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Russian Academy of Sciences Pulkovo Observatory

On systematic and stochastic errors of radio source position catalogues
Zinovy Malkin
Pulkovo Observatory and St. Petersburg State University malkin@gao.spb.ru

JournИes 2013, Paris, France, September 2013


Topics to discuss

The following topics related to the radio source position catalogues are considered: 1. Formal uncertainties 2. External stochastic errors (see Malkin, A&A, 2013,
DOI: 10.1051/0004-6361/201322334 for more detail)

3. Several points related to systematics


Assessment of external errors of catalogues
N-cornered-hat method

i = 1,n-1, j = i+1,n
ij - variance of differences between catalogues ij - correlation coefficient between catalogues

i, j - unknown external errors of catalogues

Estimation of ij is a key point of the method!


Correlation between catalogues


Weighted correlation
Standard correlation coefficient:

Weighted correlation coefficient:


Weighted correlation


Weighted correlation
Catalogues AUS/GSF BKG/GSF CGS/GSF GSF/IGG GSF/OPA GSF/RFC GSF/SHA GSF/USN Standard corr. RA / DE +0.1861/+0.2032 +0.5082/+0.6095 +0.7711/+0.7746 -0.0193/+0.2334 +0.5210/+0.4823 -0.2497/-0.0311 +0.1528/+0.1270 -0.0268/-0.0832 Weighted corr. RA / DE +0.1125/+0.1129 +0.4794/+0.5038 +0.6395/+0.6348 +0.3732/+0.3693 +0.4711/+0.4931 +0.2184/+0.2582 +0.1218/+0.1195 +0.0099/+0.0346


Systematic differences (small)


Systematic differences (small)


Systematic differences (large)


Systematic differences (large)


Correlation between catalogues
Catalogue

B09

B10

B11

B12

G09 G10

G11

G12 O09 O10

O11

O12 O13

ICRF2 BKG2009 BKG2010 BKG2011 BKG2012 GSF2009 GSF2010 GSF2011 GSF2012 OPA2009 OPA2010

0.458 0.227 0.128 0.065 0.315 0.077 0.009 -0.052 -0.244 -0.295 -0.276 -0.283 -0.258 0.784 0.676 0.586 0.220 0.187 0.152 0.130 -0.078 -0.085 -0.017 -0.009 0.003 0.929 0.808 0.136 0.281 0.256 0.229 -0.016 -0.054 -0.051 -0.057 -0.039 0.923 0.105 0.272 0.284 0.274 0.012 -0.024 -0.051 -0.074 -0.069 0.091 0.260 0.275 0.327 0.033 -0.003 -0.047 -0.087 -0.119 0.639 0.519 0.335 0.404 0.268 0.224 0.183 0.172 0.909 0.648 0.295 0.309 0.298 0.248 0.225 0.777 0.266 0.271 0.331 0.285 0.250 0.189 0.206 0.269 0.289 0.276 0.738 0.503 0.394 0.320 0.730 0.519 0.427

OPA2011
OPA2012

0.857 0.732
0.901

Correlation between catalogues from the same AC are shown in red


Catalogue errors [as]


External vs. formal error


ICRF2: position uncertainty vs. # of observations

Special handling sources are shown in red STD of one-session measurement, not STD of mean?


Conclusions
1. A new approach to assess the external stochastic errors of radio source position catalogues has been presented. Using this approach, we obtained independent estimates of the stochastic errors of the nine recently published catalogues, some of them for the first time. 2. Modern radio source position catalogues show significant and complicated systematic differences, which must be accounted for during combination.
3. Catalogues obtained at the same AC are in close correlation with each other. This may show that AC-specific systematic errors do exist caused by specific modeling and analysis options. 4. The external catalogue stochastic errors closely correlate with the formal source position uncertainty, most probably because of the quality of the software used and analysis strategy details such as modelling and parameterization. 5. The ICRF2 source position uncertainties are not homogeneous for 'global' and 'arc' sources.


Thank you for your attention!

The End