X-RAY-SPECTRUM AND TIME-VARIATION OF X1850-087 IN THE GLOBULAR-CLUSTER NGC-6712

We observed the energy spectrum and the time variation of the X-rays from X1850-087 in the globular cluster NGC 6712 with the Large Area Counter on board Ginga. The luminosity of X1850-087, when we observed it, was 1.3 x 10(36) (D/6.8 kpc)2 ergs s-1. The X-ray energy spectrum can be represented by a single power-law type spectrum with a photon index of 2.3, with an interstellar absorption of less than 10(21) H atoms cm-2. A model consisting of disk blackbody and radiation from the neutron star requires an unphysically small inner-disk-radius and a small emission region on the neutron star surface where allowances have been made for the difference between the color temperature and the effective temperature. On the other hand, a model where the main X-ray formation mechanism is Compton scattering indicates that the plasma, which is responsible for Compton scattering, becomes thin and hot in the low accretion rate state. No significant periodic variation was detected, but a significant variation below 1 Hz was found, which is similar to a high-frequency noise observed in the island state of the atoll sources.