Broad-line region structure and line profile variations in the changing look AGN HE 1136-2304

Abstract

Aims.A strong X-ray outburst was detected in HE 1136-2304 in 2014. Accompanying optical spectra revealed that the spectral type has changed from a nearly Seyfert 2 type (1.95), classified by spectra taken 10 and 20 years ago, to a Seyfert 1.5 in our most recent observations. We seek to investigate a detailed spectroscopic campaign on the spectroscopic properties and spectral variability behavior of this changing look AGN and compare this to other variable Seyfert galaxies. Methods. We carried out a detailed spectroscopic variability campaign of HE 1136-2304 with the 10 m Southern African Large Telescope (SALT) between 2014 December and 2015 July. Results. The broad-line region (BLR) of HE 1136-2304 is stratified with respect to the distance of the line-emitting regions. The integrated emission line intensities of Hα, Hβ, He i λ5876, and He ii λ4686 originate at distances of 15.0 +4.2 −3.8 , 7.5 +4.6 −5.7 , 7.3 +2.8 −4.4 , and 3.0 +5.3 −3.7 light days with respect to the optical continuum at 4570 Å. The variability amplitudes of the integrated emission lines are a function of distance to the ionizing continuum source as well. We derived a central black hole mass of 3.8 ± 3.1 × 10 7 M ⊙ based on the linewidths and distances of the BLR. The outer line wings of all BLR lines respond much faster to continuum variations indicating a Keplerian disk component for the BLR. The response in the outer wings is about two light days shorter than the response of the adjacent continuum flux with respect to the ionizing continuum flux. The vertical BLR structure in HE 1136-2304 confirms a general trend that the emission lines of narrow line active galactic nuclei (AGNs) originate at larger distances from the midplane in comparison to AGNs showing broader emission lines. Otherwise, the variability behavior of this changing look AGN is similar to that of other AGN.

Spectral changes and BLR kinematics of eruptive changing-look AGN

“…The 2D velocity maps of the Balmer line profiles reveal a faster response of the line wings (0−10 d) in comparison to a slower response of the line centers (10 − 30 d). A similar behaviour is observed in the He I λ5876 and He II λ4686 line (Kollatschny et al, 2018). The resulting kinematics is consistent with thin Keplerian disk BLR models (Horne et al, 2004).…”

“…Evidently, the spectrum of HE 1136-2304 exhibits clear variations of its continuum level. Furthermore, the RMS spectrum cleary shows variations not only in the broad Balmer lines but also -albeit lower -in the very broad higher ionization lines He I λ5876 and He II λ4686 (Kollatschny et al, 2018) 1 . In order to determine the time-lag between continuum and broad emission line variations -a method known as reverberation mapping -we extracted continuum and emission line light curves from all of the spectra.…”

“…We sliced the velocity profiles of the emission lines into segments with a width of v = 400 km s −1 and extracted the light curve for each individual segment. We then correlated these light curves with the 4570Å light curve (Kollatschny et al, 2018). The result is a 2D velocity delay map showing the time delay for each velocity line profile segment.…”

“…As the flux of the narrow emission line [OIII] λ5007 is treated to be constant on time scales of several years, the reduced spectra were calibrated to the absolute [OIII] λ5007 flux given in Reimers et al (1996). For further details on the instrumental setup and the data reduction we refer to Kollatschny et al (2018).…”

Preliminary Spectral Analysis of the NLS1 Galaxy WPVS48

“…Flat field, arc images (xenon and argon lamps) and spectra of standard stars were taken for the reduction and calibration process. The spectra were reduced in a homogeneous way (bias subtraction, cosmic ray correction, flat-field correction, 2D-wavelength calibration, night-sky subtraction and flux calibration) using IRAF reduction packages according to (Kollatschny et al, 2018). No further denoising was performed.…”