Discovery of a fast, broad, transient outflow in NGC 985

¹ XMM-Newton Science Operations Centre, ESAC, Camino Bajo del Castillo s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
e-mail: jebrero@sciops.esa.int
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
⁴ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 2 October 2015
Accepted: 18 November 2015

Abstract

Aims. We observed the Seyfert 1 galaxy NGC 985 on several occasions to search for variability in its UV and X-ray absorption features to establish their location and physical properties.

Methods. We used XMM-Newton to obtain X-ray spectra using the EPIC-pn camera, and the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) to obtain UV spectra. Our observations were simultaneous and span timescales of days to years.

Results. We find that the soft X-ray obscuration that absorbed the low energy continuum of NGC 985 in August 2013 diminished greatly by January 2015. The total X-ray column density decreased from 2.1 × 10²² cm^-2 to ~6 × 10²¹ cm^-2. We also detect broad, fast UV absorption lines in COS spectra obtained during the 2013 obscuration event. Lines of C iii*, Lyα, Si iv, and C iv with outflow velocities of −5970 km s^-1 and a full-width at half-maximum of 1420 km s^-1 are prominent in the 2013 spectrum, but have disappeared in all but Lyα in the 2015 spectra. The ionization state and the column density of the UV absorbing gas is compatible with arising in the same gas as that causing the X-ray obscuration. The high velocity of the UV-absorbing gas suggests that the X-ray obscurer and the associated UV outflow are manifestations of an accretion disk wind.