Intranight optical variability of radio-loud broad absorption line quasars

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.Comment: 10 pages, 2 figures, 3 tables; accepted in MNRAS (main journal

Dependence of Residual Rotation Measure (RRM) on Intervening MgII Absorbers at Cosmic Distances

We investigate the dependence of residual rotation measure (RRM) on intervening absorption systems at cosmic distances by using a large sample of 539 SDSS quasars in conjunction with the available rotation measure catalog at around 21cm wavelength. We found an excess extragalactic contribution in standard deviation of observed RRM of about 8.11+/-4.83 Rad/m^2 in our sample with intervening MgII absorber as compare to the sample without MgII absorber. Our results suggest that intervening absorbers could contribute to the enhancement of RRM at around 21cm wavelength, as was found earlier for RM measurements at around 6cm wavelength.Comment: 7 Pages, 4 Figures, Accepted for publication in MNRAS main-journa

Incidence of Strong MgII Absorbers Towards Different Types of Quasars

We report the first comparative study of strong MgII absorbers seen towards radio-loud quasars of core-dominated (CDQs) and lobe-dominated (LDQs) types and normal QSOs. The MgII associated absorption systems having a velocity offset v < 5000km/s from the systemic velocity of the background quasar were also excluded. Existing spectroscopic data for redshift-matched sightlines of 3975 CDQs and 1583 LDQs, covering a emission redshift range 0.39-4.87, were analysed and 864 strong MgII absorbers were found, covering the redshift range 0.45-2.17. The conclusions reached using this well-defined large dataset of strong MgII absorbers are: (i) The number density, dN/dz, towards CDQs shows a small, marginally significant excess over the estimate available for QSOs; (ii) In the redshift space, this difference is reflected in terms of a 1.6sigma excess of dN/dz over the QSOs, within the narrow redshift interval 1.2-1.8; (iii) The dN/dbeta distribution (with beta=v/c) for CDQs shows a significant excess over the distribution found for a redshift and luminosity matched sample of QSOs, at beta in the range 0.05-0.1. This leads us to infer that a significant fraction of strong MgII absorption systems seen in this offset velocity range are probably associated with the CDQs and might be accelerated into the line of sight by their powerful jets and/or due to the accretion-disk outflows close to our direction. Support to this scenario comes from a consistency check in which we only consider the spectral range corresponding to beta > 0.2. The computed redshift distribution for strong MgII absorbers towards CDQs now shows excellent agreement with that known for QSOs, as indeed is expected for purely intervening absorption systems. Thus, it appears that for CDQs the associated strong MgII absorbers can be seen at much larger velocities relative to the nucleus than the commonly adopted upper limit of 5000km/s.Comment: 9 Pages, 6 Figures, 1 Table, Accepted for the publication in MNRAS main-journa

Intranight Optical Variability of Radio-Quiet Weak Emission Line Quasars-III

This is continuation of our programme to search for the elusive radio-quiet BL Lacs, by carrying out a systematic search for intranight optical variability (INOV) in a subset of `weak-line quasars' which are already designated as `high-confidence BL Lac candidate' and are also known to be radio-quiet. For 6 such radio-quiet weak-line quasars (RQWLQs), we present here new INOV observations taken in 11 sessions of duration >3 hours each. Combining these data with our previously published INOV monitoring of RQWLQs in 19 sessions yields INOV observations for a set of 15 RQWLQs monitored in 30 sessions, each lasting more than 3 hours. The 30 differential light curves, thus obtained for the 15 RQWLQs, were subjected to a statistical analysis using the F-test, and the deduced INOV characteristics of the RQWLQs then compared with those published recently for several prominent AGN classes, also applying the F-test. From our existing INOV observations, there is a hint that RQWLQs in our sample show a significantly higher INOV duty cycle than radio-quiet quasars and radio lobe-dominated quasars. Two sessions when we have detected strong (blazar-like) INOV for RQWLQs are pointed out, and these two RQWLQs are therefore the best known candidates for radio-quiet BL Lacs, deserving to be pursued. For a proper comparison with the INOV properties already established for (brighter) members of several prominent classes of AGN, a factor of 2-3 improvement in the INOV detection threshold for the RQWLQs is needed and it would be very interesting to check if that would yield a significantly higher estimate for INOV duty cycle than is found here.Comment: 9 pages, 1 figure and 4 tables, accepted for publication in MNRAS main journal. arXiv admin note: text overlap with arXiv:1212.5384, arXiv:1403.744

