GAMMA-RAY FLARES FROM Mrk421 IN 2008 OBSERVED WITH THE ARGO-YBJ DETECTOR

Journal Article · Mon May 10 00:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/714/2/L208· OSTI ID:21448903

Aielli, G; Camarri, P ^[1]; Bacci, C; Bussino, S; Celio, P ^[2]; Bartoli, B; Catalanotti, S ^[3]; Bernardini, P; Bleve, C ^[4]; Bi, X J; Cao, Z; Chen, S Z; Chen, Y; Cheng, N ^[5]; Branchini, P; Budano, A ^[6]; Melcarne, A K. Calabrese ^[7]; Cappa, A ^[8]; Cardarelli, R ^[9]; Cattaneo, C ^[10]

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1. Dipartimento di Fisica dell'Universita 'Tor Vergata' di Roma, via della Ricerca Scientifica 1, 00133 Roma (Italy)
2. Dipartimento di Fisica dell'Universita 'Roma Tre' di Roma, via della Vasca Navale 84, 00146 Roma (Italy)
3. Dipartimento di Fisica dell'Universita di Napoli, Complesso Universitario di Monte Sant'Angelo, via Cinthia, 80126 Napoli (Italy)
4. Dipartimento di Fisica dell'Universita del Salento, via Arnesano, 73100 Lecce (Italy)
5. Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Science, P.O. Box 918, 100049 Beijing (China)
6. Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre, via della Vasca Navale 84, 00146 Roma (Italy)
7. Istituto Nazionale di Fisica Nucleare-CNAF, Viale Berti Pichat 6/2, 40127 Bologna (Italy)
8. Istituto Nazionale di Fisica Nucleare, Sezione di Torino, via P. Giuria 1, 10125 Torino (Italy)
9. Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma (Italy)
10. Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, via Bassi 6, 27100 Pavia (Italy)

In 2008, the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet), we monitored the source at gamma-ray energies E>0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emission from day 41 to 180 was almost twice the Crab level, with an integral flux of (3.6 {+-} 0.6) x 10{sup -11} photons cm{sup -2} s{sup -1} for energies E>1 TeV, and decreased afterward. This Letter concentrates on the flares that occurred in the first half of June. This period has been deeply studied from optical to 100 MeV gamma rays, and partially up to TeV energies, since the moonlight hampered the Cherenkov telescope observations during the most intense part of the emission. Our data complete these observations, with the detection of a signal with a statistical significance of 3.8 standard deviations on June 11-13, corresponding to a gamma-ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed differential spectrum, corrected for the intergalactic absorption, can be represented by a power law with an index {alpha} = -2.1{sup +0.7} {sub -0.5} extending up to several TeV. The spectrum slope is fully consistent with previous observations reporting a correlation between the flux and the spectral index, suggesting that this property is maintained in different epochs and characterizes the source emission processes.

• OSTI ID: 21448903
• Journal Information: Astrophysical Journal Letters, Vol. 714, Issue 2; Other Information: DOI: 10.1088/2041-8205/714/2/L208; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
BL LACERTAE OBJECTS
CRAB NEBULA
EMISSION
FLARING
GAMMA RADIATION
PHOTONS
TELESCOPES
TEV RANGE
BOSONS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ENERGY RANGE
IONIZING RADIATIONS
MASSLESS PARTICLES
NEBULAE
RADIATIONS
SORPTION
SUPERNOVA REMNANTS