# The HAWC real-time flare monitor for rapid detection of transient events

## TL;DR

This paper introduces a real-time flare monitor for the HAWC observatory, capable of detecting very high energy transient events from blazars on short timescales, enabling rapid multiwavelength and multimessenger follow-up.

## Contribution

It presents the development and operational performance of a novel real-time VHE flare detection system for HAWC, expanding survey capabilities for blazar transient events.

## Key findings

- Detection of three high-confidence VHE events from blazars
- Demonstrated sensitivity of the flare monitor
- Operational since January 2017 with real-time capabilities

## 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.