Radio Emission from the Sun, Heliosphere, & Planets

T. S. Bastian

NRAO

Plan of Talk

• Instrumentation

• Emission mechanisms

• Low frequency solar and IP radio emission

• Planetary radio emission (Jupiter)

An aside: extrasolar planets

• Radio emission from the outer limits

Instrumentation

• Current groundbased UTR-2 (10 – 30 MHz) Guaribindanur (40 – 150 MHz) GMRT (150, 235, 327 MHz) Nancay Radioheliograph (150 – 450 MHz) VLA (74, 327 MHz) Numerous spectrographs (e.g., GB/SRBS 17-1050 MHz)

• Current Spacebased WIND / WAVES (20 kHz – 1040 kHz, 1.075 – 13.825 MHz)

Ulysses URAP RAR (1.25 – 48.5 KHz, 52 – 940 kHz)

Instrumentation

• Planned groundbased

FASR (50 MHz – 20 GHz) MWA (80 – 300 MHz)

LWA (10 – 80 MHz)

• Spacebased (imminent!) STEREO / WAVES two spacecraft!

(10 – 40 kHz, 40 – 160 kHz, 0.16 – 16.075 MHz, plus 50 MHz)

Emission Mechanisms

• Plasma radiation ( = pe, 2pe pe= 9 ne1/2 kHz)

coronal and IP radio bursts – e.g., bursts of type II and type III

• Cyclotron maser ( = Be, 2Be Be = 2.8 B MHz)

planetary radio emission – e.g., terrestrial AKR, Jovian DAM

• Synchrotron radiation solar type IV bursts, CMEs, Jovian magnetosphere

• Thermal radiation Ubiquitous – e.g., solar corona, CMEs, planetary disks

“coronal”

RAD 1

RAD 2

pe

pe

Plasma radiation

ground

space

ionosphere

Solar Radio Bursts Type I McCready, Pawsey, Payne-Scott 1947; Allen 1947; Wild & McCready 1950

Type II Wild & McCready 1950

Type III Wild & McCready 1950

Type IV Boischot & Denisse 1957

Type V Wild 1959

Numerous, short-lived (~1 s), narrow-band (few MHz) bursts occurring over a BW of 10s of MHz in storms lasting hours to days

Rare slow-drift bursts (~ -0.25 MHz/s) that occur in association w/ flares, lasting 5-20 min. Narrow-band emission often occurs in harmonic lanes.

Broadband (~100s MHz), fast-drift bursts (~ -20 MHz/s) that occur in association w/ impulsive phase of flares.

Broadband (~10s-100s MHz) continuum following large solar flares, often following an associated type II burst, lasting >10 min.

Continuum emission following groups of type III radio bursts, typically polarized in the opposite sense.

Dulk 1985

GB/SRBS

type III

type III + type II

type II + type IV + fadeout

ground

space

ionosphere

SA type IIIs

type II

type IV

type III

WIND/WAVES

Culgoora

Interplanetary Radio Bursts

Dulk et al. 2001

Motivating issues

Understanding relationship between flares, coronal mass ejections (CMEs), solar energetic particles (SEPs), and radio proxies:

• CME initiation & propagation Bastian et al 2001, Kathaviran & Ramesh 2005, Maia et al 2006

• Drivers of coronal type IIs Cliver et al (2004)

• Interplanetary shocks (type II proxies) Gopalswamy et al (2001), Knock et al (2001, 2003ab, 2005)

• Coronal energy release (type III/IV proxies) Cane et al. 2002, Klein et al. (2005)

• Relativistic electron delays (type III, in situ measurements)

Krucker et al. (1999), Haggerty & Roelof (2002)

Green Bank

Solar Radio Burst Spectrometer

(White et al. 2006)

WIND / WAVES R1 & R2

Knock et al. 2001, 2003ab, 2005

Haggerty & Roelof 2002

Delay of near-relativistic electron acceleration

Cane et al. 2002

Cane et al (2002) identify a correlation between long duration type III bursts (~20 min), CMEs, and solar proton events.

Suggests type-III-l-producing electrons accelerated in the corona in the aftermath of a CME.

Role of flares in SEP production

CME “cannibalism”?

