March 2, 2017

Sources and X-ray cosmic background

228 gamma-ray sources have been discovered by Integral, a bid addition to previous catalogues. 20 of these sources are new objects.

The top image below shows the sky distribution of four of the main soft gamma-ray source populations observed in the 3rd Integral/IBIS survey catalogue. This newly-released catalogue contains 421 sources. Of the known systems, the low-mass X-ray binaries (LMXB) are old systems mainly populating the galactic bulge, the high-mass X-ray binaries (HMXB) are younger systems seen along the Galactic plane, and the active galactic nuclei (AGN) are extragalactic sources seen over the whole sky. Around one out of four of the sources seen by Integral are unidentified, and their distribution is also shown. The bottom picture is a false-colour image of the central region of our galaxy. This is a composite image based on all-sky IBIS/ISGRI maps in three energy windows (between 17 and 100 keV) and represents the true 'X-ray colours' of the sources. Red sources are dominated by emission below 30 keV, while blue sources have harder spectra, emitting strongly above 40 keV.

3rd INTEGRAL IBIS/ISGRI Catalog Skymap
3rd Integral IBIS/ISGRI Catalogue Skymap
(Credits IBIS survey team: ESA).

A fourth version of the gamma sources IBIS/Integral catalogue was published in July 2010, containing 331 new sources when compared to the 3rd catalogue. This version of the catalogue now contains more than 700 gamma sources. This latest version represents a major expansion in scope compared to its three predecessors.

Sky distribution of new sources in 4th INTEGRAL/IBIS catalogue, © ESA
Sky distribution of sources in 4th Integral/IBIS catalogue
showing only the 331 new gamma sources, © ESA

Moreover, Integral has recently discovered a new class of astronomical object: a pulsar with an extremely high magnetic field, 1 billion times stronger than what can be produced in the laboratory. IGR J00291+5934, a new millisecond pulsar, has been also detected.

Carte complete des trous noirs realisee par INTEGRAL
Integral black hole census
(Credits: ESA/IKI Integral team and ESA/Eumetsat Meteosat satellite)

This all-sky image was obtained by ESA's Integral gamma-ray observatory over four years of operations and is an important step towards estimating how many black holes there are in the Universe. The concentration of sources along the mid plane of the image is due to neutron stars and stellar mass black holes in our Galaxy, while the majority of sources located far away from the Galactic plane are super-massive black holes in other galaxies. The Cosmic X-ray Background is composed of the emission of tens of millions of similar objects much further away from us.

Overlaid is an Earth image from ESA/Eumetsat's Meteosat satellite. Using the Earth as a shield to block the emission from the population of distant black holes, astronomers precisely gauged the X-ray and gamma-ray background.

Evaluation du fond cosmique dans la gamme des Rayons-X
Cosmic X-Ray Background derived from taking a picture of Earth
and setting its emission in the X-ray part of the spectrum,
as null (with corrections due to albedo among other things).
(Credits: INTEGRAL team CESR)

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