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. Full details of the co-observing scheme can be found on the ASTRON pages.
Getting help from the LoTSS team
Once you have read the instructions below, please email lotss-admin (at) strw.leidenuniv.nl with any questions about co-observing.
Example standard text for technical section of proposals
In this proposal we request a total of 8 hours of HBA observations of object XX which we propose to observe as part of the LOFAR Two-metre Sky Survey (LoTSS) co-observing scheme. Due to the small separation of our target from the nearest LoTSS pointing we will place both pointings on LoTSS grid positions.
We will use the HBA-dual inner mode to conduct the observations, with the 48 MHz bandwidth (120-168 MHz) on each pointing, book-ended by 10-min flux-calibrator scans. In agreement with the LoTSS observing strategy we request to observe with international stations and to store the data for the LoTSS pointings at 16ch/sb and 1 s in the LTA. On CEP2/4 we will do pre-processing only (flagging and averaging) with no de-mixing. We will perform further processing off-line using computing clusters. The pre-processed and averaged 8h40m of data will be 32 TB (16TB for each pointing). These data should be stored in the LTA.
In summary we request 8 hours 40 minutes of HBA observing time, 14.7hrs of processing time (based on previous observations we use a P/O ratio of 1.7) and 32 TB of LTA data storage.
Please note that some variations are often needed to accommodate cases where e.g. one beam is centred on the target, the desired averaging changes between pointings or when the targets are at low declination. E.g.
- Due to the large separation of our target from the nearest LoTSS pointing we will place one pointing on the LoTSS grid and the other at the location of our target.
- the pointing towards object XX can be averaged to 8ch/sb and 2s
- As our target is at low declination we propose to observe in two 4 hour integrations.
Completing the online proposal form
- Is nighttime required? up to the user — not essential for survey-quality data
- Are there parallel observations planned with other facilities? up to the user
- Do you request using international stations? Yes
- Are the IS essential/critical for your observations? up to the user
- Elaborate: Not essential for the science goal of this proposal but requested following the LoTSS co-observing scheme setup OR Essential to this proposal because ... and compatible with the LoTSS co-observing scheme setup.
- Are there other scheduling constraints? up to the user (no additional constraints are required for co-observing)
- Are combined data products requested in the setup? up to the user (nothing to be specified for the co-observing scheme)
- Give the noise level you wish to achieve for your observations: 0.1/cos^2(z) mJy/beam where z = abs(dec-53).
- What is the expected maximum data rate? 4 GB/s
- Do you request any processing offered by the RO?Yes
- Do you request your data to be stored at a specific site? up to the user (nothing to be specified for the co-observing scheme)
- Do you require off-line data processing on RO facilities?up to the user (remember that if both pointings are centered on the LoTSS grid the co-observing agreement provides for running the full calibration pipeline, both independent and dependent direction calibration on dedicated facilities. However, even in this case the user may still consider to ask off-line data processing on RO facilities for further calibration and imaging)
- Do you have access to external processing facilities?As stated in the survey co-observing policy the grid pointings will be processed by the survey team using their external facilities using the standard survey direction dependent and independent calibration pipelines. The rest of the processing (including further imaging of the grid pointings or calibration and imaging of the pointings unrelated to the grid) will be conducted on ...
- Do you request a CEP4 processing time which is different from the Northstar calculations?YES
- Elaborate: Following the guidelines of the co-observing strategy, we request X hrs of processing time instead of the X hrs calculated by Northstar, because we assume P/O=0.85 instead of P/O=0.81 for the processsing of the calibrators and the LoTSS pointing without the de-mixing. This is based on the experience gained by the survey team during previous observations.
- Do you request co-observing with the LOFAR Two-meter Sky Survey? Yes
- Observation strategy: 10 min calibrator; 8 h target multi beam HBA-dual observation with 243 subbands on each source; 10 min calibrator (but see below for low-dec fields).
Telescope configuration: Interferometer Mode Setting Chose stations: All (24,14,13) Choose clock: 200 MHz Choose filter: 110-190 MHz Choose antenna: HBA Dual Inner (48) Channels per subband: 64 Integration time: 1 Keep correlated visibilities: up to the user (not required by the survey co-observing scheme) Required noise level: see above
Pipeline configurationThis is the setup that should be used for the processing of the pointings on the survey grid according to the co-observing setup. If one pointing is not taken in a grid direction the user is free to specify a new pipeline following a different processing strategy.
