Log-parabolic spectra and particle acceleration in blazars. III. SSC emission in the TeV band from Mkn 501

By E. Massaro, A. Tramacere, M. Perri, P. Giommi, G. D. D. Fisica, Universita' La Sapienza, Roma, Italy Spitzer Science Center, Esrin, Frascati and 4 more. 2005

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Curved broad-band spectral distributions of non-thermal sources like blazars are described well by a log-parabolic law where the second degree term measures the curvature. Log-parabolic energy spectra can be obtained for relativistic electrons by means of a statistical acceleration mechanism whose probability of acceleration depends on energy. In this paper we compute the spectra radiated by an electron population via synchrotron and Synchro-Self Compton processes to derive the relations between the log-parabolic parameters. These spectra were obtained by means of an accurate numerical code that takes the proper spectral distributions for single particle emission into account. We found that the ratio between the curvature parameters of the synchrotron spectrum to that of the electrons is equal to ∼0.2 instead of 0.25, the value foreseen in the δ-approximation. Inverse Compton spectra are also intrinsically curved and can be approximated by a log-parabola only in limited ranges. The curvature parameter, estimated around the SED peak, may vary from a lower value than that of the synchrotron spectrum up to that of emitting electrons depending on whether the scattering is in the Thomson or in the Klein-Nishina regime. We applied this analysis to computing the synchro-self Compton emission from the BL Lac object Mkn 501 during the large flare of April 1997. We fit simultaneous BeppoSAX and CAT data and reproduced intensities and spectral curvatures of both components with good accuracy. The large curvature observed in the TeV range was found to be mainly intrinsic, and therefore did not require a large pair production absorption against the extragalactic background. We regard this finding as an indication that the Universe is more transparent at these energies than previously assumed by several models found in the literature. This conclusion is supported by recent detection of two relatively high redshift blazars with HESS.

Subfields: Atomic and Molecular Physics, and Optics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/15a70483195010174150d8c04765cf191652d243

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In Atomic and Molecular Physics, and Optics

1. V. Petrosian
2. Usa
3. P. Padovani

In Nuclear and High Energy Physics

1. Ł. Stawarz
2. F. Tavecchio
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4. F. Zandanel
5. P. Padovani
6. P. Giommi
7. Italy.
8. W. Rhode

Citations in the corpus

• A simplified view of blazars: clearing the fog around long‐standing selection effects (2011, methodology): “…the non-thermal/jet component, we assume a simple homogeneous synchrotron self-Compton model (SSC, see, e.g. Tramacere et al. 2009, and references therein) with relativistic electrons distributed as a power law at low energies and as a log-parabola at high energies (Massaro et al. 2004, 2006).”
• Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission (2009, background): “The condition γmin > γUV may occur when we observe a PL (case b) or a LPPL (case c).”
• On the Momentum Diffusion of Radiating Ultrarelativistic Electrons in a Turbulent Magnetic Field (2008, background): “…very interesting to note that almost exactly this kind of curvature is observed at synchrotron X-ray frequencies in several BL Lac objects (Massaro et al. 2004, 2006; Perlman et al. 2005; Tramacere et al. 2007a, 2007b; Giebels et al. 2007), in particular those detected also at TeV photon…”
• Variable Very High Energy γ-Ray Emission from Markarian 501 (2007, methodology): “The logparabola is a simple function to describe curved spectra and, as pointed out by Massaro et al (2004, 2006), can be directly related to the intrinsic physical processes occurring in the source.”
• STOCHASTIC ACCELERATION AND THE EVOLUTION OF SPECTRAL DISTRIBUTIONS IN SYNCHRO-SELF-COMPTON SOURCES: A SELF-CONSISTENT MODELING OF BLAZARS’ FLARES (2011, methodology): “(31) The relation between bs and Es is: bs = a log(Es/E0) (32) with a = 3/5 = 0.6 The spectral properties of the IC emission are more complex, depending on the transition from the TH to the KN regime (see Massaro et al. 2006, for a detailed discussion).”
• THE SPECTRAL ENERGY DISTRIBUTIONS OF FERMI BLAZARS (2016, result): “Similar result was presented for Mkn 501 (Massaro et al. 2006).”