During the Fall of this year, ESA's gamma-ray observatory INTEGRAL
was observing the Galactic centre region for about 4 weeks as part
of its first Key Programme. By chance it spotted a rare type of
gamma-ray outburst on October 17th, 2006, at 1 degree from the
Galactic Centre. Within the next few days follow-up observations
were carried out by several X-ray observatories as well as in the
optical. The development of the outburst with time allows to
recognize the signature of a large increase of accretion rate on a
new compact object that was never observed before. This compact
object is most probably a new black-hole.
The largest image (top left) shows the IBIS/ISGRI image of the
field including the new erupting source, named IGR
J17497-2821. The images on the right show the INTEGRAL source as
observed in the X-rays by XMM-Newton (top right) and in the
optical (I filter) by the "Leonhard Euler" telescope from La
Silla, Chile four days after the discovery. The figures below
shows the lightcurve of the X-ray Nova, as measured by INTEGRAL,
with a fast rise over 5 days and a slow exponential decay over two
weeks.The spectral characteristics indicate an outburst in a
low-hard state that is expected if most accretion occurred through
the hot corona of the accretion disk.
This discovery highlights the unique capability of INTEGRAL in
monitoring the inner Galaxy at hard X-rays.
