Proper motions of ROSAT discovered isolated neutron stars measured with Chandra: First X-ray measurement of the large proper motion of RX J1308.6+2127∕RBS 1223

Abstract

The unprecedented spatial resolution of the Chandra observatory opens the possibility to detect with relatively high accuracy proper motions at X‐ray wavelengths. We have conducted an astrometric study of three of the “Magnificent Seven”, the thermally emitting radio quiet isolated neutron stars (INSs) discovered by ROSAT. These three INSs (RX J0420.0‐5022, RX J0806.4‐4123 and RX J1308.6+2127/RBS 1223) either lack an optical counterpart or have one too faint to be used for astrometric purposes. We obtained ACIS observations 3 to 5 years apart to constrain or measure the displacement of the sources on the X‐ray sky using as reference the background of extragalactic or remote galactic X‐ray sources.Upper limits of 138 mas/yr and 76 mas/yr on the proper motion of RX J0420.0‐5022 and RX J0806.4‐4123, respectively, have already been presented in [7]. Here we report the very significant measurement (∼10 sigma) of the proper motion of the third INS of our program, RX J1308.6+2127/RBS 1223. Comparing observations...