X-ray solar flare loops: temporal variations in length, corpulence, position, temperature and pressure.

Transcription

1 e- X-ray solar flare loops: temporal variations in length, e- corpulence, position, temperature and pressure. e- Natasha Jeffrey and Eduard Kontar University of Glasgow, Scotland, UK 23rd August 2005

2 Flare X-ray (>3 kev) emission - corona to chromosphere corona 13-May-2013 standard flare chromosphere ~3-25 kev thermal/ non-thermal? loop-top X-rays X-ray bremsstrahlung ~ > 30 kev non-thermal footpoint X-rays RHESSI

3 Flare X-ray (>3 kev) emission - coronal X-rays only ~3-25 kev non-thermal? loop-top X-rays RHESSI 13-May Aug-2005 strong coronal corona emission Bulk of X-ray emission is produced in the coronal loop. chromosphere weak or no footpoint X-rays

4 Spatial properties of coronal X-ray sources with energy :27-14:31 Loop Length: :27-14:31 E2<E1 Acceleration region kev Pixon VIS FWDFIT Direction parallel to the guiding B-field. L(E) ~ LAR+1/(2Kn) E 2 non-thermal emission (Xu et al (2008), Kontar et al (2011), Guo et al (2012,2013)) chromosphere

5 Spatial properties of coronal X-ray sources with energy Loop Width: :27-14:31 E2<E1 Acceleration region kev Direction Pixon VIS FWDFIT perpendicular to the guiding B-field. W(E) ~ W0 + DM E Presence of magnetic turbulence (Kontar et al. (2011)). chromosphere

6 RHESSI and Visibility forward fitting (VIS FWDFIT) :27-14:31 explain the measured vertical sizes of the sources. 2. X-RAY VISIBILITIES AND CHARACTERISTIC SIZ X-ray visibilities - 2D Fourier components of the X-ray source (Hurford et al. 2002; Schmahl et al. 2007) The spatial information about an X-ray source measured RHESSI for a given energy range and time interval can presented (Hurford et al. 2002; Schmahletal. 2007) ast dimensional Fourier components or X-ray visibilities: V (u, v; ɛ) = I(x,y; ɛ)e 2πi(xu+yv) dxdy, x y kev Pixon VIS FWDFIT where I(x,y; ɛ) istheobservedimageatphotonenergy Then, the VIS reconstructed FWDFIT takes X-raya image simple I(x,y; form, ɛ) such istheinve as Fourier transformation of measured X-ray visibilities V (u, v an elliptical gaussian - compares this with Each of the nine RHESSI RMCs measures V (u, v; ɛ) atafi spatial frequency the real X-ray (or a circle visibilities in the (u, v) plane)correspond to its angular resolution and with a position angle along circles, which varies continuously as the spacecraft rotates. N detector grids with angular resolutions growing with dete number are logarithmically spaced in the (u, v)plane.since measured visibilities sparsely populate the (u, v)planeandh statistical uncertainties, the direct inverse Fourier transform impractical (Hurford et al. 2002;Schmahletal.2007;Mass et al. 2009) andalternativemethodsshouldbeused. Assuming a characteristic shape of the X-ray source, one directly find the position and characteristic sizes by fitting a

7 RHESSI and Visibility forward fitting (VIS FWDFIT) :27-14: kev Pixon VIS FWDFIT explain the measured vertical sizes of the sources. 2. X-RAY VISIBILITIES AND CHARACTERISTIC SIZ X-ray visibilities - 2D Fourier components of the X-ray source (Hurford et al. 2002; Schmahl et al. 2007) The spatial information about an X-ray source measured RHESSI for a given energy range and time interval can presented (Hurford et al. 2002; Schmahletal. 2007) ast dimensional Fourier components or X-ray visibilities: V (u, v; ɛ) = I(x,y; ɛ)e 2πi(xu+yv) dxdy, x y where I(x,y; ɛ) istheobservedimageatphotonenergy Then, the VIS reconstructed FWDFIT takes X-raya image simple I(x,y; form, ɛ) such istheinve as Fourier transformation of measured X-ray visibilities V (u, v an elliptical gaussian - compares this with Each of the nine RHESSI RMCs measures V (u, v; ɛ) atafi spatial frequency the real X-ray (or a circle visibilities in the (u, v) plane)correspond to its angular resolution and with a position angle along circles, which varies continuously as the spacecraft rotates. N detector grids with angular resolutions growing with dete number are logarithmically spaced in the (u, v)plane.since measured visibilities sparsely populate the (u, v)planeandh statistical uncertainties, the direct inverse Fourier transform impractical (Hurford et al. 2002;Schmahletal.2007;Mass et al. 2009) andalternativemethodsshouldbeused. Assuming a characteristic shape of the X-ray source, one directly find the position and characteristic sizes by fitting a We studied 3 M-class events observed by Xu et al. (2008) and Kontar et al. (2011), concentrating on loop changes with time instead of energy: 1. 23rd August 2005, 2. 14th/15th April 2002 and 3. 21st May 2004

8 Jeffrey and Kontar: The time varying spatial and spectral properties o Flare 1-23rd August 2005 event Lightcurve peak X-rays kev kev kev kev 14:24 14:28 14:32 14:36 14:40 Observation Time Limb event with coronal emission in the range ~ kev. Imaging time - 14:22:00-14:40:00 in two or four minute intervals. Weak kev footpoints emerging at 14:36:00. 14:22-14:26 14:28-14:30 14:32-14:34 14:36-14: kev kev kev

