Absorption Line Variability Research Articles

Co-variability Between the Broad Absorption Lines and Narrow Absorption Lines

We investigate the relationship between the variability of broad absorption lines (BALs) or narrow absorption lines (NALs) and that of continuum using a data set of two-epoch SDSS spectra containing 134 C iv NAL-BAL pairs. Our analysis reveals an anti-correlation between the fractional equivalent width (EW) variations in NALs (or BALs) and the fractional flux variations of the continuum, with Spearman rank correlation coefficients of r = −0.47 (p = 1E-08) and r = −0.58 (p = 1E-13), respectively. In addition, we find a positive correlation between the fractional EW variations in NALs and BALs (r = 0.72, p = 1E-22), and derive a regression equation ΔEWNAL/〈EWNAL〉 = 0.803ΔEWBAL/〈EWBAL〉 + 0.008, with an intrinsic scatter of 0.14. These results suggest that the variability in the ionizing continuum may play a significant role in the observed changes in C iv NALs and BALs, supporting the idea of photoionization-driven variability. The co-variability between C iv NALs and BALs may imply that they originate from outflows with similar physical conditions.

Time variability of ultra-fast BAL outflows using SALT: C iv absorption depth based analysis

ABSTRACT We probe the small-scale absorption line variability using absorption depth based analysis of a sample of 64 ultra-fast outflow (UFO) C iv broad absorption line (BAL) quasars monitored using the Southern African Large Telescope. We confirm the strong monotonic increase in the strength of variability with increasing outflow velocity. We identify regions inside the BAL trough for each source where the normalized flux difference between two epochs is >0.1 for a velocity width ≥500 km s−1 (called ‘variable regions’). We find that the total number of variable regions increases with the time interval probed and the number of BALs showing variable regions almost doubles from short (<2 yr) to long (>2 yr) time-scales. We study the distributions of variable region properties such as its velocity width, depth, and location. These regions typically occupy a few-tenths of the entire width of the BAL. Their widths are found to increase with increasing time-scales having typical widths of ∼2000 km s−1 for Δt > 2 yr. However, their absolute velocity with respect to zem and their relative position within the BAL profile remain random irrespective of the time-scale probed. The equivalent width variations of the BALs are strongly dependent on the size and depth of the variable regions but are little dependent on their total number. Finally, we find that ∼17 per cent of the UFO BALs show uncorrelated variability within the BAL trough.

Investigating the Origin of the Absorption-line Variability in the Narrow-line Seyfert 1 Galaxy WPVS 007

Broad absorption line quasars are actively accreting supermassive black holes that have strong outflows characterized by broad absorption lines in their rest-UV spectra. Variability in these absorption lines occurs over months to years depending on the source. WPVS 007, a low-redshift, low-luminosity narrow-line Seyfert 1 (NLS1) shows strong variability over shorter timescales, providing a unique opportunity to study the driving mechanism behind this variability that may mimic longer-scale variability in much more massive quasars. We present the first variability study using the spectral synthesis code SimBAL, which provides velocity-resolved changes in physical conditions of the gas using constraints from multiple absorption lines. Overall, we find WPVS 007 to have a highly ionized outflow with a large mass-loss rate and kinetic luminosity. We determine the primary cause of the absorption-line variability in WPVS 007 to be a change in covering fraction of the continuum by the outflow. This study is the first SimBAL analysis where multiple epochs of observation were fit simultaneously, demonstrating the ability of SimBAL to use the time domain as an additional constraint in spectral models.

