[Paper Review] LOFAR: A powerful tool for pulsar studies

B. W. Stappers, J. van Leeuwen+3 more|arXiv (Cornell University)|Jan 9, 2007

Pulsars and Gravitational Waves Research3 citations

TL;DR

LOFAR is proposed as a transformative low-frequency radio array for pulsar studies, leveraging its wide bandwidth, high sensitivity (0.015 mJy at 200 MHz), and multibeaming capability to conduct a sensitive all-sky survey. Simulations predict it will discover approximately 1,500 new pulsars, significantly improving the census of the local pulsar population and enabling breakthroughs in understanding pulsar emission physics, neutron star populations, and the interstellar medium.

ABSTRACT

The LOw Frequency ARray, LOFAR, will have the sensitivity, bandwidth, frequency range and processing power to revolutionise low-frequency pulsar studies. We present results of simulations that indicate that a LOFAR survey will find approximately 1500 new pulsars. These new pulsars will give us a much better understanding of the low end of the luminosity function and thus allow for a much more precise estimate of the true total local pulsar population. The survey will also be very sensitive to the ultra-steep spectrum pulsars, RRATs, and the pulsed radio emission from objects like Geminga and AXPs. We will also show that by enabling us to observe single pulses from hundreds of pulsars, including many millisecond pulsars, LOFAR opens up new possibilities for the study of emission physics.

Motivation & Objective

• To conduct a sensitive, all-sky pulsar survey in the Northern Hemisphere using LOFAR’s low-frequency capabilities.
• To improve the precision of the local pulsar population estimate by measuring the low-end of the pulsar luminosity function.
• To detect previously undetected pulsar populations, including ultra-steep spectrum pulsars, RRATs, and radio-quiet neutron stars like Geminga and AXPs.
• To enable high-time-resolution studies of single-pulse emission from hundreds of pulsars, including millisecond pulsars.
• To enhance monitoring of transient and intermittent neutron stars, such as glitching pulsars and pulsars active <10% of the time.

Proposed method

• Simulate pulsar detection rates using realistic population and scattering models across the LOFAR frequency range (30–240 MHz).
• Utilize LOFAR’s core array with 7700 low-band and 7700 high-band antennae, forming 77 stations with multibeaming to enable wide-field, simultaneous observations.
• Apply integration times of 1 hour, 2 polarizations, and 32 MHz of bandwidth to estimate sensitivity (down to 0.015 mJy at 200 MHz).
• Leverage LOFAR’s wide field of view (up to 21° at 30 MHz) and long pointings to increase sensitivity to intermittent sources like RRATs.
• Combine single-pulse stacking techniques with high dynamic range to detect weak, sporadic emission from pulsars.
• Use dispersion measure, rotation measure, and scintillation studies to probe the ionized interstellar medium and magnetic field structure.

Experimental results

Research questions

• RQ1 How many new pulsars can LOFAR discover in an all-sky survey, and what fraction will be low-luminosity or exotic sources?
• RQ2 To what extent can LOFAR improve the precision of the local pulsar population estimate by measuring the low-end of the luminosity function?
• RQ3 Can LOFAR detect radio emission from neutron stars like Geminga and AXPs that are undetected at higher frequencies?
• RQ4 How does LOFAR’s sensitivity and bandwidth enhance the study of single-pulse emission and emission physics in millisecond and intermittent pulsars?
• RQ5 What improvements can LOFAR bring to interstellar medium studies through dispersion, rotation, and scintillation measurements?

Key findings

• LOFAR is projected to discover approximately 1,500 new pulsars in an all-sky survey, nearly doubling the known pulsar population.
• The survey will significantly improve the measurement of the low-end of the pulsar luminosity function, enabling a more precise estimate of the true local pulsar population.
• LOFAR’s sensitivity at 30–80 MHz makes it uniquely capable of detecting ultra-steep spectrum pulsars, including those with spectral indices steeper than -3.0.
• LOFAR will detect previously radio-quiet neutron stars such as Geminga and AXPs, which are only detectable at low frequencies.
• LOFAR’s multibeaming and wide-field capabilities will allow simultaneous monitoring of hundreds of pulsars, enabling detailed single-pulse studies and discovery of intermittent sources like RRATs.
• LOFAR will provide a dense grid of new pulsar sight lines, improving global models of the ionized interstellar medium, its clumpiness, and the Milky Way’s magnetic field structure.