1999A&A...351..225P

During a BeppoSAX observation of the X-ray source XB 1746-371 located in the globular cluster NGC 6441 a type I X-ray burst, parts of 4 intensity dips, and energy dependent flaring were detected. The dips repeat every 5.8±^0.3_0.9hr and show no obvious energy dependence. If the dips are due to electron scattering this energy independence implies an abundance >130 times less than solar, confirming an earlier measurement. Since the overall cluster abundance is close to solar this low abundance is unexpected. Photoionization of the absorbing material, obscuration of an extended source, and variations in multiple components that combine to produce an apparent energy independence are all excluded. Thus, the nature of the dips remains uncertain. The best-fit model to the overall 0.3-30 keV spectrum is a disk-blackbody with a temperature of 2.82±0.04keV, together with a cutoff power-law with a photon index of -0.32±0.80 and a cutoff energy of 0.90±0.26keV. Absorption, consistent with the optical extinction to NGC 6441 of (0.28±0.04)x10²²atom/cm² is required. All previous best-fit spectral models for this source are excluded at high confidence. The spectrum is dominated by the blackbody-like component, with the cutoff power-law only contributing an average of 12% of the 1-10keV flux. During flaring intervals the contribution of this component decreases to ∼6% with variations in the intensity of the blackbody-like component being responsible for most of the flaring activity.