Bibcode
Aleksić, J.; Alvarez, E. A.; Antonelli, L. A.; Antoranz, P.; Asensio, M.; Backes, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becerra-González, J.; Bednarek, W.; Berdyugin, A.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnoli, G.; Borla Tridon, D.; Braun, I.; Bretz, T.; Cañellas, A.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Cossio, L.; Covino, S.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Cea del Pozo, E.; De Lotto, B.; Delgado-Mendez, C.; Diago-Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Eisenacher, D.; Elsaesser, D.; Ferenc, D.; Fonseca, M. V.; Font, L.; Fruck, C.; García-López, R. J.; Garczarczyk, M.; Garrido, D.; Giavitto, G.; Godinović, N.; Gozzini, S. R.; Hadasch, D.; Häfner, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Hrupec, D.; Jogler, T.; Kellermann, H.; Klepser, S.; Krähenbühl, T.; Krause, J.; Kushida, J.; La Barbera, A.; Lelas, D.; Leonardo, E.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López, R.; López-Oramas, A.; Lorenz, E.; Makariev, M.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Moldón, J.; Moralejo, A.; Munar-Adrover, P.; Niedzwiecki, A.; Nieto, D.; Nilsson, K.; Nowak, N.; Orito, R.; Paiano, S.; Paneque, D. et al.
Bibliographical reference
Astronomy and Astrophysics, Volume 544, id.A75
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8
2012
Journal
Citations
9
Refereed citations
8
Description
Context. The high frequency peaked BL Lac PKS 2155-304 with a redshift
of z = 0.116 was discovered in 1997 in the very high energy (VHE, E >
100 GeV) γ-ray range by the University of Durham Mark VI
γ-ray Cherenkov telescope in Australia with a flux corresponding
to 20% of the Crab Nebula flux. It was later observed and detected with
high significance by the southern Cherenkov observatory H.E.S.S.
establishing this source as the best studied southern TeV blazar.
Detection from the northern hemisphere is difficult due to challenging
observation conditions under large zenith angles. In July 2006, the
H.E.S.S. collaboration reported an extraordinary outburst of VHE
γ-emission. During the outburst, the VHE γ-ray emission was
found to be variable on the time scales of minutes and with a mean flux
of ~7 times the flux observed from the Crab Nebula. Follow-up
observations with the MAGIC-I standalone Cherenkov telescope were
triggered by this extraordinary outburst and PKS 2155-304 was observed
between 28 July to 2 August 2006 for 15 h at large zenith angles.
Aims: We studied the behavior of the source after its extraordinary
flare. Furthermore, we developed an analysis method in order to analyze
these data taken under large zenith angles. Methods: Here we
present an enhanced analysis method for data taken at high zenith
angles. We developed improved methods for event selection that led to a
better background suppression. Results: The quality of the
results presented here is superior to the results presented previously
for this data set: detection of the source on a higher significance
level and a lower analysis threshold. The averaged energy spectrum we
derived has a spectral index of (-3.5 ± 0.2) above 400 GeV, which
is in good agreement with the spectral shape measured by H.E.S.S. during
the major flare on MJD 53 944. Furthermore, we present the spectral
energy distribution modeling of PKS 2155-304. With our observations we
increased the duty cycle of the source extending the light curve derived
by H.E.S.S. after the outburst. Finally, we find night-by-night
variability with a maximal amplitude of a factor three to four and an
intranight variability in one of the nights (MJD 53 945) with a similar
amplitude.
Related projects
Particle Astrophysics
The MAGIC Collaboration is integrated by 20 research institutes and university departments from Armenia, Bulgaria, Finland, Germany, Italy, Poland, Spain, Switzerland and USA. The collaboration comprises two 17m diameter telescopes, located at the Roque de los Muchachos Observatory, designed to measure the Cherenkov radiation associated with
Ramón
García López