Letter to the Editor

Variable oxygen emission from the accretion disk of Mrk 110

¹ Department of Physics, Institute for Astrophysics and Computational Sciences, The Catholic University of America, Washington, DC 20064, USA
e-mail: james.n.reeves456@gmail.com
² INAF, Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, LC, Italy
³ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁴ European Space Agency (ESA), European Space Astronomy Centre (ESAC), 28691 Villanueva de la Cañada, Madrid, Spain

Received: 31 March 2021
Accepted: 16 April 2021

Abstract

Six XMM-Newton observations of the bright narrow line Seyfert 1, Mrk 110, from 2004–2020, are presented. The analysis of the grating spectra from the Reflection Grating Spectrometer (RGS) reveals a broad component of the He-like Oxygen (O VII) line, with a full width at half maximum of 15 900 ± 1800 km s⁻¹ measured in the mean spectrum. The broad O VII line in all six observations can be modelled with a face-on accretion disk profile, where from these profiles the inner radius of the line emission is inferred to lie between about 20–100 gravitational radii from the black hole. The derived inclination angle, of about 10 degrees, is consistent with studies of the optical Broad Line Region in Mrk 110. The line also appears variable and for the first time, a significant correlation is measured between the O VII flux and the continuum flux from both the RGS and EPIC-pn data. Thus the line responds to the continuum, being brightest when the continuum flux is highest, similar to the reported behaviour of the optical He II line. The density of the line emitting gas is estimated to be n_e ∼ 10¹⁴ cm⁻³, consistent with an origin in the accretion disk.