1999MNRAS.305..409M

The transient X-ray source GS 1843+00 was observed in the hard X-ray region from 20 to 200 keV, during its flare mode in 1997 March. Spectral measurements were made during a balloon flight experiment using a newly designed large-area scintillation counter telescope. The present observations correspond to the mid-point of the transient phase. The X-ray spectrum, observed for the first time beyond 40 keV, is quite hard and the estimated intensity of the source corresponds to ∼ 100 mCrab in the 20–180 keV region. The time-averaged spectrum can be represented by a photon power-law index α ∼ 1.7±0.2. A complex function consisting of a power law with exponential term is necessary to produce the best fit to the data. We discuss the new data in terms of the source geometry and the X-ray emission mechanism.