Solar Radio Astronomy CHRISTOPHE MARQUÉ BASIC SIDC SEMINARS
source: NASA
History
The beginning • 1902 : First (failed) attempt to observe radio waves from the Sun by Charles Nordmann (1902) in the French Alps, near Chamonix • 1933: Discovery of cosmic radio emission by Karl Jansky • 1944: First mention of solar radio emissions by G. Reber (ApJ 1944) & first mention of interferences! • 1946: First report of radar jamming by the Sun (Hey, Nature)
The beginning • 1902 : First (failed) attempt to observe radio waves from the Sun by Charles Nordmann (1902) in the French Alps, near Chamonix • 1933: Discovery of cosmic radio emission by Karl Jansky • 1944: First mention of solar radio emissions by G. Reber (ApJ 1944) & first mention of interferences! • 1946: First report of radar jamming by the Sun (Hey, Nature)
Grote Reber source: NRAO
The radio sun
Solar imaging ❖ Essentially interferometric imaging for having enough resolution ❖ Sampling of the Fourier transform of the source ❖ Imaging possible between ~ 60 MHz and a few 100s of GHz ❖ Difficulties: • Large source • High temporal and intensity variability • Ionosphere at low frequency Thompson et al.
Solar imaging ❖ Essentially interferometric imaging for having enough resolution ❖ Sampling of the Fourier transform of the source ❖ Imaging possible between ~ 60 MHz and a few 100s of GHz ❖ Difficulties: • Large source • High temporal and intensity variability • Ionosphere at low frequency Thompson et al.
Solar imaging ❖ Essentially interferometric imaging for having enough resolution ❖ Sampling of the Fourier transform of the source ❖ Imaging possible between ~ 60 MHz and a few 100s of GHz ❖ Difficulties: • Large source • High temporal and intensity variability • Ionosphere at low frequency Thompson et al.
Solar imaging ❖ Essentially interferometric imaging for having enough resolution ❖ Sampling of the Fourier transform of the source ❖ Imaging possible between ~ 60 MHz and a few 100s of GHz ❖ Difficulties: • Large source • High temporal and intensity variability • Ionosphere at low frequency Thompson et al.
Nançay 150 – 450 MHz 151 MHz 445 MHz
VLA 50 MHz – 50 GHz (non solar dedicated) 4.6 GHz NRAO NRAO & S. White
Nobeyama 17 & 34 GHz
LOFAR 20 – 240 MHz (non solar dedicated)
LOFAR 20 – 240 MHz (non solar dedicated)
LOFAR 20 – 240 MHz (non solar dedicated)
Dynamic spectra • Solar emission outside flaring events evolve type III slowly (timescale of days) • Energy release can occur on timescales of milliseconds • Accelerated electrons emits radio waves through different mechanisms • Spectral signatures give access to the flaring scenario Source: P. Lantos
Group of type III/type U bursts
Type IIIs, type II and type IV linked to M flare
Type II, high freq. counterpart with M flare
Variabilility of the quiet solar emission • Continuum emission: no lines “The excitement of the eclipse observations • Thermal emission (hot coronal gas) • Gyro emission (in AR) [at 10.7 cm] was soon followed by the sobering thoughts that solar radio emission from sunspots • Slow variation from day to day would be variable…” • Measurements since WWII in several bands (1000 – 4000 MHz) A. Covington, Proc. NRAO Workshop, 1983
Solar Flux radio Observatories
Solar Flux radio Observatories 1000 MHz 2000 MHz 3750 MHz 2800 MHz 9400 MHz 17000 MHz 245 MHz 410 MHz 610 MHz 1415 MHz 2695 MHz 4995 MHz 8800 MHz 15400 MHz
Antenna & telescopes
Gain and radiation patterns SPADE gain pattern; A. Martinez
Dipole antenna • Detection of the Electric component of the E.M Wave • Half-wave dipole : tuned to a given frequency • Resonant element source: wikipedia source: Schwarzbeck
Dipole antenna • Detection of the Electric component of the E.M Wave • Half-wave dipole : tuned to a given frequency • Resonant element source: wikipedia source: Schwarzbeck
Antenna derived from dipoles YAGI SIMULATED RADIATION PATTERN One “active” • element Passive • elements drive waves interfering additively forward and destructively backward Tuned for one • source: BRAMS - BISA source: A. Martinez frequency
Antenna derived from dipoles YAGI SIMULATED RADIATION PATTERN One “active” • element director Passive • elements drive radiator waves interfering reflector additively forward and destructively backward Tuned for one • source: BRAMS - BISA source: A. Martinez frequency
