3 Ultraviolet Emission from the Millisecond Pulsar J 0437 − 4715 1

We observed PSR J0437−4715 with the FUV-MAMA detector of the Hubble Space Telescope Imaging Spectrometer (STIS) to measure the pulsar’s spectrum and pulsations. For the first time, UV emission from a millisecond pulsar is detected. The measured flux, (2.0± 0.2)× 10 erg s cm in the 1150–1700 Å range, corresponds to the luminosity LFUV = (4.7 ± 0.5) × 10 27 erg s, for the distance of 140 pc and negligible interstellar extinction. The shape of the observed spectrum suggests thermal emission from the neutron star surface with a surprisingly high temperature of about 1 × 10 K, above the upper limit on the surface temperature of the younger “ordinary” pulsar J0108−1431. For the few-Gyr-old J0437−4715, such a temperature requires a heating mechanism to operate. The spectrum of J0437−4715 shows marginal evidence of an emission line at 1372 Å, which might be a gravitationally redshifted Zeeman component of the Hydrogen Lyα line in a magnetic field ∼ 7 × 10 G. No pulsations are detected, with a 3σ upper limit of 50% on pulsed fraction. Subject headings: pulsars: individual (PSR J0437–4715) — stars: neutron — UV: stars