Prompt VERITAS Observations Triggered by High Energy Fermi-LAT Photons

TL;DR

This paper reports on a new VERITAS target-of-opportunity program that triggered observations based on high-energy Fermi-LAT photons, aiming to detect very high energy sources not previously associated with known emitters.

Contribution

It introduces a novel method of triggering VERITAS observations using high-energy Fermi-LAT photons, enhancing the search for unknown VHE sources.

Findings

Detection of VHE signals in follow-up observations

Validation of high-energy photon triggers for VHE source discovery

Potential identification of new VHE emitters

Abstract

In any given 24-hour period, the Fermi-LAT detects photons with energies of order 100 GeV not associated with any known VHE emitter. The RA/Dec of these photons frequently falls into the field of view of VERITAS the following evening. A single photon in the LAT can potentially mean many detectable photons on the ground due to the superior collection area of the IACT (Imaging Atmospheric Cherenkov Technique) method. During the 2011-2012 observing season, VERITAS implemented a new target-of-opportunity (ToO) program to trigger VERITAS observations on a small sample of the highest energy LAT photons. Each photon that triggered observation was detected by the LAT within the previous 24-hour period and was not spatially associated with a known VHE emitter. We present here the results of these ToO observations, a discussion of the method used, and our future plans.