The Green Bank Telescope

MUSTANG-1.5

MUSTANG-1.5 is a 32-feedhorn bolometer camera which will be commissioned on the GBT in Winter 2014. Several features distinguish it from its predecessor, MUSTANG:

  • A new, microstrip-coupled detector design will yield higher sensitivity and less susceptibility to environmental microphonics.
  • Detectors will be feedhorn coupled, with two linear polarizations per feed (althought not designed specifically for polarimetry).
  • The instantaneous field of view will be 2.5 arcminutes (vs 40 arcseconds for MUSTANG)
  • The receiver design incorporates a tilted refrigerator and receiver rotator, resulting in much lower dependence of cooling performance on telescope elevation.
  • The dewar, electronics, and receiver optics are straightforwardly expandable to a much larger bolometer camera (MUSTANG-2), pending funding.
  • The detector readout will be the first use of microwave resonators to multiplex TES bolometers.
MUSTANG-1.5 is being built on a highly scalable platform to facilitate construction of the final MUSTANG-2 camera: the 223-feedhorn, 4 arcminute diameter field of view camera ultimately desired can straightforwardly use the existing optics, readout electronics, and cryostat. MUSTANG-1.5 is being developed by a collaboration including the University of Pennsylvania, NIST, NRAO, the University of Michigan, and Cardiff University. It is being made available on a shared-risk basis in current and upcoming proposal calls; proposals require collaboration with the instrument team.

Some basic performance information is as follows:

  • The expected sensitivity of MUSTANG-1.5 on the GBT yields a 50 microJy RMS in one hour of integration time mapping a 4'x4' region. The noise scales as the square root of the integration time up to at least several hours; and the noise increases with the square root of the area covered for larger areas. Mapping smaller areas is not efficient in terms of noise performance. For photometry projects, however, a center-weighted "daisy" scan pattern can be used which will reduce the RMS noise by a factor of 1.9 on the central field of view compared to what would be attained covering an equal area uniformly for an equal total time. For significantly larger areas faster scanning can be used which will reduce the noise by up to 35%. Proposals must explicitly state a target map RMS in order to be evaluated for scheduling.
    • This sensitivity assumes an effective smoothing of 8" FWHM provided (effectively) by the standard gridding kernel. If heavier smoothing is acceptable the sensitivity is better by a factor of (FWHM/8 arcsec).
  • Extended emission on scales of 30" to a few arcminutes can be imaged with reasonable fidelity, but faint emission more extended than this may be difficult to detect. Bright emission (20 mJy/beam or more) can be reconstructed over scales of many arcminutes. The angular resolution of MUSTANG on the GBT is tyipcally 9" (FWHM) and the instantaneous field of view is 2'.5 x 2'.5.
  • Allowing for weather and calibration and observing overheads, observers should conservatively allow an observing efficiency of 50% (i.e., assume equal times integrating on source, and for calibrating and general overheads - so 100% overheads relative to observing time).
  • Daytime observing at 90 GHz is currently not advised. The changing solar illumination gives rise to thermal distortions in the telescope structure which make calibrating 90 GHz data extremely difficult. Useful 3mm observations are currently only possible between 3h after sunset and sunrise.

Please contact Brian Mason (bmason - nrao - edu) with further questions.

MUSTANG Publications

We request that publications resulting from MUSTANG observations on the GBT include the following acknowledgement: "The authors would like to thank the MUSTANG instrument team from the University of Pennsylvania, NRAO, Cardiff University, NASA-GSFC, and NIST for their efforts on the instrument and software that have made this work possible. ". Additionally, we request that you cite Dicker et al. (2008) in the paper text. NRAO offers page charge support if you do a few simple things.

Links


NEWS

MUSTANG-2 is Under Construction!

MUSTANG-1.5 is currently being integrated and tested in the lab at U.Penn., with first light on the GBT scheduled for winter 2014.

MUSTANG-2 Detectors delivered to U.Penn!

In June 2014 72 packaged detectors were delivered to U.Penn for testing and characterization.

Left: Cutaway view of tapered feed design; Right: the final MUSTANG-2 feed horn array as fabricated (223 feeds). The feed array weighs 8kg and has been successfully cooled to 300 mK in the MUSTANG-2 cryostat.

