RSRO, March 2010 - September 2011

^[] Interim receivers pair the new EVLA receiver with the old VLA-style orthomode transducer (OMT). The polarization purity and sensitivity of the interim receivers typically is good only over the traditional VLA tuning range

Figure 1 shows the expected rate of antenna retrofits and installation of the final EVLA receiver systems for the remainder of the EVLA construction project. Note that for certain bands some antennas that do not have final EVLA receiver systems typically do have VLA (X-band) or interim (L-band) receivers. The maximum bandwidth that can be brought back from the antennas to the correlator is currently 2 GHz; this will increase to 8 GHz at a later date when the antennas have been outfitted with fast 3-bit samplers.

Figure 1: Availability of EVLA antennas and final EVLA receiver systems as a function of time.

WIDAR correlator

Boards for a 4-station test version of the WIDAR correlator were tested in Socorro prior to the WIDAR critical correlator production review at the beginning of December 2008. Delivery of production WIDAR boards continues into 2010, and boards are being installed and commissioned throughout this year. The operational capabilities of the EVLA correlator will depend on the order in which the station boards (approximately equivalent to the number of antennas that can be correlated) and the baseline boards (approximately equivalent to the total bandwidth that can be correlated) are installed and commissioned in the correlator, and (ii) the delivery of correlator control software (simple modes will be available first, more complex ones later).

The first step in commissioning WIDAR will be to implement the functionality to be offered for the OSRO program. As additional baseline boards are added, the total bandwidth correlated by WIDAR will continue to grow. It is expected that close to the full bandwidth will be available to participants of the RSRO program, subject to the outfitting of antennas with 3-bit samplers (Figure 1).

The precise capabilities available to the RSRO program are less well-defined than those for OSRO, in part because observing and correlator modes will be commissioned by RSR observers according to the needs of the science proposed. Nevertheless, we outline a possible growth path for RSRO capabilities below, to inform potential RSRO science proposals (see Table 1 for an overview; new capabilities are in boldface in the table). The following timeline is purely notional, since it assumes the commissioning resources provided by the RSRO program. If these resources are unavailable the correlator commissioning will likely follow the path outlined, although at a slower rate. Potential RSR observers are advised to contact NRAO staff about whether a particular observation may be possible before submitting a proposal. All questions about correlator capabilities should be addressed to the NRAO helpdesk.

Table 1: Overview of correlator capabilities for RSRO; further details are described below

2010 (D-configuration):

The maximum bandwidth available will be 2 GHz, using 8-bit samplers, implemented as 2x1 GHz basebands that can be tuned independently within a given receiver band. The correlator will provide 16 independently-tunable sub-band pairs (with some restrictions). For this initial mode, each sub-band pair must be identical in bandwidth, number of channels, and number of polarization products, and can be configured as shown in Table 2, with the additional flexibility that the number of polarization products can be traded for an increase in the number of channels (e.g., correlating just the parallel hands doubles the number of channels per polarization product, and halves the spectral resolution).

Table 2: Initial correlator capabilities per sub-band for RSRO; the number of polarization products can be traded for an increase in the number of channels

2010 (C-configuration):

The maximum bandwidth available will be 2 GHz, implemented as 2x1 GHz basebands that can be tuned independently within a given receiver band. The correlator will have more than 16 independently-tunable sub-band pairs (with some restrictions), which may be set up as shown in Table 2, with identical bandwidths, number of channels, and number of polarization products, to cover the maximum available bandwidth. It will also be possible to trade sub-bands for channels, so that the correlator resources for one sub-band might be used to double the number of channels in another sub-band. For example, one could use 32 sub-bands with 64 channels each, full polarization, or 16 sub-bands with 128 channels, full polarization. The number of polarization products can also be traded for an increase in the number of channels.

2011 (B-configuration):

The maximum bandwidth available will be 2 GHz, implemented as 2x1 GHz basebands that can be tuned independently within a given receiver band. There will be 64 independently-tunable sub-band pairs (with some restrictions; please contact NRAO staff before proposing if you need this feature), which must have identical bandwidths, number of channels, and number of polarization products, although it will also be possible to trade sub-bands for channels. The number of polarization products can also be traded for an increase in the number of channels.

