Solar Radio Astronomy

1
Solar Radio Astronomy

• Adriana V. R. Silva
• Center for Radio Astronomy and Astrophysics
• Mackenzie University

MFU Angra dos Reis, 29/11/2004
2
Solar Group _at_ CRAAM

• Pierre Kaufmann
• Adriana V. R. Silva
• C. Guillermo Gimenez de Castro
• Emília Correia
• Jean-Pierre Raulin
• Joaquim E. R. Costa

3
Solar Atmosphere

• Photosphere surface to 300 km, T5780 K,
  sunspots

• Cromosphere up to 3,000 km above the surface,
  T104-105 K

• Corona several solar radii, T2-4 million K,
  solar wind

4
White light
Ca
Infrared
Radio
H?
UV
X-ray
EUV
5
Magnetic Field
6
Global magnetic field

• Generated by a dynamo in tachocline layer
• Dipole close to the surface
• Stronger in active regions
• Magnetosphere envelops all the solar system

7
Active regions
Active region (sunspot)
8
Active regions
9
Solar Activity
10
Solar Activity

• Location Solar atmosphere
• Energy source magnetic field
• 3 timescales
• 11 years (solar activity cycle)
• Weeks (sunspot lifetime)
• Seconds to hours (flare and CME duration)

11
Activity

• Sunspots
• Flares
• Coronal Mass Ejection
• Occurrence follows the 11 year activity cycle

12
Sunspots

• Dark regions of solar disk
• Regions of intense magnetic field 100-2000 G
• Cooler than their surroundings 4000-5000 K

13
Solar Flare

• Sudden release of 1030-1032 erg (seconds to
  hours)
• Energy source magnetic field

14

• Particle acceleration up to MeV
• Radiation
• Local plasma heating

15
Coronal Mass Ejection

• Associated to proeminence eruption and/or flares
• matter (electrons, protons, and ions) is thrown
  into the interplanetary medium
• Some of it may reach the Earth.

16
Ejeção de Massa
17
SOHO
visible
visible
UV (195 A)
18
Solar-Terrestrial Interaction

• When the radiation and energetic particles from
  CME hit the Earth
• Lethal doses of X-ray radiation to astronauts
• Satellite orbit alterations due to drag
• Magnetic storms

19
Effects at the Earth

• Ionospheric alterations ? affect long distance
  communication
• Spikes on high voltage lines
• Blackouts
• Erratic behavior of navegation instruments
• Alterations in the ozone layer
• Auroras
• Influence Earths climate.

20
Solar Emission at Radio Frequencies
21
Types of emission

• Quiet calm atmosphere
• Height in the atmosphere where the emission at a
  certain frequency is produced may be inferred
  from the limb position, i.e., the solar radius.
• Quiescent active region observation
• Emission at different frequencies due to distinct
  mechanisms.
• Transient flares and CMEs
• Energetic particle emission

22
Emission Mechanisms (electrons)

• gyrosynchrotron
• flares (microwave e mm)

• Thermal gyrosyn. and gyroresonance
• Active regions (microwave)

• Thermal bremstrahlung
• Quiet sun
• Active regions (mm)

23
Quiet radio emission

• Multiple wavelengths observations ? information
  about the different layers of the atmosphere.

24
Solar Radio Observation

• 17 GHz Nobeyama Solar Heliograph
• 212 and 405 GHz Submillimetric Solar Telescope

25
Nobeyama 17 and 34 GHz

• Japan
• Interferometer 84 antennae with 80 m diameter
• High spatial resolution (10)
• Daily maps since 1991.

26
Radius at 17 GHz

• Radius measured where the emission equals 50 of
  its most common value
• points fit by a circle
• Radius at 15 (or 11,000 km) above the
  photosphere
• Chromospheric emission.

27
Radius temporal variation
Selhorst et al. (2004)
28
Intensity profile
visible
radio
29
Limb brightening
atmosphere
30
Selhorst et al. (2003)

• North polar limb

• South solar limb

• Sunspot number

31
Atmospheric Model
Selhorst et al. (2005)

• From the high resolution 17 GHz observations of
• Disk center brightness temperature (1-400 GHz)
• Limb brightening
• Solar radius.
• Density and temperature distribution of
  atmosphere.

