INTEGRAL maps the Galactic center field in standard X-rays
INTEGRAL, with onboard its unique IBIS/ISGRI gamma-ray imager, provided
us with the first deep (down to ~0.2 mCrab) hard X-ray (> 20 keV) mosaic
images of the sky, with a wide coverage of the Galaxy and an angular
resolution (~12 arcmin) sufficient to resolve point sources (see Picture of
the Month
May 2003,
September 2003,
November 2003,
April 2004,
August 2005,
January 2007,
July 2010,
August 2012 and
December 2015).
Several hundreds of new X-ray sources (accreting black holes, neutron stars
and white dwarfs, and many supermassive black holes in active galactic nuclei)
have been discovered, in addition to ~250 previously known sources (see,
e.g., Picture of the Month
February 2007 and
October 2009).
These discoveries stimulated successful new studies of accretion process in
X-ray binaries and AGN.
Shown here are the mosaic images of the Galactic center field (18x11 deg in
size), which were obtained by another instrument on board INTEGRAL - the
Joint European X-ray Monitor (JEM-X), sensitive in the softer (standard)
X-ray band (3-35 keV). The images were produced in the course of the first
deep X-ray survey of the field on the basis of 10 years of JEM-X observations,
during 2003-2013. A total of 105 sources are detected in the Galactic center
region of 20 deg in radius. Most of them are low-mass X-ray binaries (LMXBs),
which allows to reproduce and analyze the luminosity function of Galactic LMXBs.
The positions of 32 sources located within the shown images are indicated by
yellow circles; the Galactic center itself is indicated by a green circle. The
two images correspond to two different energy bands, i.e., 5-10 (top) and
10-25 keV (bottom). It can be seen that some of the sources, for example,
XTE J1739-285, SLX 1746-331, SLX 1746-370, GRS 1747-312, are brighter in the
softer X-ray image, while others, such as GRS 1734-292 and GRS 1758-258, are
brighter in the harder X-ray one.
While JEM-X is supplementary to the IBIS instrument (and the other gamma-ray
instrument onboard INTEGRAL, the spectrometer SPI), the better (3 arcmin FWHM)
angular resolution gives it obvious advantage in the crowded fields like that
of the Galactic center. The JEM-X survey is of great importance: so far, no
surveys of such a large area (more than 1200 sq. deg) at a sufficiently high
sensitivity (down to ∼1 mCrab) and a good angular resolution (arcmin) have
been conducted in the standard X-ray band. Thus, INTEGRAL/JEM-X adds another
achievement to its list.