9 23rd August 2005 event - Imaging results 23-August-2005 flare clean vis fwdfit The loop length and loop width change with time. Length [arcsec] Width [arcsec] Radial distance [arcsec] Peak X-rays kev kev kev 14:24 14:28 14:32 14:36 14:40 Observation Time

10 I [photons s -1 kev -1 cm -2 ] Residuals rd August 2005 event - Spectroscopy results 23-August-2005 flare data-background thermal thick target background Energy [kev] The loop length and loop width change with time Energy [kev] EM x [cm -3 ] Temperature [MK] kev Peak X-rays 14:24 14:28 14:32 14:36 14:40 Observation Time Peak temperature before peak X-rays Fig. 5. (left column) 23rd August 2005, (middle at Antiochos each of the& selected Sturrock plotting 1978; energies Siding (see & each time, 4th row - changes in loop radial position w temperature Fig. Spicer 5. (left 1980; column) Gunkler with time. 23rd et The August al. 1984; dashed 2005, lines (middle on all p these at McTiernan each peaks of the are et selected points al of plotting change energies in the source (see each time, 4th row - changes in loop radial position w

11 oop. This is important as a loop that is very curved and approaching 3. Inferring other the parameters shape centroid towards ends of the loop, often masking small eters 23rd August 2005 event - Inferred parameters Peak position with orand energy (this was especially significant for the X-raysV, at a given tim From the time width length parameters we can infer the changes in source volume, 23-August-2005 flare 6 2 Loop volume x 1027 [cm3] 5 rameters we can infer the changes in source volume, V, at πwal given time August 2005 event). and energy, by assuming that the volume of the loop is given by V = that is, a cylindrical loop πw L the where volume isfwhm given and by V is,3fwhm a cylindrical loop,an accurat L isof thethe looploop length W= is the4loopthat width of each source. estimate ofw theissource volumewidth is very FWHM important as it each allows source. many other parameters to be inferred WHM and the loop of An accurate 2 ers Number density x 1010 [cm-3] By performing spectroscopy of each of our events we can obtain two useful parameters: emissio 1 e is very important as it allows many other parameters to be inferred. meters we can infer the changes in source volume, V, at a given time measure, clean EM and plasma temperature, T. Then, the combination of imaging and spectroscop L vis fwdfit 6 each of our events we obtain two useful parameters: emission eof volume of the ishow given by Vcan = πw that is, a cylindrical loop, allows us toloop infer other parameters are changing throughout the life of the flare. The plasm andp,spectroscopy HM and W is the width FWHM of Antheaccurate number density, n, can be viaeach n = source. EM/V, pressure, from P = nkb T, where kb i mperature, T. loop Then, theobtained combination of imaging kev kev kev s very asconstant it allowsand many other to bee,inferred. theimportant Boltzmann finally theparameters energy density, from 2 E = 3nkB T. I [photons s-1 kev-1 cm-2] parameters are changing throughout the life of the flare. The plasma clean 10 each of our events we data-background can obtain two useful parameters: emission fwdfit thermalthe pressure, P, from P 250 tained viavis n= EM/V, = nkb T, where kb is 4 ally the energy density, E, from E = 3nkB T changes with time 10 Energy [kev] 50 Pressure [g/(cm s2)] perature, T. Then, the combination of imaging and spectroscopy thick target Spatial and spectral changes with time 200 background rametersthe are energy changingdensity, throughout life of flare.bthe finally E,the from E the = 3nk T. plasma ned10via n = EM/V, the pressure, P, from P = nkb T, where kb is :24 14:28 14:32 14:36 Observation Time 14:40

12 23rd August 2005 flare - 3 phases: Phase 1- Peak in plasma temperature Phase 2 - Peak in X-ray emission and smallest loop width Width [arcsec] Lightcurve Plasma Temperature [MK] kev kev kev Phase 3 - Peak in thermal pressure. Pressure [g/(cm s 2 )] kev 14:24 14:28 14:32 14:36 14:40

13 Results summary and other events We observed two main temporal results for this type of event: Contraction and then an expansion of the loop volume before and after the peak in X-ray emission. Three temporal phases: peak in plasma temperature, peak in X- ray emission/smallest loop size and peak in thermal pressure. changes in time at selected energies of kev (left), kev (middle) and kev (right). elected time of 14:28:00-14:30:00 for each energy range allowing the overall shape of the source to be ntours (size) and correspondingly coloured asterisks (sourcefig. centroid 2. Asposition). Figure 2 but for Flare 2-14th April We see the same results for two other coronal X-ray events. 14/15 April st May 2004

14 Pressure [g/(cm s 2 )] Width [arcsec] Lightcurve Plasma Temperature [MK] :00 00:04 00:08 00:12 00:16 14/15 Apr :20 Pressure [g/(cm s 2 )] Width [arcsec] Lightcurve Plasma Temperature [MK] st May :44 23:48 23:52 23:56

15 Possible explanations and future work? 1. A reduction in B pressure? Liu et al. 2009, Gosain 2012 etc. 2. Thermal conduction chromospheric evaporation? 3. Thermal pressure balances and overcomes the reduction in B pressure?

16 Possible explanations and future work? 1. A reduction in B pressure? 2. Thermal conduction chromospheric evaporation? 3. Thermal pressure balances and overcomes the reduction in B pressure? Future studies/common or different trends for all flares? New events with SDO data multiple loops interacting? An X-class event showed similar results using Clean (Caspi & Lin 2010). What about events with strong coronal emission and footpoints? Jeffrey, N., Kontar, E.: 2013, Temporal Variations of X-Ray Solar Flare Loops: Length, Corpulence, Position, Temperature, Plasma Pressure, and Spectra. The Astrophysical Journal, Volume 766, Issue 2, article id. 75, 12 pp