LBA co-observing strategy

Due to the rapid improvement of the LBA imaging techniques, in Cycle 15 we are exploring the possibility for PIs of standalone proposals, who are interested in exploiting the LBA imaging capabilities of LOFAR, to co-observe and co-process data in shared-risk mode with the LOFAR LBA Sky Survey (LoLSS) team. The LOFAR LBA Sky Survey aims to cover the entire northern sky down to the sensitivity of 1 mJy and the resolution of 15 arcsec. Here we summarize the procedure to follow to adopt this option:


  • Any proposer interested in co-observing should contact the coordinator of the LBA Sky Survey well in advance before the proposal deadline (contact: Francesco de Gasperin, fdg [at] hs [dot] uni-hamburg [dot] de) to discuss whether a Co-observing strategy would be mutually beneficial. The LBA Survey coordinator will decide if the project for which he is approached would make mutual sense to do as co-observing. Note that we have limited experience on observations pointed on the galactic plane.

  • Any of the selected proposers should clearly state so in the technical section of their proposals.

  • Co-observing consists of requesting LOFAR observing and processing time in multi-beam mode to observe four pointings simultaneously, allowing one to be on the calibrator, one to be used by the proposer, and two on nearby survey fields.


The benefits of co-observing with the LBA Survey are:

  • The LBA survey team will assist the PI in preparing the technical part of the proposal providing a standard text detailing the observation setup.

  • The LBA survey team will assist the proposer to check the observation setup in MoM.

  • The processing of the calibrator and of the target up and including the direction independent calibration will be taken care of by the LBA survey team. The intention is that calibrated visibilities and images will be made available 4-8 weeks after the observations.

  • The LBA survey team will provide standard text detailing the data processing that has been performed to be included in publications.


Characteristics of the final products:

  • Each pointing is observed with the full dutch array (the use of the full array, including international stations, is possible but needs to be discussed).

  • The frequency coverage is contiguous in the range 42-66 MHz (mid frequency: 54 MHz).

  • The total integration time is 8 hrs.

  • The time resolution is 2 sec, the frequency resolution is 4 ch/SB (0.049 MHz).

  • The direction independent calibrated image will have ~3 mJy/b rms noise and ~45" resolution. Consider however that due to the ultra-low frequencies, substantial direction dependent errors will decrease the image fidelity.

  • The process to obtain a full direction dependent calibrated image is possible but it is still experimental and it is not provided as part of the co-observing mode, however it may be conducted on a best effort basis upon agreement with the survey coordinator. Currently, we were able to reach an rms noise of ~1-1.5 mJy/b and a resolution of 15" in a few testing fields. The presence of some errors in the vicinity of bright sources (>1 Jy @ 54 MHz) is expected.


Policies:

  • After the ILT PC meeting, the PIs of successful proposals who were selected for co-observing will be put in contact with the LBA Survey Coordinator for the necessary project preparations. If awarded observing and processing time, the co-observing project will run with the same observing and processing setups as adopted by the LBA Survey  team.

  • Data will be recorded and archived under the co-observing project; both that project and LBA Survey  teams will have simultaneous proprietary access to data placed into the LTA as processed by the RO.

  • The observing/processing hours will be accounted to the allocation of the co-observing project.

  • The ILT-PC is the final authority for stipulating science use rights and limitations, proprietary time (default 1 year), etc.; PIs should ensure that any requests they have in this regard are justified in their proposal.


Example of DIE calibrated image:

 

 

Example of DDE calibrated image:

 

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