Correcting the Contamination of Second-order Spectra: Improving Hα Measurements in Reverberation Mapping Campaigns

Abstract

Long-term spectroscopic monitoring campaigns on active galactic nuclei (AGNs) provide a wealth of information about its interior structure and kinematics. However, a number of the observations suffer from the contamination of second-order spectra (SOS) which will introduce some undesirable uncertainties at the red side of the spectra. In this paper, we test the effect of SOS and propose a method to correct it in the time domain spectroscopic data using the simultaneously observed comparison stars. Based on the reverberation mapping (RM) data of NGC 5548 in 2019, one of the most intensively monitored AGNs by the Lijiang 2.4 m telescope, we find that the scientific object, comparison star, and spectrophotometric standard star can jointly introduce up to similar to 30% SOS for Grism 14. This irregular but smooth SOS significantly affects the flux density and profile of the emission line, while having little effect on the light curve. After applying our method to each spectrum, we find that the SOS can be corrected effectively. The deviation between corrected and intrinsic spectra is similar to 2%, and the impact of SOS on time lag is very minor. This method makes it possible to obtain the H alpha RM measurements from archival data provided that the spectral shape of the AGN under investigation does not have a large change.

References in corpus (22)

• Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• The Low-Luminosity End of the Radius-Luminosity Relationship for Active Galactic Nuclei
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• Reverberation Mapping Measurements of Black Hole Masses in Six Local Seyfert Galaxies
• Supermassive black holes with high accretion rates in active galactic nuclei: I. First results from a new reverberation mapping campaign
• The Lick AGN Monitoring Project: Reverberation Mapping of Optical Hydrogen and Helium Recombination Lines
• The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
• The Sloan Digital Sky Survey Reverberation Mapping Project: First Broad-line Hbeta and MgII Lags at z>~0.3 from six-Month Spectroscopy
• The Lick AGN Monitoring Project: Velocity-Delay Maps from the Maximum-Entropy Method for Arp 151
• Reverberation Mapping of Optical Emission Lines in Five Active Galaxies
• Velocity-resolved reverberation mapping of five bright Seyfert 1 galaxies
• Supermassive black holes with high accretion rates in active galactic nuclei: X. Optical variability characteristics
• Reverberation Mapping of Changing-look Active Galactic Nucleus NGC 3516
• Velocity-resolved Reverberation Mapping of Changing-look Active Galactic Nucleus NGC~4151 During Outburst Stage: Evidence for Kinematics Evolution of Broad-line Region
• Velocity-resolved Reverberation Mapping of Changing-look AGN NGC 2617
• The Lick AGN Monitoring Project 2016: Dynamical Modeling of Velocity-Resolved H\b{eta} Lags in Luminous Seyfert Galaxies
• Supermassive Black Hole and Broad-line Region in NGC~5548: Results from Five-season Reverberation Mapping
• The black hole mass of the $z=2.805$ multiply imaged quasar SDSS J2222+2745 from velocity-resolved time lags of the CIV emission line
• Quasi-simultaneous Spectroscopic and Multi-band Photometric Observations of Blazar S5 0716+714 during 2018-2019
• Multi-wavelength Variation Phenomena of PKS 0735+178 on Diverse Timescale
• A correction method for the telluric absorptions and application to Lijiang Observatory