We report the detection of the millisecond pulsar B1257+12 with the Chandra X-ray Observatory. In a 20 ks exposure we detected 25 photons from the pulsar, with energies between 0.4 and 2.0 keV, corresponding to the flux Fx = (4.4 ±0.9) x 10-15 ergs s-1 cm-2 in this energy range. The X-ray spectrum can be described by a power-law model with photon index T ≈2.8 and luminosity Lx ≈2.5 × 10 29 ergs s-1 in the 0.3-8 keV band, for a plausible distance of 500 pc and hydrogen column density NH = 3 × 10 20 cm-2. Alternatively, the spectrum can be fitted by a blackbody model with kT ≈ 0.22 keVand projected emitting area ∼2000 m-2. If the thermal X-rays are emitted from two symmetric polar caps, the bolometric luminosity of the two caps is 2Lbol ∼ 3 × 1029 ergs s-1 . We compared our results with the data on other 30 millisecond pulsars observed in X-rays and found that the apparent X-ray efficiency of PSR B1257+12, LxIE ∼ 3 x 10-5 for d -500 pc, is lower than those of most millisecond pulsars. This might be explained by an unfavorable orientation of the X-ray pulsar beam if the radiation is magnetospheric, or by strong asymmetry of polar caps if the radiation is thermal (e.g., one of the polar caps is much brighter than the other and remains invisible for most part of the pulsar period). Alternatively, it could be attributed to absorption of X-rays in circumpulsar matter, such as a flaring debris disk left over after formation of the planetary system around the pulsar.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science