SIMBAD references

This Letter presents the serendipitous discovery of a large arc in an X-ray selected cluster detected in the ROSAT North Ecliptic Pole (NEP) survey. The cluster, associated with Abell 2280, is identified as the optical counterpart of the X-ray source RX J1743.5+6341. This object is a medium-distant (z=0.326) and luminous (L_0.5–2keV=5.06x10⁴⁴ergs/s) cluster dominated by a central bright galaxy. The arc is located ∼14" to the North-West of the cD and it is detected in the R and I bands but not in the B band. Photometric and spectroscopic observations of the cluster and of the arc are presented. Other similar discoveries in the course of imaging and spectroscopic surveys of ROSAT are expected in the future.