QSO Rest Frame Research Articles

Rapidly varying Mg ii broad absorption line in SDSS J133356.02 + 001229.1

We report the discovery of rapid variations of a high-velocity Mg ii broad absorption line (BAL) trough in the quasar SDSS J133356.02+001229.1 (zem ~ 0.9197). Vivek et al. (2012a) revealed the emergence and subsequent near disappearance of a BAL component in this source having an ejection velocity of ~ 28000 km s-1. Our further follow up studies with South African Large Telescope (SALT) reveal the dramatic nature of the absorption line variability in this source. The absorption line emerged again at the same velocity and nearly disappeared within the SALT observations. Our observations allow us to probe variability over timescales of the order of few days to 4.2 years in the QSO rest-frame. The observed velocity stability of BAL absorption does not point to any line of sight acceleration/deceleration of BAL clouds. The ionization parameter of the absorbing cloud is constrained from the column density ratio of Mg II to Fe II ground state absorption. In the absence of strong optical continuum variability, we suggest that photoionization driven BAL variability due to changes in the shielding, multiple streaming clouds across our line of sight in a co-rotating wind or a combination of both as possible explanations for the observed strong equivalent width variations.

BROAD BALMER ABSORPTION LINE VARIABILITY: EVIDENCE OF GAS TRANSVERSE MOTION IN THE QSO SDSS J125942.80+121312.6

ABSTRACT We report on the discovery of broad Balmer absorption lines variability in the QSO SDSS J125942.80+121312.6, based on the optical and near-infrared spectra taken from the SDSS-I, SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and TripleSpec observations over a timescale of 5.8 years in the QSO's rest-frame. The blueshifted absorption profile of Hβ shows a variation of more than 5σ at a high velocity portion ( > 3000 km s − 1 ?> ) of the trough. We perform a detailed analysis for the physical conditions of the absorber using Balmer lines as well as metastable He i and optical Fe ii absorptions (λ4233 from b4P5/2 level and λ5169 from a6S5/2) at the same velocity. These Fe ii lines are identified in the QSO spectra for the first time. According to the photoionization simulations, we estimate a gas density of n ( H ) ≈ 10 9.1 cm − 3 ?> and a column density of N col ( H ) ≈ 10 23 cm − 2 ?> for the BOSS data, but the model fails to predict the variations of ionic column densities between the SDSS and BOSS observations if changes in ionizing flux are assumed. We thus propose transverse motion of the absorbing gas being the cause of the observed broad Balmer absorption line variability. In fact, we find that the changes in covering factors of the absorber can well-reproduce all of the observed variations. The absorber is estimated ∼0.94 pc away from the central engine, which is where the outflow likely experiences deceleration due to the collision with the surrounding medium. This scheme is consistent with the argument that LoBAL QSOs may represent the transition from obscured star-forming galaxies to classic QSOs.

On the covering fraction variability in an EUV mini-BAL outflow from PG 1206+459

We report on the first detection of extreme-ultraviolet (EUV) absorption variability in the NeVIII 770,780 mini-broad absorption line (mini-BAL) in the spectrum of the quasar (QSO) PG 1206+459. The observed equivalent width (EW) of the NeVIII doublet show a ~4 sigma variation over a timescale of 2.8 months in the QSO's rest-frame. Both members of the NeVIII doublet exhibit non-black saturation, indicating partial coverage of the continuum source. An increase in the NeVIII covering fraction from f_c = 0.59\pm0.05 to 0.72\pm0.03 is observed over the same period. The NeVIII profiles are too highly saturated to be susceptible to changes in the ionization state of the absorbing gas. In fact, we do not observe any significant variation in the EW and/or column density after correcting the spectra for partial coverage. We, thus, propose transverse motions of the absorbing gas being the cause of the observed variability. Using a simple model of a transiting cloud we estimate a transverse speed of ~1800 km/s. For Keplerian motion, this corresponds to a distance between the absorber and the central engine of ~1.3 pc, which places the absorber just outside the BLR region. We further estimate a density of ~5\times10^6 cm^(-3) and a kinetic luminosity of ~10^43 - 10^44 erg/s. Such large kinetic powers suggest that outflows detected via EUV lines are potentially major contributors to AGN feedback.

