RSRO, September 2011 - January 2013

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 per polarization; this will increase to 8 GHz per polarization at a later date when the antennas have been outfitted with fast 3-bit samplers (dashed black line in the plot).

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

WIDAR correlator

All production WIDAR boards have been delivered and installed. Delivery of the correlator control software and the outfitting of antennas with 3-bit samplers set the pace for the availability of further operational capabilities.

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 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

2011 June - September (A-configuration):

The maximum bandwidth available was 2 GHz, implemented as 2x1 GHz basebands that can be tuned independently within a given receiver band. There were 64 independently-tunable sub-band pairs (with fewer restrictions on the placement/tuning of the sub-bands), which had to have identical bandwidths, number of channels, and number of polarization products. It was also possible to trade sub-bands for channels. Recirculation (a time multiplexing scheme that provides more channels per sub-band at narrower bandwidths) was enabled in the correlator, to give the capabilities per sub-band pair shown in Table 3 below. Some restrictions were imposed on the number of channels based on the maximum allowed data rate of 25 MB/s; based on a 27 antenna array with 1 sec dumps, this restriction breaks down to:

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

2011 September - 2012 May (D, C and hybrids):

After implementing recirculation the next step is to introduce more flexibility by allowing each of the independently-tunable 64 sub-band pairs to have different bandwidths and numbers of channels. The number of polarization products will be the same for all sub-bands. In addition, the sub-bands will be independently tunable with few restrictions. The available bandwidths and numbers of channels are as shown in Table 3. Incremental increases in data rate will be supported up to those listed in Table 1. Increasing numbers of the fast 3-bit samplers will be available for testing and potential science.

2012 May - 2013 January (B, A and hybrids; End of construction):

At this time, most of the array will be outfitted with fast 3-bit samplers to provide 8 GHz instantaneous bandwidth for all receivers capable of delivering this bandwidth; this number will increase throughout the year until the array is fully equipped.

Up until this point the WIDAR capabilities expected to be available will be for more or less "standard" types of observations. Special correlator 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
• 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 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 is available, as described below.

There are 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 at all regular proposal deadlines through the end of the RSRO program in 2012. Such proposals are allowed an extra two pages compared with OSRO proposals and 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 are not part of the Proposal Submission Tool, however. Instead, a separate web-based form allows 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. During WIDAR commissioning astronomical observing has been maintained between 50% and 60% of all possible available hours; we therefore expect approximately 1200 hours per year to be devoted to the RSRO program.

   One month of resident commissioning effort is 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. Graduate students may satisfy the residency requirement, provided relevant expertise is demonstrated in section (b) of the proposal. Graduate students should be accompanied by their advisor at the start of their residency. 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 a regular 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.

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 in 2012

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 in 2012 is given below.

• Multiple sub-arrays
• Mosaicing (both multiple single pointing and OTF)
• Phased EVLA
• Pulsar observing
• Observing with the 3-bit sampler system
• Fast correlator dumps
• Pipeline heuristics, including automated flagging and data quality analysis
• Testing of new full-field, wide-bandwidth imaging algorithms
• Advanced data analysis tools

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).