Co-observing with the Surveys KSP team

To maximise the telescope efficiency the International LOFAR Telescope encourages PIs of standalone proposals to co-observe and co-process data with the LOFAR Two-Metre Sky Survey (LoTSS) team. This procedure is described in detail below, while in the following a summary of the main points is outlined.

  • Any proposers interested in this opportunity should clearly state so in the technical section of their proposals.
  • Before requesting LOFAR observing & processing time, proposers are invited to check if the target of interest has been covered in any of the performed / planned pointings of the LoTTS by using the linked ALADIN interface.
  • Any questions regarding co-observing can be directed to lotss-admin [at] strw [dot] leidenuniv [dot] nl.
  • Except in cases where tailored processing is required and a collaboration is formed between LoTSS members and the proposers, there will be no requirement for joint science analysis or publications and only an acknowledgement will be required in any resulting publications.
  • Co-observing consist of requesting LOFAR observing & processing time in multi-beam mode to observe two pointings simultaneously, allowing one to be used by the proposer and the other by the LoTSS team.
  • Each pointing is observed with the full LOFAR array, with almost contiguous frequency coverage from 120-168MHz and an integration time of 8hrs.
  • The desired target of the proposer can be observed either by observing the closest pointing on the SKSP grid or by observing directly at the target. In both cases, the second beam will be placed on the LoTSS grid.
  • As a result of the collaboration the LoTSS team will provide proposers with:
    • assistance with the preparation for observations with the observatory;
    • within a period of 4 weeks (except in exceptional circumstances) the products from the standard direction independent calibration pipeline (for the quality of the images that can be produced from these data see Shimwell et al. 2017, A&A, 598, A104) in addition to the regular data products provided by the observatory;
    • if both pointings are placed on the LoTSS grid, within 8 weeks of the observations, the LoTSS team will also run the standard surveys direction dependent calibration and imaging pipeline and provide the user with the resulting images. If either pointing is not placed on the LoTSS grid this pipeline will be run on a best efforts basis;
    • if additional, more tailored, processing is still required to produce science quality images, the LoTSS team will be open to discussion of a collaboration with the proposers on the data processing in an attempt to help provide science quality images.

RATIONALE

Before requesting LOFAR observing & processing time, proposers must check the presence of any data in the Long Term Archive that may fit their science goals. In particular, proposers that are interested in interferometric data are also requested to check if the target of interest has been covered in any of the performed / planned pointings of the LoTTS. If so, proposers are encouraged to collaborate with the LoTTS team in order to have access to the processed data by contacting lotss-admin [at] strw [dot] leidenuniv [dot] nl. Otherwise proposers can review the sections detailed below and contact the LoTTS team, in order to co-observe in a multi-beam mode. To this aim, PIs will first need to check with the LoTTS team if any survey pointing can be selected around the target of interest.

In order to verify either if:

  • any of the performed / planned pointings of the LoTTS survey is available to cover target of interest,
  • any survey pointing can be selected around the target of interest

proposers can use the ALADIN interface linked below, which shows the progress with the survey (red unobserved, blue observed and yellow is planned for the upcoming observing cycle). By clicking on the centre a popup window will list details about the selected pointing. Furthermore, details of all observed LoTSS pointings are summarized in a table.

Tier 1 HBA progress

 

OBSERVATIONAL AND PROCESSING DETAILS

The LoTSS team is aiming to observe the entire Northern sky with 3168 pointings above declination 0 as described in Shimwell et al. 2017, A&A, 598, A104. Each pointing is observed with almost contiguous frequency coverage from 120-168MHz and an integration time of 8hrs.  The separation between LoTSS pointings is typically 2.6 degrees implying that every target above declination 0 is contained (well) within the primary beam of a LoTSS pointing. To facilitate co-observing the LoTSS project is using 8-bit mode and exploiting the multi-beam capability of LOFAR to observe two pointings simultaneously, allowing one to be used by the proposer and the other by the LoTSS team. To co-observe with LoTSS the desired target can be observed either by observing the closest pointing on the SKSP grid (this is the preferred option) or if the source is sufficiently far from any LoTSS pointing centre that sensitivity loss becomes important, by observing directly at the target and placing the second beam on the LoTSS grid.

A summary of the LoTSS setup, which must also be adopted for any co-observing project is given below:

* an HBA Dual Inner, 8 hours long (split in multiple observations at low-declination if necessary) observation which is book-ended with 10 min flux calibrators;

* the full (CS,RS,IS) LOFAR array is used;

* the bandwidth for each pointing (at least one on the LoTSS grid) is 243 subbands and one subband is used to centre the tile beam between the two observed pointings.

* the data will be averaged to 16 channels per subband and 1 secs.

 

As a result of the collaboration:

- the LoTSS team will provide standard text detailing the data processing that has been performed and text describing the observation setup for the technical case of a proposal (see http://lofar.strw.leidenuniv.nl/doku.php?id=tier1_hba_coobserving);

- the LoTSS team will assist the proposer with the preparation for observations with the observatory;

- within a period of 4 weeks (except in exceptional circumstances) the LoTSS team will send the PI of the co-observing proposal the products from the standard direction independent calibration pipeline (https://github.com/lofar-astron/prefactor) in addition to the regular data products provided by the observatory. This calibration is for the Dutch stations only and international stations are removed from the calibrated datasets. The quality of the images that can be produced from these data without any further calibration is detailed in Shimwell et al. 2017, A&A, 598, A104;

- many science cases will require higher quality images that can only be obtained with some form of direction dependent calibration. Therefore if both pointings are placed on the LoTSS grid, within 8 weeks of the observations, the LoTSS team will run the standard surveys direction dependent calibration and imaging pipeline (https://github.com/mhardcastle/ddf-pipeline) and provide the user with the resulting images. If either pointing is not placed on the LoTSS grid this pipeline will be run on a best efforts basis.  The quality of the images produced by the standard surveys pipeline will be detailed in a forthcoming article but typically the sensitivity achieved, at optimal declinations, is 0.1mJy/beam at a resolution of 6arcsec. However, there are significant variations depending on the ionospheric conditions, the source environment and target declination;

- if additional, more tailored, processing is still required to produce science quality images, the LoTSS team will be open to discussion of a collaboration with the proposers on the data processing in an attempt to help provide science quality images.

Except in cases where tailored processing is required and a collaboration is formed between LoTSS members and the proposers, there will be no requirement for joint science analysis or publications and only an acknowledgement will be required in any resulting publications.

 

POLICY

- After the ILT PC meeting, the PIs of successful proposals who have expressed an interest in the aforementioned opportunity will be placed in contact with the Surveys KSP team, who will select (if available) the LoTSS pointing to be observed in parallel with the PIs target.

-  If awarded observing & processing time, the co-observing project will run with the same observing and processing setups as adopted by the LoTSS team.

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

- The observing 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.

- The acknowledgments required on any publications resulting from co-observingprojects can be found on http://lofar.strw.leidenuniv.nl/doku.php?id=tier1_hba_coobserving

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