Which detectors can I use to analyze this flare?

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This is the most common question we get asked by many people trying to analyze RHESSI imaging and/or spectroscopy data.  The answer is not always easy and it is becoming more and more difficult as the individual detectors respond differently to radiation damage and to the four anneals that have now been completed.  However, we now have new front-segment spectral plots available in Browser for all identified flares that can help answer this question.  These plots can be obtained for any given flare by selecting "Detector spectra" under "Flare Quicklook" in Browser.
This is the most common question we get asked by many people trying to analyze RHESSI imaging and/or spectroscopy data.  The answer is not always easy and it is becoming more and more difficult as the individual detectors respond differently to radiation damage and to the four anneals that have now been completed.  However, we now have new front-segment spectral plots available in Browser for all identified flares that can help answer this question.  These plots can be obtained for any given flare by selecting "Detector spectra" under "Flare Quicklook" in Browser.
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An example of these plots is shown in Figure 1.  The nine total count-flux spectra in units of counts s^-1 cm^-2 keV^-1, one for each front segment, are each fully corrected for decimation and live time and use 0.3 keV energy bins from 1 to 100 keV.  The photon flux spectra are computed from the corresponding count flux spectra using only the diagonal component of the detector response matrix applicable for that particular time.  Note that since no background spectra are subtracted, the photon spectra determined in this way serve only to show the relative responses of the different detectors and how well the detector response matrices correct for the know sensitivities of the different detectors.can only be used to show the relative response of the 
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[[Image:Hsi_sepdet_spectrum_20140502_005436to005536.png|200px|thumb|left|'''Figure 1''': Total count and photon flux spectra for individual detector front segments during a flare on 02 May 2014 at 00:54:36 UT.]]
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[[Image:Hsi_sepdet_spectrum_20140502_005436to005536.png|200px|thumb|right|'''Figure 1''': Total count and photon flux spectra for individual detector front segments during a flare on 02 may 2014 at 00:54:36 UT.]]
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An example of these plots is shown in Figure 1.  The nine total count-flux spectra in units of counts s^-1 cm^-2 keV^-1, one for each front segment, are each fully corrected for decimation and live time and use 0.3 keV energy bins from 1 to 100 keV.  The photon flux spectra are computed from the corresponding count flux spectra assuming all the counts were from solar photons - no background was subtracted and only the diagonal component of the detector response matrix applicable for that particular time was used.  Note that since no background was subtracted, the photon spectra determined in this way serve only to show the relative responses of the different detectors and how well the detector response matrices correct for the known sensitivities of the different detectors. The photon spectra determined in this way approximate to the actual solar spectrum only in the energy range where the solar counts are significantly above the background levels.  For the case shown in figure 1, this would be below ~20 keV.  Since the attenuator state for this time was A0, i.e. no attenuators were in place above the detectors, an estimate of the photon spectrum can be made down to ~3 keV, the approximate energy level of the electronic lower threshold level for each detector and the effective cutoff from the absorption of material in front of the detectors including the thermal blankets, both inside the cryostat and above the top grids, and the beryllium windows on the cryostat.  Counts recorded below ~3 keV are thought to be electronic noise and cannot be used in the determination of the photon spectrum, hence the hatched areas in the plots.
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Another example from earlier in the mission is shown in Figure 2.
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[[Image:Hsi_sepdet_spectrum_20050120_065040to065140.png|200px|thumb|right|'''Figure 1''': Similar to Figure 1 during an X-class flare on 20 January 2005 at 06:50:40 UT.]]

Revision as of 13:36, 4 September 2014

This is the most common question we get asked by many people trying to analyze RHESSI imaging and/or spectroscopy data. The answer is not always easy and it is becoming more and more difficult as the individual detectors respond differently to radiation damage and to the four anneals that have now been completed. However, we now have new front-segment spectral plots available in Browser for all identified flares that can help answer this question. These plots can be obtained for any given flare by selecting "Detector spectra" under "Flare Quicklook" in Browser.

Figure 1: Total count and photon flux spectra for individual detector front segments during a flare on 02 May 2014 at 00:54:36 UT.

An example of these plots is shown in Figure 1. The nine total count-flux spectra in units of counts s^-1 cm^-2 keV^-1, one for each front segment, are each fully corrected for decimation and live time and use 0.3 keV energy bins from 1 to 100 keV. The photon flux spectra are computed from the corresponding count flux spectra assuming all the counts were from solar photons - no background was subtracted and only the diagonal component of the detector response matrix applicable for that particular time was used. Note that since no background was subtracted, the photon spectra determined in this way serve only to show the relative responses of the different detectors and how well the detector response matrices correct for the known sensitivities of the different detectors. The photon spectra determined in this way approximate to the actual solar spectrum only in the energy range where the solar counts are significantly above the background levels. For the case shown in figure 1, this would be below ~20 keV. Since the attenuator state for this time was A0, i.e. no attenuators were in place above the detectors, an estimate of the photon spectrum can be made down to ~3 keV, the approximate energy level of the electronic lower threshold level for each detector and the effective cutoff from the absorption of material in front of the detectors including the thermal blankets, both inside the cryostat and above the top grids, and the beryllium windows on the cryostat. Counts recorded below ~3 keV are thought to be electronic noise and cannot be used in the determination of the photon spectrum, hence the hatched areas in the plots.


Another example from earlier in the mission is shown in Figure 2.

Figure 1: Similar to Figure 1 during an X-class flare on 20 January 2005 at 06:50:40 UT.
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