An extraordinary new celestial X-ray source

The discovery of an extraordinary new X-ray source detected during a guest observer programme carried out with the Einstein X-ray Observatory is reported here. The object, designated G109.1-1.0, was found using the imaging proportional counter detector (IPC) on 17 December 1979. The IPC is sensitive to X-ray photons with energies between 0.1 and 4.5 keV. A longer exposure (3.6×10³ s) IPC picture of a 1° field of view centred on the SNR was obtained on 8 July 1980 and is shown in Fig. 1. The picture shows a clear semicircular arc with an angular diameter of 36 arc min which appears to be the outer shell of the SNR. The resolution of the picture is 1 arc min. At the exact centre of the curvature of the shell is a strong compact source which we designate GF2259+586. The X-ray coordinates of GF2259+586 are RA=22 h 59 min 02.5 s and dec = 58° 36' 38''. The 1 arc min accuracy of the coordinates is limited by systematic calibration errors in the IPC detector. Emerging from the east side of the central source is a jet-like structure which curves northwards in another continuous arc smoothly joining the outer shell. On closer inspection, the jet appears to bifurcate with a second component continuing radially outwards from the central compact source. This very unusual structure has parallels with the W50 SNR with its central X-ray source SS433 and jet (F. D. Seward, personal communication).