We we have developed a flexible format for exchanging data between EPN pulsar groups. We have written a suite of Fortran-77 sub-routines which can be easily incorporated within existing software which can read and write data in this format. The format has proved so successful that we now advocate its use as a useful world-wide utility for pulsar data exchange. Astrophysical applications of such a format currently being pursued by EPN groups include the establishment of a data bank of pulse profiles as well as simultaneous observations of pulsars by several European observatories.
Operating system independence:
To make the data format as portable as possible between present and
future operating systems, we have opted to use only ASCII-data throughout.
We have arrange these data so that words are aligned over 80-byte boundaries,
this simplifies inspection and printing of the files.
Completeness:
The data should contain all information for the identification of the
source and the observing circumstances useful for further analyses of the
data by others.
Compactness:
Descriptive information should not dominate the format. The measured
values that form the bulk of a block of data are given as scaled four-character
hexadecimal numbers, giving a dynamic range of 65536:1.
Versatility:
The format should be suitable for continuously sampled multi-channel
filterbank search data, synchronous integrated and single-pulse data as
well as processed data. In addition, we have designed the format, so that
it can be used for observations of pulsars outside the radio regime i.e.
variable units for the observing frequency and bandwidth, as well as topocentric
telescope coordinates which are time variable for satellite observatories.
Space is left for more descriptors and future adaptations and expansions.
Simplicity and ease of access:
We describe a data format consisting of a standardised fixed length
header with a variable length data structure attached to it. The header
fully describes the structure of the data, this structure is not changed
within one file but can vary between files. That way it is possible to
calculate the length of a data block within each file after reading its
header. The file can then be opened for random access with fixed block
length, faster than a sequential read.
Many of the above mentioned requirements were already met by a format in use at Jodrell Bank to which we made suitable modifications and extensions to make it more flexible.
The basic structure of an EPN file consists of a common fixed length header followed by a number of individual data streams of equal length. The header describes the data, containing information on the pulsar itself, the observing system used to make the observation as well as some free-form information about the processing history of the data. The onus is on the site-specific conversion process to ensure correct conversion to the standardised entries and reference to common catalogues (e.g. the Princeton Pulsar Catalog).
The data streams themselves may be outputs of different polarisation channels, or individual channels (bands) of a filterbank or a combination thereof. In total, there may be a number of data streams of i.e. different frequencies for each polarisation. Each data stream starts with a small, fixed length sub-header in front of the actual data values. The number of streams and their length may vary between different EPN files, but is constant within each file. A character field and an ordinal number is provided for each stream for its identification.
To uncompress and extract the contents of the tar file, issue the commands:
gunzip epnsoft.tar.gz
tar xvf epnsoft.tar
The present package contains some sample data and two example programs - ``plotepn'' and ``viewepn'' which plot and view EPN files respectively. The ASCII file 00README in this packages gives further details of the software and how to use it.