RHESSI Wiki - Recent changes [en]

Dips and Waves

2009-11-22T13:30:55Z

Revised conclusions

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	== Introduction ==		== Introduction ==

-	There ~~have~~ been some heated discussion (for instance [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The_Rise_and_Fall_of_The_Low_Energy_Cut_Off]) as to whether ~~the~~ "dip" seen in the mean electron spectrum ~~<nFV>~~ derived from RHESSI ~~flare~~ observations is a real feature ~~since it~~ can often be removed be correcting for albedo. But for flares with relatively low thermal mission the standard "thick-target" interpretation says that the "dip" must be there. ~~This~~ model only accounts for Coulomb collisions between the propagating beam of accelerated electrons and the background plasma. In this ~~nugget~~ we present simulation results from our recent ~~paper~~ [http://arxiv.org/abs/0911.0314] where we show what happens to the dip when you also include wave-particle interactions between the beam and background plasma.	+	Solar flares feature the acceleration of non-thermal particles ofseveral descriptions.
		+	One of RHESSI's primary tasks is to study these particles via their [bremsstrahlung] X-rays.
		+	The X-ray spectrum typically follows a power law at high energies "hard X-rays", and an exponential at lower "soft X-ray" energies; in the standard interpretation these components reveal (respectively) the primary
		+	particle acceleration and its [Maxwellianized] "thermal" heating.The theory of the nonthermal radiation involves several processes: the
		+	initial acceleration of the particles, their propagation through the solar atmosphere, and their X-ray production as they lose energy to thebackground plasma.With several assumptions, all of this theory can be wrapped up intoa tractable problem in [inverse theory].
		+	When this was first done at RHESSI's [high spectral resolution], a new and unexpected feature tended to appear: a [dip] in the spectrum at about 30 keV.</p>
		+
		+	<p>There has been some heated discussion (for instance in this earlier
		+	[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The_Rise_and_Fall_of_The_Low_Energy_Cut_Off Nugget])
		+	as to whether this "dip" seen in the mean
		+	electron spectrum derived from RHESSI X-ray observations
		+	is a real feature.
		+	It can often be removed by correcting for the
		+	[albedo] flux of X-rays scattered back to the observer
		+	from the solar atmosphere beneath the source.
		+	But for flares with relatively low thermal mission the
		+	standard [thick-target] interpretation says that the dip
		+	must be there.
		+	The thick-target model only accounts for Coulomb collisions between the
		+	propagating beam of accelerated electrons and the background plasma.
		+	In this Nugget we present simulation results from our recent
		+	[http://arxiv.org/abs/0911.0314 paper], where
		+	we show what happens to the dip when you also include wave-particle
		+	interactions between the beam and the background plasma.

	== Wave-particle Interactions ==		== Wave-particle Interactions ==
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	== Conclusions ==		== Conclusions ==

-	The work shown here is a step towards a more complete treatment of electron transport in solar flares ~~and highlights that the~~ inclusion of wave-particle interactions ~~flattens~~ sharp low energy ~~cutoffs~~ in the inital accelerated electron distribution. There are still other processes ~~that are~~ not included here but ~~it does demonstrate~~ that the standard "thick-target" interpretation is insufficient to explain the RHESSI observations.	+	The work shown here is a step towards a more complete treatment of electron transport
		+	in solar flares by consideration of wave-particle interactions.
		+	The inclusion of such effects goes beyond the traditional propagation theory, which typically relies on Coulomb scattering alone.
		+	The wave-particle interactions turn out to flatten any sharp low-energy cutoff in the inital accelerated electron distribution.
		+	There are still other processes not included here, but this first look strongly suggests that the standard "thick-target" interpretation is insufficient to explain the RHESSI spectral observations.

