Rossi X-ray Timing Explorer observation of PSR B1706-44 and implications for theoretical models of pulsar emission

We report on results of an observation with the Rossi X-Ray Timing Explorer (RXTE) of PSR B1706-44, with a live time of 132 ks, to search for pulsed X -ray emission. PSR B1706-44 is a radio and high-energy gamma-ray pulsar (de tected by EGRET), but no pulsed emission has been detected in the X-ray ban d. Since most of the other known gamma-ray pulsars emit pulsed X-rays, it i s expected that PSR B1706-44 would also be an X-ray pulsar. However, while the ROSAT PSPC detected a source at the pulsar position, it did not detect pulsations, giving a pulsed fraction upper limit of 18%. The RXTE observati ons to search for modulation at the pulsar period were carried out in 1996 November and 1997 May during the low states of the nearby X-ray binary 4U 1 705-44. No significant modulation was detected at the pulsar period, giving an upper limit of 10(-6) photons cm(-2) s(-1) keV(-1) in the interval 9 le ss than or equal to E less than or equal to 18.5 keV. The implications of t his upper limit of the pulsed flux from the RXTE observation, taken togethe r with multiband observations of this pulsar, are examined in the context o f theoretical models of pulsar particle acceleration zones and associated h igh-energy electromagnetic emission.