Research Note

San Pedro Mártir observations of microvariability in obscured quasars

¹ Instituto de Astrofísica de Canarias, C/via Lactea s/n, 38205 La Laguna, Spain
e-mail: jana@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38207 La Laguna, Spain
³ Centro de Estudios de Física del Cosmos de Aragón, 44001 Teruel, Spain
⁴ Instituto de Astronomía, Universidad Nacional Autónoma de México, 04310 México D.F., Mexico
⁵ Instituto de Astrofísica de Canarias − Universidad de La Laguna, CEI Canarias: Campus Atlántico Tricontinental, 38205 La Laguna, Spain
⁶ Instituto de Física de Cantabria (CSIC-Universidad de Cantabria), 39005 Santander, Spain
⁷ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁸ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁹ ASPID Association, Ap. correos 412, La Laguna, Spain
¹⁰ XMM/Newton Science Operations Centre, ESAC/ESA, Villanueva de la Cañada, 28691 Madrid, Spain
¹¹ Ingeniería de Sistemas para la Defensa de España (Isdefe), Madrid, Spain
¹² Centro de Astrobiología, INTA-CSIC, Villanueva de la Cañada, 28850 Madrid, Spain
¹³ Herschel Science Centre, ESAC/ESA, Villanueva de la Cañada, 28692 Madrid, Spain

Received: 24 February 2015
Accepted: 20 April 2015

Abstract

Fast brightness variations are a unique tool to probe the innermost regions of active galactic nuclei (AGN). These variations are called microvariability or intra-night variability, and this phenomenon has been monitored in samples of blazars and unobscured AGNs. Detecting optical microvariations in targets hidden by the obscuring torus is a challenging task because the region responsible for the variations is hidden from our sight. However, there have been reports of fast variations in obscured Seyfert galaxies in X-rays, which rises the question whether microvariations can also be detected in obscured AGNs in the optical regime. Because the expected variations are very small and can easily be lost within the noise, the analysis requires a statistical approach. We report the use of a one-way analysis of variance, ANOVA, with which we searched for microvariability. ANOVA was successfully employed in previous studies of unobscured AGNs. As a result, we found microvariable events during three observing blocks: in two we observed the same object (Mrk 477), and in another, J0759+5050. The results on Mrk 477 confirm previous findings. However, since Mrk 477 is quite a peculiar target with hidden broad-line regions, we cannot rule out the possibility that we have serendipitously chosen a target prone to variations.