Processing mode: Pre processing only Flagging strategy: HBA Averaging time steps : 1.0 Averaging frequency steps: 4.0 Demixing: False Demixing time steps: Demixing frq. steps: Demixing sources: x
The choice of 'calibration pipeline' and 'calibration+imaging pipeline' is up to the user as it does not affect the surveys co-observation.
New Target: Calibration beam? No Field Name: first beam coordinates (target coordinates in case the observation is not pointed in the grid direction) Subband list: 104..136,138..163,165..180,182..184,187..209,212..213,215..240,242..255,257 ..273,275..300,302..328,330..347,349,364,372,380,388,396,404,413,421,430,438,447 Run: 1 Exposure time in minutes: 480 Select observations: see above Select processing pipeline: this pipeline must be the pipeline associated with the survey co-observing scheme if the pointing is on the grid, or a different pipeline if required for a pointing that is not placed on the grid New Target: Calibration beam? No Field Name: second beam coordinates (in case this is left free to be decided to the survey collaboration set the coordinates to 0 and name to TBD) Subband list: 104..136,138..163,165..180,182..184,187..209,212..213,215..240,242..255,257 ..273,275..300,302..328,330..347,349,364,372,380,388,396,404,413,421,430,438,447 Run: 1 (this must be the same run as the pointing before as it is the second beam of the same run) Exposure time in minutes: 480 Select observations: see above Select processing pipeline: this pipeline must be the pipeline associated with the survey co-observing scheme
To specify the calibrator in the target list, either:
- include a comment in the target run saying ‘book-ended by two 10min calibrator TBD’ (in this case though the 20 minutes dedicated to the calibrator observations will not be included in the automatic computation of observing and processing time so the user should calculate and specify manually the extra time).
- include a new target in a new run with coordinates of the calibrator (if already decided or blank if not), Exposure time in minutes: 40, Subband list: 104-346, Run: 2, Select observations: same as target, Select processing pipeline: same as target, Comments: 10min before and 10 min after the target observation of each beam
- if the declination of the requested grid pointing is below ~25 degrees it is recommended to split the observation in 2 x 4h observing blocks. For advice contact the surveys team.
- According to the co-observing policy all data acquired (both beams) will be available to both the proposer and the survey collaboration
- the LTA storage suggested by the survey team for an 8-hour dual beam observations + 2x10minutes calibrator observations x 2beams is 32TB
- if the target of interest is within ~1deg (correct?) from the closest survey grid, the survey team encourages the proposer to point the observation in the direction of the grid pointing, as such an offset will not compromise the target imaging quality
- If an observation longer than 8h is required you may still co-observe, but LoTSS only requires 8h per grid position so you should then co-observe with different grid pointings. Contact the surveys team for help with this.
Standard text for technical description in publications
Standard acknowledgements for co-observing projects
Any publications resulting from co-observing projects must, in addition to the standard acknowledgement for the use of the ILT, include the following acknowledgement “These data were (partly) processed by the LOFAR Two-Metre Sky Survey (LoTSS) team. This team made use of the LOFAR direction independent calibration pipeline (https://github.com/lofar-astron/prefactor) which was deployed by the LOFAR e-infragroup on the Dutch National Grid infrastructure with support of the SURF Co-operative through grants e-infra 160022 and e-infra 160152 (Mechev et al. 2017, PoS(ISGC2017)002). ” or, where additional direction dependent processing has been used “These data were (partly) processed by the LOFAR Two-Metre Sky Survey (LoTSS) team. This team made use of the LOFAR direction independent calibration pipeline (https://github.com/lofar-astron/prefactor) which was deployed by the LOFAR e-infragroup on the Dutch National Grid infrastructure with support of the SURF Co-operative through grants e-infra 160022 e-infra 160152 (Mechev et al. 2017, PoS(ISGC2017)002). The LoTSS direction dependent calibration and imaging pipeline (http://github.com/mhardcastle/ddf-pipeline/) was run on compute clusters at Leiden Observatory and the University of Hertfordshire which are supported by a European Research Council Advanced Grant [NEWCLUSTERS-321271] and the UK Science and Technology Funding Council [ST/P000096/1].”