Search for very high energy gamma-ray emission from a sample of high redshift blazars with MACE

Abstract

Blazars, a subclass of face-on jetted active galactic nuclei, are the most persistent and powerful sources of cosmic gamma-rays in the Universe. They represent a dominant population of gamma-ray sources, spread all over the sky with known and unknown redshifts up to z ∼ 6 (e.g. Belladitta et al. (2020)). Detection of more than 3500 blazars by the space-based Fermi-Large Area Telescope (LAT) in the high energy (HE, above 100 MeV) band reveals that a significant amount of power carried by the relativistic plasma jets in blazars is dissipated at gamma-ray energies. However, a small fraction of only less than 3% are detected at very high energies (VHE, above 30 GeV) by the ground-based Cherenkov telescopes. Therefore, their detection at the highest possible energies is extremely important to understand the blazar-phenomenon in the Universe. In this paper, we report observational results obtained from the recent monitoring of the six high redshift ($z>0.3$) blazars with the Major Atmospheric Cherenkov Experiment (MACE) in the energy range above ∼ 80 GeV. No statistically significant detection of the sources is found. Thus, for the null detections, we estimate 99% confidence level upper limit on the integral flux for the individual sources and use the Fermi-LAT measurements to constrain their gamma-ray emission behavior.