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 (<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 (SDSS-RM) 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 (55 +18 −14 %), 19 of 37 C iv BAL troughs (51 +15 −12 %), 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.

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

“…Absorption line variability study is an important technique which can constrain the kinematics and physical conditions of the absorbing gas. Previous BAL variability studies have established that BALs are variable on time-scales ranging from a few days (for eg., Grier et al 2015;Hemler et al 2019) to a few years (Lundgren et al 2007;Gibson et al 2008Gibson et al , 2010Capellupo et al 2011Capellupo et al , 2012Filiz Ak et al 2012;Capellupo et al 2013;Filiz Ak et al 2013;Vivek et al 2014;Welling et al 2014;Vivek et al 2016;McGraw et al 2017;De Cicco et al 2018;Rogerson et al 2018). However, the exact cause of the absorption line variability still remain unclear.…”

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

“…BAL troughs vary on timescales ranging from several days to years [20][21][22][23][24][25] . There are two possibles causes of BAL variability, i.e.…”

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

“…As a rare case, C IV BAL of SDSS J141007.74+541203.3 showed an extremely short time scale variability within 1.20 days in the quasar rest-frame (Grier et al 2015). Recently, as a first attempt, Hemler et al (2019), hereafter H19, systematically investigated BAL variability in short timescale (<10 days) for 27 BAL quasars spectroscopically monitored by the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project (Shen et al 2015), and 15 quasars (55%) had exhibited significant C IV BAL variability within 10 days in the quasar rest frame. This result implies that short time scale BAL variability are common phenomena in BAL quasars, since these BAL quasars have similar physical properties compared with those of the non-BAL quasars.…”