Toward Understanding the B[e] Phenomenon. IX. Nature and Binarity of MWC645

We present the results of optical and near-IR spectroscopy and multicolor photometry of the emission-line star MWC 645, which exhibits the B[e] phenomenon. The presence of positionally variable absorption lines of a cool star detected for the first time indicates that the object is a binary system. Using a combination of the photometric and spectroscopic data as well as the Gaia EDR3 distance (D = 6.5 ± 0.9 kpc), we disentangled the components’ contributions and estimated their surface temperatures and luminosities (18, 000 ± 2000 K and 4250 ± 250 K, log L/L ⊙ = 4.0 ± 0.5 and 3.1 ± 0.3 for the hot and cool components, respectively). Quasi-cyclic short-period (months) and long-period (∼4 yr) photometric variations were detected in both optical and near-IR regions, and are most likely due to variable circumstellar extinction. Our analysis suggests that MWC 645 is a member of the FS CMa group. The object’s properties can be described by an evolutionary model of a close binary system that currently undergoes a nonconservative mass transfer between intermediate-mass stars (e.g., 7 M ⊙ + 2.8 M ⊙).

Emergence of a new H i 21-cm absorption component at z ∼ 1.1726 towards the γ-ray blazar PKS 2355-106

ABSTRACT We report the emergence of a new H i 21-cm absorption at zabs = 1.172 635 in the damped Lyα absorber (DLA) towards the γ-ray blazar PKS 2355-106 (zem∼1.639) using science verification observations (2020 June) from the MeerKAT Absorption Line Survey (MALS). Since 2006, this DLA is known to show a narrow H i 21-cm absorption at zabs = 1.173019 coinciding with a distinct metal absorption-line component. We do not detect significant H i 21-cm optical depth variations from this known H i component. A high-resolution optical spectrum (2010 August) shows a distinct Mg i absorption at the redshift of the new H i 21-cm absorber. However, this component is not evident in the profiles of singly ionized species. We measure the metallicity ([Zn/H] = −(0.77 ± 0.11) and [Si/H]= −(0.96 ± 0.11)) and depletion ([Fe/Zn] = −(0.63 ± 0.16)) for the full system. Using the apparent column density profiles of Si ii, Fe ii, and Mg i, we show that the depletion and the N(Mg i)/N(Si ii) column density ratio systematically vary across the velocity range. The region with high depletion tends to have a slightly larger N(Mg i)/N(Si ii) ratio. The two H i 21-cm absorbers belong to this velocity range. The emergence of zabs = 1.172 635 can be understood if there is a large optical depth gradient over a length-scale of ∼0.35 pc. However, the gas producing the zabs = 1.173 019 component must be nearly uniform over the same scale. Systematic uncertainties introduced by the absorption-line variability has to be accounted for in experiments measuring the variations of fundamental constants and cosmic acceleration even when the radio emission is apparently compact as in PKS 2355-106.

A Sharp Rise in the Detection Rate of Broad Absorption Line Variations in a Quasar SDSS J141955.26+522741.1

Abstract We present an analysis of the variability of broad absorption lines (BALs) in a quasar SDSS J141955.26+522741.1 at z = 2.145 with 72 observations from the Sloan Digital Sky Survey Data Release 16 (SDSS DR16). The strong correlation between the equivalent widths of BALs and the continuum luminosity, reveals that the variation of BAL troughs is dominated by the photoionization. The photoionization model predicts that when the time interval ΔT between two observations is longer than the recombination timescale t rec, the BAL variations can be detected. This can be characterized as a “sharp rise” in the detection rate of BAL variation at ΔT = t rec. For the first time, we detect such a “sharp rise” signature in the detection rate of BAL variations. As a result, we propose that the t rec can be obtained from the “sharp rise” of the detection rate of BAL variation. It is worth mentioning that the BAL variations are detected at the time intervals less than the t rec for half an order of magnitude in two individual troughs. This result indicates that there may be multiple components with different t rec but the same velocity in an individual trough.

