1. LONG-TERM MONITORING OF MRK 501 FOR ITS VERY HIGH ENERGY γ EMISSION AND A FLARE IN 2011 OCTOBER.
- Author
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Bartoli, B., Bernardini, P., Bi, X. J., Bleve, C., Bolognino, I., Branchini, P., Budano, A., Calabrese Melcarne, A. K., Camarri, P., Cao, Z., Cardarelli, R., Catalanotti, S., Cattaneo, C., Chen, S. Z., Chen, T. L., Chen, Y., Creti, P., Cui, S. W., Dai, B. Z., and D'Alí Staiti, G.
- Subjects
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BL Lacertae objects , *GALACTIC nuclei , *SPECTRAL energy distribution , *SPECTRUM analysis , *GALAXIES , *ASTROPHYSICS research , *GAMMA rays - Abstract
As one of the brightest active blazars in both X-ray and very high energy γ-ray bands, Mrk 501, is very useful for physics associated with jets from active galactic nuclei. The ARGO-YBJ experiment has monitored Mrk 501 for γ-rays above 0.3 TeV since 2007 November. The largest flare since 2005 was observed from 2011 October and lasted until about 2012 April. In this paper, a detailed analysis of this event is reported. During the brightest γ-ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6σ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the γ-ray flux above 1 TeV by a factor of 6.6 ± 2.2 from its steady emission. In particular, the γ-ray flux above 8 TeV is detected with a significance better than 4σ. Based on time-dependent synchrotron self-Compton (SSC) processes, the broadband energy spectrum is interpreted as the emission from an electron energy distribution parameterized with a single power-law function with an exponential cutoff at its high-energy end. The average spectral energy distribution for the steady emission is well described by this simple one-zone SSC model. However, the detection of γ-rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and γ-rays are also investigated. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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