	[[category:Nugget]]		[[category:Nugget]]

Template:Infobox Nugget

2009-11-19T22:45:57Z

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	\|-		\|-
	!colspan="2" style="background-color:#00394a; text-align:center; color:#ffff42; font-size:110%;"\|{{{name}}}		!colspan="2" style="background-color:#00394a; text-align:center; color:#ffff42; font-size:110%;"\|{{{name}}}

Dips and Waves

2009-11-19T22:43:30Z

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		+	{{Infobox Nugget
		+	\|name = Dips and Waves
		+	\|title = Nugget Details
		+	\|number = 115
		+	\|first_author = Iain Hannah
		+	\|second_author =
		+	\|publish_date = 23 November 2009
		+	\|next_nugget = TBD
		+	\|previous_nugget = [[STEREO observations of flares and their associations with CMEs]]
		+	}}
		+
	== Introduction ==		== Introduction ==

Dips and Waves

2009-11-19T15:41:29Z

←Older revision		Revision as of 15:41, 19 November 2009
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	== Introduction ==		== Introduction ==

-	There ~~has~~ been some heated discussion (for instance [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The_Rise_and_Fall_of_The_Low_Energy_Cut_Off]) as to whether the "dip" seen in the mean electron spectrum derived from RHESSI flare observations is a real feature as it can often be removed be correcting for albedo. But for flares with relatively low thermal mission the standard "thick-target" interpretation says that the "dip" must be there. This model only accounts for Coulomb collisions between the propagating beam of accelerated electrons and the background plasma. In this nugget we present simulation results from our recent paper [http://arxiv.org/abs/0911.0314] where we show what happens to the dip when you also include wave-particle interactions between the beam and background plasma.	+	There have been some heated discussion (for instance [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The_Rise_and_Fall_of_The_Low_Energy_Cut_Off]) as to whether the "dip" seen in the mean electron spectrum <nFV> derived from RHESSI flare observations is a real feature since it can often be removed be correcting for albedo. But for flares with relatively low thermal mission the standard "thick-target" interpretation says that the "dip" must be there. This model only accounts for Coulomb collisions between the propagating beam of accelerated electrons and the background plasma. In this nugget we present simulation results from our recent paper [http://arxiv.org/abs/0911.0314] where we show what happens to the dip when you also include wave-particle interactions between the beam and background plasma.

	== Wave-particle Interactions ==		== Wave-particle Interactions ==

-	In the standard interpretation of RHESSI's hard x-ray emission, a powerlaw of acceelerated electrons above a sharp low energy cutoff ~~leave~~ the corona travelling down to the chromosphere. As they propagate they lose energy to the background plasma through Coloumb collisions, eventually losing their energy in the dense chromosphere, where they emit hard X-rays as observed by RHESSI, heating the local plasma which expands back upwards.	+	In the standard interpretation of RHESSI's hard X-ray emission, a negative powerlaw of acceelerated electrons (F<sub>0</sub>(E) ~E<sup>-δ<sub>0</sub></sup>) above a sharp low energy cutoff leaves the corona travelling down to the chromosphere. As they propagate they lose energy to the background plasma through Coloumb collisions, eventually losing their energy in the dense chromosphere, where they emit hard X-rays as observed by RHESSI, heating the local plasma which expands back upwards. It can be analytically shown the the resulting mean electron flux spectrum <nVF(E)> will also have a neagtive powerlaw above the cutoff (<nVF>~E<sup>-δ<sub>1</sub></sup>) but will have a positive one (<nVF(E)>~E<sup>δ<sub>1</sub></sup>) below the cutoff. The combination of this positive slope (increasing with increasing energy) and the falling thermal spectrum results in a local minima or "dip" in the total <nVF>.
		+
		+	We have simulated the propagation of such a powerlaw of acceleration electrons, Coulomb colision acting on the beam only, as shown in the left panel of Figure 1. But we have also ran a second set of numerical simulations in which we include the wave-particle interaction of the beam and background plasma. Namely we include beam-driven Langmuir wave turbulence. We want to include the waves-particle interactions as this non-collisional process is faster than collisions and the development of Langmuir waves from electron beams in solar flares is inferred from radio observations. These are self-consitently simulated using the quasi-linear approach describing the resonant interaction between the electrons and Langmuir waves. In these simulations we follow through time the electron distribution function f(v,x,t) and spectral energy density of the waves W(v,x,t). In Figure 1 we have snapshot from during the simulations showing f(v,x,t) for the coulomb collision only simulation (left) and f(v,x,t) and W(v,x,t) for the wave-particle simulation (middle and right panel). A movie of this can also be found [http://www.youtube.com/watch?v=uO2U7WeHu1Q here].

