The near-UV pulse profile and spectrum of the pulsar PSR B0656+14

¹ Ioffe Physico-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russia e-mail: shib@astro.ioffe.ru
² Stockholm Observatory, AlbaNova Science Center, Department of Astronomy, 106 91 Stockholm, Sweden
³ Goddard Space Flight Center, Exploration of the Universe Division, Code 667, USA
⁴ Advanced Computer Concepts, Inc. Potomac, MD, USA

Received: 4 March 2005
Accepted: 1 June 2005

Abstract

We have observed the middle-aged pulsar PSR B0656+14 with the prism and the NUV MAMA detector of the Space Telescope Imaging Spectrograph (STIS) to measure the pulsar spectrum and periodic pulsations in the near-ultraviolet (NUV). The pulsations are clearly detected, double-peaked and very similar to the optical pulse profile. The NUV pulsed fraction is %. The spectral slope of the dereddened phase-integrated spectrum in the ~ Å range is ~ which together with the high pulse fraction indicates a non-thermal origin for the NUV emission. The total flux in the range ~ Å is estimated to be  erg s^-1 cm^-2 when corrected for  mag. At a distance of 288 pc this corresponds to a luminosity  erg s^-1 assuming isotropy of the emission. We compare the NUV pulse profile with observations from radio to gamma-rays. The first NUV sub-pulse is in phase with the gamma-ray pulse marginally detected with EGRET, while the second NUV sub-pulse is similar both in shape and in phase with the non-thermal pulse in hard X-rays. This indicates a single origin of the non-thermal emission in the optical-NUV and in the X-rays. This is also supported by the observed NUV spectral slope, which is compatible with a blackbody plus power-law fit extended from the X-ray range, but dominated by the power-law component in most of the NUV range.