Simultaneous spectra and radio properties of BL Lac's

TL;DR

This nine-year study of 290 blazars, mainly BL Lacs, analyzed their radio spectra and variability across multiple frequencies, revealing significant differences between blazar subclasses in flux, spectra, and variability.

Contribution

The paper provides a comprehensive multi-frequency radio analysis of blazars, highlighting differences between HSP and LSP BL Lac objects based on nine years of observational data.

Findings

LSP BL Lacs have higher flux densities and flatter spectra.

HSP BL Lacs are fainter, have steeper spectra, and are less variable.

Spectral flattening above 7.7 GHz is observed in HSPs.

Abstract

We present the results of nine years of the blazar observing programme at the RATAN-600 radio telescope (2005-2014). The data were obtained at six frequency bands (1.1, 2.3, 4.8, 7.7, 11.2, 21.7 GHz) for 290 blazars, mostly BL Lacs. In addition, we used data at 37 GHz obtained quasi-simultaneously with the Metsahovi radio observatory for some sources. The sample includes blazars of three types: high-synchrotron peaked (HSP), low-synchrotron peaked (LSP), and intermediate-synchrotron peaked (ISP). We present several epochs of flux density measurements, simultaneous radio spectra, spectral indices and properties of their variability. The analysis of the radio properties of different classes of blazars showed that LSP and HSP BL Lac blazars are quite different objects on average. LSPs have higher flux densities, flatter spectra and their variability increases as higher frequencies are considered. On the other hand, HSPs are very faint in radio domain, tend to have steep low frequency spectra, and they are less variable than LSPs at all frequencies. Another result is spectral flattening above 7.7 GHz detected in HSPs, while an average LSP spectrum typically remains flat at both the low and high frequency ranges we considered.