Decay of X-ray source A0535+26

THE All-Sky Monitor (ASM) aboard Ariel V is a pinhole camera sensitive to X rays in the energy range 3-6 keV. It has an effective area of 0.6 cm² with a duty cycle of ~ 1% for a given source, and monitors more than 3π of the celestial sphere each orbit¹. It is important to note that the regions of sky inaccessible to the ASM include the spacecraft spin axis and a band about the spacecraft equator, so that its field of view and those of the other five Ariel V experiments are mutually exclusive.