2011 (A-configuration):

The maximum bandwidth available will be 2 GHz, implemented as 2x1 GHz basebands that can be tuned independently within a given receiver band. There will be 64 independently-tunable sub-band pairs (with fewer restrictions on the placement/tuning of the sub-bands; please contact NRAO staff before proposing if you need this feature), which must have identical bandwidths, number of channels, and number of polarization products. It will also be possible to trade sub-bands for channels. Recirculation (a time multiplexing scheme that provides more channels per sub-band at narrower bandwidths) will be enabled in the correlator, to give the capabilities per sub-band pair shown in Table 3 below. We anticipate some restrictions in the number of channels based on the advised maximum allowed data rate of 75 MB/s; based on a 27 antenna array with 1 sec dumps, the restriction breaks down to:

Table 3: Correlator capabilities per sub-band with recirculation; the number of polarization products may be traded for number of channels

2011 (D-configuration):

2012 and following:

At this time the array will be outfitted with fast 3-bit samplers to provide 8 GHz instantaneous bandwidth for all receivers capable of delivering this bandwidth.

Up until this point the WIDAR capabilities expected to be available will be for more or less "standard" types of observations. Special modes will then be implemented and tested. The order in which these special modes are developed will, to a large extent, be driven by the proposed RSRO science and the presence of an expert user to help with the commissioning, subject to practicalities of hardware and software development. Indeed, some of these may be commissioned sooner if an expert user is available to help through the RSRO program, and the necessary software development can be accelerated. The special modes are given below (no priority is intended by the order of this list).

• (Even) more flexibility in the allocation of correlator resources
• Multiple subarrays
• Phased array and single-dish VLBI
• Solar mode
• Planetary mode
• Burst mode
• Radar mode
• Pulsar binning
• Pulsar gating
• On-the-fly mosiacing
• 7-bit correlation
• Fast switching between correlator set-ups
• Very fast dumps
• Mixing of 3-bit and 8-bit samplers
• More processing by the correlator back-end
• Enable more channels for single-polarization observations
• Online RFI flagging
• Multiple phase/delay tracking centers
• Output to user instruments

Although some very straightforward datasets may be reduced in AIPS it is expected that in general RSRO data will be reduced using CASA, and that testing the post-processing software will be part of the RSRO commissioning effort.

Participation in the RSRO program

The primary requirement of the RSRO program is that there be at least one expert from each participating group in residence in Socorro. These experts must be able to contribute effectively to commissioning while incurring as little overhead from EVLA staff as possible. Some support for accommodation may be available, as described below.

There will be two possible routes to obtaining observing time through the RSRO program:

1. The successful submission and acceptance of a proposal received in response to a Call for Resident Shared Risk Observing Proposals for the October 1, 2009 deadline, and subsequent proposal deadlines through the end of the RSRO program in 2011. Such proposals will be allowed an extra two pages compared with OSRO proposals and will have three parts:

   1. A scientific justification, to be peer reviewed as part of NRAO's current time allocation process, submitted through the Proposal Submission Tool. The RSRO resources will not be part of the Proposal Submission Tool, however. Instead, a separate web-based form will allow proposers to specify their expected observing set-up, data rate, data volume, and post-processing requirements.
   2. A technical section naming the personnel who will be involved in the residency and describing how their expertise will be used to address the critical priorities of EVLA commissioning. The proposed dates of the residency must be included, so that the residency can be matched to EVLA commissioning planning. This section will be reviewed by NRAO staff.
   3. A budget specifying the level and nature of any support requested from NRAO. It is expected that NRAO will be able to provide accommodation in the NRAO Guest House, subject to availability. Other support may be available separately through the NRAO Visitor's Program. Proposals that do not require Observatory support will have a substantial advantage over those that request NRAO resources.

   The acceptance of a RSRO proposal will depend on the merits of all three sections of the proposal, and will be judged in terms of the benefits to the EVLA commissioning process by NRAO staff.