32
Submillimetric Solar Telescope (SST)

• Location CASLEO Observatory in the Argentinean
  Andes (2500 m)
• 2 frequencies
• 212 GHz
• (4 receptors)
• 405 GHz
• (2 receptors)
• 40 ms temporal resolution
• Solar Dedicated

33
Submm solar radius

• Limb region where the intensity is 50 of its
  most common value
• Points fit by a circle.
• Results
• 212 GHz 969 ? 5 arcsec ( 6700 km)
• 405 GHz 972 ? 8 arcsec ( 8400 km)

34
Solar radius at radio frequencies
Costa, Homor e Kaufmann (1986)
35
Active Regions

• Temperature and density distribution
• Atmospheric height of a certain emission
  frequency (radius)
• Emission mechanism (spectra)
• Oscillations

36
Active regions

• Bright regions (not dark as sunspots)
• Emission is a combination of thermal
  bremsstrahlung gyroresonance
• AR at 17, 34, 212, and 405 GHz

37
Brightness temperature
Silva et al. (2005)

• Brightness temperature above quiet Sun value

38
(No Transcript)
39
Active region spectra

• Increasing spectrum with slope 2
• Fit by thermal bremsstrahlung for three
  parameters temperature, density, and height
• Obtain minimum density by assuming that 405 GHz
  is transition to optically thin.

40
Spectra of 23 AR

• Emission from an optically thick cylindrical
  source of height 108cm
• Plasma effective temperature 10,000-20,000 K.
• Minimum source density 1011 cm-3 (assuming ??1
  at 405 GHz.

41
Radio emission from active regions
42
Minute Oscillation

• Tracking an active region
• SST beam position
• 212 GHz (1,2,3,4) 4 FWHM
• 405 GHz (5,6) 2 FWHM

Silva et al. (2004)
43
Subtraction of Earth atmosphere
(01/06/2002)
44
Fourier analysis

• Oscillation is no symmetric (rise longer than
  fall)
• Dominant frequencies by Fourier analysis

45
Oscillation periods

• Results from the data of 54 whole days between
  june and July of 2002
• Periods between 4 and 7 minutes
• Most common period is 5 minutes (3.3 mHz) as
  found in optical and visible data.

46
5 min p-mode
2
3
SST beams
47
Solar flare at 17 GHz
48
Solar flares

• Temporal evolution in radio similar to that of
  X-rays, which are also produced during flares
• Radio and X-ray emission produced by the same
  population of accelerated electrons
• Radio emission produced by different mechanisms
  depending on the frequency
• Decimetric coherent emission
• Microwaves gyrosynchrotron
• Mm and submm gyrosynchrotronbremsstrahlung

49
Flares in X-rays
50
Soft X-rays
Hard X-rays
microwave
mm
51
Solar flares in radio

• It is possible to obtain estimates of coronal
  magnetic fields, not possible by direct
  measurements
• Radio telescopes are much more sensitive, thus it
  is possible to detect the accelerated electrons,
  even in the smallest events.

52
04-nov-2003 flare

• X28 flare - GOES (biggest ever detected)
• Time 1940-1950 UT
• Observed at X-rays, ultraviolet, Ha, microwaves
  and submillimetric wavelengths

• pulses of 1000 sfu with duration of 500-700 ms
• increasing spectrum even at 405 GHz

Kaufmann et al. (2004)
53
Microwave
405 GHz
212 GHz
Pulses
54
(No Transcript)
55
Radio spectrum
New THz component
56
Subsecond pulses
Raulin et al. (2003)

• Duration of 100 ms to 1 s.
• Pulse occurrence rate and amplitude time profile
  follow the temporal evolution of the bulk
  emission.
• Increasing spectra.

bulk
amplitude
rate
57
Pulses X CME
Kaufmann et al. (2003)

• 22-mar-2000 flare
• 100 K pulses with duration of 100 to 300 ms
• start of the pulses coincide with the lift off
  time of the coronal mass ejection (CME).

58
Radio observations-summary

• Solar radius
• Detect the height in the atmosphere where the
  emission is coming from.
• Radius varies in time (11 years)
• Model the solar atmosphere from
• central intensity, radius, and limb brightening
• Active regions
• Thermal bremsstrahlung from sources of 1-2 104 K,
  and densities gt 1011 cm-3 (chromosphere)
• 5 min oscillations in active regions

59
Radio submm flares -summary

• Two component emission
• bulk (minutes), spectra is a prolongation of the
  gyrosynchroton, and
• pulses (subsecond) with increasing spectra.
• Very large flare (4-nov-2003)
• bulk emission with increasing spectrum peak at
  THz.

60
Pulses - summary

• Subsecond duration
• Occurrence rate follows the time profile of bulk
  emission
• Increasing spectra
• Start time coincides with the launch time of CMEs
  (even when there is no flare)
• Unknown origin.