LONG-TERM MONITORING OF MRK 501 FOR ITS VERY HIGH ENERGY {gamma} EMISSION AND A FLARE IN 2011 OCTOBER

Journal Article · Wed Oct 10 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/758/1/2· OSTI ID:22092129

Bartoli, B.; Catalanotti, S. ^[1]; Bernardini, P.; Bleve, C. ^[2]; Bi, X. J.; Cao, Z.; Chen, S. Z.; Chen, Y. ^[3]; Bolognino, I. ^[4]; Branchini, P.; Budano, A. ^[5]; Calabrese Melcarne, A. K. ^[6]; Camarri, P. ^[7]; Cardarelli, R. ^[8]; Cattaneo, C. ^[9]; Chen, T. L. ^[10]; Creti, P. ^[11]; Cui, S. W. ^[12]; Dai, B. Z. ^[13]; others, and

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1. Dipartimento di Fisica dell'Universita di Napoli 'Federico II', Complesso Universitario di Monte Sant'Angelo, via Cinthia, I-80126 Napoli (Italy)
2. Dipartimento di Matematica e Fisica 'E. De Giorgi' dell'Universita del Salento, via per Arnesano, I-73100 Lecce (Italy)
3. Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918, 100049 Beijing (China)
4. Dipartimento di Fisica Nucleare e Teorica dell'Universita di Pavia, via Bassi 6, I-27100 Pavia (Italy)
5. Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre, via della Vasca Navale 84, I-00146 Roma (Italy)
6. Istituto Nazionale di Fisica Nucleare-CNAF, Viale Berti-Pichat 6/2, I-40127 Bologna (Italy)
7. Dipartimento di Fisica dell'Universita di Roma 'Tor Vergata', via della Ricerca Scientifica 1, I-00133 Roma (Italy)
8. Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tor Vergata, via della Ricerca Scientifica 1, I-00133 Roma (Italy)
9. Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, via Bassi 6, I-27100 Pavia (Italy)
10. Tibet University, 850000 Lhasa, Xizang (China)
11. Istituto Nazionale di Fisica Nucleare, Sezione di Lecce, via per Arnesano, I-73100 Lecce (Italy)
12. Hebei Normal University, Shijiazhuang 050016, Hebei (China)
13. Yunnan University, 2 North Cuihu Rd., 650091 Kunming, Yunnan (China)

As one of the brightest active blazars in both X-ray and very high energy {gamma}-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 {gamma}-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 {gamma}-ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6{sigma} is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the {gamma}-ray flux above 1 TeV by a factor of 6.6 {+-} 2.2 from its steady emission. In particular, the {gamma}-ray flux above 8 TeV is detected with a significance better than 4{sigma}. 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 {gamma}-rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and {gamma}-rays are also investigated.

• OSTI ID: 22092129
• Journal Information: Astrophysical Journal, Vol. 758, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
BL LACERTAE OBJECTS
CORRELATIONS
COSMIC GAMMA SOURCES
COSMIC X-RAY SOURCES
ELECTRONS
ENERGY SPECTRA
GALAXIES
GALAXY NUCLEI
GAMMA ASTRONOMY
MONITORING
QUASARS
TEV RANGE
TIME DEPENDENCE
X RADIATION