MWA “burst mode”: Nov 2008 Solar 32 T Observations

Vasili Lobzin and Iver Cairns,

School of Physics, University of Sydney

Canberra 19/1/2009

I. ContextII. Observations & InterpretationIII. Summary

I. Context for “Burst Mode” Solar Obs

• MWA has strong solar, heliospheric, and ionospheric science objectives

• Burst Mode: – 0 – 328 MHz spectra, 256 * 1.28 MHz channels– 1 spectrum per 0.78 μs every 1 ms (0.938 ms)– “engineering” mode, but great for solar science

• Highest known cadence, resolution and bandwidth• Imaging?

– 17 and 20 November 2008, close to local noon.

3

Solar Radio Bursts

II. “Burst Mode” Solar Obs: 20 Nov 2008

• mwadas1,2,&4, each 16 pipes,~ 600 files

• ~ 04:00:30 – 04:02:27 (~0.1 s accuracy)

• Power spectrum summed over all pipes

“Burst Mode” Solar Obs: 20 Nov 2008

f (MHz)

0

328

04:00:30.804:02:26.8Time

• Vertical, variable signals? Bands of noise? Interference signals? • Any natural signals ….?

Spectra: averaging & background subtraction

• (Left) Averaging & (top) background subtraction structure in interference

• Vertical signals not solar type IIIs since:

1. no freq drift &

2. don’t have Δt ↑ as f ↓

0

f

328MHz

Time (2 mins)

AVG

MWA “vertical signals”: no analogues at Culgoora interference

• No similar bursts in Culgoora (NSW) data (duration or appearance)

noise at MWA

0

f

328MHz

Time (2 mins)

57

180MHz

18

Culgoora lightning (storm near Sydney)

57Freq

18

75

180MHz

MWA “vertical signals”: impulsive local interference

• Δf ~ 100 – 300 MHz spikes ~ 10 - 3 ns duration.

• 50 sweep (0.05s) averages, then subtract background periodicity ≈ 3.6 Hz

• Intensifies with other interference.

0

f

328MHz

Time (2 mins)

0 10 20 30 40 50 60 70 80 90 100-2

-1.5

-1

-0.5

0

0.5

1

time, array index

0 1 2 3 4 5 6 7 8 9 1010

11

1012

1013

1014

frequency, Hz

Pow

er S

pect

ral D

ensi

ty

65

“signal energy”

Frequency (Hz)

power spectrum

Vertical signals intensify with other interference

65

Freq

0

75

328MHz

mwa1, files 400-499, averaging over 100 sweeps + background subtraction

time, array index

freq

uenc

y, a

rray

inde

x

10 20 30 40 50 60 70 80

50

100

150

200

250-1

0

1

2

3

4

5

6

7

8

9x 10

5

III. Summary

• “Burst mode” data should be attractive for solar work (very high cadence, wide bandwidth).

• Analysis of 2 mins of 20 Nov 32T data show – Noise & interference bands,– Vertical signals that don’t appear to be natural:

• No analogues in Learmonth & Culgoora data;• 3.6 Hz periodicity in energy;• They intensify with other interference; likely impulsive signals ~ 3 -10 ns in duration.

• Desire to remove interference sources for future burst mode observations.