Formation of magnetized spatial structures in the Beta Lyrae system. II. Reflection of magnetically controlled structures in the visible spectrum

This article proposes a picture of magnetized accretion structures formed during the mass transfer in the Beta Lyrae system. It is shown that the structure of the gaseous flows between the donor and the gainer is due to the spatial configuration of the donor magnetic field. Its dipole axis is deviated substantially from the line joining the centers of the components and is inclined to the orbital plane of the binary system; the center of the magnetic dipole is displaced from the donor center toward the gainer. The surface around the donor magnetic pole, which is close to the gainer, is a region of an additional matter loss from the donor surface. The effective collision of the magnetized plasma with the accretion disk is enhanced by the fast counter-rotation of this disk, especially in the secondary quadrature phases, in which the high-temperature medium and the system of formed accretion flows are observed. This concept is demonstrated, primarily, in the obvious correlations between the phase variability of the donor magnetic field and the corresponding variability of the dynamic and energy characteristics of the various complex lines. This refers to the behavior of the radial velocity curves of the emission-absorption lines formed in the gaseous structures of type H$\alpha$, HeI $\lambda$ 7065, or the variability of their equivalent width and intensity, and the variability of conventional absorption lines of the donor atmosphere. This is true for the phase variability of the absolute flux in the H$\alpha$ emission line and the fast varying of the continuum in the H$\alpha$ region as certain parameters, which reflect the phase variability of the donor magnetic field. This approach made it possible to determine the phase boundaries of the location of the magnetic polar region on the donor surface above which the matter outflows are formed.

Successive line-locked C iv doublets in quasar SDSS J115122.14+020426.3

ABSTRACT Rodríguez Hidalgo et al. (2013, ApJ, 775, 14) have reported the transition of a C iv mini-broad absorption line (mini-BAL) into a BAL in quasar SDSS J115122.14+020426.3 (hereafter J1151+0204). Based on the two-epoch spectra obtained from the Sloan Digital Sky Survey, we further investigate the three BAL systems (systems A, B and C) in J1151+0204. First, we confirm that the absorption-line variability in J1151+0204 is most likely caused by the change in ionization in response to the continuum variation, according to at least the following observational factors: coordinated strengthening is detected between multiple absorption troughs, and the continuum shows obvious weakening. According to photoionization simulations, asynchronized variability between the continuum and absorption lines indicates that the mini-BAL (system A) of J1151+0204 actually represents the state of a higher ionization level and lower C iv column density of the outflow, while its BAL identifies the state of a lower ionization level and higher C iv column density. Second, we find a rare case of a quintuple, which is due to four successive line-locked C iv doublets, within system C. This indicates that these outflow clouds have achieved a high degree of clumpiness, and that the radiative forces play a significant role in the acceleration process of these clumpy outflow clouds.

A Comparison of Properties of Quasars with and without Rapid Broad Absorption Line Variability

Abstract We investigate the correlation between rest-frame UV flux variability of broad absorption line (BAL) quasars and their variability in BAL equivalent widths (EWs) in a various timescale from <10 days to a few years in the quasar rest frame. We use the data sets of BAL EWs taken by the Sloan Digital Sky Survey Reverberation Mapping project and photometric data taken by the intermediate Palomar Transient Factory in the g and R bands and the Panoramic Survey Telescope and Rapid Response System in grizy bands. Our results are summarized as follows: (1) the distributions of flux variability versus BAL variability show weak, moderate, or a strong positive correlation; (2) there is no significant difference in flux variability amplitudes between BAL quasars with significant short timescale EW variability (called class S1) and without (class S2); (3) in all timescales considered in this paper, the class S1 quasars show systematically larger BAL variability amplitudes than those of the class S2 quasars; and (4) there are possible correlations between BAL variability and physical parameters of the quasars such as black hole masses (moderate positive), Eddington ratios, and accretion disk temperature (strong negative) in the class S2 quasars. These results indicate that the BAL variability requires changing in the ionizing continuum and an ancillary mechanism such as variability in X-ray shielding gas located at the innermost region of an accretion disk.

