Log-parabolic spectra and particle acceleration in blazars

Free access article

Issue		A&A Volume 422, Number 1, July IV 2004


Page(s)		103 - 111
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20047148

A&A 422, 103-111 (2004)
DOI: 10.1051/0004-6361:20047148

II. The BeppoSAX wide band X-ray spectra of Mkn 501

E. Massaro^{1, 2}, M. Perri³, P. Giommi³, R. Nesci¹ and F. Verrecchia³

¹ Dipartimento di Fisica, Università La Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy
² IASF - Sezione di Roma, INAF-CNR, via del Fosso del Cavaliere, 00113 Roma, Italy
³ ASI Science Data Center, ESRIN, 00044 Frascati, Italy

(Received 27 January 2004 / Accepted 13 April 2004)

Abstract
We present the results of a spectral and temporal study of the complete set of BeppoSAX NFI (11) and WFC (71) observations of the BL Lac object Mkn 501. The WFC 2-28 keV data, reported here for the first time, were collected over a period of about five years, from September 1996 to October 2001. These observations, although not evenly distributed, show that Mkn 501, after going through a very active phase from spring 1997 to early 1999, remained in a low brightness state until late 2001. The data from the LECS, MECS and PDS instruments, covering the wide energy interval 0.1-150 keV, have been used to study in detail the spectral variability of the source. We show that the X-ray energy distribution of Mkn 501 is well described by a log-parabolic law in all luminosity states. This model allowed us to obtain good estimates of the SED synchrotron peak energy and of its associated power. The strong spectral variability observed, consisting of strictly correlated changes between the synchrotron peak energy and bolometric flux ( $E_{\rm peak} \propto F_{\rm b}^{\sim 1.4}$ ), suggests that the main physical changes are not only due to variations of the maximum Lorentz factor of the emitting particles but that other quantities must be varying as well. During the 1997 flare the high energy part of the spectrum of Mkn 501 shows evidence of an excess above the best fit log-parabolic law suggesting the existence of a second emission component that may be responsible for most of the observed variability.

Key words: radiation mechanisms: non-thermal -- galaxies: active -- galaxies: BL Lacertae objects: individual: Mkn 501 -- X-rays: galaxies

Offprint request: E. Massaro, enrico.massaro@uniroma1.it

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.