Swift, NuStar and XMM-Newton observations of the NLS1 galaxy RX J2317.8–4422 in an extreme X-ray low flux state

Abstract

We report the discovery of RX J2317.8&ndash;4422 in an extremely low X-ray flux state by the <em>Neil Gehrels Swift</em> observatory in 2014 April/May. In total, the low-energy X-ray emission dropped by a factor of 100. We have carried out multiwavelength follow-up observations of this narrow-line Seyfert 1 galaxy. Here we present observations with <em>Swift</em>, <em>XMM&ndash;Newton</em>, and <em>NuSTAR</em> in 2014 October and November and further monitoring observations by <em>Swift</em> from 2015 to 2018. Compared with the beginning of the <em>Swift</em> observations in 2005, in the November 2014 <em>XMM&ndash;Newton</em> and <em>NuSTAR</em> observations RX J2317&ndash;4422.8 dropped by a factor of about 80 in the 0.3&ndash;10&thinsp;keV band. While the high-state <em>Swift</em> observations can be interpreted by a partial covering absorption model with a moderate absorption column density of <strong><em>N</em>_H</strong> = 5.4 &times; 10²²&thinsp;cm^&minus;2 or blurred reflection, due to the dominating background at energies above 2&thinsp;keV the low-state <em>XMM&ndash;Newton</em> data cannot distinguish between different multicomponent models and were adequately fitted with a single power-law model. We discuss various scenarios like a long-term change of the accretion rate or absorption as the cause for the strong variability seen in RX J2317.8&ndash;4422.