To: odell@cosmos.msfc.nasa.gov Subject: FLUENCE calculation on Day 286.5 cc: plucinsk, ybutt, rac, mwb@space.mit.edu, das Date: Fri, 05 Nov 1999 20:32:03 -0500 From: Shanil Virani Hi Steve, At http://asc.harvard.edu/acis/radbelt/ you will find a file called d286p4.ps, please print it out. The postscript file contains 2 plots: the top panel is a plot of the SCP4 flux as function of time on Day 286. The bottom panel is just a plot of the "flare" at Day 286.4 that occurred just prior to entrance to the magnetopause/rad belt. Also superimposed on the top panel plot again is the radmon disable/enable time interval (the OFLS duration of radbelt transit) and the SIM translation time span (period of time that ACIS was in NIL). Anyway, I have now calculated the fluence in the P4 "event" that occurred at 286.4; I find a value of roughly 5x10^5 P4 COUNTS/CM**2/SR. In your earlier email dated 24 Oct, you suggested a maximum acceptable fluence per event of about 1*10^10 EXTERNAL 0.1-MeV proton (cm^2 sr MeV)^-1 per event. If you can now roughly calculate what the 0.1 MeV fluence might have been in this event, we can then compare that value against this maximum acceptable fluence per event. If they are similar, I think that this then argues for using a 100 P4 counts/s/cm**2/sr threshold that I suggested yesterday. What do you think? Cheers, Shanil ------------------------------------------------------------------------ Shanil N. Virani svirani@head-cfa.harvard.edu Chandra X-ray Observatory Center Harvard-Smithsonian Center for Astrophysics http://hea-www.harvard.edu/~svirani 60 Garden Street, MS-70 FAX: 617-495-7356 Cambridge, MA 02138 USA PHONE: 617-496-7855 "The most pathetic person in the world is someone who has sight but has no vision." -- Helen Keller ------------------------------------------------------------------------ To: ybutt Subject: Rule out perigee crossing on Day 289 Cc: plucinsk, das, rac, mwb@space.mit.edu, odell@cosmos.msfc.nasa.gov Date: Sat, 06 Nov 1999 16:26:14 -0500 From: Shanil Virani Hi Yousaf, Yesterday, you suggested that based on that 10 day plot I produced the day before, where I implicated the proton flare seen on Day 286.4 as being the most likely cause of the recent ACIS CTI change, that you couldn't disregard perigee crossing on Day 289 as being another potential source of protons which would have also harmed our detector. However, I think we can. If you look at my huge series of plots in radhist-log.ps (available from my web page), have a look at the P4 profile on Day 289. This plot affords better time-resolution of the data on this day than on the previous plot you commented on. If you look at this data, you will see that ACIS was adequately protected for perigee crossing on this day. Furthermore, there was no P4 "flare" prior to perigee crossing that had ACIS exposed like there was on Day 286.4. So I think we can safely rule out perigee crossing on Day 289 as contributing to the recent ACIS cti change now. However, Paul contends that he can't rule out the CME on Day 289 as contributing to the problem. Since there was very little proton activity seen by EPHIN, and if the CME was responsible for the CTI change, then this would identify electrons as being responsible for ACIS degradation. Now, I know everyone assumes it is ~100 keV protons that are responsible, however, I don't know if anyone has definitively ruled out electrons as a possible source of the problem. At any rate, I think we can narrow down the list of possible causes of the recent ACIS CTI degradation seen in this time-frame to either the proton flare seen by the EPHIN P4 channel on Day 286.4 or the electrons produced by the CME seen in the SCE150 electron channel. Cheers, Shanil ------------------------------------------------------------------------ Shanil N. Virani svirani@head-cfa.harvard.edu Chandra X-ray Observatory Center Harvard-Smithsonian Center for Astrophysics http://hea-www.harvard.edu/~svirani 60 Garden Street, MS-70 FAX: 617-495-7356 Cambridge, MA 02138 USA PHONE: 617-496-7855 "The most pathetic person in the world is someone who has sight but has no vision." -- Helen Keller ------------------------------------------------------------------------