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

A Yohkoh search forAxions

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

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Axions and X-rays

• Conversion in coronal field

• CAST and other experiments

• Carlson & Tseng, Phys. Letters B 365, 193 (1996) for Yohkoh

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The CERN Axion Solar Telescope (CAST)

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CAST results

Zioutas et al., 2006

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QuickTime™ and aTIFF (Uncompressed) decompressor

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Spectrum of the solar axion source

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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:

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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

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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

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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

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Predicted solar flux

Carlson & Tseng, Phys. Letters B 365, 193 (1996)

10 mCrab X-ray spectrum

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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

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A typical Schrijver-DerosaPFSS solar magnetic model

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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

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Magnetic indices - one year

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Magnetic indices - one month

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The RHESSI Quiet-Sun SearchHannah et al., RSI, 2007a

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QuickTime™ and aGIF decompressor

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Thanks to Gordon Hurford

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Slat modulation for off-axis pointing

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RHESSI off-axis pointing in the“tail-dragging mode”

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RHESSI fan-beam observation of a GOES A-class microflare

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RHESSI fan-beam observation of the Crab Nebula

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RHESSI fan-beam observation of…Nothing

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A small RHESSI fan-beam puzzle:Why is the GOES correlation so good?

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The RHESSI Axion SearchHannah et al., ApJL 2007b

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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

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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

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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

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Studying the Yohkoh/SXT data

QuickTime™ and aTIFF (LZW) decompressor

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Studying the Yohkoh/SXT data

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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Studying the Yohkoh/SXT data

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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Axion parameter space

Zioutas et al., 2006

Yohkoh?

RHESSI

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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?

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End

Thanks for discussion and input:Iain Hannah, Gordon Hurford, Bob Lin, Karl van Bibber