Extending Radio Frequencies for Astrometry: 24 GHz Observations and Results in KQ VLBI Survey Collaboration

1. IVS General Meeting 2006 Extending the ICRF To Higher Radio Frequencies: 24 GHz Astrometry C.S. Jacobs JPL (Caltech/NASA) P. Charlot, E.B. Fomalont, D. Gordon, G.E. Lanyi, C.Ma, C.J. Naudet, O. J. Sovers, L.D. Zhang, and the KQ VLBI Survey Collaboration 11 Jan 2006

2. Outline • Motivation for a radio frame above 8 GHz (X-band) • Game plan • Observations • Results • Accuracy • Future Plans/Conclusions

3. Collaborators on Astrometry • P. Charlot Observatory of Bordeaux • E. B. Fomalont NRAO-Charlottesville • D. Gordon Goddard/NASA • C. S. Jacobs JPL/Caltech NASA • G.E. Lanyi JPL/Caltech NASA • C. Ma Goddard/NASA • C.J. Naudet JPL/Caltech NASA • O.J. Sovers RSA Systems/JPL • L.D. Zhang JPL/Caltech NASA This team is a subset of the larger KQ VLBI Collaboration which includes: National Radio Astronomy Observatory -Socorro U.S. Naval Observatory

4. Motivation • Astrometry, Geodesy and Deep Space navigation, now at 8.4 GHz (X-band) Going to Higher radio frequencies allows • Potentially more compact sources Potentially more stable positions • Higher Telemetry Rates to Spacecraft • Avoid 2.3 GHz RFI issues • Ionosphere &solar plasmadown 15X !! at 32 GHz (Ka-band) compared to 8 GHz. Drawbacks of Higher radio frequencies: • More weather sensitive • Weaker sources, shorter coherence times • Many sources resolved Picture credit: SOHO/ESA/NASA

5. Why Ka-band? Valleys are microwave windows The three curves show absorption in a dry atmosphere, in the same atmosphere with 20 kg/m2 of added water vapour, and with both water vapour and 0.2 kg/m2 of stratus cloud added. . Murphy, R. et al., 1987, Earth Observing System Volume IIe: HMRR High-Resolution Multifrequency Microwave Radiometer. Published by NASA, Goddard Space Flight Centre, Greenbelt, Maryland 20771, USA, 59pp. Murphy, R. et al., 1987, Earth Observing System Volume IIe: HMRR High-Resolution Multifrequency Microwave Radiometer. Published by NASA, Goddard Space Flight Centre, Greenbelt, Maryland 20771, USA, 59pp.

6. AGN schematic Schematic of Active Galactic Nuclei Redshift z~ 0.1 to 5 Distance: billions light years Parallax = 0 Proper motion < 0.1 nrad/yr Centroid of radiation Gets closer to central engine (black hole) As one goes to higher Frequencies, therefore, K/Ka/Q better than X (Credit: C.M. Urry and P. Padovani ) http://heasarc.gsfc.nasa.gov/docs/objects/agn/agn_model.html

7. AGN Cen-A in X-ray, Optical, Radio Credits: X-ray (NASA/CXC/M. Karovska et al.); Radio 21-cm image (NRAO/VLA/Schiminovich, et al.), Radio continuum image (NRAO/VLA/J.Condon et al.); Optical (Digitized Sky Survey U.K. Schmidt Image/STScI)

8. Source Structure vs. Frequency S-band X-band K-band Q-band 2.3 GHz 8.6 GHz 24 GHz 43 GHz 13.6cm 3.6cm 1.2cm 0.7cm Ka-band 32 GHz 0.9cm The sources become better ----->

9. Game Plan • Long term - simultaneous 8.4 and 32 GHz (X/Ka-bands) at present instrumentation not completely operational • Interim plan: Bracket 32 GHz with currently available 24 GHz (K-band) 43 GHz (Q-band) - Interpolate behavior at 32 GHz (Ka-band) identifies likely detectable sources • Ka-band - DSN 34m Beamwaveguide antennas: FRINGES! Goldstone California Madrid, Spain Tidbinbilla, Australia - VLBA: 32 GHz proposal not funded at this time - Others??

10. Initial Observations Mauna Kea OVRO Brewster N. Liberty Hancock Ft. Davis Los Alamos St. Croix Kitt Peak Pie Town • VLBA ten 25m antennas 8 sessions each 24 hours ~ 60 sources per session 3-5 snapshots, 2 min each 400 MHz spanned bandwidth 128 Mbps record rate • Simultaneous astrometry and imaging • more sessions planned for 2006 (photos credit NRAO/NSF/AUI http://www.aoc.nrao.edu/vlba/html/vlbahome/thesites.html)

11. Results: 24 GHz Celestial Frame

12. Results: 24 GHz vs 2.3/8.4 GHz Frame

13. ∆RA accuracy: K (3 constraint) vs. S/X ICRF

14. ∆Dec accuracy: K (3 const.) vs. S/X ICRF

15. RA-RA corr. vs. Arc: Effect of More Data • After 3 sessions After 8 sessions • 3-D orientation set by fixing 1.5 sources i.e. minimal constraint • RAs not well separated by least squares

16. RA-RA correlations: Effect of constraints 3 rotation constraints 8 rotation constraints • 3-D orientation set by fixing 1.5 vs. 4 sources • RAs not yet well separated by least squares “fix” at cost of 5 external constraints

17. ∆RA accuracy: K (8 const.) vs. S/X ICRF

18. ∆Dec accuracy: K (8 const.) vs. S/X ICRF

19. 3 Constraint Zonal Errors: ∆Dec vs. Dec

20. 8 Constraint Zonal Errors: ∆Dec vs. Dec

21. Conclusions • ICRF now extended to K-band with sub-mas accuracy! Observations: K-band (24 GHz): 8 VLBA sessions 259 sources, but unevenly observed Accuracy: ~ 350 / 470 µas (RA/Dec) with 3 constraints ~ 200 / 300 µas (RA/Dec) with 8 constraints Source parameters starting to separate with only few days data - more data needed. • Future Plans: More K-band data on the way. Make 8.4 / 32 GHz (X/Ka) operational

22. Results: 43 GHz Reference Frame

23. Basis of VLBI: Point source at infinity How Does VLBI work? Extragalactic “nebulae” idea goes back to 18th c. ? • Relies on point source at infinity - Active Galactic Nuclei Concept: Nav by “fixed” stars • Advantages: Parallax unobservable Proper Motions < 0.1 nrad/yr BUT . . . • Price to be paid is Very weak sources 1 Jy = 1.0E-26 watt/m**2/Hz need lots of square meters => > 25m Antenna lots of Hz bandwidth => 100 Mbps – 1Gbps low system temp => Tsys = 20-40 Kelvin (Hubble Deep Field STScI/NASA)