Suzaku Observation of Strong Fluorescent Iron Line Emission from the Young Stellar Object V1647 Ori during Its New X-ray Outburst

TL;DR

The Suzaku satellite observed a young stellar object, V1647 Ori, during an X-ray outburst, revealing strong fluorescent iron emission and variability, indicating changes in circumstellar material and accretion processes.

Contribution

This study presents the first detection of a large equivalent width fluorescent iron line from V1647 Ori during its outburst, highlighting changes in circumstellar structure over time.

Findings

Detected strong fluorescent iron Kalpha line with ~600 eV EW.

Observed significant X-ray flux variability during the outburst.

Indications of changing circumstellar material between 2005 and 2008.

Abstract

The Suzaku X-ray satellite observed the young stellar object V1647 Ori on 2008 October 8 during the new mass accretion outburst reported in August 2008. During the 87 ksec observation with a net exposure of 40 ks, V1647 Ori showed a high level of X-ray emission with a gradual decrease in flux by a factor of 5 and then displayed an abrupt flux increase by an order of magnitude. Such enhanced X-ray variability was also seen in XMM-Newton observations in 2004 and 2005 during the 2003-2005 outburst, but has rarely been observed for other young stellar objects. The spectrum clearly displays emission from Helium-like iron, which is a signature of hot plasma (kT ~5 keV). It also shows a fluorescent iron Kalpha line with a remarkably large equivalent width of ~600 eV. Such a large equivalent width suggests that a part of the incident X-ray emission that irradiates the circumstellar material and/or the stellar surface is hidden from our line of sight. XMM-Newton spectra during the 2003-2005 outburst did not show a strong fluorescent iron Kalpha line, so that the structure of the circumstellar gas very close to the stellar core that absorbs and re-emits X-ray emission from the central object may have changed in between 2005 and 2008. This phenomenon may be related to changes in the infrared morphology of McNeil's nebula between 2004 and 2008.