MUSTANG-2

Note: If you are interested in using MUSTANG-2 in the future please see the note below ^[1] about the status and plans for future GBT observing.

MUSTANG-2 at a glance

MUSTANG-2 is a 223-feedhorn bolometer camera which was commissioned on the GBT in spring 2016, and has been offered for observations on a shared risk basis, in collaboration with the instrument team, since the 2018A GBO proposal call. Several features distinguish it from its predecessor, MUSTANG:

• A new, microstrip-coupled detector design yields higher sensitivity and less susceptibility to environmental microphonics.
• Detectors are feedhorn coupled, with the sum of two linear polarizations measured by a single TES per feed.
• The instantaneous field of view is 4 arcminutes (vs 42 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 detector readout is the first astronomical use of microwave resonators to multiplex TES bolometers.

MUSTANG-2 has been developed by a collaboration including the University of Pennsylvania, NIST, NRAO, the University of Michigan, and Cardiff University. All critical MUSTANG-2 systems have already been proven in operation on the GBT in early 2015 during an engineering run using a partially populated version of the receiver (“MUSTANG-1.5”, which had 64 populated feed horns).

MUSTANG-2 mapping speeds

Some basic performance information is as follows:

• MUSTANG-2’s primary scanning method is that of a Lissajous Daisy of varying radii. The mapping speed profiles have been scaled to a zenith opacity of 0.1 and elevation of 45 degrees.
  • This sensitivity assumes an effective smoothing of 10″.0 FWHM. If heavier smoothing is acceptable the sensitivity is better by a factor of (FWHM/10.0 arcsec).
• Historically, we have reported mapping speeds based on the RMS within a circle of radius 2 arcminutes. These values have now been extended to a range of scan sizes.

Scan size (radius, arcminutes)	Mapping speed in central 2 arcminutes (μK hr1/2)	Sensitivity (μJy/beam)	Sensitivity (compton y)
2.5	73	56.2	2.0E-5
3.0	74	57	2.0E-5
3.5	77	59.3	2.1E-5
4.0	85	65.5	2.3E-5
4.5	98	75.5	2.7E-5
5.0	117	90.1	3.2E-5

• The conversion from μK to μJy/beam is roughly 0.77; i.e. multiple the μK noise by 0.77 to get a noise estimate in μJy/beam.
• The conversion from μK to Compton y is roughly 2.74E-7; i.e. multiple the μK noise by 2.74E-7 to get a noise estimate in Compton y.
• As a general rule one can use the relationship between integration time (t) and sensitivity (σ) where t α 1/σ^2 and the values in the table above to calculate the required integration time or desired sensitivity. For example, if one would like to calculate the required integration time corresponding to a desired sensitivity:
  • Assume that t α 1/σ^2
  • thus, t2/t1 α (σ1/σ2)^2 where t2 is the required integration time, t1 is 1 hour, σ1 is the sensitivity corresponding to the map size from the table above, and σ2 is the desired sensitivity
  • t2 α (σ1/σ2)^2 *t1
• MUSTANG-2 mapping speeds memo ^[10]
• Extended signal on scales up to 5′ should be imaged with reasonable fidelity, but faint signal 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 typcally 9″ (FWHM) and the instantaneous field of view is a 4′ diameter circle.
  • Recovery of signal depends on data processing.
• 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). A minimum setup and calibration time of 1 hour is generally required for each observing session.
• 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 a half hour past sunrise.

Please contact Emily Moravec (emoravec – nrao – edu) or Brian Mason (bmason – nrao – edu) with further questions.

MUSTANG-2 Bandpass

Spectral Index	Center Frequency (GHz)
-4.0	85.453782
-3.5	85.822352
-3.0	86.199666
-2.5	86.585006
-2.0	86.977568
-1.5	87.376465
-1.0	87.780735
-0.5	88.189355
0.0	88.601248
0.5	89.015301
1.0	89.430375
1.5	89.845321
2.0	90.258998
2.5	90.670285
3.0	91.078096
3.5	91.481391
4.0	91.879194
4.5	92.270596
5.0	92.654768

You can download a text file with these values here: M2_center_frequencies_07082023.txt ^[11]

The Status of Future GBT Open-Skies Observing

In order to cope with an evolving funding landscape the GBT is in the process of moving to a model which relies upon a larger fraction of private and collaborative (“pay-to-play”) partnerships. It is expected that a significant fraction of GBT time, depending on the future level of NSF funding, will remain open under something like the current proposable, open-skies arrangement; however the mix of observing capabilities that is available under this arrangement is TBD. If you are interested in forming or contributing to such a partnership to ensure continued access to MUSTANG-2 on the GBT, please contact the director of the Green Bank Observatory, Jim Jackson.

Information for Proposers

• Instrument overview, proposal requirements, instrument team ^[12]
• Noise documentation (under construction)
• Filtering (data processing) documentation ^[13]

Observing Quick Guide

Setup and Observing Quick Guide: On-sky documentation ^[14]

Information for Observers

• Data processing documentation ^[15]
• Description of (current) deliverables ^[16]

Further information

• MUSTANG-2, the instrument
  • Instrument documentation (under construction)
  • Timeline of MUSTANG-2 development (historical) ^[17]
• Publications
  • Peer-reviewed ^[18]
  • Press releases ^[19]
• Deprecated/unmaintained MUSTANG-2 page ^[20]