Solar radio spectral irradiance Christophe Marqu Royal Observatory

Solar radio spectral irradiance Christophe Marqué Royal Observatory of Belgium 14/10/13 SOLID Meeting WP 2 1

The beginning • Solar radio astronomy started during WWII • Conversion of radar equipments into radiotelescopes • No choice of frequencies 14/10/13 SOLID Meeting WP 2 2

The beginning Active Sun • Sporadic activity linked to solar eruptive events • Accelerated electrons (non thermal populations) • Different spectral types 14/10/13 SOLID Meeting WP 2 3

The beginning Non active Sun • Thermal emission from the corona (T~106 K, Pawsey, 1946) • Bremsstrahlung, Gyroresonance • 2 components: Quiet Sun & SVC 14/10/13 SOLID Meeting WP 2 4

The beginning “The excitement of the eclipse observations [at 10. 7 cm] was soon followed by the sobering thoughts that solar radio emission from sunspots would be variable…” A. Covington, Proc. NRAO Workshop, 1983 14/10/13 SOLID Meeting WP 2 5

Solar radio observations The Sun is observed in radio in a large spectral window: from far I. R to km wavelengths Unknown Chromosphere Thermal bremsstrahlung Gyrosynchrotron Transition region Thermal bremsstrahlung Low corona Gyroresonance Plasma emission Gyrosynchroton corona Thermal. High bremsstrahlung Plasma emission Interplanetary medium

Solar radio spectral irradiance • Continuum emission: no lines • Flux density: W. m-2. Hz-1 • Solar Flux Unit: 10 -22 W. m-2. Hz-1 = 104 Jansky • Intensity as Brightness Temperature 14/10/13 SOLID Meeting WP 2 7

Solar Flux radio Observatories 1000 MHz 2000 MHz 3750 MHz 9400 MHz 17000 MHz 2800 MHz 245 MHz 410 MHz 610 MHz 1415 MHz 2695 MHz 4995 MHz 8800 MHz 15400 MHz 14/10/13 SOLID Meeting WP 2 8

Flux Measurement • Full Sun • Parabolic dish • Horn antenna • Pentincton: strict calibration procedure 3 times per day 14/10/13 SOLID Meeting WP 2 9

Flux measurement: calibration • Tanaka (1973) paper • Toyokawa: reference station • Flux correction (0. 9 for F 10. 7) • Standard for absolute calibration • Precision 1 -2 % 14/10/13 SOLID Meeting WP 2 10

Flux measurement: natural sources of error • Atmospheric absorption • Rain • Humidity (dew/snow) on antenna • Temperature variation • Ionospheric disturbances 14/10/13 SOLID Meeting WP 2 11

Flux measurements: examples Ground interference Quiet Sun level Solar flare calibration Quiet sun level Ground interference

Cycle 23 -24 14/10/13 SOLID Meeting WP 2 13

Emission mechanism After Schmahl & Kundu 1998 14/10/13 SOLID Meeting WP 2 14

Spectrum of QS &SVC 2001 -2002 • QS : S~f 2 -> Thermal Bremstrahlung • SVC: ~Flat spectrum Gyroresonance/Free 14/10/13 SOLID Meeting WP 2 15

Free-Free / Gyroresonance 14/10/13 SOLID Meeting WP 2 16

Quiet Sun: essentially Free-Free Zirin, 1991 14/10/13 SOLID Meeting WP 2 17

SVC S. White 14/10/13 SOLID Meeting WP 2 18

Last words • Long term spectral irradiance with good stability (with proper calibration procedure) • Care should be taken about the meaning of daily values • No Instrument degration (apart from rust & spare parts availability) • Possibility to use radio data for EUV/UV calibrations • Gold mine for long term studies of coronal evolution (n, T, & B) 14/10/13 SOLID Meeting WP 2 19