RX J1301.9+2747: A Highly Variable Seyfert Galaxy with Extremely Soft X-ray Emission

TL;DR

This study analyzes the highly variable and ultrasoft X-ray emission of Seyfert galaxy RX J1301.9+2747, revealing distinct spectral states and providing insights into accretion disk and corona characteristics around black holes.

Contribution

It presents the first detailed temporal and spectral analysis of RX J1301.9+2747, highlighting its unique steep spectrum and rapid state transitions, advancing understanding of ultrasoft AGN behavior.

Findings

Quiescent state has an unprecedentedly steep photon index (~7.1).

State transitions occur within 1-2 ks, with count rate changes by factor of 5-7.

Spectrum dominated by a ~30-40 eV black body component in quiescent state.

Abstract

In this paper we present a temporal and spectral analysis of X-ray data from the XMM and Chandra observations of the ultrasoft and variable Seyfert galaxy RX J1301.9+2747. In both observations the source clearly displays two distinct states in the X-ray band, a long quiescent state and a short flare (or eruptive) state which differs in count rates by a factor of 5--7. The transition from quiescent to flare state occurs in 1--2 ks. We have observed that the quiescent state spectrum is unprecedentedly steep with a photon index Gamma~7.1, and the spectrum of the flare state is flatter with Gamma~4.4. X-rays above 2 keV were not significantly detected in either state. In the quiescent state, the spectrum appears to be dominated by a black body component of temperature about ~30--40 eV, which is comparable to the expected maximum effective temperature from the inner accretion disk. The quiescent state however, requires an additional steep power-law, presumably arising from the Comptonization by transient heated electrons. Optical spectrum from the Sloan Digital Sky Survey shows Seyfert-like narrow lines for RX J1301.9+2747, while the HST imaging reveals a central point source for the object. In order to precisely determine the hard X-ray component, future longer X-ray observations are required. This will help constrain the accretion disk model for RX J1301.9+2747, and shed new light into the characteristics of the corona and accretion flows around black holes.