Research Note

The stability of the optical flux variation gradient for 3C 120^⋆

¹ Astronomisches Institut, Ruhr–Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany
e-mail: ramolla@astro.rub.de
² Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Casilla 1280, Antofagasta, Chile

Received: 29 June 2015
Accepted: 6 August 2015

Abstract

New B- and V-band monitoring in 2014–2015 reveals that the Seyfert 1 Galaxy, 3C 120, has brightened by a magnitude of 1.4, compared to our campaign that took place in 2009–2010. This allowed us to check for the debated luminosity and time-dependent color variations claimed for SDSS quasars. For our 3C 120 data, we find that the B/V flux ratio of the variable component in the bright epoch is indistinguishable from the faint one. We do not find any color variability on different timescales ranging from about 1 to 1800 days. We suggest that the luminosity and time-dependent color variability is an artifact caused by analyzing the data in magnitudes instead of fluxes. The flux variation gradients of both epochs yield consistent estimates of the host galaxy contribution to our 7''̣5 aperture. These results confirm that the optical flux variation gradient method works well for Seyfert galaxies.