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          Institute: MPI für Physik     Collection: MPI für Physik     Display Documents



ID: 544946.0, MPI für Physik / MPI für Physik
Simultaneous Multiwavelength observation of Mkn 501 in a low state in 2006
Authors:The MAGIC Collaboration; Anderhub, H.; Sato, R.; Ushio, M.; Kataoka, J.; Madejski, G.; Takahashi, T.
Date of Publication (YYYY-MM-DD):2009
Title of Journal:Astrophysical Journal
Journal Abbrev.:Astrophys.J.
Issue / Number:705
Start Page:1624
End Page:1649
Audience:Not Specified
Intended Educational Use:No
Abstract / Description:We present results of the multiwavelength campaign on the TeV blazar Mkn 501 performed in 2006 July, including MAGIC for the VHE gamma-ray band and Suzaku for the X-ray band. A VHE gamma-ray signal was clearly detected with an average flux above 200 GeV of ~20 % of the Crab Nebula flux, which indicates a low state of source activity in this energy range. No significant variability has been found during the campaign. The VHE gamma-ray spectrum can be described by a simple power-law from 80 GeV to 2 TeV with a photon index of 2.8+/-0.1, which corresponds to one of the steepest photon indices observed in this energy range so far for this object. The X-ray spectrum covers a wide range from 0.6 to 40 keV, and is well described by a broken power law, with photon indices of 2.257+/-0.004 and 2.420+/-0.012 below and above the break energy of 3.24+/-0.13 keV. No apparent high-energy cut off is seen above the break energy. Although an increase of the flux of about 50 % is observed in the X-ray band within the observation, the data indicate a consistently low state of activity for this source. Time-resolved spectra show an evidence for spectral hardening with a flux level. A homogeneous one-zone synchrotron self-Compton (SSC) model can adequately describe the SED from the X-ray to the VHE gamma-ray bands with a magnetic field intensity B=0.313 G and a Doppler beaming factor delta = 20, which are similar to the values in the past multiwavelength campaigns in high states. Based on our SSC parameters derived for the low state, we are able to reproduce the SED of the high state by just changing the Lorentz factor of the electrons corresponding to the break energy in the primary electron spectrum. This suggests that the variation of the injected electron population in the jet is responsible for the observed low-high state variation of the SED.
Classification / Thesaurus:MAGIC
Comment of the Author/Creator:25 pages, 8 figures, accepted for publication in ApJ
External Publication Status:published
Document Type:Article
Communicated by:N.N.
Affiliations:MPI für Physik
Identifiers:LOCALID:MPP-2009-20
URL:http://www.slac.stanford.edu/spires/find/hep/www?r...
URL:http://arXiv.org/abs/arxiv:0910.2093
URL:http://publications.mppmu.mpg.de/?action=search&mp...
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