ACIS Spectral Line Monitoring

Monitoring and analysis of ACIS spectral line centroids and widths by the instrument team. Gaussian are fit to the Mn-K (5.9 keV) and Al-K (1.5 keV) lines from the bottom and top 64-rows of the CCD. S3 and I3 are used as typical of BI and FI CCDs, while I2 is included in the centroid analysis because of its anomalous gain change.

Updated monthly.

5.9 keV Line Centroids

The centroid of the spectral lines decreases with time as a result of increasing CTI and decreasing detector gain. For the nominal CCDs I3 and S3, the CTI change dominates the centroid decrease for the top of the CCDs, while the detector gain change dominates the centroid decrease at the bottom of the CCDs. The anomalous gain increase on I2 is large enough that it counteracts the CTI change. The October 2003 CME can be seen as a jump in the centroid for the top rows of the FI CCDs.

1.5 keV Line Centroids

5.9 keV Line Widths

The width of the spectral lines increases with time as a result of increasing CTI. So far this increase has been relatively small except for the top of the FI CCDs at 5.9 keV.

1.5 keV Line Widths

Change history:

04/19/07 - Temperature filter upper limit changed from -119.7 to -119.4 which increases the number of data points for 2005 and beyond.

Last update August 25, 2008
Web page by Catherine E. Grant ( cgrant@space.mit.edu )
MIT Kavli Institute for Astrophysics and Space Research
Massachusetts Institute of Technology