FirstNuSTAR observations of MRK 501 within a radio to TeV multi-instrument campaign
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Furniss, A.,Noda, K.,Boggs, S.,Chiang, J.,Christensen, F.,Craig, W.,Giommi, P.,Hailey, C.,Harisson, F.,Madejski, G.,Nalewajko, K.,Perri, M.,Stern, D.,Urry, M.,Verrecchia, F.,Zhang, W.,Ahnen, M. L.,Ansoldi, S.,Antonelli, L. A.,Antoranz, P.,Babic, A.,Banerjee, B.,Bangale, P.,de Almeida, U. Barres,Barrio, J. A.,Becerra Gonzalez, J.,Bednarek, W.,Bernardini, E.,Biasuzzi, B.,Biland, A.,Blanch, O.,Bonnefoy, S.,Bonnoli, G.,Borracci, F.,Bretz, T.,Carmona, E.,Carosi, A.,Chatterjee, A.,Clavero, R.,Colin, P.,Colombo, E.,Contreras, J. L.,Cortina, J.,Covino, S.,Da Vela, P.,Dazzi, F.,De Angelis, A.,De Caneva, G.,De Lotto, B.,de Ona Wilhelmi, E.,Delgado Mendez, C.,Di Pierro, F.,Prester, D. Dominis,Dorner, D.,Doro, M.,Einecke, S.,Eisenacher Glawion, D.,Elsaesser, D.,Fernandez-Barral, A.,Fidalgo, D.,Fonseca (2015) 'FIRST NuSTAR OBSERVATIONS OF MRK 501 WITHIN A RADIO TO TeV MULTI-INSTRUMENT CAMPAIGN'. Astrophysical Journal, 812 (11).
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 GASPWEBT program, as well as radio observations by OVRO, Metsähovi, 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 eventby-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 selfCompton (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.