The outbursts and orbit of the accreting pulsar GS 1843-02=2S 1845-024

We present observations of a series of 10 outbursts of pulsed hard X-ray fl ux from the transient 10.6 mHz accreting pulsar GS 1843-02, using the Burst and Transient Source Experiment on the Compton Gamma Ray Observatory. Thes e outbursts occurred regularly every 242 days, coincident with the ephemeri s of the periodic transient GRO J1849-03, which has recently been identifie d with the SAS 3 source 2S 1845-024. Our pulsed detection provides the firs t clear identification of GS 1843-02 with 2S 1845-024. We present a pulse t iming analysis that shows that the 2S 1845-024 outbursts occur near the per iastron passage of the neutron star's highly eccentric (e = 0.88 +/- 0.01) 242.18 +/- 0.01 day period binary orbit about a high-mass (M-c > 7 M.) comp anion. The orbit and transient outburst pattern strongly suggest that the p ulsar is in a binary system with a Be star. Our observations show a long-te rm spin-up trend, with most of the spin-up occurring during the outbursts. From the measured spin-up rates and inferred luminosities we conclude that an accretion disk is present during the outbursts.