1. Axions from the Sun? H. S. Hudson SSL, UC Berkeley http://sprg.ssl.berkeley.edu/~hhudson/presentations/berkeley.090220/

2. SSL Feb. 20, 2009 2/28 What is this about? Axions are elementary particles theorized by Peccei and Quinn to “solve the strong CP problem” The name, due to F. Wilczek, refers to the soap powder Axions, being charge-neutral and weakly interacting, are a prime candidate to explain dark matter in the Universe The solar core should be a copious source of axions and we might detect them using X-ray techniques

3. SSL Feb. 20, 2009 3/28 Outline Basic ideas Solar tutorial - spectral, spatial, temporal properties - why the chromosphere is important Existing instrumentation Future instrumentation

4. SSL Feb. 20, 2009 4/28 Outline Basic ideas Solar tutorial - spectral, spatial, temporal properties - why the chromosphere is important Existing instrumentation Future instrumentation

5. SSL Feb. 20, 2009 5/28 Outline Basic ideas Solar tutorial - spectral, spatial, temporal properties - why the chromosphere is important) Existing instrumentation Future instrumentation Solar atmosphere

6. SSL Feb. 20, 2009 6/28 Predicted solar fluxes Carlson & Tseng (1996) 10 mCrab X-ray spectrum Moriyama (1996) The 14.4 keV line is the  -ray used in Mössbauer studies, here photonuclear The main ~5 keV emission, due to the Primakoff effect, is shown here for a specific value of the coupling constant g

7. SSL Feb. 20, 2009 7/28 Geometries for solar axion detection Solar core Photosphere Coronal B-Field Earth 123 1: RHESSI, Yohkoh, Hinode 2: CAST * or 57 Fe resonance 3: Conversion in the Earth’s field * Geomagnetic Field X-ray/axion flux * Davoudiasl & Huber, 2005 * Andriamonje et al. 2007

8. SSL Feb. 20, 2009 8/28 Solar atmosphere

9. SSL Feb. 20, 2009 9/28 Giant magnet

10. SSL Feb. 20, 2009 10/28 CAST at CERN

11. SSL Feb. 20, 2009 11/28 Churazov et al. (2008) Solar X-ray spectra X-ray background (negative source!) RHESSI upper limits (Hannah et al. 2007) Albedo CR interactions { 11-year cycle

12. SSL Feb. 20, 2009 12/28 Signatures Spectral: main axion X-ray component is 4-5 keV Spatial: sources should be near disk center and correlate with B perp Temporal: should be steady modulo B perp Polarization: following B

13. SSL Feb. 20, 2009 13/28 X-ray Images 1

14. SSL Feb. 20, 2009 14/28 X-ray Images 2

15. SSL Feb. 20, 2009 15/28 X-ray Timeseries from GOES High activity - October 2003Low activity - January 2009

16. SSL Feb. 20, 2009 16/28 Conversion in the solar atmosphere : Need Need n < n 0 (m) What (n, B) do we have?

17. SSL Feb. 20, 2009 17/28 First approximation to solar (B, n): dipole field, spherical symmetry B perp ~ 10 -3 T at photosphere “VAL-C” semi-empirical model

18. SSL Feb. 20, 2009 18/28 Second approximation: complex field and dynamic plasma Druckmuller eclipse imagery* Gary (2001) * http://www.zam.fme.vutbr.cz/~druck/Eclipse/index.htm

19. SSL Feb. 20, 2009 19/28 Simulations of the chromosphere MHD simulations by O. Steiner (Kiepenheuer Institut für Sonnenphysik, Freiburg)

20. SSL Feb. 20, 2009 20/28 The solar magnetic field 1 We only really know the line-of-sight component of the photospheric field (Zeeman splitting, Hanle effect) The coronal field is force-free and currents circulate in it (  xB =  B) Some of the field is “open,” ie linking to the solar wind We estimate the coronal field by extrapolation All knowledge is also limited by telescope resolution to scales of 100 km or so A potential representation (no coronal currents) is often used as a first approximation (“PFSS”)

21. SSL Feb. 20, 2009 21/28 The solar magnetic field 2 The “seething field” (Harvey et al., 2007) Hidden magnetism (Trujillo Bueno et al., 2004) The Hinode 40-gauss field (Lites et al., 2008)

22. SSL Feb. 20, 2009 22/28 Using the Schrijver-DeRosa PFSS solar magnetic model Line-of-sight B component derived from photospheric Zeeman observations Potential-field extrapolation used to approximate the coronal field Integration across theoretical axion source distribution => 2

23. SSL Feb. 20, 2009 23/28 PFSS Prediction for solar 2 Strengths and Weaknesses The solar 2 product is much larger than that achievable in laboratories The field is strongly variable in both space and time, and not well known quantitatively Strong fields drive solar activity, potentially confused with the axion signal or a source of background

24. SSL Feb. 20, 2009 24/28 Solar X-ray telescopes Yohkoh (focusing) RHESSI (image modulation) Hinode (focusing)

25. SSL Feb. 20, 2009 25/28 RHESSI “tail dragging mode”

26. SSL Feb. 20, 2009 26/28 Studying the Yohkoh and Hinode soft X-ray data Prediction: increasing levels of theoretical source intensity Yohkoh observation: selection for no disk center active regions at solar minimum (1996) Hinode observation via histogram analysis of 400 images

27. SSL Feb. 20, 2009 27/28 Churazov et al. (2008) Solar X-ray spectra X-ray background (negative source!) RHESSI upper limits (Hannah et al. 2007) Albedo CR interactions { 11-year cycle

28. SSL Feb. 20, 2009 28/28 Signatures Spectral: main axion X-ray component is 4-5 keV Spatial: sources should be near disk center and correlate with B perp Temporal: should be steady modulo B perp Polarization: following B

29. SSL Feb. 20, 2009 29/28 Figure of Merit for X-ray and  -ray observations  = efficiency A = detector area  t = integration time B = background rate  E = energy range

30. SSL Feb. 20, 2009 30/28 Figure of Merit results CAST  1.0 RHESSI0.005 57 Fe*2 x 10 3 X-ray**7 x 10 4 *14.4 kev photonuclear  -ray **1000 cm 2, B = 2x10 -4 (cm 2.sec.keV) -1 n.b. X-ray and  -ray estimates based on a SMEX-level satellite plan - one could do better! This model is better than a “cubesat”

31. SSL Feb. 20, 2009 31/28 Conclusions Conversion in the solar magnetic field should be the best way to see solar thermal axions of low mass The solar atmosphere is not well understood, so any interpretation of an axion signal will be fuzzy (we should be so lucky!) Calculations of resonance conditions in solar (B, n) distribution need to be done Future instrumentation could greatly improve on the sensitivity

32. Axions from the Sun? H. S. Hudson SSL, UC Berkeley http://sprg.ssl.berkeley.edu/~hhudson/presentations/berkeley.090220/