	[[Image:Fwc_10009.jpg\|frame\|center\|'''Figure 1:''' The electron distribution f and energy density of the waves W showing the simulation results from the 2 different simulations: Coulomb collisions only on the left, including wave-particle interactions on the right.) A movie of this can be found [http://www.youtube.com/watch?v=uO2U7WeHu1Q here]]]		[[Image:Fwc_10009.jpg\|frame\|center\|'''Figure 1:''' The electron distribution f and energy density of the waves W showing the simulation results from the 2 different simulations: Coulomb collisions only on the left, including wave-particle interactions on the right.) A movie of this can be found [http://www.youtube.com/watch?v=uO2U7WeHu1Q here]]]
		+
		+	The immediate thing that happens is that the wave-particles very quickly flatten the low energy cutoff, producing a plateau in the electron distribution at low energies or velocities. The Coulomb collision alone are far slower at removing the low energy cutoff and produce the expected positive gradient in the electron distribution below the cutoff energy. To calculate the mean electron flux spectrum from our simulations we use the simulated f(v,x,t)/m, spatially integrating and averaging over time. The resulting spectra are shown in Figure 2.

	[[Image:fig3b.png\|frame\|center\|'''Figure 2:''' The mean electron flux spectrum <nVF> for the simulation with Coulomb collisions actng on the beam only (left) and the inclusion of wave-particle interaction (right). The black line shows the simulation result, the orange dashed line an overplotted thermal model spectrum. The total spectrum is the dashed green line, indicating the presence of a dip in the Coulomb collision only case.]]		[[Image:fig3b.png\|frame\|center\|'''Figure 2:''' The mean electron flux spectrum <nVF> for the simulation with Coulomb collisions actng on the beam only (left) and the inclusion of wave-particle interaction (right). The black line shows the simulation result, the orange dashed line an overplotted thermal model spectrum. The total spectrum is the dashed green line, indicating the presence of a dip in the Coulomb collision only case.]]

		+	The positive slope increase in the Coulomb colision only case (left panel Figure 2) is clearly evident in the mean electron spectrum. As is the almost flat, though slighlty negative, spectrum at low energies when the wave-particle interactions are also considered. With the inclusion of a thermal model spectrum, using typical parameters for a small flare, we see the apearance of the local minima or "dip" in the beam only case but in the beam and waves case there is always a negative gradient.


	== Conclusions ==		== Conclusions ==

-	The work shown here is a step towards a more complete treatment of electron transport in solar flares and highlights that the inclusion of wave-particle interactions flattens sharp low energy cutoffs in the inital accelerated electron distribution.	+	The work shown here is a step towards a more complete treatment of electron transport in solar flares and highlights that the inclusion of wave-particle interactions flattens sharp low energy cutoffs in the inital accelerated electron distribution. There are still other processes that are not included here but it does demonstrate that the standard "thick-target" interpretation is insufficient to explain the RHESSI observations.

	[[category:Nugget]]		[[category:Nugget]]

Image:Fwc 10009.jpg

2009-11-19T14:56:29Z

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-	The electron distribution f and energy density of the waves W showing the simulation results from the 2 different simulations: Coulomb collisions only on the left, including wave-particle interactions on the right.	+	The electron distribution f and energy density of the waves W showing the simulation results from the 2 different simulations: Coulomb collisions only on the left, including wave-particle interactions on the right.) A movie of this can be found [http://www.youtube.com/watch?v=uO2U7WeHu1Q here]

