EVLA Early Science

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VLA capabilities September 2011 - January 2013

1. Introduction

EVLA early science is provided by two programs for outside users and one for EVLA commissioning staff. All early science programs are peer-reviewed. In keeping with a primary construction project goal, the EVLA will continue to be used for science throughout the commissioning of the telescope into full operations in 2013. Observing during this period thus involves an element of risk associated with the large stepwise increases in throughput bandwidth that are offered to the community at the start of each new array configuration cycle in 2010, 2011, and 2012.

The Open Shared Risk Observing (OSRO) program provides early science capabilities to the general user community. These capabilities initially provided a maximum 256 MHz bandwidth that increased to 2 GHz for the D configuration in mid-2011 and will increase further to 8 GHz at the end of 2012. The Resident Shared Risk Observing (RSRO) program will provide these capabilities, and other more powerful ones, much sooner to users who can reside in Socorro and help with the EVLA commissioning efforts. These same enhanced capabilities will also be made available to EVLA commissioning staff via the EVLA Commissioning Staff Observing (ECSO) program.

2. Expected Capabilities

All EVLA antennas are outfitted with either EVLA or "interim" L, EVLA C, VLA X, EVLA K, EVLA Ka, and EVLA Q-band receivers. (Interim receivers are EVLA receivers with narrowband VLA polarizers. All interim receivers will be converted to full EVLA capabilities by the end of 2012. The polarization purity and sensitivity of the interim receivers typically is good only over the traditional VLA tuning range.) As of July 2012, 25 of the EVLA antennas will be outfitted with S-band receivers, 23 EVLA antennas will have Ku-band receivers, and 22 will have new EVLA-style X-band receivers. Figure 1 shows the expected installation rate of final EVLA receiver systems for the rest of the EVLA construction project. The 8-GHz maximum bandwidth availability depends on the implementation of the fast 3-bit samplers, expected to be commissioned by the end of 2012. Prior to this, the maximum available bandwidth will be 2 GHz per polarization.

Figure 1 does not tell the entire story of frequency availability for observing with the EVLA, however, since there are interim or VLA receivers at L and X-bands that can be used in the absence of the final EVLA receivers. Table 4 gives a prediction of the new frequency capabilities that are available in September 2011 and January 2012, along with the expected "total" numbers of receivers for a given band, including VLA-style and/or interim receivers. New receiver bands will be offered for general use when the performance of at least five antennas has been verified by EVLA commissioning staff.

Note: The "EVLA+VLA/interim" columns give the total numbers of receivers expected to be available for a given band, including all VLA-style and/or interim receivers (see Figure 1).

3. Open Shared Risk Observing

NRAO has been offering "shared risk" access to the VLA for all users since the EVLA construction project began. The OSRO program has extended this into the EVLA era by providing early access to a number of EVLA correlator capabilities and observing modes that represent a significant improvement over the capabilities of the VLA correlator. They are described in detail in Performance of the EVLA. NRAO will make every effort to ensure projects awarded time under the OSRO program obtain good quality data. The highest risk will be for time-critical observations such as observations of triggered transients or observations coordinated with other observatories.

4. Resident Shared Risk Observing

The WIDAR correlator and the EVLA provides a vastly more powerful instrument than the VLA. The RSRO program offers participants early access to the growing capabilities of the EVLA as it is being commissioned, in exchange for a period of residence in Socorro to assist with the commissioning. It is intended to accelerate the development of the EVLA's full scientific capabilities by gaining enhanced resources and expertise through community participation. It will at the same time help quickly optimize the scientific productivity of the EVLA. The RSRO program is now expected to run through the end of 2012, with up to 25% of the EVLA time available for astronomical observations allocated to the RSRO program, depending on demand and quality of science proposed. Full operations of the EVLA will begin in 2013. This document describes only those capabilities available to the general user community through the OSRO program for the upcoming DA configuration cycle, Sep 2011 through Dec 2012. Users interested in participating in the RSRO program should refer to the relevant web page for a general description of the expected capabilities available through the RSRO program, and should check with EVLA staff for further details.