Transient C iv broad absorption lines in radio-detected QSOs

We study the transient (i.e. emerging or disappearing) C IV broad absorption line (BAL) components in 50 radio detected QSOs using multi-epoch spectra available in Sloan Digital Sky Survey DR10. We report the detectionof 6 BALQSOs having at least one distinct transient C IV absorption component. Based on the structure function analysis of optical light curves, we suggest that the transient absorption is unlikely to be triggered by continuum variations. Transient absorption components usually have low C IV equivalent widths (< 8 \AA), high ejection velocities (> 10000 \kms) and typically occur over rest-frame timescales > 800 days. The detection rate of transient C IV absorption seen in our sample is higher than that reported in the literature. Using a control sample of QSOs, we show that this difference is most likely due to the longer monitoring time-scale of sources in our sample while the effect of small number statistics cannot be ignored. Thus, in order to establish the role played by radio jets in driving the BAL outflows, we need a larger sample of radio detected BALs monitored over more than 3 years in the QSO's rest frame. We also find that the transient phenomenon in radio detected and radio quiet BALs does not depend on any of the QSO properties i.e. the Eddington ratio, black hole mass, bolometric luminosity and optical-to-IR colours. All this suggests that transient BAL phenomenon is simply the extreme case of BAL variability.

Variability in Low Ionization Broad Absorption Line outflows

We present results of our time variability studies of Mg II and Al III absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs (LoBAL QSOs) at 0.2 <= zem <= 2.1 using the 2m telescope at IUCAA Girawali Observatory over a time-scale of 10 days to 7.69 years in the QSO's rest frame. Spectra are analysed in conjunction with photometric light curves from Catalina Real-Time Transient Survey. Long time-scale (i.e >= 1 year) absorption line variability is seen in 8 cases (36% systems) while only 4 of them (i.e 18% systems) show variability over short time-scales (i.e < 1 year). We notice a tendency of highly variable LoBAL QSOs to have high ejection velocity, low equivalent width and low redshift. The detection rate of variability in LoBAL QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in QSOs having continuum dominated by Fe emission lines compared to rest of the QSOs. Confirming these trends with a bigger sample will give vital clues for understanding the physical distinction between different BAL QSO sub-classes. We correlate the absorption line variability with various parameters derived from continuum light curves and find no clear correlation between continuum flux and absorption line variabilities. However, sources with large absorption line variability also show large variability in their light curves. We also see appearance/disappearance of absorption components in 2 cases and clear indications for profile variations in 4 cases. The observed variability can be best explained by a combination of process driven by continuum variations and clouds transiting across the line of sight.

Gamma-ray absorption method (GRAM) application to the identification of EGRET unidentified sources

Recently we reported the very first detection of γ -ray resonant absorption along the line of sight toward γ -ray bright quasars (QSOs) like 3C 273, 3C 279, PKS 0528+0134, and BL Lacertae. These detections resulted from the analysis of absorption troughs in SEDs derived on the base of mostly EGRET data that were collected during monitoring campaigns of the Virgo and galactic anticenter regions by the Compton Gamma Ray Observatory (CGRO), as well as during ToO observations of QSOs flares. Among three resonant absorption mechanisms that affect the γ -ray spectrum of point-like sources, we now pinpoint the Δ -isobar resonance that has a very stable peak energy of the absorption cross-section for all elements (nuclei) and for individual nucleons. From two absorbers that are usually detected on the sight lines towards γ -ray bright QSOs, we concentrate here on the only one that is at the QSO rest frame. We discuss the advantages and drawbacks of this method distinguishing between a galactic and extragalactic origin of the EGRET unidentified sources (EUIDs). This is compared to the multiwavelength identification approach that was succesfully used in a few cases to identify galactic and extragalactic objects among EUIDs. We applied the GRAM to identifying two of the EGRET unidentified sources as blazars, and predict their respective redshifts.

