Daily Monitoring of TeV Gamma-Ray Emission from Mrk 421, Mrk 501, and the Crab Nebula with HAWC

Abstract:

We present results from daily monitoring of gamma-rays in the energy range from∼0.5 to ∼100TeV with the first 17 months of data from the High Altitude Water Cherenkov (HAWC) Observatory. Its wide field of view of 2 steradians and duty cycle of >95% are unique features compared to other TeV observatories that allow us to observe every source that transits over HAWC for up to ∼6 hr each sidereal day. This regular sampling yields unprecedented light curves from unbiased measurements that are independent of seasons or weather conditions. For the Crab Nebula as a reference source, we find no variability in the TeV band. Our main focus is the study of the TeV blazars Markarian (Mrk) 421 and Mrk 501. A spectral fit for Mrk 421 yields a power-law index G = 2.21 0.14 0.20 stat sys and an exponential cut-off E0 stat sys = 5.4 1.1 1.0 TeV. For Mrk 501, we find an index G = 1.60 0.30 0.20 stat sys and exponential cut-off E0 stat sys = 5.7 1.6 1.0 TeV. The light curves for both sources show clear variability and a Bayesian analysis is applied to identify changes between flux states. The highest per-transit fluxes observed from Mrk 421 exceed the Crab Nebula flux by a factor of approximately five. For Mrk 501, several transits show fluxes in excess of three times the Crab Nebula flux. In a comparison to lower energy gamma-ray and X-ray monitoring data with comparable sampling, we cannot identify clear counterparts for the most significant flaring features observed by HAWC.

Año de publicación:

2017

Keywords:

• gamma-rays: general
• ISM: individual objects (Crab Nebula)
• Galaxies: active
• acceleration of particles
• BL Lacertae objects: individual (Mrk 421, Mrk 501)

Fuente:

scopus