A Yohkoh search for Axions H. S. Hudson (SSL Berkeley) L. W. Acton (MSU)
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Transcript of A Yohkoh search for Axions H. S. Hudson (SSL Berkeley) L. W. Acton (MSU)
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
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
Bozeman, April 2007
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Spectrum of the solar axion source
Bozeman, April 2007
Axion conversion in a magnetic field
Bottom line: the X-ray intensity will increase as <(BL)2>, but a dense medium induces oscillations that suppress the conversion:
Bozeman, April 2007
Ways to detect solar axions
Solar core
Photosphere
AR
Solar“dipole”
Earth
1 2 3
1: RHESSI, Yohkoh, etc2: CAST or other ground-based3: Conversion in the Earth’s field
Bozeman, April 2007
Merits of the different solar axion sites
• Sunlit space (e.g., Yohkoh): one gets a huge advantage in <BL>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 <BL>2 , but free of solar noise
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
Bozeman, April 2007
Predicted solar flux
Carlson & Tseng, Phys. Letters B 365, 193 (1996)
10 mCrab X-ray spectrum
Bozeman, April 2007
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
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 2.5Rsun 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
Bozeman, April 2007
QuickTime™ and aGIF decompressor
are needed to see this picture.
Thanks to Gordon Hurford
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
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
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
Bozeman, April 2007
Studying the Yohkoh/SXT data
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Bozeman, April 2007
Studying the Yohkoh/SXT data
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Bozeman, April 2007
Studying the Yohkoh/SXT data
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Bozeman, April 2007
The competition:Who gets to find the first axion?
• CAST continues• Neat idea for CAST observations of 57Fe -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?