Title: First NuSTAR observations of the BL Lac - type blazar PKS 2155-304: constraints on the jet content and distribution of radiating particles

Abstract

Here 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 $$\beta ={0.3}_{-0.1}^{+0.2}$$ 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_min = 1 and that there is one proton per electron, an unrealistically high total jet power of L_p ~ 10⁴⁷ erg s^–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 $${n}_{{\rm{e}}+{\rm{e}}-}/{n}_{{\rm{p}}}\sim 30$$, or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor γ_br1 ~ 100. In either case, the jet composition is expected to be strongly matter-dominated.

Authors:

Madejski, G. M. ^[1]; Nalewajko, K.  ^[2];

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Madsen, K. K.  ^[3];

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Chiang, J. ^[1]; Baloković, M. ^[3]; Paneque, D. ^[4]; Furniss, A. K.  ^[5];

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Hayashida, M.  ^[6];

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Urry, C. M. ^[7]; Sikora, M. ^[8]; Ajello, M.  ^[9];

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Blandford, R. D. ^[1]; Harrison, F. A.  ^[3];

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Sanchez, D. ^[10]; Giebels, B. ^[11]; Stern, D.  ^[12];

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Alexander, D. M.  ^[13];

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Barret, D.  ^[14];

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Boggs, S. E. ^[15]; Christensen, F. E.  ^[16]

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more »; Craig, W. W. ^[17]; Forster, K. ^[3]; Giommi, P. ^[18]; Grefenstette, B.  ^[3];

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Hailey, C.; Hornstrup, A. ^[16]; Kitaguchi, T. ^[19]; Koglin, J. E. ^[1]; Mao, P. H. ^[3]; Miyasaka, H.  ^[3];

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Mori, K.  ^[20];

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Perri, M. ^[21]; Pivovaroff, M. J. ^[22]; Puccetti, S.  ^[21];

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Rana, V. ^[3]; Westergaard, N. J. ^[16]; Zhang, W. W. ^[23]; Zoglauer, A. ^[15] « less

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+ Show Author Affiliations

1. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States)
2. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States); Polish Academy of Sciences (PAS), Warsaw (Poland)
3. California Institute of Technology (CalTech), Pasadena, CA (United States)
4. Max Planck Inst. fuer Physik, Munich (Germany)
5. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States); California State Univ., East Bay, Hayward, CA (United States)
6. Univ. of Tokyo (Japan)
7. Yale Univ., New Haven, CT (United States)
8. Polish Academy of Sciences (PAS), Warsaw (Poland)
9. Clemson Univ., SC (United States)
10. Univ. de Savoie, Annecy-le-Vieux (France)
11. Ecole Polytechnique, Palaiseau (France)
12. California Institute of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab. (JPL)
13. Durham Univ. (United Kingdom)
14. Univ. of Toulouse (France); Centre National de la Recherche Scientifique (CNRS), Toulouse (France)
15. Univ. of California, Berkeley, CA (United States)
16. Technical Univ. of Denmark, Lyngby (Denmark)
17. Univ. of California, Berkeley, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
18. ASI Science Data Center, Rome (Italy)
19. Inst. of Physical and Chemical Research (RIKEN), Wako (Japan)
20. Columbia Univ., New York, NY (United States)
21. ASI Science Data Center, Rome (Italy); Istituto Nazionale di Astrofisica (INAF), Monteporzio (Italy)
22. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
23. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)

Publication Date:

Thu Nov 03 00:00:00 EDT 2016

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); National Aeronautics and Space Administration (NASA); Polish National Science Centre (NCN)

Contributing Org.:

Fermi-LAT Collaboration

OSTI Identifier:

1876966

Report Number(s):

LLNL-JRNL-837152
Journal ID: ISSN 1538-4357; 1056887; TRN: US2307352

Grant/Contract Number:  

AC52-07NA27344; NNG08FD60C; 2015/18/E/ST9/00580; NNX14AQ07H

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 831; Journal Issue: 2; Journal ID: ISSN 1538-4357

Publisher:

IOP Publishing

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; BL lacertae objects; individual (PKS 2155-304); galaxies: active; galaxies: jets; gamma rays; galaxies; radiation mechanisms; non-thermal