Log-parabolic spectra and particle acceleration in the BL Lac object Mkn 421: Spectral analysis of the complete BeppoSAX wide band X-ray data set

By E. Massaro, M. Perri, P. Giommi, R. Nesci. 2003

302 citations recorded by the source corpus.

We report the results of a new analysis of 13 wide band BeppoSAX observations of the BL Lac object Mkn 421. The data from LECS, MECS and PDS, covering an energy interval from 0.1 to over 100 keV, have been used to study the spectral variability of this source. We show that the energy distributions in different luminosity states can be fitted very well by a log-parabolic law F(E) = K (E/E1) −(a+b Log(E/E1)) , which provides good estimates of the energy and flux of the synchrotron peak in the SED. In the first four short observations of 1997 Mkn 421 was characterized by a very stable spectral shape, with average values a = 2.25 and b = 0.45, independently of the source brightness and of the fact that the source luminosity was increasing or decreasing. In the observations of 1998 smaller values for both parameters, a � 2.07 and b � 0.34, were found and the peak energy in the SED was in the range 0.5-0.8 keV. The observations of May 1999 and April-May 2000 covered runs of a duration of several days and provided a very high number of events for all the instruments. The resulting spectral fits were then limited by some instrumental systematics. Also in these cases, the log-parabolic model gave a satisfactory description of the overall SED of Mkn 421. In particular, in the observations of spring 2000 the source was brighter than the other observations and showed a large change of the spectral curvature. Spectral parameters estimates gave a � 1. 8a ndb � 0.19 and the energy of the maximum in the SED moved to the range 1-5.5 keV. We give a possible interpretation of the log-parabolic spectral model in terms of particle acceleration mechanisms. An energy distribution of emitting particles with curvature close to the one observed can be explained by a simple model for statistical acceleration with the assumption that the probability for a particle to increase its energy is a decreasing function of the energy itself. A consequence of this mechanism is the existence of a linear relation between the spectral parameters a and b ,w ell confirmed by the estimated values of these two parameters for Mkn 421.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/1b562e5c3404e3fa2aa568e7eae12a03f07963de

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In Astronomy and Astrophysics

1. Bing Zhang
2. A. Strong
3. E. Orlando
4. F. Tavecchio
5. C. Dermer
6. Anna Franckowiak
7. Y. Kovalev
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In Nuclear and High Energy Physics

1. A. Strong
2. E. Orlando
3. Anna Franckowiak
4. F. Tavecchio
5. C. Dermer
6. Y. Kovalev
7. M. Lister
8. Troy A. Porter

Citations in the corpus

• THE THIRD CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE (2015, methodology): “…spectral fits were carried out with a single power-law function (dN dE N E E( )0 0 ) and a log-parabola function (dN dE N E E( ) E E0 0 log( )0 , Massaro et al. 2004), where N0 is a normalization factor, Γ, α and β are spectral parameters, and E0 is an arbitrary reference energy adjusted on a…”
• STOCHASTIC ACCELERATION AND THE EVOLUTION OF SPECTRAL DISTRIBUTIONS IN SYNCHRO-SELF-COMPTON SOURCES: A SELF-CONSISTENT MODELING OF BLAZARS’ FLARES (2011, methodology): “For a log-parabolic shaped n(γ) we have: log(γ3p) = log(γp) + 3 2r (30) and, using the relation bs ≈ r/5 (Massaro et al. 2004), or, more precisely, from the analysis presented in Sec.”
• Using the Fundamental Plane of black hole activity to distinguish X-ray processes from weakly accreting black holes (2011, unknown): “We fit parabolas (in log νFν − log ν) to these SEDs: log νFν = A1(log ν)2 + B1log ν + C1 (e.g. Massaro et al. 2004).”
• THE SPECTRAL ENERGY DISTRIBUTIONS OF FERMI BLAZARS (2016, methodology): “Our statistical results confirm the anti-correlation (Massaro et al. 2004, Tramacere et al. 2007, 2009), and this kind of anti-correlation is a strong signature of a stochastic component in the acceleration (Tramacere et al. 2011).”
• Simultaneous Planck, Swift, and Fermi observations of X-ray and γ-ray selected blazars (2011, methodology): “When deviations from a single power-law model were found, we adopted a log-parabolic law of the form F(E) = KE(a+b log E) (Massaro et al. 2004), which has been shown to fit the X-ray spectrum of blazars of the HSP type well (e.g. Giommi et al. 2005; Tramacere et al. 2009).”
• THE FIRST FERMI LAT SUPERNOVA REMNANT CATALOG (2015, background): “…added source was 6Note: Eb is a scale parameter which should be set near the lower energy range of the spectrum being fit and is usually fixed, see Massaro et al. (2004) – 14 – between 3◦ and 5◦ of the center of the RoI, just its normalization was freed, and if greater than 5◦ all its source…”
• Log-parabolic spectra and particle acceleration in blazars. III. SSC emission in the TeV band from Mkn 501 (2005, methodology): “In two previous papers (Massaro et al. 2004a, 2004b, hereafter Paper I and Paper II, respectively) we used the log-parabolic modelto fit the BeppoSAX broad band X-ray spectra of the BL Lac objects Mkn 421 and Mkn 501 and studied the relations between the spectral parameters and the luminosity.”
• 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).”
• 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.”
• INSIGHTS INTO THE HIGH-ENERGY γ-RAY EMISSION OF MARKARIAN 501 FROM EXTENSIVE MULTIFREQUENCY OBSERVATIONS IN THE FERMI ERA (2011, methodology): “We adopted a log-parabolic model for the photon flux spectral density (Massaro et al. 2004a,b) of the form log[F(E)] = logK−a log[E/keV]−b log2[E/keV], with an absorption hydrogen-equivalent column density fixed to the Galactic value in the direction of the source, namely 1.56 × 1020 cm−2 (Kalberla…”
• 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…”