The Sun in X-rays

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The Sun in X-rays

• Low Energies To Be Further Investigated
• Marino Maiorino

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Summary

• The Sun and Its Structure
• Light as a Measurement Tool
• The Corona Mistery
• The Present Theories
• Watch the Sun!
• Going to Space
• X-ray Imaging Detectors
• New Technologies
• Conclusions

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The Sun and Its Structure

• Core
• p-p reaction
• 1.5107 K
• Radiative Zone
• Convective Mantle
• Outer, atmosphere layers
• Photosphere (5800 K)
• Chromosphere
• Transition region
• Corona

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Light as a Measurement Tool

• Black body spectrum and a bunch of laws
• Temperature as a Function of Depth
• lmaxT constant!

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The Corona Mystery

• Whats Corona?
• Outer atmosphere of the Sun.
• Thickness is a million km, but is possibly even
  larger.
• The Corona is too hot to emit visible light.

• How can we see it?
• During a solar eclipse, observe light reflected
  from the dust particles associated with it.
• Directly, using an X-ray telescope.

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The Corona Mystery

• Temperatures in Corona
• Temperature gt 106 K emission in X-rays!

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The Corona Mystery

• In literature you can find
• The reason for the enormous temperatures in the
  corona is not well understood, but may relate to
  heating by the Sun's magnetic field lines
• Theories
• Wave dissipation
• Nano-flares
• Also see
• http//arxiv.org/PS_cache/astro-ph/pdf/0203/020316
  7.pdf

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The Present Theories

• Wave Dissipation
• Acoustic heating ruled out due to dependency of
  Lx on rotational speed
• Magneto-acoustic heating heating by waves and/or
  particles induced from magnetic fields at the
  bottom of the corona.

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The Present Theories

• Nano-Flares
• Sun emits strong bursts of X-rays before the UV
  lightning of flares
• A large number of very small nano-flares was
  proposed as a mechanism to heat Corona
• Theory at 250000 K some magnetic reconnection
  takes place between chromosphere and corona
• SOHO saw low temp. gas (lt400000K) going down
  hotter gas going up
• Nowadays it is thought to be one of the
  mechanisms involved in coronal heating, NOT the
  most important one

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Watch the Sun!

• Usefulness of a Sun-staring mission to monitor
  Space weather
• Short radio waves propagation (e.g. cellphones,
  radars and antennas)
• Artificial satellite communications (research,
  GPS-navigation satellites)
• Artificial satellite orbits (Earth atmosphere
  inflation)
• Electric power grids (tranformers overload)
• Health-damaging radiations (astronauts, jet
  passengers)

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Going to Space

• Our atmosphere, again...

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X-ray Imaging Detectors

• History of X-ray detection in space
• Uhuru (US), 1970-73, 2-20 keV, proportional
  counters
• OSO7 (US), 1971-74, 1 keV 10 MeV, prop.
  counters X-ray telescope
• SAS3 (US), 1975-79, 0.1-60 keV, prop. counters
  collimated
• HEAO1 (US), 1977-79, 0.2 keV 10MeV, plenty of
  experiments
• Einstein (US), 1978-81, 0.2-20 keV, grazing
  incidence telescope
• Ginga (JAP), 1987-91, 1-500 keV, prop. counters
• GRANAT (RUS-EU), 1989-98, 2 keV 100 MeV, coded
  mask telescope
• ROSAT (D-US-UK), 1990-99, 0.1-2.5 keV, X-ray
  telescope high resolution imager
• XMM-Newton (EU), 1999, 0.1-15 keV, grazing
  incidence X-ray imaging telescope
• Chandra (US), 1999, 0.1-10 keV, grazing incidence
  telescope

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X-ray Imaging Detectors

• So low energies?
• 2106 K / 11604 172 eV (a few nm)
• In the soft X-ray band (0.12 - 5 keV) the Sun
  is the brightest X-ray source (by a factor of
  106)
• X-ray Sun Luminosity 1027 erg/s!

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X-ray Imaging Detectors

• Focusing Technologies
• X-ray (grazing) telescopes
• Coded mask aperture telescopes
• Detection Technologies
• Imaging Proportional Counters
• Microchannel Plates
• CCD Spectrometers
• Imaging Gas Scintillation Proportional Counters

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X-ray Imaging Detectors

• Existing Projects
• SOHO (NASA-ESA)
• Yohkoh (JAP)
• GOES-12 (NASA-NOAA)
• TRACE (NASA) 171-1600 Å
• RHESSI (NASA) 3 keV 20 MeV

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New Technologies

• Single-photon counters (Medipix)
• An X-ray photon generates two particle showers
  (h and e-) in a solid-state detector
• By suitably biasing the detector, one shower is
  sent to an electronic device, able to see it as a
  pulse
• The electronic device is divided in picture
  elements any of these pixels is able to count
  the incoming pulses
• Lower energy limit a few keV

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New Technologies

• 3D detectors
• Electrodes are close
• Low full depletion bias
• Low collection distance
• Thickness NOT related to collection distance
• No charge spreading
• Fast charge collection
• Micron scale
• USE Latest MEM techniques
• Pixel device
• Readout each p column

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New Technologies

• Josephson Junction Arrays
• Two superconductors, separated by an insulating
  layer, form a Josephson Junction.
• Cooper pairs can flow from one side to the other
• If a small voltage (a few millivolts) is applied,
  an alternating current of frequency in the
  microwave range results
• Tecnology already used in SQUID detectors
  (sensitive to magnetic fields)
• By coupling the junction material to a particle
  absorber, you can see particles (infrared
  photons!) hitting the detector by monitoring the
  voltage in the circuit

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Conclusions

• Sun, our nearest star, still hides secrets...
  even there where its more transparent...
• Study of Sun is straightforward (well... lets
  get to space, first...)
• Imaging technologies are ready for new
  challenges
• A Sun-staring mission offers unusual economical
  points of interest!