WSRTThe Westerbork Synthesis Radio Telescope

Contact details:

René Vermeulen
ASTRON, PO Box 2, 7990AA, Dwingeloo

The Westerbork Synthesis Radio Telescope (WSRT), owned and operated by ASTRON in the Netherlands, has 14 fully steerable parabolic dish reflectors, distributed in an East-West configuration of 2700m lengths. The WSRT is a long-time world-leading telescope with particular strengths for studies of the evolution and dynamics of Galactic and extragalactic neutral hydrogen (HI), and more recently in pulsar astrophysics. The WSRT has been substantially upgraded several times, to further its position as a leading edge facility. A major instrument upgrade is underway now: the Apertif project, bringing 121-element phased-array feeds (PAFs) and digital beamformers at 12 radio telescopes, with a digital correlator and Tied Array beamformer to match. With Apertif, 37 beams are formed simultaneously at each dish, enlarging the instantaneous field-of-view by a factor of 30, to 8 square degrees. There are 24576 spectral channels over a 300 MHz contiguous bandpass that can be tuned anywhere between 1130 and 1730 MHz. These new capabilities increase the survey speed of the WSRT by more than a factor of ten, enabling large-scale survey projects to address a range of cutting-edge science cases. Furthermore, WSRT will continue its participation as part of VLBI arrays, with a single telescope, a modified MFFE receiver providing frequency coverage from 300 MHz to 8.4 GHz.

The Westerbork Synthesis Radio Telescope (WSRT), owned and operated by ASTRON in the
Netherlands, has 14 fully steerable parabolic dish reflectors, distributed in an East-West
configuration of 2700m lengths. The WSRT is a long-time world-leading telescope with particular
strengths for studies of the evolution and dynamics of Galactic and extragalactic neutral hydrogen
(HI), and more recently in pulsar astrophysics.
The WSRT has been substantially upgraded several times, to further its position as a leading edge
facility. A major instrument upgrade is underway now: the Apertif project, bringing 121-element
phased-array feeds (PAFs) and digital beamformers at 12 radio telescopes, with a digital correlator
and Tied Array beamformer to match. With Apertif, 37 beams are formed simultaneously at each
dish, enlarging the instantaneous field-of-view by a factor of 30, to 8 square degrees. There are
24576 spectral channels over a 300 MHz contiguous bandpass that can be tuned anywhere between
1130 and 1730 MHz. These new capabilities increase the survey speed of the WSRT by more than a
factor of ten, enabling large-scale survey projects to address a range of cutting-edge science cases.
Furthermore, WSRT will continue its participation as part of VLBI arrays, with a single telescope, a
modified MFFE receiver providing frequency coverage from 300 MHz to 8.4 GHz.
With Apertif, the WSRT will continue as a cutting-edge facility, making significant steps forward not
only on many of the science themes that have generated significant demand on the WSRT in recent
years, but will also significantly contribute in new scientific areas. A significant part of the observing
time will be awarded to smaller, self-contained projects from the full international user community,
selected on excellence, catering to topics of high immediate interest and stimulating diversity and
innovation in science use. However for a large part of the available observing time, the Apertifequipped
WSRT will be operated as a survey instrument, addressing the following elements:
• A Shallow Northern Sky survey where the continuum observations will obtain a census of
tar- forming galaxies, radio-loud AGN and galaxy cluster radio emission and possibly radio
lenses. The spectral line observations will probe HI in local galaxies; study the HI Mass
Function in the nearby Universe, HI absorption line systems and the large-scale structure
and flow,
• A Medium Deep Survey, which among others, will study the HI mass function in different
cosmic environments, magnetic fields, the star formation history and AGN feedback activity,
• A Pulsar and Transients Survey (PTS) that can detect tens of extragalactic bursts in realtime
and characterize, to much lower luminosity than before, the population of
intermittently active neutron stars, and better understand the Galactic neutron-star
population.
Being one of the largest wide-field survey instruments the Apertif equipped WSRT is not only be an
important SKA pathfinder but with its unique access to the northern hemisphere sky, it will leave an
important legacy in the next decades, as its full results will be accessible by the astronomical
community in the open Apertif Long Term Archive.