Extreme Variability in a Broad Absorption Line Quasar

Abstract

CRTSJ084133.15+200525.8 is an optically bright quasar at z=2.345 that has shown extreme spectral variability over the past decade. Photometrically, the source had a visual magnitude of V∼17.3 between 2002 and 2008. Then, over the following five years, the source slowly brightened by approximately one magnitude, to V∼16.2. Only ∼1 in 10,000 quasars show such extreme variability, as quantified by the extreme parameters derived for this quasar assuming a damped random walk model. A combination of archival and newly acquired spectra reveal the source to be an iron low-ionization broad absorption line quasar with extreme changes in its absorption spectrum. Some absorption features completely disappear over the 9 years of optical spectra, while other features remain essentially unchanged. We report the first definitive redshift for this source, based on the detection of broad Hα in a Keck/MOSFIRE spectrum. Absorption systems separated by several 1000 km s −1 in velocity show coordinated weakening in the depths of their troughs as the continuum flux increases. We interpret the broad absorption line variability to be due to changes in photoionization, rather than due to motion of material along our line of sight. This source highlights one sort of rare transition object that astronomy will now be finding through dedicated timedomain surveys.

Understanding extreme quasar optical variability with CRTS – II. Changing-state quasars

“…These aim to capture specific patterns of behavior associated with particular underlying physical processes. In this way, we have identified sources exhibiting periodic activity (Graham et al 2015a,b), major flaring (Graham et al 2017;Drake et al 2019), and extreme broad line variability (Stern et al 2017Ross et al 2018). emission lines (BELs, prototypically Hβ) in their optical spectra and often large, order of magnitude changes in the optical photometry Ruan et al 2016;Runnoe et al 2016;MacLeod et al 2016;Gezari et al 2017;Runco et al 2016;Yang et al 2018;Assef et al 2018;Stern et al 2018;Wang, Xu & Wei 2018;Ross et al 2018;.…”

A Mid-IR Selected Changing-look Quasar and Physical Scenarios for Abrupt AGN Fading

“…In addition to observing such rare phenomena as periodic quasars (e.g., Graham et al 2015aGraham et al , 2015bLiu et al 2015), flaring quasars (e.g., Lawrence et al 2016;Graham et al 2017;Kankare et al 2017), extreme broad absorption line variability (e.g., Rafiee et al 2016;Stern et al 2017), and tidal disruption events (e.g., Arcavi et al 2014;Blagorodnova et al 2017), this work has also identified a new class of "changing-look quasars" in which the strong UV continuum and broad hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of years (e.g., LaMassa et al 2015;Macleod et al 2016;Ruan et al 2016aRuan et al , 2016bRunnoe et al 2016;Gezari et al 2017;Yang et al 2018). The physical processes responsible for these changing-look quasars are still debated, but physical changes in the accretion disk structure appear to be the more likely cause rather than changes in obscuration.…”

Broad Absorption Line Disappearance/Emergence in Multiple Ions in a Weak Emission-line Quasar

“…BAL emergence or disappearance, an extreme and relatively rare form of BAL variability, is often interpreted as gas moving into or out of our LOS (e.g., Junkkarinen et al 2001;Hamann et al 2008;Leighly et al 2009;Krongold et al 2010;Hall et al 2011;Vivek et al 2012;Rafiee et al 2016). Some studies, however, report observational evidence in support of ionization changes (e.g., McGraw et al 2017;Stern et al 2017;Vivek et al 2018). A few studies based on relatively large samples confirm that both the ionization-change and transverse-motion mechanisms account for most BAL-emergence/disappearance phenomena (e.g., Filiz Ak et al 2012;Wang et al 2015;McGraw et al 2017;De Cicco et al 2018;Rogerson et al 2018;Sameer et al 2019).…”