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Stephen White
Radio and Hard X-ray Studies
Energy distributions
• Still a discrepancy between the electron energy distribution derived from radio observations and from HXR spectra: radio data show flatter energy distributions
LOw Frequency ARray (LOFAR)
low-energy brems. (solid yellow), high-energy brems. (solid orange), nuclear line and cont. (solid blue), pion-decay (solid purple), 2223 MeV (dotted purple), solar 511 keV (dashed purple), solar-scattered N-capture (solid light green), He line (dashed light blue).
Energy distributions
• Still a discrepancy between the electron energy distribution derived from radio observations and from HXR spectra: radio data show flatter energy distributions
• Traditional explanation has been that the energy ranges are different: HXR below 100 keV depend on 200-300 keV electrons, radio depends on >500 keV electrons.
• Easy, right: just compare in same energy range. But: HXR spectra above 500 keV are complicated.
• Similarly, in big flares the radio spectra are difficult because the peak in the spectrum is at high frequencies and it is hard to get the spectral index
• And when you do have high frequencies, there is a surprise waiting …
High-frequency observations from the Solar Submillimeter Telescope show a rising component above 200 GHz – not a continuation of the microwave component.
Morphology
Low-frequency/decimeter radio telescopes
• Nancay Radio Heliograph: continuing, may add 600 MHz
• Brazilian Decimetric Array (BDA)
• Chinese Spectral Radio Heliograph (CSRH)
• LOFAR: spread across Europe, core in the Netherlands, high spatial resolution
• Murchison Widefield Array (MWA): joint US-Australia project based in Western Australia at proposed location of SKA
• Long Wavelength Array: US project in New Mexico
Microwave/millimeter telescopes• Frequency Agile Solar Radio Telescope (FASR): still pending at
NSF/AGS, “OVSA upgrade” should receive $5M this month
• Siberian Solar Radio Telescope upgrade (SSRT)
• Nobeyama Radio Heliograph: will cease operations
• Solar Submillimeter Telescope: expanding frequencies
• Expanded Very Large Array: broad frequency coverage, excellent resolution, little observing time
• Allen Telescope Array: plan to do some solar work, F10.7
• Atacama Large Millimeter Array: limited flare observations, small field of view
Future needs 1
• Better spatial resolution at both HXR and radio: in large eruptive flares there must be time-variable structure on small scales in HXR; want radio to test connectivity (below 10 GHz to see loops better; FASR)
• In order to achieve better spatial resolution, (both) need both better sensitivity and dynamic range
• Compare radio/HXR spectra from the footpoints with radio/HXR spectra in the loops separately
• Better time resolution (both) to look for motion
Future needs 2• Coronal magnetic field strength measurements: where
is the energy in the corona that is available for conversion? (compare with PF) (FASR)
• Continuous spectral coverage in the radio in order to exploit information in gyrosynchtotron spectra, in particular measure magnetic fields on flaring loops (FASR)
• Imaging of energy release sites: if indeed radio spikes are release sites, high-resolution decimeter images, previously unavailable, will show them (FASR)
• Per Gordon Hurford: “every pixel in a dynamic spectrum is an image” (FASR)
• … including shocks detected in regions of weak plasma emission (FASR)
Telescope Freq. range(GHz)
Bandwidth(MHz)
Resolution Agile?
LOFAR 0.030-0.240 32 10” Y
MWA 0.080-0.300 32 60” Y?
LWA 0.010-0.080 32 10” ?
NRH 0.169-0.500 0 60” Fixed
BDA 1.2-2 6 60” Fixed
FASR 0.1-20 500 2” Y
CSRH 0.1-15 500? 5” Y
SSRT 4.5-9 120 20” Fixed
NoRH 17,34 0 10” Fixed
EVLA 1-50 4000 1” N
SST 212,405,higher 0 60” Fixed
ALMA 80-600 8000 0.1” N