Gopalswamy et al. (2001)

Emission from CMEs

ThermalSheridan et al. 1978: exceptionally slow (60 km s-1) coronal transient observed at 80 and 160 MHz by Culgoora RH

Gopalswamy & Kundu 1992, 1993: thermal footprint of a CME possibly observed at 74 MHz by the Clark Lake CH

Ramesh et al. 2003: observation of CME with Gauribidanur RH at 109 MHz

Kathiravan & Ramesh 2005: an example of a halo CME observed by the GRH at 109 MHz

21 Jan 1998

SOHO LASCO C2

Guaribindanur RH

Kathiravan & Ramesh 2005

109 MHz

Nonthermal emissionSmerd & Dulk 1971?: “expanding arch”, “advancing front” classifications of 80 MHz observations of moving type IV radio bursts with the Culgoora Radioheliograph

Bastian et al. 2001: multi-band observations of the 20 April 1998 fast CME with the Nançay Radioheliograph

Gopalswamy et al. 2005: microwave detection of synchrotron radiation from the 18 April 2001 fast CME with the Nobeyama Radioheliograph

Maia et al. 2006: multi-band observations of the 15 April 2001 fast CME with the Nancay Radioheliograph

Maia et al. 2006

Nançay Radioheliograph: 15 Aprl 2001

421 MHz

1 1.81 1.45 234 2.5 x 107 1.47 330

2 0.54 2.05 218.5 1.35 x 107 1.03 265

3 0.03 2.4 219.5 6.5 x 106 0.69 190

4 -1.07 2.8 221 5 x 105 0.33 30

LoS Rsun (deg) ne (cm-3) B(G) RT (MHz)

Bastian et al. 2001

Planetary Radio Emission

from R. Sault

While all planets emit thermal radiation, the presence of a magnetosphere (and in the case of Jupiter, satellites) greatly complicates and enriches the observed radio phenomena.

The cyclotron maser mechanisms (Wu & Lee 1979) is believed to account for the auroral radio emissions which are pumped by the variable solar wind. For Jupiter, interaction between the magnetosphere and the Galilean satellites (Io) also modulates the radio emission in a complex way.

13 cm

22 cm

Jupiter

Jovian Decameter-wavelength Radiation

Auroral footprints

L bursts

S bursts

90 s

160 ms

Earth: 108 Watts

Jupiter: 1011 Watts

Gurnett et al. 2002

Solar wind modulation of Jovian auroral radio emission

Carr et al. 1983, Zarka et al. 1992, Bastian et al. 2000

Jovian DAM can be six orders of magnitude more intense than the synchrotron and thermal emissions!

What are the consequences for the detection of exoplanets?

Exoplanet searches• Winglee et al (1986) first pointed out possibility of detecting cyclotron maser

emission from exoplanets and performed blind search at 327 MHz and 1.4 GHz using the VLA

• With discovery of bone fide planets by Mayor & Queloz (1995), Bastian et al (2000) targeted six known exoplanets and two brown dwarfs at 74, 327, and 1.4 GHz with the VLA

• On the basis of the “radiometric Bodes Law” (Desch & Kaiser 1984, Zarka 1992, Farrell et al 1999) and Zarka et al (2001) suggested interaction of “hot Jupiters” with stellar winds could produce emissions orders of magnitude stronger than Jupiter’s. See also Lazio et al (2004).

Several subsequent attempts to detect exoplanets: e.g., Desch et al. (2003) using the VLA; Ryabov et al (2004) using the UTR-2; Lazio et al (2004) using the VLA; Winterhalter et al (2005) and Majid et al (2005) using the GMRT

No detections at radio wavelengths to date.

• Lack of sensitivity• Frequency mismatch • Low duty cycle • Source directivity• Planet unmagnetized• No source of energetic electrons

Possible reasons for non-detections:

Studies of requirements for next-generation instrumentation for exoplanet detection and study underway: e.g., Taylor et al 1998 (SKA), Farrell et al. 2004; Zarka et al. 2004, 2006 (LOFAR); Lazio et al 2004 (SKA); LWA science

Jans

kyFreq (MHz)

Radiation from the Outer Limits

Kurth et al. 1984, Cairns et al. 1992, Gurnett et al. 1993, Gurnett and Kurth 1996, Cairns & Zank 2002,

Concluding Remarks

• Low frequency observations of the Sun, planets, and interplanetary medium vigorous and ongoing

• Observations reveal rich and dynamic environments and complex physical processes

• Observations yielding insights into particle acceleration and transport, shocks, and plasma & radiation processes

• The future looks bright!