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 ∼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 % 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 and an exponential cut-off TeV. For Mrk 501, we find an index and exponential cut-off 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.

Searching for TeV DM evidence from Dwarf Irregular Galaxies with the HAWC Observatory

“…The HAWC Observatory has an instantaneous field of view of ∼2 sr and a duty cycle > 95%, and is sensitive to gamma-rays with energies in the range from 1 TeV to 100 TeV. Therefore it is able to investigate the emission from several kind of sources [5,6], such as AGNs [7], GRBs [8,9], PWNs [10], and, in particular, the expected production of photons from annihilating or decaying DM [11,12].…”

Time-dependent search for neutrino emission from Mrk 421 and Mrk 501 observed by the HAWC gamma-ray observatory

“…Moreover, these are two of four sources detected in the 0.6-2.0 TeV band by Fermi-LAT out of the Galactic plane, |b| > 5 • , and at low redshift, z < 0.3 [5]. Both sources have been significantly detected in the 2HAWC catalog [6], and flare information were recently reported in [7] (see section 3.1).…”

“…The HAWC Observatory is located at an elevation of 4,100 m above sea level on the flanks of the Sierra Negra volcano in the state of Puebla, Mexico (18 • [7,15,16]. Such capabilities make unprecedented TeV light curve data available for studying flaring behavior of blazars.…”

“…Variability of Mrk 421 has been observed down to time scales of hours or less and its spectral shape is known to vary with its brightness. Various studies of Mrk 501 at TeV energies have shown different features of low flux states emission and extreme outbursts [7]. The VHE spectrum of Mrk 421 has been successfully modeled with both leptonic and hadronic models and conclusive results have been achieved yet about origin and both models are still under debate [8].…”

New gamma/hadron separation parameters for a neural network for HAWC

“…HAWC is composed of 300 water Cherenkov detector (WCDs), each instrumented with 4 photomultiplier tubes (PMTs) that detect the Cherenkov light from charged particles in extensive air showers. Given that 99 % of the events detected by HAWC come from cosmic-ray air showers, the study of gamma-ray sources requires the development of efficient techniques to achieve gamma-hadron separation [1,2,3].…”