On the nature of AX J2049.6+2939/AX J2050.0+2914

AX J2049.6+2939 is a compact X-ray source in the vicinity of the southern blow-up region of the Cygnus Loop supernova remnant. This source was the brightest X-ray source inside the Cygnus Loop observed during the ASCA survey project. The X-ray spectrum was well fitted by a power-law function with a photon index of -2.1±0.1. Short-term timing analysis was performed, and no coherent pulsation was found. Follow-up observations with ASCA have revealed a large variation in X-ray intensity by a factor of ≃50, whereas the spectral shape did not change within the statistical uncertainties. In the second ASCA observation, we found another X-ray source, AX J2050.0+2941, to the northeast of AX J2049.6+2939. During the three ASCA observations, the X-ray intensity of AX J2050.0+2941 varied by a factor of ≃4. No coherent pulsations could be found for AX J2050.0+2941. We have performed optical photometric and spectroscopic observations in the vicinity of AX J2049.6+2939 at KPNO. As a result, all objects brighter than a B-band magnitude of 22 in the error box can be identified with normal stars. Combined with the X-ray results and the fact that there are no radio counterparts, AX J2049.6+2939 is not likely to be either an ordinary rotation-powered pulsar or an active galactic nucleus (AGN). The nature of AX J2049.6+2939 is still unclear, and further observations over a wide energy band are strongly required. As to AX J2050.0+2941, the long-term X-ray variability and the radio counterpart suggests that it is an AGN.