Detection of Pulsed X-ray Emission from Psr B1706−44

We report the first detection of pulsed X-ray emission from the young, energetic radio and gammaray pulsar PSR B1706−44. In a 47 ks observation with the High Resolution Camera on-board the Chandra X-ray Observatory we find a pulsed signal at a frequency consistent with the radio ephemeris, f = 9.7588081± 0.0000027 Hz (at epoch 51585.34104 MJD). The broad, single-peaked pulse profile has a pulsed fraction of 23%±6%; this is not in conflict with a ROSAT PSPC upper limit of < 18% because this instrument could not resolve the pulsar from a surrounding synchrotron nebula. The probability that this pulsed detection is a chance occurrence is 1.8× 10−4 as judged by the Rayleigh test. We also fitted Chandra spectroscopic data on PSR B1706−44, which require at least two components, e.g., a blackbody of T∞ = (1.66 −0.15) × 10 K and a power-law of Γ = 2.0± 0.5. The blackbody radius at the nominal 2.5 kpc distance is only R∞ = 3.6± 0.9 km, indicating either a hot region on a cooler surface, or the need for a realistic atmosphere model that would allow a lower temperature and larger area. Because the power-law and blackbody spectra each contribute more than 23% of the observed flux, it is not possible to decide which component is responsible for the modulation in the spectrally unresolved light curve. Subject headings: pulsars: individual (PSR B1706−44) — stars: neutron — X-rays: stars