Title: ROSAT AND FOLLOW-UP INFRARED OBSERVATIONS OF THE X-RAY BURSTER KS 1731-260
Abstract: We report on the ROSAT HRI (High Resolution Im- ager) observation of the X-ray burster KS 1731-260. The ob- servation was split in two parts; the rst took place in 1995, March 16 lasting for 1 kilosecond and the second one be- tween September 3rd and 14th, 1996 for about 5 kiloseconds. In both observations, KS 1731-260 was clearly detected with a count rate of 0.82 and 7.9ctss respectively. From the rst ob- servation we found that the X-ray source is located at a position =1 7 h 34 mn 13.5 s and = 26 05' 16.8 (equinox 2000) with an associated error radius of 10.1 arcsec (90% condence level combining the attitude and centroid uncertainties). The position derived from the second part of the observation is con- sistent with the previous one. The ROSAT HRI position rules out the two counterparts that have been proposed so far. Our CFHT J and H infrared imaging of the HRI error box reveals at least 13 possible candidates. As expected from a comparison with other X-ray bursters, the upper limits derived for the in- frared brightness of KS 1731-260 imply the presence of a low mass companion for the neutron star. WealsoreportonarenedspectralanalysisofthePSPCdata taken during the all sky survey in September 1990. These data, together with data recorded by TTM and PCA/RXTE indicate that the column density towards KS 1731-260 varies between 1t o 610 22 H atoms cm 2 ; thus suggesting that the source is characterized by variable intrinsic absorption. The change in the HRI count rate could be better explained by a change in the column density between the two observations rather than by a true source intensity variation. The numerous detections of the source since its discovery in 1988 together with its re- centmonitoringbytheRXTE/ASMshowthatKS 1731-260 isa persistent source rather than a soft X-ray transient, as originally thought.
Publication Year: 1998
Publication Date: 1998-01-01
Language: en
Type: article
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Cited By Count: 4
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