IGR J16318-4848: an X-ray source in a dense envelope?

Authors:
M. Revnivtsev (1,2),
S. Sazonov (1,2),
M. Gilfanov (1,2),
R. Sunyaev (1,2) ((1)-MPA, Garching, Germany;(2)- IKI, Moscow, Russia)

Comments: Accepted for publication in Astronomy Letters

The hard X-ray source IGR J16318-4848 was recently discovered by the INTEGRAL
observatory (Courvoisier et al.) and subsequently uncovered in archival data of
ASCA observations in 1994 (Murakami et al.). We present results of a detailed
analysis of the ASCA data. The spectrum of the source in the 0.5–10 keV band
is extraordinarily hard and is virtually unobservable below 4 keV because of
strong photoabsorption NHL L>4e23 cm^-2. The 4–10 keV emission is dominated by
a Kalpha line of neutral or weakly ionized iron with an equivalent width of
~2.5 keV. There is also an indication for a second line at ~7 keV. Our
analysis of archival observations of the IGR J16318-4848 infrared counterpart,
discovered by Foschini et al., shows that the point source is detected at
different wavelengths in the 1–15 micron range. The available data suggest
that IGR J16318-4848 is an X-ray binary system enshrouded by a dense envelope.
It is possible that the source is a wind-fed high-mass X-ray binary similar to
GX 301-2. We argue that IGR J16318-4848 might be the first representative of a
previously unknown population of highly absorbed galactic X-ray sources, which
remained undetected with X-ray missions before INTEGRAL.

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