Sdss J102347.6+003841: a Millisecond Radio Pulsar Binary That Had a Hot Disk

The Sloan Digital Sky Survey (SDSS) source J102347.6+003841 is a binary star with a 4.75 hr orbital period. A recent radio pulsar survey showed that its primary is a millisecond pulsar (MSP). Here we analyze the SDSS spectrum of the source in detail. The spectrum was taken on 2001 February 1, when the source was in a bright state and showed broad, double-peaked hydrogen and helium lines — dramatically different from the G-type absorption spectrum seen from 2003 onward. The lines are consistent with emission from a disk around the compact primary. We derive properties of the disk by fitting the SDSS continuum with a simple disk model, and find a temperature range of 2000–34000 K from the outer to inner edge of the disk. The disk inner and outer radii were approximately 10 and 5.7×10 cm, respectively. These results further emphasize the unique feature of the source: it is evidently a system at the beginning of its life as a recycled radio pulsar. The disk mass is estimated to have been ∼ 10 g, most of which would have been lost due to the pulsar wind ablation (or due to the propeller effect if the disk had extended inside the light cylinder of the pulsar) before the final disk disruption event. The system could undergo repeated episodes of disk formation. Close monitoring of the source is needed to catch the system in its bright state again, so that this unusual example of a pulsar-disk interaction can be studied in much detail. Subject headings: binaries: close — stars: individual (J102347.6+003841) — stars: low-mass — stars: neutron