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Register a new userInvestigating the radio-loud phase of broad absorption line quasars
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Broad absorption lines (BALs) are present in the spectra of ~20% of quasars (QSOs); this indicates fast outflows (up to 0.2c) that intercept the observers line of sight. These QSOs can be distinguished again into radio-loud (RL) BAL QSOs and radio-quiet (RQ) BAL QSOs. The first are very rare, even four times less common than RQ BAL QSOs. The reason for this is still unclear and leaves open questions about the nature of the BAL-producing outflows and their connection with the radio jet. We explored the spectroscopic characteristics of RL and RQ BAL QSOs with the aim to find a possible explanation for the rarity of RL BAL QSOs. We identified two samples of genuine BAL QSOs from SDSS optical spectra, one RL and one RQ, in a suitable redshift interval (2.5$<z<$3.5) that allowed us to observe the Mg II and H$beta$ emission lines in the adjacent near-infrared (NIR) band. We collected NIR spectra of the two samples using the Telescopio Nazionale Galileo (TNG, Canary Islands). By using relations known in the literature, we estimated the black-hole mass, the broad-line region radius, and the Eddington ratio of our objects and compared the two samples. We found no statistically significant differences from comparing the distributions of the cited physical quantities. This indicates that they have similar geometries, accretion rates, and central black-hole masses, regardless of whether the radio-emitting jet is present or not. These results show that the central engine of BAL QSOs has the same physical properties with and without a radio jet. The reasons for the rarity of RL BAL QSOs must reside in different environmental or evolutionary variables.
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We present the results of an optical photometric monitoring program of 10 extremely radio loud broad absorption line quasars (RL-BALQSOs) with radio-loudness parameter, R, greater than 100 and magnitude g_i < 19. Over an observing run of about 3.5-6.5 hour we found a clear detection of variability for one of our 10 radio-loud BALQSOs with the INOV duty cycle of 5.1 per cent, while on including the probable variable cases, a higher duty cycle of 35.1 per cent is found; which are very similar to the duty cycle of radio quiet broad absorption line quasars (RQ-BALQSOs). This low duty cycle of clear variability per cent in radio-loud sub-class of BALQSOs can be understood under the premise where BALs outflow may arise from large variety of viewing angles from the jet axis or perhaps being closer to the disc plane.
If broad absorption line (BAL) quasars represent a high covering fraction evolutionary state (even if this is not the sole factor governing the presence of BALs), it is expected that they should show an excess of mid-infrared radiation compared to normal quasars. Some previous studies have suggested that this is not the case. We perform the first analysis of the IR properties of radio-loud BAL quasars, using IR data from WISE and optical (rest-frame ultraviolet) data from SDSS, and compare the BAL quasar sample with a well-matched sample of unabsorbed quasars. We find a statistically significant excess in the mid- to near-infrared luminosities of BAL quasars, particularly at rest-frame wavelengths of 1.5 and 4 microns. Our sample was previously used to show that BALs are observed along many lines of sight towards quasars, but with an overabundance of more edge-on sources, suggesting that orientation factors into the appearance of BALs. The evidence here---of a difference in IR luminosities between BAL quasars and unabsorbed quasars---may be ascribed to evolution. This suggests that a merging of the current BAL paradigms is needed to fully describe the class.
We present multi-frequency 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 display mostly convex radio spectra which typically peak at about 1-5 GHz (in the observers rest-frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e., >~ 20 GHz. VLA 22-GHz maps (HPBW ~ 80 mas) show unresolved or very compact sources, with linear projected sizes of <= 1 kpc. About 2/3 of the sample look unpolarised or weakly polarised at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarised intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and 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 polarisation properties shows that radio BAL QSOs share several properties common to young radio sources like Compact Steep Spectrum (CSS) or Gigahertz-Peaked Spectrum (GPS) sources.
This work presents the results of a Chandra study of 21 broad absorption line (BAL) radio-loud quasars (RLQs). We conducted a Chandra snapshot survey of 12 bright BAL RLQs selected from SDSS/FIRST data and possessing a wide range of radio and CIV absorption properties. Optical spectra were obtained nearly contemporaneously with the Hobby-Eberly Telescope; no strong flux or BAL variability was seen between epochs. We also include in our sample 9 additional BAL RLQs possessing archival Chandra coverage. We compare the properties of (predominantly high-ionization) BAL RLQs to those of non-BAL RLQs as well as to BAL radio-quiet quasars (RQQs) and non-BAL RQQs for context. All 12 snapshot and 8/9 archival BAL RLQs are detected, with observed X-ray luminosities less than those of non-BAL RLQs having comparable optical/UV luminosities by typical factors of 4.1-8.5. (BAL RLQs are also X-ray weak by typical factors of 2.0-4.5 relative to non-BAL RLQs having both comparable optical/UV and radio luminosities.) However, BAL RLQs are not as X-ray weak relative to non-BAL RLQs as are BAL RQQs relative to non-BAL RQQs. While some BAL RLQs have harder X-ray spectra than typical non-BAL RLQs, some have hardness ratios consistent with those of non-BAL RLQs, and there does not appear to be a correlation between X-ray weakness and spectral hardness, in contrast to the situation for BAL RQQs. RLQs are expected to have X-ray continuum contributions from both disk-corona and small-scale jet emission. While the entire X-ray continuum in BAL RLQs cannot be obscured to the same degree as in BAL RQQs, we calculate that the jet is likely partially covered in many BAL RLQs. We comment briefly on implications for geometries and source ages in BAL RLQs.
We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey (SDSS) Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network (JVN). We aimed at selecting BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10^5 K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.
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