Blazar Times - No. 45 - July 2002
The Blazar Times
A Research Newsletter Dedicated to the BL Lac and Blazar Phenomena
No. 45 - July 2002 Editor: Travis A. Rector (


Journal Abstracts 1

Abstract Guidelines 3

Journal Abstracts

BL Lac Objects in the Synchrotron Proton Blazar Model

A. Mücke1,2, R.J. Protheroe3, R. Engel4, J.P. Rachen5,6  and T. Stanev4

1 Département de Physique, Université de Montreal, Montreal, QC, H3C 3J7, Canada
2 present address: Ruhr-Universität Bochum, Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, D-44780 Bochum, Germany
3 Department of Physics and Mathematical Physics, The University of Adelaide, Adelaide, SA 5005, Australia
4 Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
5 Sterrenkundig Instituut, Universiteit Utrecht, 3508 TA Utrecht, The Netherlands
6 present address: T-Systems GEI GmbH, Munich, Germany

We calculate the spectral energy distribution (SED) of electromagnetic radiation and the spectrum of high energy neutrinos from BL Lac objects in the context of the Synchrotron Proton Blazar Model. In this model, the high energy hump of the SED is due to accelerated protons, while most of the low energy hump is due to synchrotron radiation by co-accelerated electrons. To accelerate protons to sufficiently high energies to produce the high energy hump, rather high magnetic fields are required. Assuming reasonable emission region volumes and Doppler factors, we then find that in low-frequency peaked BL Lacs (LBLs), which have higher luminosities than high-frequency peaked BL Lacs (HBLs), there is a significant contribution to the high frequency hump of the SED from pion photoproduction and subsequent cascading, including synchrotron radiation by muons. In contrast, in HBLs we find that the high frequency hump of the SED is dominated by proton synchrotron radiation. We are able to model the SED of typical LBLs and HBLs, and to model the famous 1997 flare of Markarian 501. We also calculate the expected neutrino output of typical BL Lac objects, and estimate the diffuse neutrino intensity due to all BL Lacs. Because pion photoproduction is inefficient in HBLs, as protons lose energy predominantly by synchrotron radiation, the contribution of LBLs dominates the diffuse neutrino intensity. We suggest that nearby LBLs may well be observable with future high-sensitivity TeV gamma-ray telescopes.

Accepted by Astroparticle Physics

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On the Nature of MeV-blazars

M. Sikora1, M. B a\.zejowski1, R. Moderski1, and G. Madejski2

1 Copernicus Astronomical Center, Bartycka 18, Warsaw, Poland
2 Stanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, CA 94025

Broad-band spectra of the FSRQ (flat-spectrum-radio quasars) detected in the high energy gamma-ray band imply that they may be two types of such objects: those with steep gamma-ray spectra, hereafter called MeV-blazars, and those with flat gamma-ray spectra, GeV-blazars. We demonstrate that this difference can be explained in the context of the ERC (external-radiation-Compton) model using the same electron injection function. Satisfactory unification is reachable, provided that: (a) spectra of GeV-blazars are produced by internal shocks formed at distances where cooling of relativistic electrons in a jet is dominated by Comptonization of broad emission lines, whereas spectra of MeV-blazars are produced at distances where cooling of relativistic electrons is dominated by Comptonization of near-IR radiation from hot dust; (b) electrons are accelerated via a two step process and their injection function takes the form of a double power-law, with the break corresponding to the threshold energy for the diffusive shock acceleration. Direct predictions of our model is that, on average, variability time scales of the MeV-blazars should be longer than variability time scales of the GeV-blazars and that both types of the blazar phenomenon can appear in the same object.

Accepted by ApJ

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The Classification of BL Lacertae Objects: the Ca H&K Break

Hermine Landt1,2, Paolo Padovani1,3, Paolo Giommi4

1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
2 Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
3 Affiliated to the Astrophysics Division, Space Science Department, European Space Agency
4 ASI Science Data Center, c/o ESRIN, Via G. Galilei, I-00044 Frascati, Italy

We investigate why BL Lacertae objects (BL Lacs) have values of the Ca H&K break (a stellar absorption feature) lower than low-power radio galaxies and if its use is justified to separate the two classes. For this purpose we relate this parameter to the radio and optical core emissions, as well as to the X-ray powers, for a sample of ~ 90 radio sources. We find that the Ca H&K break value decreases with increasing jet powers, and that it also anti-correlates with the radio core dominance parameter but not with extended radio emission. Based on this we conclude that the Ca H&K break value of BL Lacs and radio galaxies is a suitable indicator of orientation. From the luminosity ratios between objects with low and high Ca H&K break values we constrain the average Lorentz factors for BL Lacs and low-power radio galaxies in the radio and X-ray band to G ~ 2 - 4 and derive average viewing angles for the galaxies. Our values are in agreement with results from independent methods. We find that the correlations between Ca H&K break and radio core and X-ray luminosity hold independently for low- (LBL) and high-energy peaked BL Lacs (HBL). We derive average viewing angles for their parent populations, which turn out to be similar to the ones for our entire sample, and compare for the first time the luminosities of LBL and HBL at different orientations.

Accepted by MNRAS.

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Abstract Guidelines

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File translated from TEX by TTH, version 2.25.
On 3 Jul 2002, 16:50.