[Paper Review] Optical timing studies of isolated neutron stars: Current Status

R. Mignani|arXiv (Cornell University)|Jul 28, 2010

Pulsars and Gravitational Waves Research6 references4 citations

TL;DR

This paper reviews the current status of high-time-resolution optical, ultraviolet, and infrared (UVOIR) timing studies of isolated neutron stars (INSs), covering rotation-powered pulsars, magnetars, thermally emitting neutron stars, and rapid radio transients. It outlines key observational challenges, instruments used, and future scientific goals, emphasizing the potential of upcoming extremely large telescopes like the E-ELT to revolutionize the field by enabling routine phase-resolved spectroscopy, polarimetry, and timing across the UVOIR band.

ABSTRACT

Being fast rotating objects, Isolated Neutron Stars (INSs) are natural targets for high-time resolution observations across the whole electromagnetic spectrum. With the number of objects detected at optical (plus ultraviolet and infrared) wavelengths now increased to 24, high-time resolution observations of INSs at these wavelengths are becoming more and more important. While classical rotation-powered radio pulsars, like the Crab and Vela pulsars, have been the first INSs studied at high-time resolution in the optical domain, observations performed in the last two decades have unveiled potential targets in other types of INSs which are not rotation powered, although their periodic variability is still related to the neutron star rotation. In this paper I review the current status of high-time resolution observations of INSs in the optical domain for different classes of objects: rotation-powered pulsars, magnetars, thermally emitting neutron stars, and rapid radio transients, I describe their timing properties, and I outline the scientific potentials of their optical timing studies.

Motivation & Objective

• To assess the current state of high-time-resolution optical, UV, and IR observations of isolated neutron stars (INSs) across different classes.
• To identify and address observational challenges in detecting and characterizing UVOIR pulsations in radio-silent INSs.
• To outline key scientific goals for UVOIR timing studies using existing facilities like HST and VLT, and to project future capabilities with the E-ELT.
• To explore the physical mechanisms behind optical pulsations in diverse INS types, including rotation-powered pulsars and magnetars.
• To promote the integration of high-time-resolution UVOIR studies into routine data analysis for INSs, enhancing understanding of neutron star physics.

Proposed method

• Systematic review of 24 INSs detected in the UVOIR domain, categorized by type: rotation-powered pulsars, magnetars, XDINSs, CCOs, and rapid transients.
• Analysis of observational data from instruments including ULTRACAM, OPTIMA, GASP, Iqueye, and HST instruments (STIS, COS) for high-time-resolution photometry and polarimetry.
• Use of phase-resolved spectroscopy and polarimetry to probe emission mechanisms, with emphasis on light curve profiles and spectral energy distributions.
• Evaluation of extinction effects and observing feasibility for faint or highly extincted sources, particularly in the near-IR.
• Identification of promising targets for future UVOIR timing studies based on existing X-ray and γ-ray detections from Chandra, XMM-Newton, and Fermi.
• Projection of future capabilities using the E-ELT, focusing on its large collecting area enabling routine high-time-resolution UVOIR studies.

Experimental results

Research questions

• RQ1 What are the current timing properties and optical pulsation characteristics of rotation-powered pulsars like the Crab, Vela, and PSR B0540−69 in the UVOIR band?
• RQ2 How do the optical light curves and polarization of magnetars compare to those of rotation-powered pulsars, and what do they reveal about emission mechanisms?
• RQ3 What are the observational challenges in detecting UVOIR pulsations in radio-silent INSs such as XDINSs and CCOs, and how can they be overcome?
• RQ4 To what extent can phase-resolved spectroscopy and polarimetry in the UVOIR band improve our understanding of neutron star magnetospheres and emission regions?
• RQ5 How will the next generation of extremely large telescopes like the E-ELT transform the field of UVOIR timing studies of INSs?

Key findings

• Twenty-four isolated neutron stars have been detected in the UVOIR domain, with high-time-resolution optical studies now feasible for several key targets including the Crab, Vela, and PSR B0540−69.
• Phase-resolved polarimetry has not yet been achieved for any INS, despite instruments like OPTIMA and GASP being capable of such measurements at the NTT and VLT.
• Giant optical pulses (GOPs), previously detected only in the Crab pulsar, could be searched for in PSR B0540−69 through long-term monitoring of its optical light curve.
• Phase-averaged optical polarization degree of ~10% has been measured for PSR B0540−69 and the Vela pulsar, but phase-resolved polarimetry remains unperformed.
• The near-UV emission of PSR B0540−69 remains unexplored, representing a key observational gap for future HST observations.
• The E-ELT is expected to expand the sample of identified INSs by at least a factor of five, enabling routine high-time-resolution UVOIR studies including spectroscopy, polarimetry, and timing.