The Lick Agn Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves

Abstract

In the Spring of 2011 we carried out a 2.5 month reverberation mapping campaign using the 3 m Shane telescope at Lick Observatory, monitoring 15 low-redshift Seyfert 1 galaxies. This paper describes the observations, reductions and measurements, and data products from the spectroscopic campaign. The reduced spectra were fitted with a multicomponent model in order to isolate the contributions of various continuum and emission-line components. We present light curves of broad emission lines and the AGN continuum, and measurements of the broad Hβ line widths in mean and root-mean square (rms) spectra. For the most highly variable AGNs we also measured broad Hβ line widths and velocity centroids from the nightly spectra. In four AGNs exhibiting the highest variability amplitudes, we detect anticorrelations between broad Hβ width and luminosity, demonstrating that the broad-line region "breathes" on short timescales of days to weeks in response to continuum variations. We also find that broad Hβ velocity centroids can undergo substantial changes in response to continuum variations; in NGC 4593 the broad Hβ velocity shifted by ∼ 250 km s −1 over a one-month duration. This reverberation-induced velocity shift effect is likely to contribute a significant source of confusion noise to binary black hole searches that use multi-epoch quasar spectroscopy to detect binary orbital motion. We also present results from simulations that examine biases that can occur in measurement of broad-line widths from rms spectra due to the contributions of continuum variations and photon-counting noise.

Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-line Analysis for NGC 5548

“…We constructed a separate reference spectrum for each telescope by averaging the highest-S/N spectra in each data set and then broadened the reference spectrum so that the Barth et al (2015) found F var values ranging from 0.5% to 3.3% for individual AGNs in the 2011 Lick AGN Monitoring Project. Figure 2 shows (in black) the mean and rms residual spectra for the MDM data set.…”

“…Both the broad Hβ and He II λ4686 emission lines exhibit strong variations, and the Hβ rms profile appears to have multiple peaks. Traditionally, the rms spectrum is constructed such that the value at each wavelength is taken to be the standard deviation of fluxes from all epochs, but this does not take into account Poisson or detector noise, which may bias the rms profile by a small amount (Barth et al 2015). Park et al (2012b) suggest using the S/N for each spectrum as the weight for that spectrum in calculating the rms, or using a maximum-likelihood method to obtain the rms.…”

“…To more accurately remove the continuum underlying the emission lines and to deblend the broad emission features from each other, we employed the spectral decomposition algorithm described by Barth et al (2015). The components fitted in this procedure include narrow [O III], broad and narrow Hβ, broad (4)) spectra from the MDM data set are shown in black, and the rms spectrum with the AGN and stellar continuum removed is shown in red (see Section 3.1).…”

“…We made several modifications to the spectral fitting procedures used by Barth et al (2015). First, because of the complex line profiles, we used sixth-order Gauss-Hermite functions (van der Marel & Franx 1993) to fit the broad and narrow Hβ and narrow [O III] lines instead of fourth-order functions.…”

The Optical Variability of SDSS Quasars From Multi-Epoch Spectroscopy. Iii. A Sudden Uv Cutoff in Quasar SDSS J2317+0005

“…If the absorbers were large enoughthey could temporarily convert a pure Type 1 AGN into a Type 1.8 or 1.9 by eclipsing the broad components of b H (Osterbrock 1981), making a socalled "changing-look" AGN. To date,only a small number of changing-look Seyfert 1 s have been found, and they all show the nonstellar continuum emission weakening dramatically when the broad line components fade or even disappear (Collin-Souffrin et al 1973; Tohline & Osterbrock 1976;Lyutyj et al 1984;Cohen et al 1986;Storchi-Bergmann et al 1993;Aretxaga et al 1999;Eracleous & Halpern 2001;Denney et al 2014;Sanmartim et al 2014;Barth et al 2015). Even factor of twochanges in broad b H are rare in Seyfert 1ʼs, having been seen in only about 4% of the pairs of repeated observations in a sixyears longmonitoring campaign of 13 AGN (Rosenblatt et al 1992).…”