Protostars -- Oral Presentation
The First Definite Detection of X-rays from an Extremely Young
Protostar
Kenji Hamaguchi, NASA/GSFC/EUD
M.F. Corcoran, R. Petre, N.E. White (NASA/GSFC), B. Stelzer (INAF), K. Nedachi, N. Kobayashi (Tokyo Univ.), A.T. Tokunaga (University of Hawaii)
Class I protostars exhibit powerful X-ray emission. Their
X-ray activity can exceed those of older stars such as T-Tauri and
main-sequence stars. Without surface convection to drive a solar-type
dynamo mechanism, X-ray activity is suspected to be driven by magnetic
activity linked to the mass accretion process. Mass accretion is thought
to be more intense in the earliest Class 0 protostar phase, but X-ray
emission from them has not been conclusively detected so far. This could
be due to stronger X-ray absorption to their protostellar cores, or a
certain transition in high energy activity between the Class 0 and Class
I phases. With two XMM-Newton observations on March 2003, we detected
for the first time strong X-ray emission from an extremely embedded
source in the R Corona Australis star forming core, IRS 7 region.
(Hamaguchi et al. 2005, ApJ, 623, 291) The source has the radio counterpart
10E (IRS7B) but no near-IR counterpart. These facts plus the strong
X-ray absorption of n$_H$ $\sim3$e23 $cm^{-2}$ (equivalent to A$_V$
$\sim180$m) indicate that the source is a Class 0 or perhaps a Class 0/I
protostar. The X-ray spectrum showed thermal emission with kT= 3-4 keV
with the luminosity up to 10$^{31.2}$ ergs/s. The light curve showed
gradual flux increase by a factor of two during 30 ksec, unlike solar-type
magnetically driven X-ray flares, which have smaller variation timescales.
The source was 10-100 times fainter during Chandra observations which
occurred before and after the XMM-Newton observations. The flux enhancement
on month timescales might be driven by sporadic mass accretion episode,
while the short-term variation during the XMM-Newton observation could
be related to the proto-stellar core rotation. We will also discuss the
relation to the sub-millimeter outflow activity of Class 0 protostars
and absence of X-ray activity on other Class 0 protostars.