Resonant absorption troughs in the gamma-ray spectra of QSO

We report the very first evidence of the possible detection of γ -ray resonant absorption along the line of sight towards γ -ray bright quasars (QSOs), like 3C 279, 3C 273, PKS 0528+0134, and BL Lacertae. These detections resulted from the analysis of COMPTEL and EGRET data that were collected either during monitoring campaigns of the Virgo and galactic anticenter regions by the Compton Gamma Ray Observatory (CGRO) or during ToO observations of QSOs flares. We discuss three resonant absorption mechanisms that affect the γ -ray spectrum of point-like sources when crossing the surrounding warm and cold absorbers, as well as the potential of this γ -ray photon absorption method to constrain the abundance of the absorber. We detected two absorbers along the line of sight towards γ -ray bright QSOs, one at the QSO rest frame redshift and another at approximately zero redshift. We tentatively identify the latter with an absorber in the Galactic halo, while the former is undoubtedly caused by photon absorption in the host galaxy of the QSO. We discuss the advantages and drawbacks of this method in studies of absorbers in different astrophysical environments and compare this new method to absorber studies at X-ray or other wavelengths. We applied this γ -ray absorption method to identify a few of the EGRET unidentified (EUID) sources as QSOs, and determine their redshifts.

Detection of an Iron Emission Feature from the Lensed Broad Absorption Line QSO H1413+117 at [CLC][ITAL]z[/ITAL][/CLC] = 2.56

We present the X-ray energy spectrum of the lensed broad absorption line QSO H1413+117 (the Cloverleaf) at z = 2.56 observed with the Chandra X-ray observatory. We detected 293 photons in a 40 ks Advanced CCD Imaging Spectrometer (ACIS-S) observation. The X-ray image consists of four lensed image components, thus the photons are from the lensed QSO itself. The overall spectrum can be described with a power-law function heavily absorbed by neutral matter at a redshift consistent with the QSO redshift. This supports the idea that intrinsic absorption is significant for BAL QSOs. The spectral fit significantly (99% confidence) improves when we include an emission line. The centroid energy and intrinsic width (Gaussian σ) of the line are 6.21 ± 0.16 keV and 220 eV (90% errors), respectively, in the QSO rest frame, assuming the absorbed power law as the continuum. The equivalent width of the line in the QSO rest frame is 960 eV. We suggest that the large equivalent width, the centroid energy, and the line broadness can be explained by iron K emission arising from X-ray reprocessing in the BAL flow, assuming it has a conical thin-sheet structure.

