1. Timing analysis

Barycentric corrections were applied to the GIS data and 34 folded pulse profiles were obtained. Pulse arrival time analysis was complicated by the variability of the pulse profile. Therefore each profile was fitted to a truncated Fourier cosine series and the pulse minimum found. The pulse minimum was then used as the fiducial phase in determining the pulse arrival times. The arrival times were fitted to a circular ephemeris of the form $$t_n = t_0 + P_0 n + a_x\sin i \cos ( {2\pi (t_n-T_{ecl})\over P_{orb}})$$
where P₀ is the inertial pulse period, a_xsin i is the projected semi-major axis of the pulsar's orbit, T_ecl is the epoch of mid-eclipse, and P_orb is the orbital period at the time of the observation. The derived orbital parameters are shown in table 1. Introduction of eccentricity (Kelley et al. (1983)) or a non-zero $\dot{P}_{0}^{}$ did not improve the fit. Once the ephemeris was determined the photon arrival times were corrected for the orbital motion of the pulsar.

Table 1: Orbital parameters from pulse arrival time analysis. Errors are for 90% confidence in one interesting parameter.

Parameter	Value
axsin i/c	39.67$\pm$0.08 s
P0	4.815988$\pm$0.000008 s
Porb	2.091$\pm$0.005 days
Tecl	MJD 49749.189$\pm$0.002