Blueshifted absorption lines from X-ray reflection in IRAS 13224−3809

ABSTRACT We explore a disc origin for the highly blueshifted, variable absorption lines seen in the X-ray spectrum of the narrow-line Seyfert 1 galaxy IRAS 13224−3809. The blueshift corresponds to a velocity of ∼0.25c. Such features in other active galactic nuclei are often interpreted as ultrafast outflows. The velocity is of course present in the orbital motions of the inner disc. The absorption lines in IRAS 13224−3809 are best seen when the flux is low and the reflection component of the disc is strong relative to the power-law continuum. The spectra are consistent with a model in which the reflection component passes through a thin, highly ionized absorbing layer at the surface of the inner disc, the blueshifted side of which dominates the flux due to relativistic aberration (the disc inclination is about 70°). No fast outflow need occurs beyond the disc.

Monitoring transitions between dispersed and school modes of sardines and anchovies with Bioacoustic Absorption Spectroscopy (BAS) measurements

BAS measurements at a biologically intense site in the Santa Barbara Channel permitted monitoring the temporal variation of absorption lines associated with fish in dispersed and school modes. Transmission Loss (TL) was measured at frequencies between 0.25 and 5 kHz between a fixed source and fixed receiver array separated by 3.7 km for 20 hours. Echo-sounder measurements: the average depth of fish at night was about 13 m. Trawls: 16 cm sardines and 10.5 cm anchovies dominated. The frequency dependence of bio-attenuation was derived through comparison of TL measurements and calculations. The latter were based on a normal mode code recently extended for broadband calculations (Porter, 2019). Bio-attenuation at 1.1 kHz, the resonance frequency of dispersed sardines, was 35 dB at 2200 l, 15 dB at 0100 l and 35 dB at 0400 l. When bio-attenuation at 1.1 kHz was minimum, bio-attenuation 0.4 kHz, attributed to schools of sardines, was maximum. The absorption line at 0.4 kHz is consistent with previously reported measurements and theoretical calculations of the resonance frequency of schools of 16 cm sardines (Diachok, 1999). Bio-attenuation at 1.8 and 0.6 kHz, attributed to 10.5 cm anchovies in dispersed and school modes respectively, were also anti-correlated. [Research supported by ONR.]BAS measurements at a biologically intense site in the Santa Barbara Channel permitted monitoring the temporal variation of absorption lines associated with fish in dispersed and school modes. Transmission Loss (TL) was measured at frequencies between 0.25 and 5 kHz between a fixed source and fixed receiver array separated by 3.7 km for 20 hours. Echo-sounder measurements: the average depth of fish at night was about 13 m. Trawls: 16 cm sardines and 10.5 cm anchovies dominated. The frequency dependence of bio-attenuation was derived through comparison of TL measurements and calculations. The latter were based on a normal mode code recently extended for broadband calculations (Porter, 2019). Bio-attenuation at 1.1 kHz, the resonance frequency of dispersed sardines, was 35 dB at 2200 l, 15 dB at 0100 l and 35 dB at 0400 l. When bio-attenuation at 1.1 kHz was minimum, bio-attenuation 0.4 kHz, attributed to schools of sardines, was maximum. The absorption line at 0.4 kHz is consistent with previously reported...

Correlations between the Variation of the Ionizing Continuum and Broad Absorption Lines in Individual Quasars

Abstract We discover the significant (significance level of >99%) correlations between the fractional variation of the ionizing continuum and that of the C iv and/or Si iv broad absorption lines (BALs) in each of 21 BAL quasars that have at least five-epoch observations from the Sloan Digital Sky Survey-I/II/III. This result reveals that the fluctuation of the ionizing continuum is the driver of most of these BAL variations. Among them, 17 show negative correlations and the other 4 positive correlations, which agrees with the prediction of photoionization models that absorption line variability response to ionization changes is not monotonic. Eight quasars out of 21 examples have been observed at least 30 times on rest-frame timescales as short as a few days, which reveals that changes in the incident ionizing continuum can cause BAL variability even in such a short period of time. In addition, we find that most of the 21 quasars show larger variation amplitude in Si iv than C iv, which reveals the ubiquity of saturation in these BALs (at least for C iv BALs).