The Very Highly Ionized Broad Absorption Line System of the QSO SBS 1542+541

We have analyzed the broad absorption line system of the bright (V ~ 16.5) high-redshift (z = 2.361) QSO SBS 1542+541 using UV spectra from the Hubble Space Telescope Faint Object Spectrograph, along with optical data from the Multiple Mirror Telescope and the Steward Observatory 2.3 m telescope. These spectra offer continuous wavelength coverage from 1200 to 8000 A, which corresponds to ~340-2480 A in the QSO rest frame. The line of sight to the object contains only three identified intervening Lyman-limit absorption systems. Only one of these is optically thick at the Lyman edge, a low-redshift (z = 0.156) system with a strong Lyman edge observed at 1055 A (314 A in the rest frame) in a Hopkins Ultraviolet Telescope spectrum from the Astro-2 mission. The spectra therefore offer a rare opportunity to study broad absorption lines in the rest-frame extreme UV. We find that the broad absorption line system is lacking in species of relatively low ionization often seen in broad absorption systems, such as C III, O III, and Si IV. Instead, the system is dominated by very high ionization species. The strongest features correspond to O VI, Ne VIII, and Si XII. In addition to other high-ionization lines, we identify apparently saturated broad Lyman-series lines of order Lyγ and higher. There is strong evidence for partial occultation of the QSO emission source, particularly from the higher order Lyman lines that indicate a covered fraction less than 0.2. With the exception of C IV and N V, which are low-ionization species in the context of this system, all of the other lines depress the flux by more than 20%. Absorption from Lyα also depresses the flux more than 20%, indicating that there are at least two different regions contributing to H I absorption. Overall, the data suggest a correlation between a larger covered fraction and a higher state of ionization. These observations reveal inhomogeneity in the ionization structure of the broad absorption line gas. We have used photoionization models to constrain the total column density and ionization state of the system. A single-slab model consistent with our observational limits on the column densities requires NH ≈ 5 × 1022 cm-2 and an incident ionization parameter U ≈ 2. Since the observed covered fractions suggest multiple zones, we also produced a two-slab model and find 1021 cm-2 < NH < 1023 cm-2 and 0.08 < U < 4 for the smaller zone, NH 3 × 1021 cm-2 and U 2 for the larger zone. We suggest that the different covered fractions can be explained either by a special line of sight through a disklike geometry or by the existence of density fluctuations of a factor of 2 in the broad absorption line gas. The large column density and high state of ionization suggest that the system is likely associated with an X-ray warm absorber.

ITAL]ORFEUS II[/ITAL] Far-Ultraviolet Observations of 3C 273: The Intrinsic Spectrum

Using the Berkeley spectrometer of the ORFEUS-SPAS II mission, we observed the spectrum of the bright, low-redshift QSO 3C 273 in the wavelength range 900-1200 Å (780-1040 Å in the QSO's rest frame). The QSO's spectrum is dominated by broad emission blends of the resonance lines of O VI, C III, N III, and S VI. Only relatively weak emission is detected at the wavelengths of the higher Lyman lines, and no significant Lyman discontinuity is present at the QSO's redshift. The reddening-corrected underlying smooth continuum shows (for the epoch of the ORFEUS observations) a turnover of the νFν spectrum at about 2.5×1015 Hz. While this turnover frequency is in the general range expected for active galactic nucleus accretion disks, it is lower than predicted for QSOs as luminous as 3C 273 by standard accretion disk models.

Time‐variable Intrinsic Absorption Lines in the Quasi‐stellar Object Q2343+125

We discuss high-resolution Keck Observatory spectra of an intrinsic absorption-line system at redshift za ≈ 2.24 in the radio-quiet QSO Q2343+125 (ze = 2.515). The absorber's physical relationship to the QSO is confirmed by time-variable line strengths and partial line-of-sight coverage of the QSO continuum source. The N V, C IV, and Si IV doublets varied in unison by factors of 4 in less than 0.3 yr in the QSO rest frame. The resolved C IV doublet ratios show that the absorber occults 20% of the QSO continuum source; therefore, the absorbing clouds are likely to have characteristic sizes less than 0.01 pc. There is evidence for smaller coverage fractions when the lines were weaker, which could explain the line-strength changes. Lower ionization species such as C II and Si II are not detected. The Lyα line at za ≈ 2.24 is contaminated by the dense forest of cosmologically intervening absorption lines, but also appears to be weak or absent. The large uncertainties in the H I column prevent reliable constraints on the metal abundances. The za ≈ 2.24 lines clearly form in high-velocity ejecta from the QSO. The line profiles are smooth and rounded, with FWHM ~ 400 km s-1 and centroids shifted -24,000 km s-1 from the QSO emission redshift. Several narrow-line systems are present inside the broader absorption profiles, but they did not vary in strength and may be due to intervening gas. The large-amplitude variability, low coverage fractions, and large ratio of centroid to FWHM velocities imply different outflow properties than those inferred from the broad absorption lines (BALs) in other sources. Nonetheless, the ejecta identified by the za ≈ 2.24 absorber could be related to the BAL phenomenon and could be ubiquitous in QSOs if the gas subtends a small fraction of the sky as seen from the emission source(s).