Intranight Optical Variability of Radio-Quiet Weak Emission Line Quasars

Based on a recently started programme, we report the first search for intranight optical variability among radio-quiet weak-line-quasars (RQWLQs). Eight members of this class were observed on 13 nights in the R-band, such that each source was monitored continuously at least once for a minimum duration of about 3.5 hours, using the recently installed 130 cm telescope at Devasthal, India. Statistical analysis of the differential light curves was carried out using two versions of the F-test. Based on the INOV data acquired so far, the radio-quiet WLQ population appears to exhibit stronger INOV activity as compared to the general population of radio-quiet quasars (RQQs), but similar to the INOV known for radio-loud quasars of non-blazar type. To improve upon this early result, as well as extend the comparison to blazars, a factor of ?2 improvement in the INOV detection threshold would be needed. Such efforts are underway, motivated by the objective to search for the elusive radio-quiet blazars using INOV observations.Comment: 8 pages, 1 figure, 3 tables; accepted for publication in MNRA

Probing the environment of high-z quasars using the proximity effect in projected quasar pairs

We have used spectra of 181 projected quasar pairs at separations $\le 1.5$ arcmins from the Sloan Digital Sky-Survey Data Release 12 in the redshift range of 2.5 to 3.5 to probe the proximity regions of the foreground quasars. We study the proximity effect both in the longitudinal as well as in the transverse directions, by carrying out a comparison of the \lya absorption lines originating from the vicinity of quasars to those originating from the general inter-galactic medium at the same redshift. We found an enhancement in the transmitted flux within 4 Mpc to the quasar in the longitudinal direction. However, the trend is found to be reversed in the transverse direction. In the longitudinal direction, we derived an excess overdensity profile showing an excess up to $r\leq 5$ Mpc after correcting for the quasar's ionization, taking into account the effect of low spectral resolution. This excess overdensity profile matches with the average overdensity profile in the transverse direction without applying any correction for the effect of the quasar's ionization. Among various possible interpretations, we found that the anisotropic obscuration of the quasar's ionization seems to be the most probable explanation. This is also supported by the fact that all of our foreground quasars happen to be Type-I AGNs. Finally, we constrain the average quasar's illumination along the transverse direction as compared to that along the longitudinal direction to be $\leq$27\% (3$\sigma$ confidence level).Comment: 23 pages, 14 figures, Accepted for publication in Ap

Intranight Optical Variability of Radio-Quiet Weak Emission Line Quasars-IV

We report an extension of our program to search for radio-quiet BL Lac candidates using intra-night optical variability (INOV) as a probe. The present INOV observations cover a well-defined representative set of 10 `radio-quiet weak-emission-line quasars' (RQWLQs), selected from a newly published sample of 46 such sources, derived from the Sloan Digital Sky Survey (Data release 7). Intra-night CCD monitoring of the 10 RQWLQs was carried out in 18 sessions lasting at least 3.5 hours. For each session, differential light curves (DLCs) of the target RQWLQ were derived relative to two steady comparison stars monitored simultaneously. Combining these new data with those already published by us for 15 RQWLQs monitored in 30 sessions, we estimate an INOV duty cycle of $\sim 3\%$ for the RQWLQs, which appears inconsistent with BL Lacs. However, the observed INOV events (which occurred in just two of the sessions) are strong (with a fractional variability amplitude $\psi >$ 10\%), hence blazar-like. We briefly point out the prospects of an appreciable rise in the estimated INOV duty cycle for RQWLQs with a relatively modest increase in sensitivity for monitoring these rather faint objects.Comment: 8 pages, 2 figures, accepted in MNRA

A comparison of X-ray photon indices among the narrow and broad-line Seyfert 1 galaxies

