A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255

Abstract

Context. Broad absorption lines indicate gas outflows with velocities from thousands of km s −1 to about 0.2 the speed of light, which may be present in all quasars and may play a major role in the evolution of the host galaxy. The variability of absorption patterns can provide information on changes in the density and velocity distributions of the absorbing gas and its ionisation status. Aims. We want to accurately follow the evolution in time of the luminosity and both the broad and narrow C IV absorption features of an individual object, the quasar APM 08279+5255, and analyse the correlations among these quantities. Methods. We have collected 23 photometrical and spectro-photometrical observations at the 1.82 m Telescope of the Asiago Observatory since 2003, plus 5 other spectra from the literature. We analysed the evolution in time of the equivalent width of the broad absorption feature and two narrow absorption systems, the correlation among them and with the R band magnitude. We performed a structure function analysis of the equivalent width variations. Results. We present an unprecedented monitoring of a broad absorption line quasar based on 28 epochs during 14 years. The shape of broad absorption feature shows relative stability, while its equivalent width slowly declines until it sharply increases during 2011. At the same time, the R magnitude stays almost constant until it sharply increases during 2011. The equivalent width of the narrow absorption redwards of the systemic redshift only shows a decline. Conclusions. The broad absorption behaviour suggests changes in the ionisation status as the main cause of variability. We show for the first time a correlation of this variability with the R band flux. The different behaviour of the narrow absorption system might be due to recombination time delay. The structure function of the absorption variability has a slope comparable with typical optical variability of quasars. This is consistent with variations of the 200 Å ionising flux originating in the inner part of the accretion disk.

A multi-epoch spectroscopic study of the BAL quasar APM 08279+5255

“…The procedure of observation and data reduction is explained in detail in previous papers (Trevese et al 2007(Trevese et al , 2013. Here we simply recall that the instrument was set in to simultaneously observe the quasar and a star S of comparable magnitude (R = 14.66; Röser et al 2010), located at α 08 31 22.3 δ +52 44 58.6 (J2000), which has been adopted as a calibration reference for both photometry and spectra.…”

“…Currently, the possible explanation of the BAL variability over multi-year timescales consider changes either in the gas ionisation level or in the covering factor, although the second possibility is favoured since: (i) the variations tend to occur in narrow portions of BAL troughs (e.g. Filiz Ak et al 2013); and (ii) they generally do not correlate with changes in the observed continuum (Gibson et al 2008;Capellupo et al 2011; but see Trevese et al 2013).…”

“…In this study, we take advantage of our long-term monitoring programme of high-luminosity quasars (Trevese et al 2007) to improve the statistical database for the bright BAL QSO APM 08279+5255 to update our study on its C IV absorption variability (Trevese et al 2013;Paper I henceforth;Saturni et al 2014) and to obtain estimates of its black hole mass through RM of Si IV and C IV emission lines. APM 08279+5255 is one of the most luminous quasars, discovered in 1998 by Irwin et al (1998).…”

Monitoring the Variability of Intrinsic Absorption Lines in Quasar Spectra, ,

“…In a relatively small number of cases, BALs have transformed into mini-BALs by becoming narrower or have disappeared completely (e.g., Hamann et al 2008;Leighly et al 2009;Krongold et al 2010;Vivek et al 2012;Filiz Ak et al 2012). Possible origins of this time variability include (1) motion of the absorbing gas parcels across our line of sight (e.g., Hamann et al 2008;Gibson et al 2008), (2) changes in the ionization state of the absorber (e.g., Hamann et al 2011;Misawa et al 2007b;Trevese et al 2013), and (3) redirection of photons around the parcels of gas that make up the absorber by scattering material of variable optical depth, resulting in time-variable dilution of the absorption troughs (e.g., Lamy & Hutsemékers 2004). None of these mechanisms are applicable to intervening absorbers because they have much larger sizes and lower densities compared to intrinsic absorbers as discussed in Narayanan et al (2004).…”

Optical variability properties of mini-BAL and NAL quasars

“…Gibson et al (2008) found no correlations between quasars and absorption lines variability in 13 BAL quasars. On the other hand, Trévese et al (2013) simultaneously monitored the equivalent widths (EWs) of BALs and the ultraviolet (UV) luminosities of their host quasars (i.e., ionizing photon density) and found clear correlations in a single quasar, supporting the VIS scenario. The VIS scenario has not been tested in mini-BAL / NAL quasars and is still being debated.…”