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Register a new userThe Extreme Ultraviolet Spectra of Low Redshift Radio Loud Quasars
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This paper reports on the extreme ultraviolet (EUV) spectrum of three low redshift ($z sim 0.6$) radio loud quasars, 3C 95, 3C 57 and PKS 0405-123. The spectra were obtained with the Cosmic Origins Spectrograph (COS) of the Hubble Space Telescope. The bolometric thermal emission, $L_{bol}$, associated with the accretion flow is a large fraction of the Eddington limit for all of these sources. We estimate the long term time averaged jet power, $overline{Q}$, for the three sources. $overline{Q}/L_{bol}$, is shown to lie along the correlation of $overline{Q}/L_{bol}$ and $alpha_{EUV}$ found in previous studies of the EUV continuum of intermediate and high redshift quasars, where the EUV continuum flux density between 1100 AA, and 700 AA, is defined by $F_{ u} sim u^{-alpha_{EUV}}$. The high Eddington ratios of the three quasars extends the analysis into a wider parameter space. Selecting quasars with high Eddington ratios has accentuated the statistical significance of the partial correlation analysis of the data. Namely. the correlation of $overline{Q}/L_{mathrm{bol}}$ and $alpha_{EUV}$ is fundamental and the correlation of $overline{Q}$ and $alpha_{EUV}$ is spurious at a very high statistical significance level (99.8%). This supports the regulating role of ram pressure of the accretion flow in magnetically arrested accretion models of jet production. In the process of this study, we use multi-frequency and multi-resolution Very Large Array radio observations to determine that one of the bipolar jets in 3C 57 is likely frustrated by galactic gas that keeps the jet from propagating outside the host galaxy.
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Studies of radio-loud (RL) broad absorption line (BAL) quasars indicate that popular orientation-based BAL models fail to account for all observations. Are these results extendable to radio-quiet (RQ) BAL quasars? Comparisons of RL and RQ BAL quasars show that many of their properties are quite similar. Here we extend these analyses to the rest-frame ultraviolet (UV) spectral properties, using a sample of 73 RL and 473 RQ BAL quasars selected from the Sloan Digital Sky Survey (SDSS). Each RQ quasar is individually matched to a RL quasar in both redshift (over the range $1.5 < z < 3.5$) and continuum luminosity. We compare several continuum, emission line, and absorption line properties, as well as physical properties derived from these measurements. Most properties in the samples are statistically identical, though we find slight differences in the velocity structure of the BALs that cause apparent differences in CIV emission line properties. Differences in the velocities may indicate an interaction between the radio jets and the absorbing material. We also find that UV FeII emission is marginally stronger in RL BAL quasars. All of these differences are subtle, so in general we conclude that RL and RQ BAL QSOs are not fundamentally different objects, except in their radio properties. They are therefore likely to be driven by similar physical phenomena, suggesting that results from samples of RL BAL quasars can be extended to their RQ counterparts.
We study the extreme ultraviolet (EUV) variability (rest frame wavelengths 500 - 920 $AA$) of high luminosity quasars using HST (low to intermediate redshift sample) and SDSS (high redshift sample) archives. The combined HST and SDSS data indicates a much more pronounced variability when the sampling time between observations in the quasar rest frame is $> 2times 10^{7}$ sec compared to $< 1.5times 10^{7}$ sec. Based on an excess variance analysis, for time intervals $< 2times 10^{7}$ sec in the quasar rest frame, $10%$ of the quasars (4/40) show evidence of EUV variability. Similarly, for time intervals $>2times 10^{7}$ sec in the quasar rest frame, $55%$ of the quasars (21/38) show evidence of EUV variability. The propensity for variability does not show any statistically significant change between $2.5times 10^{7}$ sec and $3.16times 10^{7}$ sec (1 yr). The temporal behavior is one of a threshold time interval for significant variability as opposed to a gradual increase on these time scales. A threshold time scale can indicate a characteristic spatial dimension of the EUV region. We explore this concept in the context of the slim disk models of accretion. We find that for rapidly spinning black holes, the radial infall time to the plunge region of the optically thin surface layer of the slim disk that is responsible for the preponderance of the EUV flux emission (primarily within 0 - 7 black hole radii from the inner edge of the disk) is consistent with the empirically determined variability time scale.
