MUSTANG

MUSTANG is a 64 pixel bolometer array which has been commissioned on the GBT for use at 90 GHz. MUSTANG proposals were accepted from June 2009 through Feburary 2012.

NEWS (December, 2012): MUSTANG's successor instrument (MUSTANG-2) is under construction. A prototype version (MUSTANG-1.5) will be made available on a shared-risk basis in the February 1, 2013 NRAO proposal call for observations in semester 2013B. contact Brian Mason for further information.

Some basic performance information is as follows:

• 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 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 4" FWHM provided (effectively) by the standard gridding kernel. If heavier smoothing is acceptable the sensitivity is better by a factor of (FWHM/4 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) 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, 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.

MUSTANG was developed as a facility instrument for the GBT by a multi-institution collaboration. 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. Don't forget that NRAO will provide some page charge support also, if you do a few simple things.

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

Publications

• 90 GHz Continuum Observations of Messier 66 (B. Nikolic & R. Bolton, submitted to MNRAS)
• A Multi-wavelength Study of the Sunyaev-Zel'dovich Effect in the Triple-Merger Cluster MACS J0717.5+3745 with MUSTANG and Bolocam (T. Mroczkowski et al., submitted to ApJ)
• Confirming the Primarily Smooth Structure of the Vega Debris Disk at Millimeter Wavelengths (A.M. Hughes et al., ApJ in press)
• Discovery of the correspondence between intra-cluster radio emission and a high pressure region detected through the Sunyaev-Zel'dovich effec (Ferrari et al. 2011, A&A 534, L12)
• MUSTANG 3.3 Millimeter Continuum Observations of Class 0 Protostars (Shirley et al. 2011, AJ 141, 39)
• MUSTANG High Angular Resolution Sunyaev-Zel'dovich Effect Imaging of Sub-Structure in Four Galaxy Clusters (Korngut et al. 2011, ApJ 734, 10)
• High-frequency Radio Spectral Energy Distributions and Polarization Fractions of Sources in an Atacama Cosmology Telescope Survey Field (Sajina et al. 2011, ApJ 732, 45)
• Implications of a High Angular Resolution Image of the Sunyaev-Zel'dovich Effect in RXJ1347-1145 (Mason et al. 2010, ApJ 716, 739)
• The Radio-2 mm Spectral Index of the Crab Nebula" (Arendt et al. 2011, ApJ 734, 54)
• 90GHz and 150GHz observations of the Orion M42 region. A sub-millimeter to radio analysis (Dicker et al., 2009 ApJ 705 226)
• Observations of M87 and Hydra A at 90 GHz (Cotton et al., 2009 ApJ 701 1872)
• 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)

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.