SIMULTANEOUS MULTIWAVELENGTH OBSERVATION OF Mkn 501 IN A LOW STATE IN 2006

Journal Article · Tue Nov 10 04:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/705/2/1624· OSTI ID:21378242

Anderhub, H; Biland, A ^[1]; Antonelli, L A ^[2]; Antoranz, P; Balestra, S; Bose, D ^[3]; Backes, M; Barrio, J A; Becker, J K ^[4]; Baixeras, C ^[5]; Bastieri, D; Bock, R K ^[6]; Becerra Gonzalez, J ^[7]; Bednarek, W; Berger, K ^[8]; Bernardini, E ^[9]; Bonnoli, G ^[10]; Bordas, P; Bosch-Ramon, V ^[11]

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1. ETH Zurich, CH-8093 (Switzerland)
2. INAF National Institute for Astrophysics, I-00136 Rome (Italy)
3. Universidad Complutense, E-28040 Madrid (Spain)
4. Technische Universitaet Dortmund, D-44221 Dortmund (Germany)
5. Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain)
6. Universita di Padova and INFN, I-35131 Padova (Italy)
7. Inst. de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain)
8. University of Lodz, PL-90236 Lodz (Poland)
9. Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen (Germany)
10. Universita di Siena, and INFN Pisa, I-53100 Siena (Italy)
11. Universitat de Barcelona (ICC/IEEC), E-08028 Barcelona (Spain)

We present results of the multiwavelength campaign on the TeV blazar Mkn 501 performed in 2006 July, including MAGIC for the very-high-energy (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 approx20% 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{sup +0.13} {sub -0.12} 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 spectral energy distribution (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.

• OSTI ID: 21378242
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 705; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BL LACERTAE OBJECTS
BOSONS
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
CRAB NEBULA
ELECTROMAGNETIC RADIATION
ELECTRON SPECTRA
ELECTRONS
ELEMENTARY PARTICLES
ENERGY RANGE
ENERGY SPECTRA
FERMIONS
GALAXIES
GAMMA RADIATION
GAMMA SPECTRA
GEV RANGE
GEV RANGE 10-100
IONIZING RADIATIONS
LEPTONS
MAGNETIC FIELDS
MASSLESS PARTICLES
NEBULAE
PHOTONS
RADIATIONS
RESOLUTION
SPECTRA
SPECTRAL HARDENING
SUPERNOVA REMNANTS
TEV RANGE
TEV RANGE 01-10
TIME RESOLUTION
TIMING PROPERTIES
X RADIATION
X-RAY GALAXIES
X-RAY SPECTRA