Astronomy & Astrophysics

Free access article

Issue		A&A Volume 391, Number 3, September I 2002
Page(s)		917 - 922
Section		Extragalactic astronomy
DOI		10.1051/0004-6361:20020969

A&A 391, 917-922 (2002)
DOI: 10.1051/0004-6361:20020969

Research Note

Radio luminosities and classificatory criteria of BL Lacertae objects

D. C. Mei, L. Zhang and Z. J. Jiang

Department of Physics, Yunnan University, Kunming 650091, PR China

(Received 17 April 2002 / Accepted 26 June 2002 )

Abstract
Using the sample of radio-selected BL Lacertae objects (RBLs) and X-ray selected BL Lacertae objects (XBLs) presented by Sambruna et al. (1996), we calculated the luminosities in radio, optical and X-ray of each source and made a statistical analysis among the luminosities at different wave-bands, broad-band spectral indices from radio to X-ray ( $\alpha_{\rm rx}$ ) and peak frequencies ( $\nu_{\rm p}$ ). Our results are as follows: (i) there is a positive correlation between radio luminosity $L_{\rm r}$ and $\alpha_{\rm rx}$ and a negative correlation between $L_{\rm r}$ and $\nu_{\rm p}$ . High-energy peak BL Lacs (HBLs) and low-energy peak BL Lacs (LBLs) can be distinguished very well; the dividing lines are probably those of $\log {L_{\rm r}}=43.25$ (erg/s) and $\alpha_{\rm rx}>$ (or $\leq$ ) 0.75 for $\log L_{\rm r}$ - $\alpha_{\rm rx}$ plot and those of $\log L_{\rm r}\leq 43.25$ (erg/s) and $\log {\nu_{\rm p}}>14.7$ for the ${\bf\log}\,L_{\rm r}$ - ${\bf\log}\,\nu_{\rm p}$ plot; (ii) there is a weak positive correlation between optical luminosity $L_{\rm o}$ and $\alpha_{\rm rx}$ and a negative weak correlation between $L_{\rm o}$ and $\nu_{\rm p}$ ; (iii) there is no correlation between X-ray luminosity $L_{\rm x}$ and $\alpha_{\rm rx}$ or between $L_{\rm x}$ and $\nu_{\rm p}$ . From our analysis, we find that synchrotron radiation is the main X-ray radiation mechanism for HBLs while inverse Compton scattering is dominant for LBLs.

Key words: galaxies: BL Lacertae objects: general -- galaxies: fundamental parameters -- radiation mechanism: non-thermal

Offprint request: D. C. Mei, kmdcmei@public.km.yn.cn

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