Dips and Waves

2009-11-19T14:55:03Z

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	In the standard interpretation of RHESSI's hard x-ray emission, a powerlaw of acceelerated electrons above a sharp low energy cutoff leave the corona travelling down to the chromosphere. As they propagate they lose energy to the background plasma through Coloumb collisions, eventually losing their energy in the dense chromosphere, where they emit hard X-rays as observed by RHESSI, heating the local plasma which expands back upwards.		In the standard interpretation of RHESSI's hard x-ray emission, a powerlaw of acceelerated electrons above a sharp low energy cutoff leave the corona travelling down to the chromosphere. As they propagate they lose energy to the background plasma through Coloumb collisions, eventually losing their energy in the dense chromosphere, where they emit hard X-rays as observed by RHESSI, heating the local plasma which expands back upwards.
		+
		+	[[Image:Fwc_10009.jpg\|frame\|center\|'''Figure 1:''' The electron distribution f and energy density of the waves W showing the simulation results from the 2 different simulations: Coulomb collisions only on the left, including wave-particle interactions on the right.) A movie of this can be found [http://www.youtube.com/watch?v=uO2U7WeHu1Q here]]]
		+
		+	[[Image:fig3b.png\|frame\|center\|'''Figure 2:''' The mean electron flux spectrum <nVF> for the simulation with Coulomb collisions actng on the beam only (left) and the inclusion of wave-particle interaction (right). The black line shows the simulation result, the orange dashed line an overplotted thermal model spectrum. The total spectrum is the dashed green line, indicating the presence of a dip in the Coulomb collision only case.]]

Image:Fig3b.png

2009-11-19T14:48:38Z

uploaded "[[Image:Fig3b.png]]" The mean electron flux spectrum <nVF> for the simulation with Coulomb collisions actng on the beam only (left) and the inclusion of wave-particle interaction (right). The black line shows the simulation result, the orange dashed line an overplotted therma

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Dips and Waves

2009-11-19T14:31:25Z

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	== Introduction ==		== Introduction ==

		+	There has been some heated discussion (for instance [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/The_Rise_and_Fall_of_The_Low_Energy_Cut_Off]) as to whether the "dip" seen in the mean electron spectrum derived from RHESSI flare observations is a real feature as it can often be removed be correcting for albedo. But for flares with relatively low thermal mission the standard "thick-target" interpretation says that the "dip" must be there. This model only accounts for Coulomb collisions between the propagating beam of accelerated electrons and the background plasma. In this nugget we present simulation results from our recent paper [http://arxiv.org/abs/0911.0314] where we show what happens to the dip when you also include wave-particle interactions between the beam and background plasma.

-	~~The standard interpretation of RHESSI's hard x~~-~~ray emission is of electrons accelerated in the corona that propgated down to the chromosphere, colliding with the background plasma and eventually stopping.~~	+	== Wave-particle Interactions ==

-	~~[[category:Nugget]]~~	+	In the standard interpretation of RHESSI's hard x-ray emission, a powerlaw of acceelerated electrons above a sharp low energy cutoff leave the corona travelling down to the chromosphere. As they propagate they lose energy to the background plasma through Coloumb collisions, eventually losing their energy in the dense chromosphere, where they emit hard X-rays as observed by RHESSI, heating the local plasma which expands back upwards.


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	The work shown here is a step towards a more complete treatment of electron transport in solar flares and highlights that the inclusion of wave-particle interactions flattens sharp low energy cutoffs in the inital accelerated electron distribution.		The work shown here is a step towards a more complete treatment of electron transport in solar flares and highlights that the inclusion of wave-particle interactions flattens sharp low energy cutoffs in the inital accelerated electron distribution.
		+
		+	[[category:Nugget]]

Tohban Report 2009-11-18

2009-11-18T20:07:05Z

New page: {{Infobox Tohban Report| |start_date = 10 November 2009 |end_date = 18 November 2009 |tohban_name = Lindsay Glesener |tohban_email = glesener@ssl.berkeley.edu |next_tohban = Juan Carlos M...

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{{Infobox Tohban Report|
|start_date = 10 November 2009
|end_date = 18 November 2009
|tohban_name = Lindsay Glesener
|tohban_email = glesener@ssl.berkeley.edu
|next_tohban = Juan Carlos Martinez-Oliveros
}}

== Solar Activity ==

There is one named new-cycle active region (11031), although some other regions with magnetic flux are also visible on the magnetogram. No RHESSI flares.

== Memory Management ==

The SSR had a minimum of 19% and a maximum of 49%. The level is higher than usual due to a reduced number of passes per day.

== Data Gaps ==

Currently investigating.

== Special Operations ==

The high voltage was lowered on a couple of the detectors.

