X-ray Production by V1647 Ori During Optical Outbursts

Kavli Affiliate: David Principe

| First 5 Authors: William K. Teets, David A. Weintraub, Nicolas Grosso, David Principe, Joel H. Kastner

| Summary:

The pre-main sequence star V1647 Ori has recently undergone two
optical/near-infrared (OIR) outbursts that are associated with dramatic
enhancements in the stellar accretion rate. Our intensive X-ray monitoring of
this object affords the opportunity to investigate whether and how the intense
X-ray emission is related to pre-MS accretion activity. Our analysis of all
fourteen Chandra X-ray Observatory observations of V1647 Ori demonstrate that
variations in the X-ray luminosity of V1647 Ori are correlated with similar
changes in the OIR brightness of this source during both (2003-2005 and 2008)
eruptions, strongly supporting the hypothesis that accretion is the primary
generation mechanism for the X-ray outbursts. Furthermore, the Chandra
monitoring demonstrates that the X-ray spectral properties of the second
eruption were strikingly similar to those of the 2003 eruption. We find that
X-ray spectra obtained immediately following the second outburst – during which
V1647 Ori exhibited high X-ray luminosities, high hardness ratios, and strong
X-ray variability – are well modeled as a heavily absorbed (N_H ~ 4×10^22
cm^-2), single-component plasma with characteristic temperatures (kT_X ~ 2-6
keV) that are consistently too high to be generated via accretion shocks but
are in the range expected for plasma heated by magnetic reconnection events. We
also find that the X-ray absorbing column has not changed significantly
throughout the observing campaign. Since the OIR and X-ray changes are
correlated, we hypothesize that these reconnection events either occur in the
accretion stream connecting the circumstellar disk to the star or in
accretion-enhanced protostellar coronal activity.

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