particularly extreme flares. We characterize the sensitivity of the online flare monitor and outline plans for its upcoming deployment.