Complex sentence: The PHEBUS instrument was meant to study Gamma-Ray bursts and other transient X-Ray sources while others such as ART-P were intended to image X-Ray sources in the 35--100 kev range.
Split into simpler sentences: The PHEBUS instrument was meant to study gamma-ray bursts and other transient X-Ray sources. Other experiments such as ART-P were intended to image X-Ray sources in the 35 to 100 keV range.