[[Category:Tohban Report]]
[[Category:Tohban]]

RHESSI Workshop Series

2009-11-18T14:30:36Z

New page

The RHESSI workshop series includes the following meetings in reverse chronological order

* [http://rhessi10.wordpress.com/ 10th General workshop], ''Annapolis Maryland'', August 1-5, 2010
* 9th General workshop, Genoa Italy, 1-5 September, 2009
* Solar activity during the onset of solar cycle 24, Napa California, 7-12 December, 2008
* 8th general workshop, Postdam Germany, 2-6 September, 2008
* 7th general workshop, Santa Cruz California, 25-29 June, 2007
* RHESSI-Nessie V, Berkeley California, 6-8 November, 2006
* 6th general workshop, Meudon France, 5-8 April, 2006
* RHESSI-Nessie IV, Paris France, 3-4 April, 2006
* 5th General workshop, Locarno Switzerland, 7-11 June, 2005
* RHESSI-Nessie III, Glasgow Scotland, March 30 - April 1, 2005
* RHESSI-SOHO-TRACE, Sonoma California, 8-11 December, 2004
* Data analysis workshop, Berkeley California, 18-22 October, 2004
* Fourth general workshop, Paris France, 26-28 July, 2004
* RHESSI-Nessie II, Glasgow Scotland, 24-26 March, 2004
* ACE-RHESSI-WIND, Taos New Mexico, 7-9 October, 2003
* RHESSI-Nessie I , Glasgow Scotland, 4-6 June, 2003
* 2nd General workshop, Greenbelt Maryland, 20-21 June, 2003
* 1st General workshop. Berkeley California, 17-20 October, 2002
* Zürich data analysis workshop

Blind Image Analysis

2009-11-16T21:23:49Z

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	[[Image:Test00 sc1-3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 1 (sam)'''		[[Image:Test00 sc1-3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 1 (sam)'''
	TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations. BOTTOM: UV smooth (s 3-9)]]		TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations. BOTTOM: UV smooth (s 3-9)]]
		+
		+	[[Image:uv_smooth_blind_map0.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 1 (anna)'''
		+	uv_smooth images with different subcollimator combinations (s1-9, s2-9, s3-9).]]
		+
	== Test Image #2 (i = 1)==		== Test Image #2 (i = 1)==

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	TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations (s1-9 did not converge). BOTTOM: UV smooth (s 3-9)]]		TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations (s1-9 did not converge). BOTTOM: UV smooth (s 3-9)]]
		+
		+	[[Image:uv_smooth_blind_map1.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 2 (anna)'''
		+	uv_smooth images with different subcollimator combinations (s1-9, s2-9, s3-9).]]

	== Test Image #3 (i = 2)==		== Test Image #3 (i = 2)==
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	[[Image:Test02 sc1-3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 3 (sam)'''		[[Image:Test02 sc1-3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 3 (sam)'''
	TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations. BOTTOM: UV smooth (s 3-9)]]		TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations. BOTTOM: UV smooth (s 3-9)]]
		+
		+	[[Image:uv_smooth_blind_map2.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 3 (anna)'''
		+	uv_smooth images with different subcollimator combinations (s1-9, s2-9, s3-9).]]

	== Test Image #4 (i = 3)==		== Test Image #4 (i = 3)==
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	[[Image:Test03 sc1-3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 4 (sam)'''		[[Image:Test03 sc1-3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 4 (sam)'''
	TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations. BOTTOM: UV smooth (s 3-9)]]		TOP: clean images (uniform weighting) with different subcollimator combinations (s1-9, s2-9, s3-9). TOP MIDDLE: same for natural weighting. BOTTOM MIDDLE: MEM_NJIT images for different subcollimator combinations. BOTTOM: UV smooth (s 3-9)]]
		+
		+	[[Image:uv_smooth_blind_map3.jpg\|border\|text-top\|center\|thumb\|600px\|'''Figure 4 (anna)'''
		+	uv_smooth images with different subcollimator combinations (s1-9, s2-9, s3-9).]]

Image:Uv smooth blind map3.jpg

2009-11-16T21:16:55Z

uploaded "[[Image:Uv smooth blind map3.jpg]]" uv_smooth images with different subcollimator combinations (s1-9, s2-9, s3-9).

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