New PHATAB File for FUV TIME-TAG Data

For FUV data taken in TIME-TAG mode, the pulse height, or photon gain, is recorded along with the x and y position of each photon event. As described in the COS Data Handbook, the calcos pipeline permits filtering on this pulse-height information as a way of lowering the detector background.

Until recently, all pulse-height values (0 - 31) were included during routine pipeline processing. However, analysis of the data has shown that including only pulse-height values of 4 through 30 on both detector segments lowers the background while having only a minimal effect (< 2%) on the throughput. In particular, several features seen in segment B background exposures essentially disappear when this thresholding is used; see the upcoming COS ISR 2010-11, Section 4.1 for an example.

As of January 29, 2010, a PHATAB file that uses these new pulse-height ranges has been delivered to the archive, and all TIME-TAG data retrieved after this date will be processed with these new thresholds. The resulting sensitivity change is only a few percent, which is within the errors of the current flux calibration.