The ultraviolet spectrum of the gravitational lens candidate UM 425 = QSO 1120+019: Evidence for broad absorption line (BAL) structure

The UV line profile structure of high-ionization resonance lines found with the International Ultraviolet Explorer (IUE) in the brightest of four multiply imaged sources (image-A) in the `candidate gravitational lens UM 425 = QSO 1120+019 indicates broad absorption line (BAL) structure. The deep-broad trough associated with the O VI line extends to velocities ~-12,000 km s^-1^, and contains discrete features that suggest multicomponent velocity structure. This structure may include contributions from C IV absorption from the early-type galaxy that is believed to lens UM 425. A strong absorption feature in the blue wing of the Lyman-α λ1216 emission line may be a Lyman-α absorption system at a z_Lya_ = 1.437 +/- 0.003, or it may be formed by the superposition of the broad N V λλ1238, 1242 absorption trough on the extended blue emission wing of the QSO Lyman-α line. We obtained a redshift of z_QSO_ = 1.471 +/- 0.003 from Lyman-α λ1215, consistent with the redshift found by Meylan and Djorgovski in the optical. The Lyman-α line appears unusually weak due to the presence of N V λ1240 BAL absorption. A Lyman-limit absorption system at λ912 was not observed in the QSO rest frame. The detection of BAL structure in the other weaker ground-state resonance lines of N II(1) and S IV (1) was not found, suggesting these lines are formed in a region that is distinct from the BAL component. Detection of BAL structure in the other fainter images in this system with HST instrumentation, similar to structure observed here in image A, could provide evidence that UM 425 is a gravitational lens.

The proximity profile of intergalactic He II resonance absorption toward high-redshift QSOs

The Gunn-Peterson effect predicts that an absorption trough should be associated with any resonance line arising in the intergalactic medium (IGM), extending blueward of the line in the QSO's rest frame. We show that such an absorption trough will not generally have a sharp edge at the QSO's redshift but should develop gradually toward shorter wavelengths. This proximity profile of the Gunn-Peterson trough arises because diffuse intergalactic gas in the vicinity of the QSO is more highly ionized than the general IGM. We consider the case of a uniform IGM in approximate photoionization equilibrium with a metagalactic UV background and investigate the proximity profile of He II lambda 304, which might be observable in QSOs with Z(sub Q) approximately 3. Assuming the QSO continuum extends beyond the He II ionization edge, the proximity profile has a characteristic width of delta z(sub p) = delta lambda/304 is approximately 0.1 f is the QSO Lyman limit luminosity in units of 10(exp 31) ergs/s/Hz averaged over the past approximately 10(exp 7) yr, omega(sub I) is the IGM density near (is less than or equal to 10 Mpc) the QSO, omega(sub b) is the normalized baryon density predicted by standard big band necleosynthesis, and f is a factor of order unity which depends weakly on several other factors. Application of this result to the reported detection of the He II Gunn-Peterson effect in Q0302-003 (Jakobsen et al. 1994) suggests that omega(sub I) is approximately equal to omega(sub b), some three orders of magnitude larger than the minimum density that may be inferred from application of the ordinary Gunn-Peterson effect to this QSO. Future observations of the He II proximity profile at higher resolution and signal-to-noise ratio in serveral ASOs should provide the means to measure the IGM density accurately.