Narrow Absorption Lines Complex. III. Gradual Transition from Type S to Type N Broad Absorption Line

Abstract We study the relationship between the broad absorption lines (BALs) that can be decomposed into multiple narrow absorption lines and those that cannot (hereafter Type N and Type S BAL, respectively), based on the analysis of three BAL systems (systems A, B, and C) in two-epoch spectra of quasar SDSS J113009.40+495247.9 (hereafter J1130+4952). As the velocity decreases (from systems A to C), these three BAL systems show a gradual transition from Type S to Type N BAL, and their equivalent widths (EWs) and profile shapes vary in a regular way. We ascribe the absorption line variability in J1130+4952 to the ionization change as a response to the fluctuation of the ionizing continuum based on several factors: (1) coordinated EW strengthening over a wide range in systems A and B, (2) the system B shows an obvious change in Si iv but no significant change in C iv BAL, and (3) asynchronized variability between the continuum and absorption lines. Based on the analysis of the variation mechanism, location, ionization state, and structure of systems A, B, and C, we hold the view that the Type S and Type N BALs in J1130+4952 probe the same clumped outflow, with the Type S BALs originating from the inner part of the outflow with a relatively higher ionization state, smaller column density, and more clumpy structures, while the Type N BALs originate from the outer part of the outflow with relatively lower ionization state, larger column density, and fewer clumpy structures.

The Correlated Variations of Absorption Lines and Quasar Continuum

Abstract Using the quasar spectra from the Sloan Digital Sky Survey and with variable C iv absorption line systems, we measure the Si iv and N v absorption line systems. We obtain 50 variable Si iv absorption line systems and 39 variable N v absorption line systems. We find that the variations in most of the C iv, Si iv, and N v absorption lines are correlated with the changes in quasar continuum. In addition, a significant portion of the variable absorption lines are the consistent variations of multiple systems with large velocity separations. Therefore, the variations of the C iv, Si iv, and N v absorption lines could be mainly driven by the changes in quasar radiations, which cause changes in ionization states or column densities of absorbing gas. We also find that the variable C iv, Si iv, and N v absorption line systems can be divided into low-ionization systems and high-ionization systems. The former positively responds to the changes in the quasar’s brightness, and the later is the oppositive case.

Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548

Abstract The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60–70 day “holiday,” suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer’s line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a “holiday.” It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.

On Si ivand C ivbroad absorption line variability in the UV spectra of 10 BALQSOs

On Si <scp>iv</scp>and C <scp>iv</scp>broad absorption line variability in the UV spectra of 10 BALQSOs

Ionization-driven intrinsic absorption line variability of BAL quasars in the Stripe 82 region

Abstract We investigate the connection between the intrinsic C iv absorption line variability and the continuum flux changes of broad absorption line (BAL) quasars using a sample of 78 sources in the Stripe 82 region. The absorption trough variability parameters are measured using the archival multi-epoch spectroscopic data from the Sloan Digital Sky Survey (SDSS), and the continuum flux variability parameters are estimated from the photometric light curves obtained by the SDSS and the Catalina Real-Time Survey surveys. We find evidence for weak correlations (ρs ∼ 0.3) between the intrinsic C iv absorption line variability and the quasar continuum variability for the final sample of 78 BAL quasars. The correlation strengths improve (ρs ∼ 0.5) for the ‘high-signal-to-noise ratio (SNR)’ sample sources that have higher spectral SNR. Using two subsets of the high-SNR sample differing on the absorption trough depth, we find that the shallow-trough subset shows an even stronger correlation (ρs ∼ 0.6), whereas the deep-trough subset does not show any correlation between the absorption line variability and the continuum variability. These results point to the important role of saturation effects in the correlation between the absorption line variability and the continuum variability of BAL quasars. Considering other effects that can also smear the correlation, we conclude that the actual correlation between the absorption line and continuum variability is even stronger.

