Proposal Call to the Worldwide Community 

    International LOFAR Telescope

    Cycle 20: 01 June 2023 – 31 May 2024

    NOTE: Proposal call covers 12 months

    Submission deadline Wednesday 08 March 2023, 12 UT

    Submission only via the online tool NorthStar.

    ** Proposers must ensure their justification files adhere to the instructions given in Northstar, including restrictions on formats and proposal length, repeated below. **


    This Cycle 20 proposal call will fill the entire 12-month period 01 June 2023 – 31 May 2024. After this “last full LOFAR1 observing window”, significant temporary impact is expected from LOFAR2.0 upgrade activities; in due course further announcements are envisaged for restricted observing opportunities until LOFAR2.0 operations commence. In order to optimize any and all science projects until 1 June 2024, Cycle 20 proposals may request any amount of observing time with any scheduling parameters (day/night, LST windows, calendar dates, etc.), and with the appropriate associated processing and data storage. It is imperative to list and justify minimum allocations, which will be taken as thresholds for scheduling. For reference: it is expected that 2750 hours of observing can be scheduled in Priority A, plus 3300 hours in Priority B (classes explained below). Proposals may entail continuation and follow-up of earlier work, or new projects, but must be observable entirely within the 12 month period of Cycle 20.


    Time on the ILT is available to scientists from the worldwide community. The time offered in this call is allocated in tandem between National Consortia and the ILT-PC. Scientific excellence and breadth as well as the technical strength of the proposals are taken along in the evaluations. The ILT-PC will define restricted data access rights (default period 1 year) based on the specific science goals and arguments in the proposal. Other groups may be allocated simultaneous access for different science.


    LST availability: The availability of observing time as a function of LST is presented online.

    Station availability: During Cycle 20, CS001 will remain a LOFAR2.0 test station and CS032 an IDOLS test station. Therefore, these will not participate to Cycle 20 observations. Two more NL Core stations will be upgraded during Cycle 20 for initial LOFAR2.0 testing, likely in January 2024. From that moment and for the remainder of the Cycle, these stations will not participate to production observations. These additional stations will be selected in the next few months. To help assess the feasibility of the projects and plan the Cycle 20 schedule, proposers should clearly specify in their proposal if and which stations they regard as essential for their projects.

    Processing time and/or data storage capacity: These can be limiting resources. Each proposal must request processing time to match the observing time within appropriate documented ratios (see documentation online), or should justify how processing will proceed elsewhere.

    Support staff effort required to support the proposed projects is considered during allocation. An online tool is available to understand whether a proposal entails a low, medium, or high support load of the Science Data Centre Operations staff. During the allocation process, the ILT-PC will be advised about the amounts of support effort requested and available, and these will be used as boundary conditions for proposal allocations; support will be treated as a scarce resource in the same way as has become customary on LOFAR for processing and data storage resources.  Advice is available online on how proposers can reduce the support load of their project by a prudent choice of observing mode. The proposal may also indicate that the support will be carried out by members of the proposing team; in that case, both the expertise and the work plan must be carefully argued in the proposal. 

    Priority classes: Due to ongoing upgrade work, system availability and stability will vary with time. The ILT-PC will classify observing allocations as A and/or B priority time; roughly half in each. Allocations in A priority will have a high likelihood to yield a successful observation; in case such an observation suffers substantial failures, it will be repeated (once) at a later date. Allocations in priority B will likely be realized partially; they are carried out on a best-efforts basis, where the total of all priority B allocations requires an optimistic availability scenario.


    The ILT is a powerful radio telescope for frequencies below 240 MHz that offers state-of-the-art observing capabilities thanks to its phased-array technology with digital beam-forming. LOFAR delivers correlated visibility data for synthesis imaging, plus (in)coherently-added single and multiple station data (several beam-formed modes) as well as transient buffer read-out, for example for studies of pulsars, transients, and cosmic rays. LOFAR capabilities are described in detail online. The functionalities offered in Cycle 20 are described in this page. These have progressed since Cycle 19. Proposals should request only the available system observing modes and functionalities. If you are unsure about the validity of your desired setup, please contact the Science Data Centre Operations group through the Helpdesk by 22 February so it can be verified on time before the proposal deadline.