TIME VARIABILITY OF BROAD-ABSORPTION-LINE QSOS

ABSTRACT We present the results of a three year project to monitor broad absorption-line QSOs (BALQSOs) with both broadband imaging (for continuum flux changes) and spectrophotometry (for broad absorption-line variations). About 10% of all optically selected QSOs show broad absorption-lines blueward of the high ionization resonance emission lines, indicating that gas is flowing outward from the QSO continuum source at velocities as high as 0.2c. Of 54 BALQSOs monitored with broadband imaging, ~33% showed significant time variability with deviations of 0.1 to 0.3 magnitudes. The time scale for variability was at least three months to a year in the QSO rest frame. Spectroscopic monitoring of 23 BALQSOs resulted in the detection of broad absorption-line time variations in 15 BALQSOs. Six of these cases showed small (marginally significant) changes, while four objects showed large BAL changes (±0.2 - 0.4 in normalized intensity). All of the BAL time variations appear to be changes in the residual intensity, or normalized flux, within the line, rather than variations in the velocity structure of the outflowing BAL gas. Our primary hypothesis is that a variable photoionizing continuum causes a change in the ionization levels, and thus a redistribution of the fractional abundances of the ions, resulting in the strengthening or weakening of the absorption lines. The BAL changes will appear nearly simultaneous with the continuum variations if the BAL variation mechanism travels in step with the continuum photons, and the mechanism induces rapid changes in the ionization levels of the gas. Therefore, unlike studies of broad emission-line variability in active galactic nuclei, BAL variability does not (for the simplest models) yield direct information about the size of the region. Our studies of BAL time variability have suggested that the velocity of the BAL gas varies monotonically with distance from the continuum source. With this assumption, BAL time variability provides the opportunity for detailed study of the ionization properties, column density, and elemental abundance of the BAL gas. In our data, we have found cases of BAL variability that appear to be correlated with a change in continuum flux. However, we have also discovered a few cases where the BALs varied, but no change was detected (to a limit of ~0.06 magnitudes) in the broadband flux. These results suggest that the ionizing flux (lambda ~100 - 400A) varies with greater amplitude and possibly in a non-synchronous manner with the observed continuum flux (λ ~2000A). For one object, we observed a large continuum level change (factor of 2) without a corresponding BAL change. However, this same QSO later exhibited BAL changes apparently synchronous with small continuum level changes. Despite this apparent conflict, ionizing flux variability of the continuum source is still the best explanation for the BAL changes. The simultaneous changes over a range of outflow velocities observed in several BALQSOs suggest that the mechanism inducing the BAL changes must propagate through the BAL region at (or close to) the speed of light. Also, there is a correlation between those QSOs which show continuum level changes and those which show BAL variations. From the changes observed in various ions (e.g. C IV lambda-1549, N V lambda-1240, Si IV lambda-1397, and Al III lambda-1857) in a few BALQSOs, we deduce that the ionization parameter (the ratio of the densities of ionizing photons and electrons) must be relatively high (U>0.05). We have also estimated a lower limit on the electron density of 104 cm-3 from limits on the response time scale of the BAL changes. From these limits, we deduce that the absorbing gas cannot be further than a few hundred parsecs from the ionizing source. In the few variable QSOs where the continuum slope (alpha, where Lnu proportional to nualpha) was measured, our data indicate that the slope increases as the continuum level increases. Our data also show that the intensities of the permitted broad emission lines often do not appear to follow changes in the observed continuum. This suggests that either this emission arises in a region larger than about one light year, or that the emitting clouds are not ionized by the continuum source seen along our line of sight to the QSO.

A statistical analysis of the radio properties of a large sample of 374 optically selected quasars

Using a large, unbiased sample of 374 optically selected QSOs, of which 54 are radio detected, we have computed for different redshift ranges the probability distribution function φ (R) of R defined as the ratio of monochromatic luminosities at 15 GHz and 2500 Å in the QSO's rest frame. A significant variation of φ (R) with redshift is noticed. At small redshifts (z &lt; 0.5), the distinctive feature of φ (R) is a peak near R∼102, arising due to the QSOs having steep radio spectrum(αr&lt;−0.5).

QSO Lyman limit absorption

The redshift distribution of QSO absorption systems which are optically thick in the Lyman continuum matches that of a non-evolving population of absorbers in a standard Friedmann cosmological model over the redshift range 0.4–3.5. The density of absorbers per unit velocity in the QSO rest frame is roughly constant for −0.01 ≲ v/c ≲ 0.2 and shows a rapid increase with QSO emission redshift, in accord with an ‘intervening’ origin for the absorbers but contrary to expectation were the material intrinsic to the QSOs.