e-MERLIN / VLBI National Radio Astronomy Facility

e-MERLIN data access and Archive

Full e-MERLIN operations are scheduled to begin in 2010. Please see the status summary for more details.

As with data from MERLIN, all e-MERLIN data will be archived and will become publicly available one year following the end of the semester in which the observations were made. Additionally in the first 5 semesters of e-MERLIN operations a significant amount of time has been granted to a series of large legacy programmes.

The data from these legacy projects will become publicly available, via a series of staggered data releases, and will be composed of both the raw data and enhanced science data products.

e-MERLIN continuum data will by default be wide-field compatible, allowing the imaging of the complete primary beam of the e-MERLIN telescopes. Publicly available archival data will thus be a rich source for data-mining exercises.

The MERLIN Data Archive

MERLIN data becomes publicly available one year after the end of the semester in which the observations were made.

The complete catalogue of MERLIN observations since June 1991 and up to the current cutoff point for publicly available data (see the archive policy statement) can be searched via the search form.

The list of time awards gives proposal titles in each semester.

Processed Data

We are in the process of calibrating all public-domain MERLIN continuum observations in a uniform manner. If you use MERLIN archive data please see the acknowledgement guidelines

More details about MERLIN can be found in the MERLIN User Guide.

A status page gives a summary on progress through the archive data. Here are some 1993 L-band archive images made by JBO work experience student Duncan Hook.

Ready-made images

This Search Form lets you browse or query the archive for preview images and FITS files. You will need to register in order to obtain FITS files (email merlin_archive [at] jb.man.ac.uk). Preview images of target and phase-reference sources can be viewed or downloaded as FITS files. Plots of the visibility data, and the associated calibration are also available.

Customised MERLIN Images via the Virtual Observatory

Customised images are available using the AstroGrid workbench MERLINImager. This (and the Visibility Data service) also use the ParselTongue scripting language developed by RadioNet to control the AIPS data reduction package.

Calibrated Visibility Data Service

Visibility data with optional calibration can be downloaded using the UVData Search Form. This can be imaged in e.g. AIPS or DIFMAP or you can repeat all or part of the calibration (in the latter case you may find the MERLIN AIPS Procedure useful).

MERLIN Data Processing

A supervised pipeline is used for uniform and reliable calibration and production of a 'reference image'. The web page for each source found using the archive search form gives links to relevant data processing information and you can email merlin_archive [at] jb.man.ac.uk for more details

These images should have absolute flux density scales accurate to 5% and the phase referencing process ensures that the map is aligned with the ICRF to within 20 mas.

The nature of sparse-aperture interferometer arrays like MERLIN means that such images can often be improved. You can download the calibrated data, edit it more carefully if required, and tailor the deconvolution process to the individual image. For the brighter sources, the pipeline does a single phase self-calibration: further cycles of self-calibration will undoubtedly improve the final image. In some cases the calibration from the reference source can also be improved. For this purpose, a multi-source file containing the target and calibrators can be downloaded from the Visibility Data service (see above).

Images covering a wider field than displayed in the reference maps can be made if the multi-channel visibility data are used.

The archive also contains images and data for the phase reference sources, which may be of interest themselves. The same search form returns details of these sources.