37 GHz observations of a large sample of BL Lacertae objects

TL;DR

This study presents 37 GHz radio observations of a large BL Lacertae sample, revealing diverse variability, spectral indices, and detection of high-energy BL Lacs at high frequencies, challenging previous notions of their radio quietness.

Contribution

First comprehensive 37 GHz observational data for a large BL Lacertae sample, including variability and spectral analysis, highlighting detection of high-energy BL Lacs at high radio frequencies.

Findings

34% of the sample detected at 37 GHz

Mean fractional variability is 0.31

High-energy BL Lacs can be detected at 37 GHz

Abstract

We present 37 GHz data obtained at Metsahovi Radio Observatory in 2001 December - 2005 April for a large sample of BL Lacertae objects. We also report the mean variability indices and radio spectral indices in frequency intervals 5 - 37 GHz and 37 - 90 GHz. Approximately 34 % of the sample was detected at 37 GHz, 136 BL Lacertae objects in all. A large majority of the detected sources were low-energy BL Lacs (LBLs). The variability index values of the sample were diverse, the mean fractional variability of the sample being \Delta S_2 = 0.31. The spectral indices also varied widely, but the average radio spectrum of the sample sources is flat. Our observations show that many of the high-energy BL Lacs (HBL), which are usually considered radio-quiet, can at times be detected at 37 GHz.