Multiwavelength campaign on Mrk 509

Aims. To elucidate the location, physical conditions, mass outflow rate, and kinetic luminosity of the outflow from the active nucleus of the Seyfert 1 galaxy Mrk 509, we used coordinated UV and X-ray spectral observations in 2012 to follow up our lengthier campaign conducted in 2009. Methods. We observed Mrk 509 with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) on 2012-09-03 and 2012-10-11 coordinated with X-ray observations using the High Energy Transmission Grating on the Chandra X-ray Observatory. Our far-ultraviolet spectra used grating G140L on COS to cover wavelengths from 920–2000 Å at a resolving power of ∼2000, and gratings G130M and G160M to cover 1160–1750 Å at a resolving power of ∼15, 000. Results. We detect variability in the blueshifted UV absorption lines on timescales spanning 3–12 years. The inferred densities in the absorbing gas are greater than log n cm−3 ∼ 3. For ionization parameters ranging over log U = −1.5 to −0.2, we constrain the distances of the absorbers to be closer than 220 pc to the active nucleus. Conclusions. The impact on the host galaxy appears to be confined to the nuclear region.

The Sloan Digital Sky Survey Reverberation Mapping Project: Systematic Investigations of Short-timescale C IV Broad Absorption Line Variability

Abstract We systematically investigate short-timescale (&lt;10 day rest-frame) C iv broad absorption-line (BAL) variability to constrain quasar-wind properties and provide insights into BAL-variability mechanisms in quasars. We employ data taken by the Sloan Digital Sky Survey Reverberation Mapping project, as the rapid cadence of these observations provides a novel opportunity to probe BAL variability on shorter rest-frame timescales than have previously been explored. In a sample of 27 quasars with a median of 58 spectral epochs per quasar, we have identified 15 quasars ( %), 19 of 37 C iv BAL troughs ( %), and 54 of 1460 epoch pairs (3.7% ± 0.5%) that exhibit significant C iv BAL equivalent-width variability on timescales of less than 10 days in the quasar rest frame. These frequencies indicate that such variability is common among quasars and BALs, though somewhat rare among epoch pairs. Thus, models describing BALs and their behavior must account for variability on timescales down to less than a day in the quasar rest frame. We also examine a variety of spectral characteristics and find that, in some cases, BAL variability is best described by ionization-state changes, while other cases are more consistent with changes in covering fraction or column density. We adopt a simple model to constrain the density and radial distance of two outflows appearing to vary by ionization-state changes, yielding outflow density lower limits consistent with previous work.

The properties of broad absorption line outflows based on a large sample of quasars

Quasar outflows carry mass, momentum and energy into the surrounding environment, and have long been considered a potential key factor in regulating the growth of supermassive black holes and the evolution of their host galaxies. A crucial parameter for understanding the origin of these outflows and measuring their influence on their host galaxies is the distance (R) between the outflow gas and the galaxy center. While R has been measured in a number of individual galaxies, its distribution remains unknown. Here we report the distributions of R and the kinetic luminosities of quasars outflows, using the statistical properties of broad absorption line variability in a sample of 915 quasars from the Sloan Digital Sky Surveys. The mean and standard deviation of the distribution of R are 10^{1.4+/-0.5} parsecs. The typical outflow distance in this sample is tens of parsec, which is beyond the theoretically predicted location (0.01 ~ 0.1 parsecs) where the accretion disc line-driven wind is launched, but is smaller than the scales of most outflows that are derived using the excited state absorption lines. The typical value of the mass-flow rate is of tens to a hundred solar masses per year, or several times the accretion rate. The typical kinetic-to-bolometric luminosity ratio is a few per cent, indicating that outflows are energetic enough to influence the evolution of their host galaxies.