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The GBT 4mm Rx

The GBT 4mm Rx . David T . Frayer (NRAO). Instrument’s purpose: 67-93.3 GHz spectral-line science {Called “4mm” since middle of band is 80GHz (3.75mm) and plans for future higher frequency Rx at 3.5-2.6mm}. First Light Spectrum: May 2011 Commissioned: Jan-Mar 2012

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The GBT 4mm Rx

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  1. The GBT 4mm Rx David T. Frayer (NRAO) Instrument’s purpose: 67-93.3 GHz spectral-line science {Called “4mm” since middle of band is 80GHz (3.75mm) and plans for future higher frequency Rx at 3.5-2.6mm} First Light Spectrum: May 2011 Commissioned: Jan-Mar 2012 Amplifier upgrade: Nov 2012

  2. 485 ft 151 ft At 100 m, the GBT is the largest fully steerable telescope in the world. Unblocked Aperture Active Surface Operates from ~100 MHz to 100 GHz Fully Steerable >85% of total sky covered δ≥-46° Pointing to 1”-2” accuracy Surface good for 3mm work 2.3 acre collecting area

  3. Improvements to Surface Makes 3mm Possible (From Todd Hunter, PTCS group)

  4. The Active Surface 2209 actuators Currently rms < 240μm at night, the goal is ~200μm University of Georgia, Sept 2011 4

  5. GBT Effective Collecting Area (ηa * Area) Assumes current ~240um rms surface errors 35% at 90 GHz  most sensitive facility at Q and 4mm (ALMA ”band2”)

  6. Weather at Green Bank good for 3mm observations for 1000-2000hrs per year Hours available per year with acceptable winds and tau: (from Ron Maddalena’s weather studies)

  7. Rx Block Diagram • Specs: • Dual beam (4.7’) separation (cold load between beams) • Dual linear polarization for both beams, 1/4plate allows circular polarization for 1 beam for VLBI observations • Frequency Range: 67-93 GHz • IF system 4 separate bands: [FL1 67-74 GHz], [FL2 73-80 GHz], [FL3 79-86 GHz], [FL4 85-93 GHz]

  8. Installation, calibration wheel and external cover

  9. 4mm Calibration Wheel Cold 1/4 1 2 3 0 Beam1 Beam2 5 4 Warm

  10. CDL LNA’s optimized for 4mm Band (installed Nov 2012)

  11. 4mm Performance and Tsys Improvement Boxes are original system, while diamonds show Tsys after new amplifiers. Aperture and main-beam efficiency of the dish given to the right as dotted and solid lines respectively. (tau_90GHz~0.18 for both sets of measurements)

  12. Latest Performance Measurements Tsys~60-70K over central band and under 100K from 70-90 GHz (tau_90 GHz~0.08)

  13. Science with 4 mm Rx, Lines: • Dense gas tracers in star-forming regions and nearby galaxies (HCN, HNC, HCO+all at ~90GHz) • D-species in cold cloud cores (~70-80GHz) • Astro/bio-chemistry (throughout the band)

  14. 4mm Rx: Cold starless-cores molecular freeze-out D-species enhanced N2D+ in L1544 at 77 GHz (S. Schnee et al.) N2H+ in W3OH at 93 GHz

  15. HCN/HCO+ in M31 Molecular Clouds, A. Schruba et al.

  16. 4mm: Dense gas and Molecular Diversity in Nearby Galaxies M82 H2CO (formaldehyde) & HC3N (J. Mangum)

  17. 4mm Mapping M82 HCO+(1-0) contours on VLA 6cm image (A. Kepley et al.)

  18. Orion-KL Spectral Line Survey 67-93.6 GHz (Frayer et al.)

  19. Zoomed in spectrum on Orion-KL 81-82 GHz

  20. Example VLBA+GBT-4mm fringes GBT VLBI will probe the physics near the base of black hole jets in nearby galaxies and directly measure the size of the galaxy via parallax of SagA*.

  21. Web Links… 4mm Web Page: http://www.gb.nrao.edu/4mm/ 4mm Wiki: https://safe.nrao.edu/wiki/bin/view/GB/Gbt4mmRx 4mm Commissioning Wiki (latest info on performance and notes for users): https://safe.nrao.edu/wiki/bin/view/GB/Gbt4mmRxCommissioning

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