Radio spectra and polarization properties of radio-loud broad absorption-line quasars

Abstract

We present multifrequency observations of a sample of 15 radio‐emitting broad absorption‐line quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They mostly display convex radio spectra which typically peak at about 1–5 GHz (in the observer's rest frame), flatten at MHz frequencies, probably due to synchrotron self‐absorption, and become steeper at high frequencies, i.e. ν≳ 20 GHz. Very Large Array (VLA) 22‐GHz maps (HPBW ∼80 mas) show unresolved or very compact sources, with linear projected sizes of ≤1 kpc. About two‐thirds of the sample looks unpolarized or weakly polarized at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarized intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non‐BAL QSOs, both in the observed and in the rest frame, finding steeper spectra among non‐BAL QSOs. However, constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarization properties shows that radio BAL QSOs share several properties common to young radio sources like compact steep spectrum or gigahertz peaked spectrum sources.

A Very Large Array Survey of Radio-Selected SDSS Broad Absorption Line Quasars

“…A significant difference between the distribution of α for BAL and non-BAL quasars has not been previously identified, but the sample sizes have typically been small (Fine et al 2011). Montenegro-Montes et al (2008) did identify a difference in the α distributions of their samples-however when they restricted their analysis to include only compact sources the difference disappeared. Additionally, BAL quasars with polar rather than equatorial outflows have likely been identified via short timescale variation in radio flux (Zhou et al 2006;Ghosh & Punsly 2007).…”

“…Becker et al (2000) find that only about 10% of BAL quasars show extended structure at 5 ′′ resolution, compared to about 50% of normal quasars. In a sample of 15 BAL quasars, Montenegro-Montes et al (2008) find that all of them are compact at FIRST resolutions, and the majority remain compact at around 80 mas resolution. Even very long baseline interferometry (VLBI) observations, which has down to milli-arcsecond resolution, often show BAL quasars as compact objects (Doi et al 2009, Jiang & Wang 2008, Kunert-Bajraszewska et al 2009).…”

Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

“…Instrumental polarisation from the Lovell and Effelsberg telescopes is known to be small (see e.g. Montenegro-Montes et al 2008;Gould & Lyne 1998), Notes. Given are the integration time (T int ), catalogue value for dispersion measure (DM, Hobbs et al 2004), the pulse period (P, determined from regular timing observations from the Lovell telescope at Jodrell Bank Observatory), the LOFAR observation ID and the number of bins across the pulse profile (N bin for each of the pulsars observed).…”

Investigating the radio-loud phase of broad absorption line quasars

“…Becker et al (2000) first used the radio emission spectral index to derive the jet orientation of BAL QSOs, and noted that this can lie in wide range of possible angles. After these works, different authors presented detailed studies about larger samples of radio-loud BAL QSOs, from which they reported a variety of possible orientations for the outflow, but also a variety of possible morphologies and ages for the radio source (Montenegro-Montes et al 2008;DiPompeo et al 2011;Bruni et al 2012Bruni et al , 2013). This does not suggest a scenario that would be clearly referable to one of the proposed models.…”