https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&feed=atom&action=historyNuSTAR detects X-ray flares in the quiet Sun - Revision history2024-03-28T22:27:13ZRevision history for this page on the wikiMediaWiki 1.16.0https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&diff=11152&oldid=prevSchriste at 11:32, 18 September 20182018-09-18T11:32:01Z<p></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[4] [http://adsabs.harvard.edu/abs/2018arXiv180308365K "NuSTAR Detection of X-Ray Heating Events in the Quiet Sun"]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[4] [http://adsabs.harvard.edu/abs/2018arXiv180308365K "NuSTAR Detection of X-Ray Heating Events in the Quiet Sun"]</div></td></tr>
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<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">[[Has observation by:: NuSTAR| ]]</ins></div></td></tr>
</table>Schristehttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&diff=10761&oldid=prevSchriste at 17:58, 22 August 20182018-08-22T17:58:25Z<p></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 26 March 2018</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 26 March 2018</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|next_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::320]]}}</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|next_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::320]]}}</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|previous_nugget=[<del class="diffchange diffchange-inline">http</del>:<del class="diffchange diffchange-inline">//sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Homologous_CME/flares_from_AR_12371 Flare/CME homology</del>]</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|previous_nugget=<ins class="diffchange diffchange-inline">{{#ask: </ins>[<ins class="diffchange diffchange-inline">[Category</ins>:<ins class="diffchange diffchange-inline">Nugget]] [[RHESSI Nugget Index::318]</ins>]<ins class="diffchange diffchange-inline">}}</ins>}}</div></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=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&diff=10318&oldid=prevHhudson: /* Future runs */2018-03-27T16:34:01Z<p><span class="autocomment">Future runs</span></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>We expect higher livetimes and even lower backgrounds in the future runs, </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>We expect higher livetimes and even lower backgrounds in the future runs, </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>which should allow for observations of even smaller events; we estimate</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>which should allow for observations of even smaller events; we estimate</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>improvement of a factor of about 70 in sensitivity<del class="diffchange diffchange-inline">. </del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>improvement of a factor of about 70 in sensitivity.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">We may also see a true hard X-ray spectrum extending into to tens of keV</del>. </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== References ==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== References ==</div></td></tr>
</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&diff=10317&oldid=prevHhudson: /* Spectra */2018-03-27T11:15:26Z<p><span class="autocomment">Spectra</span></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the nonthermal signal is not a constraining result.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the nonthermal signal is not a constraining result.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[[File:319f2.png|<del class="diffchange diffchange-inline">500px</del>|thumb|center|Figure 2:</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[[File:319f2.png|<ins class="diffchange diffchange-inline">600px</ins>|thumb|center|Figure 2:</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>NuSTAR QS events in the context of previous studies. </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>NuSTAR QS events in the context of previous studies. </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Left: Frequency distribution of flares as estimated from various </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Left: Frequency distribution of flares as estimated from various </div></td></tr>
</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&diff=10316&oldid=prevHhudson: added the main event2018-03-27T11:14:34Z<p>added the main event</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Future runs ==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Future runs ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">A fuller account of this work is in Ref. [4].</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>With the decreasing solar activity towards solar minimum in 2019/2020, </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>With the decreasing solar activity towards solar minimum in 2019/2020, </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>we expect progressively better conditions for NuSTAR QS observations. </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>we expect progressively better conditions for NuSTAR QS observations. </div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[3] [http://adsabs.harvard.edu/abs/1997ApJ...488..499K "X-Ray Network Flares of the Quiet Sun"]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[3] [http://adsabs.harvard.edu/abs/1997ApJ...488..499K "X-Ray Network Flares of the Quiet Sun"]</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">[4] [http://adsabs.harvard.edu/abs/2018arXiv180308365K "NuSTAR Detection of X-Ray Heating Events in the Quiet Sun"]</ins></div></td></tr>
</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=NuSTAR_detects_X-ray_flares_in_the_quiet_Sun&diff=10308&oldid=prevHhudson: 319 first draft2018-03-26T20:51:07Z<p>319 first draft</p>
<p><b>New page</b></p><div>{{Infobox Nugget<br />
|name = Nugget<br />
|title = NuSTAR detects X-ray flares in the quiet Sun <br />
|number = 319<br />
|first_author = Matej Kuhar <br />
|second_author = <br />
|publish_date = 26 March 2018<br />
|next_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::320]]}}<br />
|previous_nugget=[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Homologous_CME/flares_from_AR_12371 Flare/CME homology]<br />
}}<br />
<br />
== Introduction ==<br />
<br />
