Мulti-frequency VLA observations of M87

Observations’ parameters

Test VLA observations (configuration D) of M87 (RA=12:28, Dec=12:40) took place on November 16th, 2005.

• There were 22 antennas enabled.

• Frequency bands: K (K1=21300, K2=22200, K3=23000 , K4=23400 MHz) и U (U1=14700, U1=15200 MHz) Total observation time were 3 hours.

• Official participants: N. Kardashev, L. Kogan, S. Likhachev, V. Vasilkov, E. Fomalont, F. Owen, E. Greisen, K. Kellermann.

Goals of the experiment

• Multi-frequency synthesis (MFS) of a M87 map on the reference frequency (19 GHz) with bandwidth of 7 GHz by means of a new class of the multi-frequency imaging (MFI) algorithms developed at the ASC.

• Multi-frequency analysis (MFA) of M87. Estimation of a spectral index maps of the source on the same reference frequency.

• Comparison of the obtained results with the existing MFI-technologies at NRAO.

• Investigations of the improvement of image fidelity by means of MFS.

Tools

• NRAO has used AIPS software (one can find the results of the data processing obtained by L. Kogan on the web site http://www.aoc.nrao.edu/~lkogan/m87plots.ps

• ASC has used ASL for Windows software (see below)

Part 1

Multi-frequency synthesis and analysis

(u,v)-coverageU-band K-band

Sequence of MFI of M87 (ASL for Windows)

• Maps synthesis be means of generalized self-calibration procedure for all six frequencies (14665, 15135, 21535, 21965, 22935, 23364 MHz).

• Synthesis of the image of M87 on the reference frequency (19014 MHz) by means of generalized linear multi-frequency deconvolution algorithm.

• Spectral analysis of the image (spectral indexes map, spectrum of different parts of the image of M87).

Generalized linear deconvolution algorithm

,

00

, , , ,x y

I x y I x y

,2

21 1 1 1

001 1 1 11 1

ˆ minx y

K N N K N Nk

ijkij kij kiji j i jk k

V V V I

F

U-band K -band

U+K band

Map Parameters

• Angular resolution: 0.6 “

• Map size: 256 by 256

• Weighting: uniform

• Tapering: uniform (no tapering)

• Gridding: by averaging

M87. Integral synthesis(two-frequencies data processing: 14.6 и 23.3 GHz)

IF1 =14.6 GHz

IF1 =23.3 GHz

IF1 =19.01 GHz (MFS)

remnantpeak flux

Dynamic range 5000:1

M87. Integral analysis(two-frequencies data processing: 14.6 и 23.3 GHz)

M87. Component analysis(two-frequencies data processing: 14.6 и 23.3 GHz)

AIPS ASL(two-frequency

analysis)

ASL(six-frequency

analysis)

Integral -0.73 -1.04 -1.17

Core -0.4 -0.35 -0.43

Right jet center -0.6 -0.84 -0.82

Left bulb -0.8 -1.09 -1.05

M87. Comparison of the Spectral Indexes(two-frequencies data processing: 14.6 и 23.3 GHz)

Spectral analysis of the right jet of М87(six-frequency analysis)

Dynamic range

where is rms of a remnant map.

Dynamic range remnant ,peak brightness

remnant

Peak brightness

[Jy/beam] rms

2 frequency 2.67 4700

6 frequencies 2.67 5600

Δ

-45.7×10

-44.8×10

Part 2

Improvement of Image Fidelity

Data Editing

The idea: to make worse fidelity of the images on each frequency and then to improve the fidelity by means of MFS

To decrease the quality of the observational data editing for all frequency bands and for all the sources (two calibration sources and a target source) was done:

1. given visibilities were edited by time;

2. edited visibilities were edited once again on the (u,v) –plane.

Time Editing

• The observation time was decreased from 3 hour to 5 minutes

Spatial EditingAfter time editing the number of the baselines were decreased from 231 to 75 with a gap between center of the (u,v)-plane and its longest baselines (similar to the high-apogee Radioastron orbit)

U-band (color maps)

IF1 =14.6 GHz

IF2 =15.1 GHz

U-band (contour maps)

IF1 =14.6 GHz

IF2 =15.1 GHz

K-band (FreqID1, color maps)

IF1 =21.5 GHz

IF1 =21.9 GHz

K-band (FreqID1, contour maps)

IF1 =21.5 GHz

IF1 =21.9 GHz

K-band (FreqID2, color maps)IF1 =22.9 GHz

IF1 =23.3 GHz

K-band (FreqID2, contour maps)IF1 =22.9 GHz

IF1 =23.3 GHz

Multi-frequency synthesis(six-frequency analysis)

Dynamic range: 4000

Reference frequency: 19014.9 MHz

Total flux: 19.3 Jy

Multi-frequency analysis(six-frequency analysis)

Spectral index map

M87 core spectra