7 PuMa

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The pulsar backend PuMaII.

Pulsar observations at Westerbork are recorded on a backend named PuMaII (Pulsar Machine II), which is a fully digital and highly flexible machine. It has been used for observations concerning many different aspects of radio pulsars, ranging from surveys, to timing, high-resolution polarimetry, and interstellar scattering studies. It as the ability to record 160 MHz of baseband data for up to 30 hours, as well as semi-realtime reduction of the raw data.

The default modes of observation are at 385 MHz (8*10 MHz bandwidth), 1380 MHz (8*20 MHz bandwidth) and 2273 MHz (8*20 MHz bandwidth).

Simultaneous multi-frequency observations are also possible with PuMaII and WSRT. These involve the splitting of the array into combinations of dishes and/or bandwidth. While this does reduce the sensitivity due a decrease in the number of telescopes and bandwidth it does provide truly simultaneous observations using the same instrument. An example set-up would be to have 5 dishes and 40 MHz of bandwidth at 21cm, 5 dishes and 30 MHz of bandwidth at 840 MHz and 4 dishes and 10 MHz of bandwidth at 328 MHz. If you are interested in this possibility please send an email to wsrt-support [at] astron [dot] nl.

The backend consists of three parts:

  • 10 storage machines with 8 TB of diskspace each; 8 of these are used  for recording 20 MHz of bandwidth. This enables us to record 160 MHz  of baseband data up to a maximum of 30 hours. Data is recorded in 10-second timedumps. The raw recorded data needs to be cleared from these machines as quickly as possible to make room for new observations.
  • A computer cluster with 31 dual-core nodes for processing. These nodes are connected to the 10 storage machines via a 1-Gb switch, which prevents data-transfer from becoming the bottleneck when reducing data.
  • A 60-TB storage facility for further processing and permanent storage of reduced data. This storage facility consists of 2 identical machines that each contain 24 3-TB disks in 2 RAID-6 arrays. One machine is located at the Westerbork site, whereas the other machine is located at ASTRON and operates as a mirror. Both machines therefore contain the exact same data, making this a reliable storage for permanent data. Basic software is installed for standard analysis of pulsar data.

Access to PuMaII, including the permanent storage facility, is limited to members of the ASTRON pulsar group. For access to reduced pulsar data that is public, please send an email to the WSRT science support team (wsrt-support [at] astron [dot] nl).


Policy of usage.

Observing with the PuMaII backend always requires the participation of a member of the ASTRON pulsar group, as the machine cannot be controlled by the operators. Typically this would be Roy Smits (smits [at] astron [dot] nl).

It is essential to reduce the raw data within a few days to make room for new pulsar observations. Reduction will be performed by a member of the ASTRON pulsar group. A default pipeline is in place for the reduction of timing-data. The product of this pipeline consists of archive files (.ar files) in filterbank format; one for every 10-second timedump and every 20-MHz band (or 10-MHz band for 92-cm observations). Each .ar file contains the integrated profile for 64 frequency channels within each 20-MHz band.  When this data-product is not suitable for the project in question, an alternative reduction procedure must be in place and tested well before the actual observation takes place.
A copy of the reduced data-product can be obtained via the contact person from the ASTRON pulsar group. One copy will always remain at Westerbork in accordance with the data-sharing policy of Westerbork.

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