Development of focal plane x-ray detector aboard a microsatellite for monitoring supermassive blackholes

We describe the development of the focal plane detector onboard a micro-satellite aimed for observing cosmic X-ray emission. Combined with an X-ray optics with focal length of approximately 40 mm, an X-ray CCD camera realizes low and stable background thanks to its capability of event classification by pulse height distribution of a event. The mission will intensively monitor a specific binary black hole to investigate periodic time variability owing to its possible binary motion. The focal plane detector adopts P-channel back-illumination type CCD. It is a miniature version of the sensors utilized in the CCD camera aboard Hitomi satellite but is upgraded in terms of the energy resolution and the prevention of visible light transmittance. We have built up an equipment for cooling and driving the device. Dark current as a function of device temperature is investigated. We see clear difference of the amount of the dark current between the imaging area and frame store area, which is probably due to the difference of the pixel size. The result indicates sufficiently low dark current can be achieved with temperature lower or equal to -80 degrees C. Number of pinholes in a surface aluminium layer is significantly different between devices. We identified a process with which we decrease the number of pinholes. To realize a whole instrument, we develop communication board and compact analog board.