First NuSTAR observations of the Bl Lac-type blazar PKS 2155-304: constraints on the jet content and distribution of radiating particles
- Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
- Cahill Center for Astronomy and Astrophysics, Caltech, Pasadena, CA 91125 (United States)
- Max-Planck-Institut fur Physik, D-80805 Munchen (Germany)
- Institute for Cosmic Ray Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8582 (Japan)
- Yale Center for Astronomy and Astrophysics, Physics Department, Yale University, P.O. Box 208120, New Haven, CT 06520-8120 (United States)
- Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw (Poland)
- Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978 (United States)
- Laboratoire d‘Annecy-le-Vieux de Physique des Particules, Universite de Savoie, CNRS/IN2P3, F-74941 Annecy-le-Vieux (France)
- Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
- Department of Physics, Durham University, Durham DH1 3LE (United Kingdom)
- Universite de Toulouse, UPS—OMP, IRAP, Toulouse (France)
- Space Science Laboratory, University of California, Berkeley, CA 94720 (United States)
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
We report the first hard X-ray observations with NuSTAR of the BL Lac-type blazar PKS 2155-304, augmented with soft X-ray data from XMM-Newton and γ-ray data from the Fermi Large Area Telescope, obtained in 2013 April when the source was in a very low flux state. A joint NuSTAR and XMM spectrum, covering the energy range 0.5–60 keV, is best described by a model consisting of a log-parabola component with curvature β=0.3{sub −0.1}{sup +0.2} and a (local) photon index 3.04 ± 0.15 at photon energy of 2 keV, and a hard power-law tail with photon index 2.2 ± 0.4. The hard X-ray tail can be smoothly joined to the quasi-simultaneous γ-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p = 2.2. Assuming that the power-law electron distribution extends down to γ {sub min} = 1 and that there is one proton per electron, an unrealistically high total jet power of L {sub p} ∼ 10{sup 47} erg s{sup −1} is inferred. This can be reduced by two orders of magnitude either by considering a significant presence of electron–positron pairs with lepton-to-proton ratio n{sub e+e−}/n{sub p}∼30, or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor γ {sub br1} ∼ 100. In either case, the jet composition is expected to be strongly matter-dominated.
- OSTI ID:
- 22868496
- Journal Information:
- Astrophysical Journal, Vol. 831, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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