The Seyfert AGN RX J0136.9-3510 and the Spectral State of Super Eddington Accretion Flows

TL;DR

This study identifies unique X-ray variability and spectral features in the AGN RX J0136.9-3510, suggesting it exemplifies a new class of super-Eddington accretion flows with extreme spectral and variability properties.

Contribution

The paper reports the discovery of distinctive energy-dependent variability and spectral characteristics in RX J0136.9-3510, linking it to a potential new class of highly accreting AGN with super-Eddington rates.

Findings

RX J0136.9-3510 shows increasing variability from 0.3 to 2 keV, then plateaus.

Its spectrum is dominated by a large soft excess similar to RE J1034+396.

The AGN has an Eddington ratio of about 2.7, indicating super-Eddington accretion.

Abstract

We have carried out a survey of long 50ks XMM-Newton observations of a sample of bright, variable AGN. We found a distinctive energy dependence of the variability in RXJ0136.9-3510 where the fractional variability increases from 0.3 to 2 keV, and then remains constant. This is in sharp contrast to other AGN where the X-ray variability is either flat or falling with energy, sometimes with a peak at $\sim$~2 keV superimposed on the overall trend. Intriguingly these unusual characteristics of the variability are shared by one other AGN, namely RE J1034+396, which is so far unique showing a significant X-ray QPO. In addition the broad band spectrum of RXJ0136.9-3510 is also remarkably similar to that of RE J1034+396, being dominated by a huge soft excess in the EUV-soft X-ray bandpass. The bolometric luminosity of RX J0136.9-3510 gives an Eddington ratio of about 2.7 for a black hole mass (from the H beta line width) of $7.9 \times 10^{7}M_{\sun}$. This mass is about a factor of 50 higher than that of RE J1034+396, making any QPO undetectable in this length of observation. Nonetheless, its X-ray spectral and variability similarities suggest that RE J1034+396 is simply the closest representative of a new class of AGN spectra, representing the most extreme mass accretion rates.