RHESSI in Cycle 24: Difference between revisions
imported>Hhudson (Began drafting as "yes, RHESSI is poised and ready" Nugget) |
imported>Hhudson (Nugget 108 through its Fig. 1 (out of 2).) |
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This process removes [http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=34 radiation damage] caused by the continual exposure of the detectors to the [http://en.wikipedia.org/wiki/Van_Allen_radiation_belt Earth's radiation belts]. | This process removes [http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=34 radiation damage] caused by the continual exposure of the detectors to the [http://en.wikipedia.org/wiki/Van_Allen_radiation_belt Earth's radiation belts]. | ||
It is a bit of a race against time for RHESSI, because we think that only a limited number of anneals will be possible; eventually they may poison the [http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=69 segmentation] of the detectors and effectively eliminate their gamma-ray response. | It is a bit of a race against time for RHESSI, because we think that only a limited number of anneals will be possible; eventually they may poison the [http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=69 segmentation] of the detectors and effectively eliminate their gamma-ray response. | ||
But, so far so good, as shown in this Nugget with a new-cycle flare. | But, so far so good, as shown in this Nugget with a [http://sprg.ssl.berkeley.edu/~tohban/browser/?show=grth+qlpcr&date=20090706&time=170552 new-cycle flare]. | ||
Regular readers may be puzzled by this, since in recent Nuggets ([http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Cycle_24_-_don%27t_panic_yet%21 April] and [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Where_are_the_flares July] 2009) we have been fretting about the great delay in Cycle 24's onset. | |||
in Cycle 24's onset. | |||
Nonetheless at the time of writing there have already been some new-cycle spots and flares, although it is still the case that | Nonetheless at the time of writing there have already been some new-cycle spots and flares, although it is still the case that | ||
activity has not turned up as expected. | activity has not turned up as expected. | ||
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by RHESSI at all energies, ie up into the gamma-ray range. | by RHESSI at all energies, ie up into the gamma-ray range. | ||
Figure 1 shows set of RHESSI collimator responses for this event. | |||
These (rudimentary) back-projection images all look fine, except that there are relative flux calibration issues. | |||
These do not stop us from making pretty pictures via more sophisticated algorithms. | |||
[[Image:108-Fig1.jpg|600px|thumb|center|'''Figure 1''' Individual collimator responses for the nine RHESSI detectors, each observing a | |||
different angular scale. | |||
This is the raw material of image formation, obtained by the elementary [http://www.ece.neu.edu/groups/rcl/projects/back_projection/index.html back projection] algorithm.]]. | |||
The July 6 flare was interesting as well because of its association with a coronal mass ejection ([CME]). | |||
Generally speaking, it appears that at solar minimum we have much weaker flare signatures with CMEs (such as this one). | |||
A future Nugget should deal with this interesting fact. | |||
== What we saw == | == What we saw == | ||
== Conclusions == | == Conclusions == | ||
Revision as of 03:35, 17 August 2009
| RHESSI in Cycle 24 | |
|---|---|
| Number: | 108 |
| 1st Author: | Säm Krucker |
| 2nd Author: | Hugh Hudson |
| Published: | 17 August 2009 |
| Next Nugget: | NUGGET 109 |
| Previous Nugget: | CMEless Flares |
Introduction
In anticipation of Solar Cycle 24 and the hoped-for huge flares it would produce, the RHESSI germanium detectors were annealed in late 2007. This process removes radiation damage caused by the continual exposure of the detectors to the Earth's radiation belts. It is a bit of a race against time for RHESSI, because we think that only a limited number of anneals will be possible; eventually they may poison the segmentation of the detectors and effectively eliminate their gamma-ray response. But, so far so good, as shown in this Nugget with a new-cycle flare. Regular readers may be puzzled by this, since in recent Nuggets (April and July 2009) we have been fretting about the great delay in Cycle 24's onset. Nonetheless at the time of writing there have already been some new-cycle spots and flares, although it is still the case that activity has not turned up as expected. We are still worried!
The flare we have imaged
This was a GOES C1 event on July 6, 2009. Its active region was at S25, a latitude where new-cycle spots tend to appear, and had the new-cycle polarity. So, no matter how feeble this cycle may turn out to be, we have tiny flares and may hope for more energetic ones that can be observed by RHESSI at all energies, ie up into the gamma-ray range.
Figure 1 shows set of RHESSI collimator responses for this event. These (rudimentary) back-projection images all look fine, except that there are relative flux calibration issues. These do not stop us from making pretty pictures via more sophisticated algorithms.
.
The July 6 flare was interesting as well because of its association with a coronal mass ejection ([CME]). Generally speaking, it appears that at solar minimum we have much weaker flare signatures with CMEs (such as this one). A future Nugget should deal with this interesting fact.