The GBT 4 mm Rx David T Frayer

The GBT 4 mm Rx David T. Frayer (NRAO) Instrument’s purpose: 67 -93. 3 GHz spectral-line science {Called “ 4 mm” since middle of band is 80 GHz (3. 75 mm) and plans for future higher frequency Rx at 3. 5 -2. 6 mm} First Light Spectrum: May 2011 Commissioned: Jan-Mar 2012 Amplifier upgrade: Nov 2012 Frayer (1)

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

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

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

GBT Effective Collecting Area (ηa * Area) Assumes current ~240 um rms surface errors 35% at 90 GHz most sensitive facility at Q and 4 mm (ALMA ”band 2”) Frayer (5)

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

Rx Block Diagram Specs: Ø Dual beam (4. 7’) separation (cold load between beams) Ø Dual linear polarization for both beams, 1/4 plate allows circular polarization for 1 beam for VLBI observations Ø Frequency Range: 67 -93 GHz Ø IF system 4 separate bands: [FL 1 67 -74 GHz], [FL 2 73 -80 GHz], [FL 3 79 -86 GHz], [FL 4 85 -93 GHz] Frayer (7)

Installation, calibration wheel and external cover Frayer (8)

4 mm Calibration Wheel Cold 1 Beam 1 1/4 2 3 Beam 2 0 5 4 Warm Wheel Position Beam 1 (defined wrt Beam 1) Beam 2 0 Observing Sky 1 Cold Warm 2 Position 2 1/4 wave circ Sky 3 Position 3 Sky 4 Cold 2 Warm Cold 5 Position 5 Sky 1/4 wave Circ Frayer (9)

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

4 mm 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_90 GHz~0. 18 for both sets of measurements) Frayer (11)

Latest Performance Measurements Tsys~60 -70 K over central band under 100 K from 70 -90 GHz (tau_90 GHz~0. 08) Frayer (12)

Science with 4 mm Rx, Lines: Ø Dense gas tracers in star-forming regions and nearby galaxies (HCN, HNC, HCO+ all at ~90 GHz) Ø D-species in cold cloud cores (~7080 GHz) Ø Astro/bio-chemistry (throughout the band) Frayer (13)

4 mm Rx: Cold starless-cores molecular freezeout D-species enhanced N 2 D+ in L 1544 at 77 GHz (S. Schnee et al. ) WVU 2/23/12 N 2 H+ in W 3 OH at 93 GHz Frayer (14)

HCN/HCO+ in M 31 Molecular Clouds, A. Schruba et al. Frayer (15)

4 mm: Dense gas and Molecular Diversity in Nearby Galaxies M 82 H 2 CO (formaldehyde) & HC 3 N (J. Mangum) Frayer (16)

4 mm Mapping M 82 HCO+(1 -0) contours on VLA 6 cm image (A. Kepley et al. ) Frayer (17)

Orion-KL Spectral Line Survey 67 -93. 6 GHz (Frayer et al. ) Frayer (18)

Zoomed in spectrum on Orion-KL 81 -82 GHz Frayer (19)

Example VLBA+GBT-4 mm 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 Sag. A*. Frayer (20)

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