    The possibility is offered to carry out imaging in co-observing mode with the LOFAR Survey projects, in their standard operating mode. This has the advantage for co-observing PIs that calibration and standard imaging are a routine process under guidance by the survey teams (see details online).


    The ILT is currently implementing in production LINC, the direction-independent calibration pipeline, which produces direction-independent calibrated visibilities and wide-band images of the target field, and diagnostic plots. Details about this pipeline, including its performance, are given online. Currently, the pipeline is only available at HBA frequencies. While LINC cannot yet be widely offered in Cycle 20, we will select a sample of appropriate HBA projects that will be given the opportunity to obtain data products processed through this pipeline. In this respect, PIs who are interested in taking advantage of this option for the reduction of their data should clearly indicate that in the technical justification of their proposals.


    •     For all proposals, the technical case must argue both the optimal and the minimal required total amount of time and other resources (and any requirements on cadence or time span). If the stated minimum time or other requirements cannot be allocated, the proposal will not be carried out at all.
    •     Proposals for multiple observations must list and argue the preferred priority order; this will be considered by the ILT-PC along with other factors in making (possibly partial) allocations.
    •     Proposers are required to verify whether any relevant data are already available in the LOFAR Long Term Archive.


    In view of the specialized and evolving character of the ILT, proposers are strongly urged to get in contact with Science Data Center Operations through the SDC Helpdesk well ahead of the deadline. Novice groups may wish to seek or request to be connected to suitable collaborators, and should also consider keeping the scope of initial projects modest while they become familiar with the complexities of data handling and analysis.

    he Science Data Centre Operations group will explore the possibility for a few users unfamiliar with the reduction of LOFAR data to come to ASTRON (or have online interaction) for assistance with this. If this is desired, it must be specified in the proposal. Limited travel subsidies for eligible users can be supported through the Horizon-Europe ORP project. Further details are given online. 

    Dr. R.C. Vermeulen

    Director, International LOFAR Telescope

    Target List Order

    If proposals request multiple observations (e.g. multiple fields/pointings, or multiple instrumental settings) these will be taken in all cases to be listed in decreasing order of preference/priority of the proposers. In case only a partial allocation can be made, the ILT-PC may, based on its science assessment, decide to deviate from the proposed priorities, but the proposer priorities must anyway be clear in advance.

    It will be assumed when dynamic scheduling is carried out that the list of targets is in priority order.

    Target Declination Limits

    As a phased-array system installed on level ground, LOFAR has greatest sensitivity when observing at high elevations.  Below approximately 30 degrees elevation sensitivity drops significantly such that the Sun becomes the only viable target for interferometric observation below about 10 degrees elevation.

    Commissioning observations have managed successful imaging of a target at -7 degrees declination, but imaging is not straightforward and the following points need to be noted:

    • The thermal noise cannot be attained at these declinations;
    • Short baselines have to be flagged;
    • Some additional flagging of data may be required.

    Furthermore, the shorter length of time that such targets are above a usable horizon can severely limit the u-v coverage attainable. Therefore, for interferometric observations, -5 degrees declination should be regarded as a lower limit and targets should preferably be above the celestial equator.  Proposers wishing to image targets below the celestial equator are expected to justify that their observing programme can attain the sensitivity and/or u-v coverage required.

    Pulsar observations have been successfully carried out in beam-formed mode at declinations down to -29 degrees.  In this mode, the main limitation is the sensitivity required and the duration of observation needed to attain this sensitivity.

    Support Load

    Support availability and User Shared Support Mode during cycle 20

    To calculate the support level required for your project please use this tool.

    To maximize the telescope observing hours on sky, more observing hours have been offered than can be supported by ASTRON. Therefore, users can assist in running their own projects in a “user shared-support mode”. To this aim, proposers should state it in the proposal, indicating that they are able to provide experienced personnel to the support activities of their full project (see details below). In this model, ASTRON personnel would only have a supervisory role. In addition, this page explains which functionality requires a higher or lower support load.

