COMIS Scientific results

COMIS has observed the X-ray sky for a net total exposure of 3 weeks. Most of the observations were carried out in 1989 (36%), 1992 (17%) and 1994 (15%). The main targets were the Galactic Center region (24%), the Large Magellanic Cloud (9%) and the Vela X-1 and Cygnus regions.

COMIS has discovered 7 new X-ray transients and positioned them with an accuracy of 1 arcmin or better. These transients are X-ray binaries that only occasionally (i.e., once every 1 to 100 years) flare up in X-rays, after mass is accreted by a neutron star or black hole. All of these transients except one are in the Galactic center field. The discovery rate in this field is one every 3 days of observation. This is a rate which was later confirmed by similar observations with the BeppoSAX Wide Field Cameras. Two of the six sources were also confirmed as neutron star systems through the detection of type-I X-ray bursts from the same position. The one transient outside the Galactic center field was later discovered to be an 18 sec pulsar.

COMIS detected at least 14 type-I bursts from 6 low-mass X-ray binaries. Two of these were thus newly discovered. One of those is one of the most frequent X-ray bursters in the whole Galaxy.

COMIS did not detect any gamma-ray burst. Based on detection rates measured with the BeppoSAX Wide Field Cameras, one would expect COMIS to have detected 0.1 gamma-ray burst in its entire lifetime, so this is not an unexpected result.

The COMIS data was the basis for as much as 9 PhD theses (5 in Russia, 3 in the UK, and 1 in the Netherlands).

Jean in 't Zand, SRON, February 12, 2001