SWG-17 Pasadena,CA

B A

Direction Finding and Triangulationfrom STEREO & Wind

M. J. Reiner

Type III burst have very characteristic intensity profiles:

• Rapid rise to a peak, followed by exponential-like decay• Peak time increases as the frequency decreases (frequency drift)• Overall duration of the profile increases with decreasing frequency

STEREO A

March 15, 2007

Type III

Direction finding provides the arrival direction of the radiation from the radio source

Auto correlations

Direction finding for STEREO is achieved from an analysis of the amplitudes (auto correlations) and phase differences (cross correlations) between pairs of antennas

STEREO Direction Finding

Ez

Ey

Ex

09:25 09:5009:4509:301.0

4.0

3.0

2.0

Time (UTC)

STEREO A

3 June 2007

type III burst time profile

Ez - Ey

Ex - Ey

Ex - Ez

09:20 09:30-1.0

Time (UTC)

STEREO A

3 June 2007

1.0

0.5

0.0

-0.5

10:0009:45

Cross correlations

EzEx

Ey

Ez

Ex Ey

sType III radio source

3 mutually orthogonalantennas

differences due to the different antenna “electrical lengths” and to

the direction of the radio source

STEREO Ahead EUVI 284

2007-08-06 02:06:30 UTCflare site

S06o W44o

WindSTEREO B STEREO A

Parker spiral interplanetarymagnetic field lines

SUN

flare siteS06o W44o

WindSTEREO B STEREO A

SUN

6o10o

16o

2007 August 6

STEREO A

2007 August 6

Wind2007 August 6

STEREO B

Lines-of-sight to the radio sourcefrom STEREO A, Wind & STEREO B

at 425 kHz

Radio source at 425 kHz locatedby STEREO/Wind triangulation

This flare produced atype III radio burst

that was “simultaneously”observed by

STEREO A, B & Wind

Spatial triangulation of a solar type III radio source

The spatial location of the radio source(0.21 AU, W48o) was determined without

using an interplanetary density model

The triangulated source location is consistentwith the 27 sec timing difference between the

type IIIs as observed at STEREO A and B

Why are these measurements important?

The DF & triangulation measurements provide:

• 3D source location - independent of a density model

• information on the size of the radio source

• information on the intrinsic source intensity

• information on the beaming characteristics of the type III radiation

• tracking of the electron beams through the interplanetary medium to 1 AU and beyond(by performing the triangulation at consecutively lower frequencies)

(needed to constrain theoretical models of type III radio generation)

(also needed to constrain theoretical models of type III radio generation)

Determining the Beaming Pattern

To deduce the intrinsic beaming pattern of the radio source, we must first factor out the 1/R2 falloff of the radiation intensity in propagating from the source to each observing s/c

To do this, we obviously need to know the location of the source from the triangulation

Since the radio source beaming pattern is a “curved surface”, we need at least 3 s/c observations

The third observation at Wind is important for distinguishing between the two possible

beaming patterns that are consistentwith the STEREO observations

A wider separation between the two STEREO s/c provides a more accurate determination of

the overall beaming pattern, but in this case the third observation at Wind is even more critical

STEREO + Wind observations can provide the first quantitative measure of the radiation beaming

Lengths of the arrows representthe observed intensity at each s/c

Lengths of the arrows representthe observed intensity at each s/c

Conclusions

• STEREO & Wind observations can be used to remotely locate radio sources in the 3D heliosphere, independently of a density model, using both timing and spatial triangulation

STEREO B STEREO A

• STEREO & Wind observations of type III bursts can be used to deduce intrinsic radiation characteristic of the radio source,

such as the beaming characteristics

Wind