    Project support consists of several labour-intensive or critical activities, such as

    • scheduling
    • preparing observations
    • reporting
    • data handling
    • project administration

    Depending on the specific characteristics of a project, the amount of support required can vary. When preparing a proposal, a tool is provided to determine the support load of a project (high, average or low). A detailed assessment of the amount of support needed (in hours) will be performed in the review process itself by the ASTRON personnel. This amount will be treated as a limited resource. Projects requiring a high degree of support should really consider using the ‘user shared support’ mode. More details about the project features that can raise the degree of support are explained below.

    User shared-support mode

    Science teams that have proven expertise in particular LOFAR observing modes and/or observing support procedures can provide personnel to handle the support workload for their full project, i.e. users are expected to handle their own projects for the full budget of allocated telescope time. This should be clearly written in the proposal. Before the start of each cycle, these users will be updated by ASTRON on current procedures & tools to handle the data flow for their project.

    High and low support load

    Examples of project features requiring high levels of support include, but are not limited to:

    • Short observations or sets of observations, especially when scheduled on different days. e.g., 2 hour interferometric observations, “lucky imaging” and “interleaved observations”.
    • Parallel observations (e.g. commonly used setups for scintillometry and solar studies.
    • Restrictive scheduling constraints, e.g., at specific orbital phases; commensal with other telescopes;
    • Responsive Telescope
    • Updates to target lists during the cycles
    • Manual execution of system tasks (e.g. dynamic spectrum pipeline, manual ingests)
    • Multi-beam observations with >4 beams

    Projects can lower the required level of support by ASTRON by adopting the following criteria:

    • Large fraction of user support in administering the project [ “user shared support mode”, explained in the previous Section]
    • In particular, projects satisfying all or most of the requirements below are considered low support:
      • can use randomly occurring time slots with no LST constrain and flexible duration
      • can be rapidly started, e.g. because their setup does not require changes or can be automatically selected
      • are conducted almost entirely by the project team with little or no involvement from Observatory staff.
      • have significant independent processing resources and place little or no pressure on the ILT data processing queue.
      • have significant flexibility in terms of the minimum number of stations required.

    Instructions for Justification File Preparation

    Instructions for the NorthStar justification file:

    The proposers should make their case in a fully self-contained science justification, uploaded as an A4 pdf file. The page-limit for the pdf-file varies per call for proposals. The document should include the science justification, additional technical information that is not provided in the "technical questions" section within the Northstar tool, and any desired ancillary material such as figures and tables.

    Page limits are dependent on the amount of observing time requested. The total of the science and technical justification, including any desired figures and tabular material, will have page limit of 4 pages for small requests, with an increase of the limit to at most 8 pages according to the following rules: the base allowance is 3 pages, plus 1 page per 250 hours of observing time requested (request 1 hour: 4 pages, from 251 hours: 5 pages, ... from 1001 hours: 8 pages). For example, the maximum, in case>1000 hrs are requested, is 8 pages.

    Proposals exceeding the page limits will be rejected.

    Northstar accepts uploads of a single pdf file with a minimum font size of 11 pt (12 pt recommended). The pdf can be generated from, e.g., Microsoft Word, LaTeX and through several other routes at the proposer's choice. An example latex template is provided below with the appropriate sections and descriptions. Note: all PI's should check the pdf of the proposal BEFORE submission, making sure that text is not overlapping with headers and, in general, that no layout issues are present that make text unreadable. Proposals affected by layout issues may be rejected.

    For a proposal to be fully considered submitted, the pdf file should contain at least the following sections:

    1. Scientific Rationale
    2. Additional technical justification (which is not covered in the "Technical questions" section of the Northstar tool).

    %%%% Example TEX file %%%%%%%%%%%%
    %%%% Howto generate the pdf %%%%%%
    %-> latex template.tex
    %-> dvipdf template.dvi

    %%%% Title of proposal
    {\bf \Large Proposal Title} \\*[3mm]

    \section{Scientific Rationale}


    %%%% Non-mandatory sections

    % \section{Technical Addendum}

    %%%% Additional technical justification which is not covered in the "Technical questions" section of the Northstar tool

    %%%% Example sections for additional technical information

    % \subsection{Sensitivity and instrument setup}
    % \subsection{data volumes/rates}
    % \subsection{Processing requirements}
    % \subsection{Data storage and LTA requirements}


    SDC Helpdesk