Positional agreement between 3U1706+32 and the cluster of galaxies A2241

Abstract

UNIDENTIFIED X-ray sources at high galactic latitudes have been the subject of much discussion (see ref. 1 and refs therein). We call attention here to the existence of a rich Abell cluster of galaxies in the error box of the Uhuru high galactic latitude source 3U1706+32. The X-ray error box is rather large (9.8 square degrees), and the apparent intensity of the source is Rx=4.1+0.6 counts s−1 in Uhuru counts2. The cluster, Abell 2241, is located at 16 h 57.8 min+32°37′ (1950)3; it belongs to distance group 3 and has an estimated redshift, z ≈ 0.07 (ref. 3). The cluster is of richness group 0 (ref. 3) and has been classified4 as an irregular (I) cluster. The positional agreement between this cluster and 3U1706+32 was not reported in the survey of positional correlations between 3U X-ray sources and Abell clusters of galaxies of distance groups, D≤3, (ref. 5). The cluster A2241 should, therefore, be added as a possible identification to the list5 of 21 clusters which have been tentatively identified with X-ray sources; no additional Abell cluster of distance group 3 or nearer lies within Uhuru2 high galactic latitude error boxes.