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Published January 1, 2015 | Version v1
Journal article Open

FIRST NuSTAR OBSERVATIONS OF MRK 501 WITHIN A RADIO TO TeV MULTI-INSTRUMENT CAMPAIGN

Creators

  • 1. Stanford Univ, Dept Phys, Stanford, CA 94305 USA
  • 2. Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany
  • 3. Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
  • 4. Stanford Univ, Kavli Inst Particle Astrophys & Cosmol, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA
  • 5. Tech Univ Denmark, Natl Space Inst, DTU Space, DK-2800 Lyngby, Denmark
  • 6. Lawrence Livermore Natl Lab, Livermore, CA 94550 USA
  • 7. Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA
  • 8. CALTECH, Cahill Ctr Astron & Astrophys, Pasadena, CA 91125 USA
  • 9. INAF OAR, I-00040 Monte Porzio Catone, RM, Italy
  • 10. CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA
  • 11. Yale Univ, Dept Phys, Yale Ctr Astron & Astrophys, New Haven, CT 06520 USA
  • 12. NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
  • 13. ETH, CH-8093 Zurich, Switzerland
  • 14. INAF Natl Inst Astrophys, I-00136 Rome, Italy

Description

We report on simultaneous broadband observations of the TeV-emitting blazar Markarian 501 between 2013 April 1 and August 10, including the first detailed characterization of the synchrotron peak with Swift and NuSTAR. During the campaign, the nearby BL Lac object was observed in both a quiescent and an elevated state. The broadband campaign includes observations with NuSTAR, MAGIC, VERITAS, the Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical Telescope, various ground-based optical instruments, including the GASP-WEBT program, as well as radio observations by OVRO, Metsahovi, and the F-Gamma consortium. Some of the MAGIC observations were affected by a sand layer from the Saharan desert, and had to be corrected using event-by-event corrections derived with a Light Detection and Ranging (LIDAR) facility. This is the first time that LIDAR information is used to produce a physics result with Cherenkov Telescope data taken during adverse atmospheric conditions, and hence sets a precedent for the current and future ground-based gamma-ray instruments. The NuSTAR instrument provides unprecedented sensitivity in hard X-rays, showing the source to display a spectral energy distribution (SED) between 3 and 79 keV consistent with a log-parabolic spectrum and hard X-ray variability on hour timescales. None (of the four extended NuSTAR observations) show evidence of the onset of inverse-Compton emission at hard X-ray energies. We apply a single-zone equilibrium synchrotron self-Compton (SSC) model to five simultaneous broadband SEDs. We find that the SSC model can reproduce the observed broadband states through a decrease in the magnetic field strength coinciding with an increase in the luminosity and hardness of the relativistic leptons responsible for the high-energy emission.

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