1. A Yohkoh search for Axions H. S. Hudson (SSL Berkeley) L. W. Acton (MSU)

2. Bozeman, April 2007 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

3. Bozeman, April 2007 Axions and X-rays Conversion in coronal field CAST and other experiments Carlson & Tseng, Phys. Letters B 365, 193 (1996) for Yohkoh

4. Bozeman, April 2007 The CERN Axion Solar Telescope (CAST)

5. Bozeman, April 2007

6. CAST results Zioutas et al., 2006

7. Bozeman, April 2007 Spectrum of the solar axion source

8. Bozeman, April 2007 Axion conversion in a magnetic field Bottom line: the X-ray intensity will increase as, but a dense medium induces oscillations that suppress the conversion:

9. Bozeman, April 2007 Ways to detect solar axions Solar core Photosphere AR Solar “dipole” Earth 123 1: RHESSI, Yohkoh, etc 2: CAST or other ground-based 3: Conversion in the Earth’s field

10. Bozeman, April 2007 Merits of the different solar axion sites Sunlit space (e.g., Yohkoh): one gets a huge advantage in 2, but is solar noise a problem? Ground-based observations (e.g., CAST): very low background, but low signal Dark-side space, using terrestrial field: low 2, but free of solar noise

11. Bozeman, April 2007 The solar axion source Carlson & Tseng, Phys. Letters B 365, 193 (1996) Zioutas et al., ApJ 607, 575 365 (2004) Zioutas et al., PRL 94, 121301 (2005) Serpico & Raffelt, internal CAST report 2007

12. Bozeman, April 2007 Predicted solar flux Carlson & Tseng, Phys. Letters B 365, 193 (1996) 10 mCrab X-ray spectrum

13. Bozeman, April 2007

14. The Solar magnetic field for axion purposes The field is highly structured and time-variable - So the axion flux will be also - These signatures may help to extract the axion signal, if any… - If there only were axions, we could use them for solar physics… The PFSS models give us a tool to investigate these dependences - The Schrijver-Derosa IDL software for PFSS magnetic modeling is very convenient

15. Bozeman, April 2007 A typical Schrijver-Derosa PFSS solar magnetic model

16. Bozeman, April 2007 What is PFSS? “Potential field source surface:” the solar photospheric field is extrapolated into the corona from a potential expansion The field lines intersecting a “source surface” at 2.5R sun become radial and “open” Such a model is purely mathematical but somehow captures the physics involved in magnetizing the solar wind The Schrijver-Derosa version constructs a full 3D map each six hours, using SOHO observations

17. Bozeman, April 2007 Magnetic indices - one year

18. Bozeman, April 2007 Magnetic indices - one month

19. Bozeman, April 2007 The RHESSI Quiet-Sun Search Hannah et al., RSI, 2007a

20. Bozeman, April 2007 Thanks to Gordon Hurford

21. Bozeman, April 2007 Slat modulation for off-axis pointing

22. Bozeman, April 2007 RHESSI off-axis pointing in the “tail-dragging mode”

23. Bozeman, April 2007 RHESSI fan-beam observation of a GOES A-class microflare

24. Bozeman, April 2007 RHESSI fan-beam observation of the Crab Nebula

25. Bozeman, April 2007 RHESSI fan-beam observation of… Nothing

26. Bozeman, April 2007 A small RHESSI fan-beam puzzle: Why is the GOES correlation so good?

27. Bozeman, April 2007 The RHESSI Axion Search Hannah et al., ApJL 2007b

28. Bozeman, April 2007 The Yohkoh/SXT Axion Search: Is it worthwhile? The advantages are - Much lower background - High-resolution direct imaging - Plenty of data The disadvantages are - Small effective area - The background is not that low really - The spectral range is not optimum

29. Bozeman, April 2007 The Yohkoh/SXT Axion Search: Is it worthwhile? Yes - The data are in wonderful shape - The software works and we remember how to use it - The data give access to a range of parameter space inaccessible to other methods - Nobody else has done this important thing before even though the data are in the public domain

30. Bozeman, April 2007 The Yohkoh/SXT Axion Search: How shall we proceed? Method 1: add up all the solar-minimum images and see if there is a bright spot Method 2: Make a search using the thick filters available in 1992 (less solar confusion) Method 3: Look for deviations of AR brightness that match the magnetic template in a time-series analysis

31. Bozeman, April 2007 Studying the Yohkoh/SXT data

32. Bozeman, April 2007 Studying the Yohkoh/SXT data

33. Bozeman, April 2007 Studying the Yohkoh/SXT data

34. Bozeman, April 2007 Axion parameter space Zioutas et al., 2006 Yohkoh? RHESSI

35. Bozeman, April 2007 The competition: Who gets to find the first axion? CAST continues Neat idea for CAST observations of 57 Fe  -ray at 14.4 keV (Jakovcic et al. 2007) Laboratory searches at radio frequencies (van Bibber) Various astrophysical consequences A dedicated solar axion observatory in space?

36. Bozeman, April 2007 End Thanks for discussion and input: Iain Hannah, Gordon Hurford, Bob Lin, Karl van Bibber