REFAG 2014 pp 191-199 | Cite as

The Effects of Simulated and Observed Quasar Structure on the VLBI Reference Frame

  • Stanislav S. Shabala
  • Lucia Plank
  • Robert G. Schaap
  • Jamie N. McCallum
  • Johannes Böhm
  • Hana Krásná
  • Jing Sun
Conference paper
Part of the International Association of Geodesy Symposia book series (IAG SYMPOSIA, volume 146)

Abstract

Radio-loud quasars making up the Celestial Reference Frame are dynamic objects with significant structure that changes on timescales of months and years. This is a problem for geodetic VLBI, which has so far largely treated quasars as point sources in analysis. We quantify the effects of various levels of source structure on the terrestrial (TRF) and celestial (CRF) reference frames using the source structure simulator recently implemented in the Vienna VLBI Software (VieVS) package. We find that source structure affects station positions at the level of 0.2–1 mm. While quasar structure contributes only \(\sim \) 10% to the total TRF error budget, which is dominated by tropospheric turbulence; the effect of quasar structure on the CRF is discernible even in present-day observations. Astrophysical properties of quasars are related to their structure and geodetic stability, and we discuss several quasar structure mitigation strategies. These include: (1) astrophysically-based quasar selection techniques; (2) scheduling sources by taking into account source structure; and (3) analyzing geodetic observations using knowledge of source structure. We find that for observed highly variable quasars, flux density is strongly anti-correlated with structure and position stability, suggesting that such quasars should preferentially be observed in their bright phase. We use simulations to investigate new scheduling strategies which avoid unfavourable jet—baseline orientations. Improvement is seen at the millimetre level on the longest baselines when our new scheduling strategy is used in simulations that only include quasar structure. This improvement disappears in the full simulations including the troposphere, because we are compromising sky coverage in order to mitigate source structure effects. This again confirms that, at present, tropospheric turbulence dominates the accuracy of TRF determination. However, the contribution of quasar structure will become more important as tropospheric effects decrease in future broadband observations.

Keywords

Astrometry Celestial reference frame (CRF) Geodesy Quasar structure Terrestrial reference frame (TRF) Very long baseline interferometry (VLBI) 

References

  1. Böhm J et al (2012) IAG Symp Proc 136:1007Google Scholar
  2. Charlot P (1990) Astron J 99:1309CrossRefGoogle Scholar
  3. Fey AL, Charlot P (2000) Astrophys J Suppl Ser 128:17CrossRefGoogle Scholar
  4. Lister ML et al (2009) Astron J 138:1874CrossRefGoogle Scholar
  5. Lovell JEJ et al (2013) J Geod 87:527CrossRefGoogle Scholar
  6. Ma C et al (2009) IERS Technical Note 35, 1. http://adsabs.harvard.edu/abs/2009ITN....35....1M
  7. Pany A et al (2011) J Geod 85:39CrossRefGoogle Scholar
  8. Petrachenko B et al (2009) IVS 2008 Ann Rep 13. http://adsabs.harvard.edu/abs/2009vlbi.rept....1P
  9. Plank L et al (2015) Mon Not R Astron Soc 455:343. http://adsabs.harvard.edu/abs/2016MNRAS.455..343P
  10. Porcas R (2010) IVS GM Proc, p 8. http://adsabs.harvard.edu/abs/2010ivs..conf....8P
  11. Schaap RG (2014) U. Tasmania Honours thesis. University of TasmaniaGoogle Scholar
  12. Schaap RG et al (2013) Mon Not R Astron Soc 434:585CrossRefGoogle Scholar
  13. Shabala SS et al (2014) J Geod 88:575CrossRefGoogle Scholar
  14. Shabala SS et al (2015) J Geod 89:873CrossRefGoogle Scholar
  15. Sun J et al (2014) J Geod 88:449CrossRefGoogle Scholar

Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  • Stanislav S. Shabala
    • 1
  • Lucia Plank
    • 1
  • Robert G. Schaap
    • 1
  • Jamie N. McCallum
    • 1
  • Johannes Böhm
    • 2
  • Hana Krásná
    • 2
  • Jing Sun
    • 3
  1. 1.School of Physical SciencesUniversity of TasmaniaTAS 7001Australia
  2. 2.Department of Geodesy and GeoinformationVienna University of Technology1040 ViennaAustria
  3. 3.Shanghai Astronomical ObservatoryShanghaiChina

Personalised recommendations