We present a detailed comparative systematic study using a sample of 221 Narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift matched sample of 154 Broad-line Seyfert 1 (BLSy1) galaxies based on their observations using ROSAT and/or XMM-Newton telescopes in soft X-ray band (0.1-2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices ($\Gamma^{s}_{X}$) and its correlations with other parameters of nuclear activities such as Eddington ratios (R$_\mathrm{Edd}$), bolometric luminosities (L$_\mathrm{bol}$), black hole masses (M$_\mathrm{BH}$) and the widths of the broad component of H$\beta$ lines (FWHM(H$\beta$)). In our analysis, we found clear evidence of the difference in the $\Gamma^{s}_{X}$ and R$_\mathrm{Edd}$ distributions among NLSy1 and BLSy1 galaxies, with steeper $\Gamma^{s}_{X}$ and higher R$_\mathrm{Edd}$ for the former. Such a difference also exists in the spectral indices distribution in hard X-ray ($\Gamma^{h}_{X}$), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2-10 keV energy band. The difference in R$_\mathrm{Edd}$ distributions does exist even after applying the average correction for the difference in the inclination angle of NLSy1 and BLSy1 galaxies. We also estimated R$_\mathrm{Edd}$, based on SED fitting of 34 NLSy1 and 30 BLSy1 galaxies over the 0.3-10 keV energy band and found that results are still consistent with R$_\mathrm{Edd}$ estimates based on the optical bolometric luminosity. Our analysis suggests that the higher R$_\mathrm{Edd}$ in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disc-corona model as proposed for the luminous AGNs.Comment: 21 pages, 12 figures, Accepted for publication in Ap

Intranight Optical Variability of Radio-Quiet Weak Emission Line Quasars-II

This is continuation of our search for the elusive radio-quiet blazars, by carrying out a systematic programme to detect intranight optical variability (INOV) in a subset of `Weak-Lines-Quasars' (WLQs) which are designated as `high confidence BL Lac candidates' and are known to be radio-quiet. For 10 such RQWLQs, we present here the INOV observations taken in 16 sessions of durations > 3.5 hours each. Combining these data with our previously published INOV monitoring of RQWLQs in 13 sessions, gives a set of INOV observations of 15 RQWLQs monitored in 29 sessions each lasting more than 3.5 hours. The 29 differential light curves (DLCs), thus obtained for the 15 RQWLQs, were subjected to an statistical analysis using the F-test and the deduced INOV characteristics of the RQWLQs are compared with those published recently for several prominent AGN classes, also using the F-test. However, since the RQWLQs are generally 1-2 magnitudes fainter, a rigorous comparison has to wait for somewhat more sensitive INOV observations than those presented here. Based on our existing INOV observations, it seems that RQWLQs in our sample show a significantly higher INOV duty cycle than radio-quiet quasars and radio lobe-dominated quasars. Two sessions when we detected rather strong (blazar-like) INOV for RQWLQs are pointed out and both these RQWLQs are therefore candidates for radio-quiet BL Lacs.Comment: 8 pages, 2 figures and 3 tables, accepted for publication in MNRAS main journa

Intra-Night Optical monitoring of three {\gamma}-ray detected Narrow-line Seyfert 1 galaxies

For 3 radio-loud $\gamma$-ray detected Narrow-Line Seyfert 1 ($\gamma$-ray NLSy1) galaxies, we report optical variability on intra-night and/or week-like time scales, based on five $\geq$ 3 hours long monitoring sessions for each galaxy. The radio-loudness factors (R$_{1.4 GHz}$) for these galaxies, namely 1H 0323$+$342 (z = 0.0629), PKS J1222$+$0413 (z = 0.966) and PKS J1505$+$0326 (z = 0.408) are $\sim$318, $\sim$1534 and $\sim$3364 at 1.4 GHz, respectively. For the most distant $\gamma$-ray NLSy1, PKS J1222$+$0413, Intra-Night Optical Variability (INOV) characterisation is presented for the first time. The blazar-like behaviour of the nearest $\gamma$-ray NLSy1 1H 0323$+$342, which showed strong INOV on 4 of the 5 nights, was unexpected in view of its recent reclassification as `radio intermediate' (R$_{5 GHz}$ $\lesssim$ 25). Its particularly violent INOV is manifested by two optical outbursts lasting $\sim$ 1 hour, whose rapid brightening phase is shown to imply a doubling time of $\sim$ 1 hour for the optical synchrotron flux, after (conservatively) deducting the thermal optical emission contributed by the host galaxy and the Seyfert nucleus. A more realistic `decontamination' could well reduce substantially the flux doubling time, bringing it still closer in rapidity to the ultra-fast VHE ($>$ 100 GeV) flares reported for the blazars PKS 1222$+$216 and PKS 2155$-$304. A large contamination by thermal optical emission may, in fact, be common for NLSy1s as they are high Eddington rate accretors. The present study further suggests that superluminal motion in the radio jet could be a robust diagnostic of INOV.Comment: Accepted for publication in MNRAS. 14 pages, 3 figure