Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector - Astrophysics > High Energy Astrophysical PhenomenaReport as inadecuate




Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector - Astrophysics > High Energy Astrophysical Phenomena - Download this document for free, or read online. Document in PDF available to download.

Abstract: In 2008 the blazar Markarian 421 entered a very active phase and was one ofthe brightest sources in the sky at TeV energies, showing frequent flaringepisodes. Using the data of ARGO-YBJ, a full coverage air shower detectorlocated at Yangbajing 4300 m a.s.l., Tibet, China, we monitored the source atgamma ray energies E > 0.3 TeV during the whole year. The observed flux wasvariable, with the strongest flares in March and June, in correlation withX-ray enhanced activity. While during specific episodes the TeV flux could beseveral times larger than the Crab Nebula one, the average emission from day 41to 180 was almost twice the Crab level, with an integral flux of 3.6 +-0.610^-11 photons cm^-2 s^-1 for energies E > 1 TeV, and decreased afterwards.This paper concentrates on the flares occurred in the first half of June.This period has been deeply studied from optical to 100 MeV gamma rays, andpartially up to TeV energies, since the moonlight hampered the Cherenkovtelescope observations during the most intense part of the emission. Our datacomplete these observations, with the detection of a signal with a statisticalsignificance of 3.8 standard deviations on June 11-13, corresponding to a gammaray flux about 6 times larger than the Crab one above 1 TeV. The reconstructeddifferential spectrum, corrected for the intergalactic absorption, can berepresented by a power law with an index alpha = -2.1 extending up to severalTeV. The spectrum slope is fully consistent with previous observationsreporting a correlation between the flux and the spectral index, suggestingthat this property is maintained in different epochs and characterizes thesource emission processes.



Author: G.Aielli et al. ARGO-YBJ Collaboration

Source: https://arxiv.org/



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