High zenith angle observations of PKS 2155-304 with the MAGIC-I telescope
Abstract
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 >100GeV) gamma-ray range by the University of Durham Mark VI gamma-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. 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 gamma-emission. During the outburst, the VHE gamma-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 hours at large zenith angles. Here we present our studies on the behavior of the source after its extraordinary flare and 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. The averaged energy spectrum we derived has a spectral index of -3.5 +/- 0.2 above 400GeV, which is in good agreement with the spectral shape measured by H.E.S.S. during the major flare on MJD 53944. 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 53945) with a similar amplitude.
Keywords
Cite
@article{arxiv.1207.1634,
title = {High zenith angle observations of PKS 2155-304 with the MAGIC-I telescope},
author = {The MAGIC Collaboration and J. Aleksić and L. A. Antonelli and P. Antoranz and M. Asensio and U. Barres de Almeida and J. A. Barrio and J. Becerra González and W. Bednarek and K. Berger and E. Bernardini and A. Biland and O. Blanch and R. K. Bock and A. Boller and G. Bonnoli and D. Borla Tridon and T. Bretz and E. Carmona and A. Carosi and P. Colin and E. Colombo and J. L. Contreras and J. Cortina and L. Cossio and S. Covino and P. Da Vela and F. Dazzi and A. De Angelis and G. De Caneva and E. De Cea del Pozo and B. De Lotto and C. Delgado Mendez and A. Diago Ortega and M. Doert and D. Dominis Prester and D. Dorner and M. Doro and D. Eisenacher and D. Elsaesser and D. Ferenc and M. V. Fonseca and L. Font and C. Fruck and R. J. García López and M. Garczarczyk and D. Garrido Terrats and M. Gaug and G. Giavitto and N. Godinović and A. González Muñoz and S. R. Gozzini and A. Hadamek and D. Hadasch and D. Häfner and A. Herrero and J. Hose and D. Hrupec and B. Huber and F. Jankowski and T. Jogler and V. Kadenius and S. Klepser and M. L. Knoetig and T. Krähenbühl and J. Krause and J. Kushida and A. La Barbera and D. Lelas and E. Leonardo and N. Lewandowska and E. Lindfors and S. Lombardi and M. López and R. López-Coto and A. López-Oramas and E. Lorenz and M. Makariev and G. Maneva and N. Mankuzhiyil and K. Mannheim and L. Maraschi and B. Marcote and M. Mariotti and M. Martínez and D. Mazin and M. Meucci and J. M. Miranda and R. Mirzoyan and J. Moldón and A. Moralejo and P. Munar-Adrover and A. Niedzwiecki and D. Nieto and K. Nilsson and N. Nowak and R. Orito and S. Paiano and M. Palatiello and D. Paneque and R. Paoletti and J. M. Paredes and S. Partini and M. Persic and M. Pilia and J. Pochon and F. Prada and P. G. Prada Moroni and E. Prandini and I. Puljak and I. Reichardt and R. Reinthal and W. Rhode and M. Ribó and J. Rico and S. Rügamer and A. Saggion and K. Saito and T. Y. Saito and M. Salvati and K. Satalecka and V. Scalzotto and V. Scapin and C. Schultz and T. Schweizer and S. N. Shore and A. Sillanpää and J. Sitarek and I. Snidaric and D. Sobczynska and F. Spanier and S. Spiro and V. Stamatescu and A. Stamerra and B. Steinke and J. Storz and S. Sun and T. Surić and L. Takalo and H. Takami and F. Tavecchio and P. Temnikov and T. Terzić and D. Tescaro and M. Teshima and O. Tibolla and D. F. Torres and T. Toyama and A. Treves and M. Uellenbeck and P. Vogler and R. M. Wagner and Q. Weitzel and V. Zabalza and F. Zandanel and R. Zanin},
journal= {arXiv preprint arXiv:1207.1634},
year = {2015}
}
Comments
10 pages, 9 figures; Accepted for publication in A&A