MUSTANG

MUSTANG is a 64 pixel bolometer array which has been commissioned on the GBT for use at 90 GHz. Proposals will be accepted in the June 1 2009 deadline for Fall/Winter 2009 (trimester 09C) observing on the GBT. Proposers are not required to collaborate with the instrument team.

Some basic performance information is as follows:

• As of March 2009, the demonstrated sensitivity of MUSTANG on the GBT yields a 0.4 mJy RMS in one hour of integration time mapping a 3'x3' 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 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.
• 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) is easily 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 40"x40".
• Allowing for weather and calibration and observing overheads, the typical observing efficiency realized on the telescope is 50%.
• 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.
• Further sensitivity improvements of a factor of two or more may be realized (due to GBT surface improvements and a new detector array) but cannot be relied upon for 09C observing.

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

Publications

• 90GHz and 150GHz observations of the Orion M42 region. A sub-millimeter to radio analysis (Dicker et al., submitted to Ap.J.)
• Observations of M87 and Hydra A at 90 GHz (Cotton et al., Ap.J. in press)
• MUSTANG: 90 GHz Science with the Green Bank Telescope (Dicker et al., Presented at the SPIE conference on astronomical instrumentation in 2008; "Millimeter and Submillimeter Detectors and Instrumentation for Astronomy IV.", Proc. SPIE, Volume 7020, pg 702005, (2008))
• A 90-GHz bolometer array for the Green Bank Telescope (Dicker et al. in Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III. Edited by Zmuidzinas, Jonas; Holland, Wayne S.; Withington, Stafford; Duncan, William D.. Proceedings of the SPIE, Volume 6275, pp. 62751B (2006))

Links

• University of Pennsylvania MUSTANG Web Page
• NRAO Proposal Submission Tool
• Resources for GBT Astronomers
• February 2009 NRAO e-news article about MUSTANG.
• February 2009 and May 2009 NRAO e-news articles about GBT surface improvements.
• NEW: Information about 90 GHz weather conditions in Green Bank

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NEWS

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)

Detector Array Upgrade (June 2009)

NIST has fabricated a 10x10 (100 pixel) detector array which is currently undergoing testing and is on track for installation in the existing MUSTANG receiver for observations in the Winter 2009/2010 season. This array promises to significantly increase the field-of-view and per-detector sensitivity of MUSTANG; quantitative results pending ongoing test results.

10x10 detector array (courtesy of NIST)

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 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 map of Cas A collected during commissioning, January 2009.

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.