S olar corona observations at decameter wavelengths

Solar corona observations at decameter wavelengths

Artem [email protected]

Institute of Radio Astronomy Kharkov, Ukraine

IntroductonSolar radio emission consists of two components:

• thermal (continuum “background” radiation)

• non-thermal (bursts, noise storms, flares and other disturbing features)

The observations of the quiet Sun at decameter wavelengths are imposed restriction by the fact that the radiation is much weaker in comparison with the burst activity.

Thus, the principal requests for radio astronomical instrument are very large dynamic range and high sensitivity as well as carrying-out observations during periods of reduced activity (sunspot minimum).

UTR-2 radio telescope is an appropriate instrument satisfying basic demands

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Quiet-Sun Radio Emission: Overview of Observations

Frequency Radio astronomical (MHz) Reference instrument _ 80.0 Sheridan (1970) Culgoora Radio Heliograph 60.0 Aubier et al. (1971) Arecibo Radio Telescope 36.9 Aubier et al. (1971) – 29.3 Aubier et al. (1971) – 25.0 Abranin et al. (1976) UTR-2 Radio Telescope 73.8 Kundu et al. (1977) Clark Lake Radio Telescope 26.3 Kundu et al. (1977) – 73.8 Erickson et al. (1977) – 57.7 Erickson et al. (1977) – 38.1 Erickson et al. (1977) – 25.8 Erickson et al. (1977) – 19.0 Erickson et al. (1977) – 73.8 Thejappa & Kundu (1992) Clark Lake Radio Heliograph 50.0 Thejappa & Kundu (1992) – 38.5 Thejappa & Kundu (1992) – 75.0 Ramesh et al. (2000) Gauribidanur Radio Telescope 34.5 Subramanian (2004) – 77.0 Ramesh et al. (2006) – 51.0 Ramesh et al. (2006) –

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UTR-2 Radio Telescope, Ukraine

Effective area 150000 m2

N-S and E-W arms 12 sections

Frequency band 8-33 MHz

The beam sizes

~25´× 25´

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Experimental equipment

W

N

S

1

2

3

4

1211109 DSP

UTR-2 antenna array

)(1 tx

)(2 tx5

6

7

8

tU sincos sincoscoscossin tV

- declination

t - hour angle - latitude of UTR-2

Digital Signal Processor

5

DSP block scheme

ADC block

Channel1

Channel 2

FPGA matrix

FPGA matrix

SOFTWARE

GPSreceiver

Hard disk

+

Visual data presentation

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DSP characteristics

ADC sampling frequency 66 MHzOperating bandwidth 8-33 MHzMax. number of output frequency channels 8192Frequency resolution 4 kHzTime resolution from 0.2 msec up to 1 secDynamic range 90 dB

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Multi-beam scanning

North

South

Pencil-shaped beams

I

II

III

IV

V

Date Number of scans September, 2010 per day

4

5

6

10

9

7

25´

25´

Total number: 26The scanning was realized using these beams

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One-dimensional scans of the quiet Sun

Example of time-frequency profiles from scans along solar equator on September 6, 2010.

Time zero corresponds to 08:59:15 UT

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Solar spectrum of quiet Sun (corona) at decameter wavelengths

4.5log3.2log SThe equation of the line:

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Chiniese RHNancy RH, NDA

Culgoora RH Gauribidanur RH

Nobeyama RH

RATAN-600 RH, SSRT

Ukraine RH

LOFAR

OVRO

Clark Lake

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Heliograph’s general functional scheme

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Principle of heliogram construction

Extra phase shift module – fast change of antenna pattern

position along U.

Extra phase shift module – fast change of antenna pattern

position along U.

1501U

WE

Multi-beam UTR-2 regime:

Ω(θ, φ) ≈ 25´× 25´ at 25 MHz

Multi-beam UTR-2 regime:

Ω(θ, φ) ≈ 25´× 25´ at 25 MHz

I

II

III

IV

V

I II III IV V VI VII VIII

1501V

N

S

81150

5.40

m

mUUm

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Heliograph field of view

Number of imageelements 5 8

Separating markers

Time of cadrecomposition

0.24 sec, 2 min4 min

The field sizes ~ 2.5 3.3

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Examples of heliographic observations

3C348 (Freq. 21 MHz; August 29, 2010)

3C123 (Freq. 21 MHz; September 3, 2010)

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Examples of heliographic observations

Solar corona (Freq. 21 MHz; August 29, 2010; 07:20 UT)

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Conclusion The two-dimensional heliograph of decameter wavelengths represents

unique radio astronomical tool (the most low-frequency and multichannel) .

The radio heliograph is capable to produce the images of the “quiet” Sun as well as to track for displacement of radiation sources in the solar corona.

The preliminary results of heliographic observations of point sources (3C123, 3C348) as well as solar corona are presented.

The new working mode of the UTR-2 radio telescope – one dimensional heliograph – has been introduced as a supplementary, multitasking tool for radio astronomical measurements, in particular to investigate a radio emission from the “quiet” Sun.

The values of integrated flux density were obtained and extended to long- wavelength region of “quiet” Sun radiation spectrum indicating good agreement with results in others (meter and so on) wavelengths.

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Thank for your attention!