First Study of Combined Blazar Light Curves with FACT and HAWC

TL;DR

This study combines data from FACT and HAWC to analyze blazar variability, leveraging their complementary observational capabilities for improved long-term and high-resolution monitoring of Mrk 421 and Mrk 501.

Contribution

It presents the first joint analysis of blazar light curves from both water and air Cherenkov telescopes, demonstrating enhanced coverage and resolution.

Findings

Correlated long-term variability patterns observed.

Flaring activities of Mrk 421 and Mrk 501 characterized.

Improved temporal resolution achieved through combined data.

Abstract

For studying variable sources like blazars, it is crucial to achieve unbiased monitoring, either with dedicated telescopes in pointing mode or survey instruments. At TeV energies, the High Altitude Water Cherenkov (HAWC) observatory monitors approximately two thirds of the sky every day. It uses the water Cherenkov technique, which provides an excellent duty cycle independent of weather and season. The First G-APD Cherenkov Telescope (FACT) monitors a small sample of sources with better sensitivity, using the imaging air Cherenkov technique. Thanks to its camera with silicon-based photosensors, FACT features an excellent detector performance and stability and extends its observations to times with strong moonlight, increasing the duty cycle compared to other imaging air Cherenkov telescopes. As FACT and HAWC have overlapping energy ranges, a joint study can exploit the longer daily coverage given that the observatories' locations are offset by 5.3 hours. Furthermore, the better sensitivity of FACT adds a finer resolution of features on hour-long time scales, while the continuous duty cycle of HAWC ensures evenly sampled long-term coverage. Thus, the two instruments complement each other to provide a more complete picture of blazar variability. In this presentation, the first joint study of light curves from the two instruments will be shown, correlating long-term measurements with daily sampling between air and water Cherenkov telescopes. The presented results focus on the study of the variability of the bright blazars Mrk 421 and Mrk 501 during the last two years featuring various flaring activities.