Studying X-ray reprocessing and continuum variability in quasars: PG 1211+143 |
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Authors: | R Bachev D Grupe S Boeva E Ovcharov A Valcheva E Semkov Ts Georgiev L C Gallo |
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Institution: | Institute of Astronomy, Bulgarian Academy of Sciences, Sofia 1784, Bulgaria;Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA;Department of Astronomy, Sofia University, 5 James Bourchier Street, 1164 Sofia, Bulgaria;Department of Astronomy and Physics, Saint Mary's University, Halifax, NS B3H 3C3, Canada |
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Abstract: | We present the results from a monitoring campaign of the Narrow-Line Seyfert 1 galaxy PG 1211+143. The object was monitored with ground-based facilities ( UBVRI photometry; from 2007 February to July) and with Swift X-ray photometry/spectroscopy and ultraviolet (UV)/optical photometry; between 2007 March and May]. We found PG 1211+143 in a historical low X-ray flux state at the beginning of the Swift monitoring campaign in 2007 March. It is seen from the light curves that while violently variable in X-rays, the quasar shows little variations in optical/UV bands. The X-ray spectrum in the low state is similar to other narrow-line Seyfert 1 galaxies during their low states and can be explained by a strong partial covering absorber or by X-ray reflection on to the disc. With the current data set, however, it is not possible to distinguish between both scenarios. The interband cross-correlation functions indicate a possible reprocessing of the X-rays into the longer wavelengths, consistent with the idea of a thin accretion disc, powering the quasar. The time lags between the X-ray and the optical/UV light curves, ranging from ~2 to ~18 d for the different wavebands, scale approximately as ~λ4/3 , but appear to be somewhat larger than expected for this object, taking into account its accretion disc parameters. Possible implications for the location of the X-ray irradiating source are discussed. |
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Keywords: | accretion accretion discs galaxies: active galaxies: photometry quasars: general quasars: individual: PG 1211+143 |
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