   Up to 25% of the hours available for astronomical observations will be reserved for this program; the actual fraction of time assigned will depend upon demand, the quality of the proposed science as judged via the peer-review process, and upon the quality of the technical support offered to the EVLA project, as determined by NRAO. Throughout the transition from the VLA to the EVLA we have maintained astronomical observing at a rate of approximately 60% of all possible available hours. Assuming this efficiency is continued during WIDAR commissioning, we expect approximately 1200 hours per year to be devoted to the RSRO program.

   One month of resident commissioning effort will be required for every 20 hours of EVLA time awarded to a RSRO project, with a minimum residency of 3 months; this is considered the minimum time useful for becoming familiar with the EVLA commissioning effort and contributing effectively, although in exceptional circumstances NRAO is prepared to consider proposals for dividing this into two or three shorter visits. The period(s) of residency may occur in advance of the observing time awarded in order to decouple essential scientific requirements (such as array configuration) from other factors which may affect when personnel are available (such as teaching schedules). However, observers should be present for one week prior to their observations in order to become familiar with the latest commissioning developments and to set up their observations. In the special case of Target of Opportunity proposals an EVLA staff collaborator will be required for setting up observations on short timescales.

   It should be noted that having a member of the NRAO-EVLA commissioning staff as a collaborator on a RSRO proposal will not satisfy the residency requirement. Furthermore, graduate students will in general not satisfy the residency requirement, although there may be exceptional cases. Graduate students will be allowed to accompany their advisor as long as the advisor takes primary responsibility for managing the student's efforts. Resident personnel will work under NRAO management in order to optimize the overall commissioning effort. A set of deliverables will be agreed upon in advance of the start of the residency.

   The types of proposals considered under the RSRO program may include both large (>200 hours) and small (~10-200 hours) projects. Qualified large projects proposed by consortia will be considered as long as the residency requirements are met. A single individual may satisfy the residency requirement for several small projects.

   Resident observers will also be permitted to take part in the "exploratory proposal" section of the NRAO EVLA Commissioning Staff Observing program, in addition to the time allocated by the process described above.

2. A participant may arrange to visit Socorro to contribute to EVLA commissioning by submitting a proposal directly to the Assistant Director for NM Operations (nraonmad@nrao.edu) containing items (b) and (c) of the RSRO Proposal requirements described above, and obtain observing time either by submitting part (a) at the October 1, 2009 (or subsequent) proposal deadline, or through the "exploratory proposal" section of the NRAO EVLA Commissioning Staff Observing program while in residence. Such visits should conform to the residency requirements above, namely, that they provide a minimum of 3 months resident commissioning effort total, but which can be divided into two or three shorter visits if agreed in advance. Proposals to visit Socorro under this program may be submitted at any time, and residence may begin as early as summer 2009.

We emphasize the "shared risk" nature of the RSRO program. Since observers will be attempting to use the full capabilities of a system under development and in the process of being commissioned, NRAO can make no guarantee of the success of any observations made under this program, and no additional commitment is made beyond granting the hours actually assigned by the peer review process.

Commissioning needs of the EVLA project

The rationale for the RSRO program is driven in part by the need for additional personnel to help accelerate the commissioning of the EVLA, WIDAR, and related software systems. Users who visit Socorro as part of the RSRO program will be required to work on aspects of EVLA commissioning that would most benefit from the increased manpower, given the expertise available in the community. A list of potential commissioning tasks that could be addressed through RSRO participation is given below. As emphasized earlier, the dates associated with these commissioning tasks assume the resources provided by the RSRO program. If the resources are not forthcoming, the commissioning will proceed at a slower pace than that outlined here.

Table 1: Overview of EVLA commissioning, 2010-2011

One of the goals of the RSRO program is also to develop EVLA expertise in the user community, so all residents will in general be astronomers with a personal stake in both their observations and the results of their commissioning efforts. Some exceptions may be considered at the discretion of the Assistant Director for New Mexico Operations.

Questions regarding the RSRO program should be directed to Claire Chandler (cchandle@nrao.edu).