X-ray binaries in the galactic plane

The brightest X-ray sources in our galaxy are X-ray binaries. These X-ray binaries are two stars which rotate around each other. One of the two is a normal star; but the other is a collapsed star, such as a neutron star or a black hole, which has about the same mass as our Sun but has shrunk to ten kilometers or less in radius. Material is drawn from the normal star and spirals in via an accretion disk onto the compact star. Intense X-ray emission is released from the inner region of the accretion disk where it falls onto the collapsed star.

In this exercise we are going to use the 2XMM catalogue together with the IPHAS catalogue to search for X-ray binaries in our Galaxy.

The 2XMM Catalogue

The 2XMM catalogue contains those sources detected in X-Ray as part of the Serendipitous Survey carried out with the XMM ESA Observatory. We are going to extract those sources which lie in the IPHAS footprint, i.e. those with galactic coordiantes |b|<5 deg and 30<l<220 deg. In order to do that we use the Query Builder as shown in the image below.

We name the file as xmm_cygb.vot and save it in my VOSpace. The resultant file contains 12791 detections and it can be displayed in TOPCAT by clicking on the resultant file and selecting Send table to TOPCAT (which only appears if TOPCAT is already running). The figure below shows at the left the whole XMM catalogue while at the right a zoom around the Cygnus OB area.

IPHAS Catalogue

For this example we are going to concentrate in the area around Cygnus OB, displayed in the left of the figure above. So we are going to extract all sources in the IPHAS catalogue in this area using again the query builder.

So we are selecting those sources in the area between R.A. 307.5 to 308.6 degrees and Dec between 41 and 42 degrees. The output file name will be again saves in my VOSPace as iphas_cygb.vot and can also be sent to TOPCAT when the query finishes.

Cross match catalogues with TOPCAT

The next step is to cross match the XMM and IPHAS catalogues. With both catalogues obtained above already loaded into TOPCAT click on the Joins menu button and select Pair Match. Then insert the values as shown below. Basically we are selecting all IPHAS sources with a XMM counterpart nearer than 2 arcsec.

The following plot shows in red all IPHAS sources and in blue those with an XMM counterpart. Note that we are not filtering out problematic sources in the IPHAS catalogue because we are only interested in those with a XMM match.