https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=RHESSI_Science_Nuggets/Quiet_Sun_III&feed=atom&action=historyRHESSI Science Nuggets/Quiet Sun III - Revision history2024-03-28T11:03:31ZRevision history for this page on the wikiMediaWiki 1.16.0https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=RHESSI_Science_Nuggets/Quiet_Sun_III&diff=10912&oldid=prevSchriste at 17:21, 23 August 20182018-08-23T17:21:55Z<p></p>
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<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">{{Infobox Nugget</del></div></td><td colspan="2"> </td></tr>
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<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">|first_author = Iain Hannah</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">|second_author = Hugh Hudson</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">|publish_date = 2010 September 27</del></div></td><td colspan="2"> </td></tr>
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<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">|previous_nugget = [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The X-ray Limb]</del></div></td><td colspan="2"> </td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Introduction ==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Introduction ==</div></td></tr>
</table>Schristehttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=RHESSI_Science_Nuggets/Quiet_Sun_III&diff=3415&oldid=prevHhudson: New page: {{Infobox Nugget |name = Nugget |title = Quiet Sun III |number = 136 |first_author = Iain Hannah |second_author = Hugh Hudson |publish_date = 2010 September 27 |next_nugget = TBD |previous...2010-09-26T16:28:17Z<p>New page: {{Infobox Nugget |name = Nugget |title = Quiet Sun III |number = 136 |first_author = Iain Hannah |second_author = Hugh Hudson |publish_date = 2010 September 27 |next_nugget = TBD |previous...</p>
<p><b>New page</b></p><div>{{Infobox Nugget<br />
|name = Nugget<br />
|title = Quiet Sun III<br />
|number = 136<br />
|first_author = Iain Hannah<br />
|second_author = Hugh Hudson<br />
|publish_date = 2010 September 27<br />
|next_nugget = TBD<br />
|previous_nugget = [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The X-ray Limb]<br />
}}<br />
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<br />
== Introduction ==<br />
<br />
Earlier Nuggets, starting in 2005, have explored various facets of<br />
high-energy radiation from the quiet Sun:<br />
[http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=16 1],<br />
[http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=21 2],<br />
[http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=37 3],<br />
[http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=50 4].<br />
Now we have the definitive RHESSI measurements in hand (reference A), in the<br />
sense that the Sun has now passed (with difficulty) a [quite unusual] [solar<br />
minimum], and RHESSI data acquisition for faint exotic hard X-ray emissions<br />
has come to an end.<br />
<br />
Reference to the earlier Nuggets cited will bring up unusual subjects such as<br />
axions, cosmic-ray electrons, albedo neutrons, and the diffuse cosmic X-ray <br />
background. <br />
Since RHESSI only obtains upper limits, we cannot say very much about these<br />
interesting things, except that they are predicted not to be very faint<br />
by non-solar astronomical standards.<br />
RHESSI's best observations are now completed, at least for the next few <br />
years, because of competition from increasing [solar activity] (see the <br />
discussion of "nanoflares" below).<br />
<br />
(Fig. 2 from Hannah et al 2010, upgraded with Edwards & McCracken,<br />
RESIK, SphinX, and maybe XRT data if I can interpret them)<br />
<br />
== The new data ==<br />
<br />
In Reference A we describe the full observing program for faint global<br />
hard X-ray emission from the Sun.<br />
We have not made any great discovery - no axions yet - but<br />
the RHESSI data have provided the best upper limits to date (Figure 1).<br />
Until focusing optics, such as those of [Nustar] or [FOXSI] become available,<br />
these are the best hard X-ray data.<br />
<br />
(Figure from the Sylwester EOS article?)<br />
<br />
This is the final statement from RHESSI on this topic owing to the<br />
increase of [solar activity].<br />
Other recent instruments (e.g., [SphinX]) or [MESSENGER] may improve<br />
on these limits, especially at lower energies, and we encourage the analysis<br />
of such data on the quiet Sun.<br />
As discussed below high spectral resolution may be very important in <br />
this domain, as well as good background rejection, to distinguish <br />
exotic sources from the expected thermal signatures (see next section).<br />
<br />
== Nanoflares ==<br />
<br />
But the Sun has a continuous level of [magnetic activity], culminating in <br />
sunspots, plage, flares, and CMEs.<br />
In particular [nanoflares] are an attractive scenario that might<br />
solve the [coronal heating] problem.<br />
In essence the nanoflare hypothesis involves episodic heating, perhaps<br />
resembling the action of true solar flares; to support a mean coronal<br />
temperature means that impulsive nanoflare heating would produce <br />
temperatures higher than the mean.<br />
In other words, the instantaneous temperature distribution of the<br />
corona would be broader than for a steady heating process that only<br />
has to attain the mean coronal temperature.<br />
This kind of process therefore competes in an ill-understood manner<br />
with our search for faint hard X-ray sources not related to solar<br />
magnetic activity.<br />
It is also interesting in its own right and the subject of a great deal<br />
of literature (e.g. ref. [2]).<br />
<br />
(Fig. 3 left from Hannah et al 2010)<br />
<br />
== Conclusions ==<br />
<br />
This Nugget reports the best upper limits on hard X-rays from<br />
the quiet Sun, including several possible mechanisms.<br />
RHESSI cannot improve on these limits for another several years,<br />
and there are no plans now for new and more sensitive hard X-ray<br />
solar instrumentation (but we look forward to [FOXSI] and [NuSTAR]).<br />
These limits may stand as definitive ones for some time to come.<br />
In the meanwhile it is important to study the 1-10 keV range with<br />
available data.<br />
<br />
== References ==<br />
<br />
[1] Hannah et al<br />
<br />
[2] Klimchuk review</div>Hhudson