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