It is still unexplained why the <br />
[https://solarscience.msfc.nasa.gov/corona.shtml solar corona]<br />
(about 1 MK) is so much hotter than the <br />
[https://solarscience.msfc.nasa.gov/surface.shtml photosphere] (about 5700 K). <br />
While it is clear that this energy comes from the Sun's magnetic field<br />
somehow, rival conversion mechanism(s) are still much discussed in the <br />
community. <br />
The <br />
[https://en.wikipedia.org/wiki/Solar_flare solar flare] mechanism <br />
is one of the most promising candidates, since <br />
a flare converts large amounts of magnetic energy into other forms. <br />
Most energetic flares are, however, too rare to explain the steady supply <br />
of energy to the corona, which maintains its high temperature even during <br />
solar minima, when no extreme solar activity takes place. <br />
It has been debated that the flares on the smallest scale might supply <br />
enough energy not through their (relatively small) individual energy <br />
budgets, but through their large numbers. <br />
Numerous studies have shown that solar flares follow a power-law <br />
distribution as a function of energy, with the power-law index <br />
fluctuating around 2. <br />
It is this value that divides the two regimes (Ref. [1]): for index &lt;2, <br />
the largest flares contribute more to coronal heating; for index &gt;2, <br />
the smallest flares are the main contributors. <br />
Parker (Ref. [2]) had proposed the scenario where <br />
[https://en.wikipedia.org/wiki/Nanoflares nanoflares] <br />
(with energies of 10<sup>24</sup> erg or less) make an ensemble of <br />
unresolved basic reconnection events that occupy the whole solar disk <br />
and thus make up the X-ray corona. <br />
<br />
== NuSTAR sees quiet-Sun flares ==<br />
<br />
NuSTAR is a focusing-optics <br />
[https://imagine.gsfc.nasa.gov/science/toolbox/xray_telescopes1.html hard X-ray telescope] operating in the energy range 3-79 keV and <br />
launched by NASA in 2012. <br />
Even though it was not designed for solar observations, it can be <br />
pointed to the Sun. <br />
This capability has led to 12 brief solar observing sessions in the <br />
last 3.5 years, which have resulted in observations of <br />
[https://apod.nasa.gov/apod/ap020801.html active-region] <br />
"microflares," quiescent active regions, high altitude coronal emissions, etc.;<br />
a microflare is just a weaker version of a true solar flare.<br />
<br />
In the July 2016 and March 2017 observing campaigns NuSTAR also observed <br />
three tiny flare-like brightenings in the quiet Sun (QS).<br />
These observations, to the authors' best knowledge, represent <br />
the first spectroscopically resolved X-ray measurements of QS flare events<br />
in hard X-rays (HXR). <br />
They were associated with the solar magnetic <br />
[http://www.scholarpedia.org/article/Solar_activity network] <br />
and, even though feeble when compared to larger <br />
[https://en.wikipedia.org/wiki/Solar_flare M- and X-class] flares, <br />
they showed complex morphologies.<br />
<br />
[[File:319f1.png|500px|thumb|center|Figure 1: <br />
Three quiet-Sun flares observed with NuSTAR. <br />
Left: Flare morphologies. <br />
Middle: Time evolution of NuSTAR and <br />
[http://aia.lmsal.com AIA] EUV fluxes. <br />
Right: Spectra of the observed events. <br />
The green points represent emission during the flare peak, <br />
while pink represents the background. <br />
]]<br />
<br />
== Spectra ==<br />
<br />
Flare-integrated spectra were made for each event, using a spectral model<br />
consisting of an isothermal component plus a fixed background.<br />
The fits provided temperatures in the range 3.1-4.2 MK and emission measures <br />
in the range (0.6-15) x 10<sup>44</sup> cm<sup>-3</sup>. <br />
These values give thermal energy contents in the range <br />
(1.8-6.0) x 10<sup>26</sup> erg and place the observed events (brown box) <br />
just between the usual microflares observed in active regions and smallest <br />
QS flares observed previously in soft X-raus and the EUV <br />
(see the left panel of Figure 2; the brown box shows the NuSTAR events). <br />
The same story is shown in the right panel of the same figure in the<br />
parameter space of temperature and emission measure, where the RHESSI <br />
observation range is shown in yellow, NuSTAR AR microflares in blue, <br />
NuSTAR QS flares in orange, while the faintest events in the soft X-rays <br />
and the EUV observed previously (e.g. Ref. [3]) are shown in green. <br />
The same classes of events in the two plots are highlighted with arrows. <br />
In the [https://www.swpc.noaa.gov/products/goes-x-ray-flux GOES] <br />
classification, our events occupy the range between <br />
1/1000 and 1/100 of a GOES A-class event, the weakest classification. <br />
The spectra did not show direct signs of a nonthermal component. <br />
However, since upper limits of energy in a hidden nonthermal component <br />
(still consistent with the observations, i.e. <br />
no emission above 5 keV) estimated at ~5 x 10<sup>26</sup> erg are within <br />
the uncertainties of thermal energy estimates, and the non-detection of <br />
the nonthermal signal is not a constraining result.<br />
<br />
[[File:319f2.png|500px|thumb|center|Figure 2:<br />
NuSTAR QS events in the context of previous studies. <br />
Left: Frequency distribution of flares as estimated from various <br />
soft X-ray, hard X-ray, and EUV observations. <br />
Right: Different types of flares in temperature-emission measure parameter <br />
space. <br />
The GOES classes are shown with isocurves.<br />
]]<br />
<br />
== Future runs ==<br />
<br />
With the decreasing solar activity towards solar minimum in 2019/2020, <br />
we expect progressively better conditions for NuSTAR QS observations. <br />
We expect higher livetimes and even lower backgrounds in the future runs, <br />
which should allow for observations of even smaller events; we estimate<br />
improvement of a factor of about 70 in sensitivity. <br />
We may also see a true hard X-ray spectrum extending into to tens of keV. <br />
<br />
== References ==<br />
<br />
[1] [http://adsabs.harvard.edu/abs/1991SoPh..133..357H "Solar flares, microflares, nanoflares, and coronal heating"]<br />
<br />
[2] [http://adsabs.harvard.edu/abs/1988ApJ...330..474P "Nanoflares and the solar X-ray corona"]<br />
<br />
[3] [http://adsabs.harvard.edu/abs/1997ApJ...488..499K "X-Ray Network Flares of the Quiet Sun"]</div>Hhudson