Capabilities of Pulse Height Amplitudes and COS ……. Or ……. Exploring the 5th dimension of COS! ì Dimensions 1,2, and 3 •  X, Y, and Intensity let us take the spectrum Large-­‐Format Cross-­‐Delay Line Detector To paraphrase from the Instrument Handbook: ì  Photon CounGng ì  Each event is Gme stamped as it comes in. Adding in dimension 4 ( X,Y,I ) …the rest of my talk Pulse Height Amplitude 4 down, 1 to go ì Pulse Height Amplitude (PHA) ì  Photon hits the surface and liberates an electron ì  Due to potenGal diff across the stack, the e-­‐ is accelerated downwards ì  e-­‐ hits the sides and produces more and more electrons ì  The size of the e-­‐ shower that strikes the boQom is recorded. This is known as the Pulse Height Amplitude (PHA) of the event. ì  e-­‐ are put into bins by on-­‐
board electronics ì  Range from 0-­‐31 All five, ready to go ì …and this does what? Correct for Gain-­‐Sag ì  Size of the charge cloud decreases with usage ì  If it gets too small, on-­‐board electronics or the calibraGon pipeline will filter out events ì  This leads to an apparent loss of observed flux Removal of Background ì  COS has such a low background count rate that background subtracGon methods have issues ì  Filtering out individual events gets rid of the background without introducing noise. ì  Gain-­‐Sag appears as absorpGon features in extracted spectra ì  The holes conGnue to deepen with Gme as the region conGnues to sag Gain-­‐sag mitigation •  Determining the sagged regions without needing to know what the spectrum SHOULD have looked like. ì PHA gives us a means to track gain-­‐sag Peak: ~9 at a given locaGon for a sample of Gme, you can get a Pulse Height DistribuGon Count ì  Summing the PHAs for all events ì  The peak of the PHD gives the Modal PHA Gain. PHA CCI Monitoring GSAGTAB Reference File ì  Measure the PHD, and modal PHA Gain for each pixel each week Modal Gain Map ì  Track the gain as a funcGon of Gme, and see when it drops below our threshold ì  New(ish) GSAGTAB reference file then idenGfies these regions and CalCOS excludes them from extracted spectra = flagged and excluded region A Gain-­‐sag free spectrum So far no gainsag at lifeGme posiGon 2, but lifeGme posiGon one needs a good cleaning. Removing Dark Counts Inst. Noise Source Ion Tail ì  Width of the distribuGon is stable ì  Well-­‐defined background regions are visible ì  We can specify the rejecGon thresholds relaGve to the found modal gain ì  Dynamically set background rejecGon limits specific for each pixel at any given Gme ì  Without this we only have global limits, that need to be acceptable for all locaGons and Gmes ?
Putting it all together MJD Modal Gain Map Gain Sagged Region PHA limits for background Putting it all together STIM PULSE LAMPFLASH SPECTRUM Bursts and Anomolies Here is a typical exposure ì ì  Can you tell where the problem starts? ì  Begins with a wild swing up and down near second 404 ì  Ends by flooding the detector with low PHA events ì  We’ve since found other similar situaGons Wide Lamp SGms Source Cropped Its an anomoly…it’s a burst…well it’s something anyway…