Anomaly in XIS0
On June 23, 02:01 UT, XIS0 suddenly showed an anomaly in Segment A. A large amount of charge produced in the imaging region filled several tens of columns in the segment. The XIS frame consists of 4 segments, A through D, and only a half of the segment, i.e. 1/8 of the whole imaging region, is affected. The unusable columns are 70-150 in the ACTX coordinate, and are thus at the edge of the field of view. The phenomenon looks similar to one that occurred in XIS2 in November, 2006, but, fortunately, the leakage of charge is much smaller this time. We are trying to identify the cause of this anomaly, and to reduce the charge leakage. Sensors XIS1 and XIS3 are working fine.
Meanwhile, we will continue the Suzaku observations as planned, because we believe nominal XIS operations are unlikely to cause any further degradation. We will mask an region 80 columns wide surrounding the affected area to prevent spurious events from filling the telemetry. Although the planned observations are being conducted, usage of the burst/window options is not supported for XIS0 until the XIS team confirms the operation of XIS0 in these modes. This confirmation will be done soon, before the start of the next observations requiring the burst/window options.
Although the anomaly is restricted in Segment A, it could affect the calibration of other segments slightly. The XIS team will perform additional calibration observations, if necessary, and will update the calibration data appropriately.
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