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

• Published in: The Astrophysical journal Vol. 841; no. 2
• Main Authors: Abeysekara, A. U., Barber, A. S., Albert, A., Alfaro, R., Rojas, D. Avila, Becerril, A., Belmont-Moreno, E., Alvarez, C., Arceo, R., Caballero-Mora, K. S., Álvarez, J. D., Arteaga-Velázquez, J. C., Solares, H. A. Ayala, Brisbois, C., Bautista-Elivar, N., Gonzalez, J. Becerra, BenZvi, S. Y., Bernal, A., Braun, J., Capistrán, T., others, and
• Format: Journal Article
• Language: English
• Published: United States 01.06.2017
• Subjects: ALTITUDE; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BL LACERTAE OBJECTS; COMPARATIVE EVALUATIONS; CRAB NEBULA; EMISSION; GALAXIES; GAMMA RADIATION; TEV RANGE 01-10
• ISSN: 0004-637X; 1538-4357

We present results from daily monitoring of gamma-rays in the energy range from ∼0.5 to ∼100 TeV 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 Γ=2.21±0.14{sub stat}±0.20{sub sys} and an exponential cut-off E{sub 0}=5.4±1.1{sub stat}±1.0{sub sys} TeV. For Mrk 501, we find an index Γ=1.60±0.30{sub stat}±0.20{sub sys} and exponential cut-off E{sub 0}=5.7±1.6{sub stat}±1.0{sub sys} 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.