Antenna derived from dipoles YAGI SIMULATED RADIATION PATTERN One “active” • improved gain element director Passive • elements drive radiator waves interfering reflector additively forward and destructively backward Tuned for one • source: BRAMS - BISA source: A. Martinez frequency
Antenna derived from dipoles LOG PERIODIC ANTENNA All elements “actives” • successive elements • connected out-of-phase Constructive • interferences forward “Flat” gain & • broadband source: A. Martinez
Antenna derived from dipoles LOG PERIODIC ANTENNA All elements “actives” • successive elements • connected out-of-phase Constructive • interferences forward “Flat” gain & • broadband source: A. Martinez
Antenna derived from dipoles LOG PERIODIC ANTENNA All elements “actives” • successive elements • connected out-of-phase Constructive • interferences forward “Flat” gain & • broadband source: A. Martinez
Fat dipoles • Broadband (here 10 – 80 MHz) • Mismatch in electrical properties is compensated by an active element (active balun with amplifier) source: LWA – NENUFAR for SPADE source: LWA – NENUFAR / LONAMOS
Horn antenna • No resonant element (broadband) • Provide a “soft” transition between free-space electrical conditions to the ones of wave guide and electronics • Radiation characteristics can be easily (analytically) calculated • High gain and lower side lobes • Used as feed systems and absolute calibration system
Horn antenna • No resonant element (broadband) • Provide a “soft” transition between free-space electrical conditions to the ones of wave guide and electronics • Radiation characteristics can be easily (analytically) calculated • High gain and lower side lobes • Used as feed systems and absolute calibration system
Horn antenna
Horn antenna
Solar radio telescopes LEARMONTH, source: Kennewell, 2008
Solar radio telescopes LEARMONTH, source: Kennewell, 2008 source: Nobeyama observatory
Solar radio telescopes Analytical calculation of ANT34 radiation field
Receiving systems
What do we measure?
ΔΩ Flux density ΔΩ sun
ΔΩ Flux density ΔΩ sun
ΔΩ Flux density ΔΩ sun
Different external noise contributions Sun dominates, but here beam size=solar diameter Antenna temperature
1: cable 2: LNA 3: cable 4: receiver System noise Freq [MHz] T_Rx [K] 611 360 1060 470 Best is to put first in the chain element 1415 1090 with hi gain and low noise
Example
Receivers
Spectrographs Wide band solar emissions Multi channel receivers High dynamic range Sweep frequency instruments Fast temporal evolution Wide band FFT spectrometer
Multichannel Dumas et al, 1982
CALLISTO Sweep frequency Parameter Specification Frequency range 45-870 MHz Frequency resolution 62.5 kHz Bandwidth 300 kHz (-3dB) Dynamic range ~50 dB • Made from consumer electronics Sensitivity 25±1 mV/dB hardware PC-controlled hardware with Noise figure <10dB RS232 connection Sampling rate 800-1000 samp/s • Software for automatic observations (frequency program, schedule…) Weight 800g • Programmable frequencies Dimensions 11x8x20.5 cm http://www.e-callisto.org
Multi band FFT spectrographs Korean Solar Radio Burst Locator, Dou et al. 2009 0,5 -18 GHz
Multi band FFT spectrographs Korean Solar Radio Burst Locator, Dou et al. 2009 0,5 -18 GHz
Multi band FFT spectrographs Korean Solar Radio Burst Locator, Dou et al. 2009 0,5 -18 GHz
“Cheap” digital spectrographs In the spirit of the Callisto instrument “cheap” digital receivers can be turned into solar spectrographs Gnuradio Python, C Open source Software Define Radio Sweep/FFT spectrometer Steps of 25 MHz BW Fully programmable CESRA SUMMER SCHOOL 2015 41
Humain
The Humain station
The Humain station
The Humain station Weather station (RMI) Meteor & whistler radio antenna (BISA) Stellar optical telescopes (ROB) Solar radio spectrographs (ROB)
Humain: Solar instruments 6-m dish Automated operations, Sun tracking ~7h30 – 16h00 UT VHF antenna (piggy back) UHF antenna at focus • VHF antenna (45 – 450 MHz) • Callisto receiver • ARCAS receiver • UHF antenna (275 – 1495 MHz) • HSRS receiver
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