Cutaway showing the design of the MUSTANG-1.5 receiver

Pictures of the receiver in the lab at U.Penn.

One ROACH board with its custom daughter cards for the microwave resonator readout.

MUSTANG retired at the end of 2013

MUSTANG-- the original 90 GHz, 64 pixel GBT bolometer camera-- was retired at the end of calendar year 2013 in anticipation of the arrival of its successor, MUSTANG-1.5 MUSTANG proposals were accepted from June 2009 through Feburary 2012.

New GBT Surface Improvements (Sept. 2009)

A concerted campaign of phase coherent holography measurements and actuator repairs has resulted in further, remarkable improvements in the GBT surface: the current Ruze-equivalent surface RMS is estimated to be better than 275 microns rms! This means that MUSTANG should be at least 50% more sensitive than it was for Spring 2009 observing. The following image shows a sequence of surface maps made over the course of the year.

(courtesy T.Hunter & F.Scwab, NRAO)

GBT Surface Improvements (July 2009)

The campaign of traditional, phase-coherent holography led by Todd Hunter & Fred Schwab is paying off, having already yielded a factor of two improvement in the GBT 90 GHz aperture efficiency with more improvements on the way. More information can be found in the February and May NRAO e-news.

Map of GBT surface irregularities before (left) and after (right) corrections based on a series of holographic surface maps. The version numbers refer to which set of surface corrections were in place at the time the map was made, with higher numbers (e.g., v3.05) indicating more recent, better maps. (Image courtesy of Todd Hunter & Fred Schwab, NRAO)

Scans across the moon at 46 GHz with the GBT with three different sets of surface corrections in place on the telescope, showing the far sidelobe response. The more recent telescope surfaces yield substantially lower sidelobe levels, as expected. (Image courtesy of Todd Hunter & Fred Schwab, NRAO)

Scan through a calibrator source with MUSTANG showing the initial, 10% efficient surface response (v1.3), and the improvement that results from an early set of holographic surface corrections (v2.35). On this scale the July 24 2009 map (v3.05) is expected to give a peak intensity of 2. (Analysis by Phil Korngut, U.Penn)

Real-time GBT Surface Updates

Using "out-of-focus" or phase-retrieval holography techniques, it is possible to make real time measurements of the medium to large scale aberrations in the GBT surface by analyzing in-focus and out-of-focus beam maps of bright calibrator sources. Acquiring the data, analyzing it, and applying the resulting corrections to the telescope surface requires less than 15 minutes with MUSTANG, and the process is essentially completely automated (requiring the user only to push a button to accept & send the solution).

In focus (center) and two out of focus (left, right) maps of a bright point source.

Left: GBT phase error map derived from the beam map data above. Color scale is in radians; note that since MUSTANG only illuminates the central r=45m, the phase at the outer edge of the dish is unconstrained and not important observationally. Right: The beam that results from applying the aperture phase corrections to the telescope (on a slightly burned in scale, common to all four beam map plots). Near-in sidelobe levels are lower and the peak foward gain is typically increased by 20-30%.

Early Science Images

MUSTANG+GBT 3mm 5'x10' map of the Orion S/KL Region on 3 Color Scales

MUSTANG+GBT 90 GHz map of Orion on 3 color scales emphasizing the dynamic range and sensitivity to extended structure that has been achieved. These maps resulted from early science observations in Spring 2008; the area covered is approximately 5'x10'. MUSTANG+GBT 3mm map of Cas A

MUSTANG+GBT map of Cas A collected during commissioning, January 2009.

MUSTANG+GBT 3mm Map of the W3 region, 0.4 deg x 0.3 deg

MUSTANG+GBT large-area map of the W3 region (0.4 deg x 0.3 deg). This map required 45 minutes to collect and was a test of MUSTANG's large-area mapping capability. Due to the high slew speeds involve it is possible to suppress instrument and atmospheric "1/f" noise to a greater extent than is possible when mapping smaller fields, resulting in a 25% improvement in sensitivity.

NRAONSFAUI

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Last updated 06 October 2014 by Brian Mason