We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low redshift ($0.2 < z < 0.3$) optically selected QSOs. Our 176 radio detections fall into two clear categories: (1) About $20$% are radio-loud QSOs (RLQs) having spectral luminosities $L_6 gtrsim 10^{,23.2} mathrm{~W~Hz}^{-1}$ primarily generated in the active galactic nucleus (AGN) responsible for the excess optical luminosity that defines a emph{bona fide} QSO. (2) The radio-quiet QSOs (RQQs) have $10^{,21} lesssim L_6 lesssim 10^{,23.2} mathrm{~W~Hz}^{-1}$ and radio sizes $lesssim 10 mathrm{~kpc}$, and we suggest that the bulk of their radio emission is powered by star formation in their host galaxies. Radio silent QSOs ($L_6 lesssim 10^{,21} mathrm{~W~Hz}^{-1}$) are rare, so most RQQ host galaxies form stars faster than the Milky Way; they are not red and dead ellipticals. Earlier radio observations did not have the luminosity sensitivity $L_6 lesssim 10^{,21} mathrm{~W~Hz}^{-1}$ needed to distinguish between such RLQs and RQQs. Strong, generally double-sided, radio emission spanning $gg 10 mathrm{~kpc}$ was found associated with 13 of the 18 RLQ cores having peak flux densities $S_mathrm{p} > 5 mathrm{~mJy~beam}^{-1}$ ($log(L) gtrsim 24$). The radio luminosity function of optically selected QSOs and the extended radio emission associated with RLQs are both inconsistent with simple unified models that invoke relativistic beaming from randomly oriented QSOs to explain the difference between RLQs and RQQs. Some intrinsic property of the AGNs or their host galaxies must also determine whether or not a QSO appears radio loud.
We report on Swift observations of four z>2 radio-loud quasars (0212+735, 0537-286, 0836+710, and 2149-307), classified as blazars. The sources, well-known emitters at soft-medium X-rays, were detected at >5sigma with the BAT experiment in 15-150 keV. No flux variability was detected within the XRT and BAT exposures, with the exception of 0836+710 which shows an increase of a factor 4 of the 15-150 keV flux on a timescale of one month. The 0.3-10 keV spectra are well fitted by power law models, with rather hard continua (photon indices Gamma_XRT ~1.3-1.5); similarly, the 15-150 keV spectra are described by power laws with Gamma_BAT ~1.3-1.8. The XRT data exhibit spectral curvature, which can be modeled either in terms of excess absorption along the line of sight, or a downward-curved broken power law. In the former case, if the excess N_H is at the rest-frame of the source, columns of N_H^z=(0.3-6)x10^22 cm^-2 are measured. Modeling of the SEDs of the four quasars shows that the emission at the higher frequencies, >~ 10^16 Hz, is dominated by the jet, while the steep optical-to-UV continua, observed with the UVOT, can be attributed to thermal emission from the accretion disk. The disk luminosity is between 1% and 10% the jet power, similar to other powerful blazars.
We report spectral, imaging, and variability results from four new XMM-Newton observations and two new Chandra observations of high-redshift (z > 4) radio-loud quasars (RLQs). Our targets span lower, and more representative, values of radio loudness than those of past samples of high-redshift RLQs studied in the X-ray regime. Our spectral analyses show power-law X-ray continua with a mean photon index, Gamma =1.74 +/- 0.11, that is consistent with measurements of lower redshift RLQs. These continua are likely dominated by jet-linked X-ray emission, and they follow the expected anti-correlation between photon index and radio loudness. We find no evidence of iron Kalpha ~ emission lines or Compton-reflection continua. Our data also constrain intrinsic X-ray absorption in these RLQs. We find evidence for significant absorption (N_H ~ 10^22 cm^-2) in one RLQ of our sample (SDSS J0011+1446); the incidence of X-ray absorption in our sample appears plausibly consistent with that for high-redshift RLQs that have higher values of radio loudness. In the Chandra observation of PMN J221-2719 we detect apparent extended (~ 14 kpc) X-ray emission that is most likely due to a jet; the X-ray luminosity of this putative jet is ~2% that of the core. The analysis of a 4.9 GHz VLA image of PMN J221-2719 reveals a structure that matches the X-ray extension found in this source. We also find evidence for long-term (450-460 days) X-ray variability by 80-100% in two of our targets.
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