Studying X-ray reprocessing and continuum variability in quasars: PG 1211+143

TL;DR

This study monitors the quasar PG 1211+143, revealing its low X-ray flux state, significant X-ray variability, and potential reprocessing of X-rays into optical/UV light, providing insights into accretion disk behavior.

Contribution

First detailed multiwavelength monitoring of PG 1211+143 during a low X-ray flux state, analyzing X-ray reprocessing and variability patterns in a Narrow-Line Seyfert 1 galaxy.

Findings

PG 1211+143 was in a low X-ray flux state at the start of observations.

X-ray variability was high, optical/UV variability was minimal.

Time lags between X-ray and optical/UV bands scale as ~lambda^(4/3).

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 February to July, 2007) and with Swift (X-ray photometry/spectroscopy and UV/Optical photometry; between March and May, 2007). We found PG 1211+143 in a historical low X-ray flux state at the beginning of the Swift monitoring campaign in March 2007. 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 onto the disk. 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 disk, powering the quasar. The time lags between the X-ray and the optical/UV light curves, ranging from ~2 to ~18 days for the different wavebands, scale approximately as ~lambda^(4/3), but appear to be somewhat larger than expected for this object, taking into account its accretion disk parameters. Possible implications for the location of the X-ray irradiating source are discussed.