skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Constraining Relativistic Bow Shock Properties in Rotation-powered Millisecond Pulsar Binaries

Abstract

Multiwavelength follow-up of unidentified Fermi sources has vastly expanded the number of known galactic-field “black widow” and “redback” millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase centering of the double-peaked X-ray orbital modulation originating from mildly relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock standoff R {sub 0}. We develop synthetic X-ray synchrotron orbital light curves and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the standoff is R {sub 0} ∼ 0.15–0.3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R {sub 0} ≲ 0.4, while X-ray light curves suggest 0.1 ≲ R {submore » 0} ≲ 0.3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy dependence in the shape of light curves, motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein.« less

Authors:
; ;  [1];  [2];  [3]
  1. Centre for Space Research, North–West University, Potchefstroom (South Africa)
  2. Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  3. Department of Physics and Astronomy, Rice University, Houston, TX 77251 (United States)
Publication Date:
OSTI Identifier:
22663698
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 839; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; ELECTRONS; ENERGY DEPENDENCE; INCLINATION; LIMITING VALUES; MODULATION; ORBITS; PULSARS; RELATIVISTIC RANGE; ROTATION; SHOCK WAVES; SPACE; STELLAR WINDS; VARIATIONS; VISIBLE RADIATION; X RADIATION

Citation Formats

Wadiasingh, Zorawar, Venter, Christo, Böttcher, Markus, Harding, Alice K., and Baring, Matthew G., E-mail: zwadiasingh@gmail.com. Constraining Relativistic Bow Shock Properties in Rotation-powered Millisecond Pulsar Binaries. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA69BF.
Wadiasingh, Zorawar, Venter, Christo, Böttcher, Markus, Harding, Alice K., & Baring, Matthew G., E-mail: zwadiasingh@gmail.com. Constraining Relativistic Bow Shock Properties in Rotation-powered Millisecond Pulsar Binaries. United States. doi:10.3847/1538-4357/AA69BF.
Wadiasingh, Zorawar, Venter, Christo, Böttcher, Markus, Harding, Alice K., and Baring, Matthew G., E-mail: zwadiasingh@gmail.com. Thu . "Constraining Relativistic Bow Shock Properties in Rotation-powered Millisecond Pulsar Binaries". United States. doi:10.3847/1538-4357/AA69BF.
@article{osti_22663698,
title = {Constraining Relativistic Bow Shock Properties in Rotation-powered Millisecond Pulsar Binaries},
author = {Wadiasingh, Zorawar and Venter, Christo and Böttcher, Markus and Harding, Alice K. and Baring, Matthew G., E-mail: zwadiasingh@gmail.com},
abstractNote = {Multiwavelength follow-up of unidentified Fermi sources has vastly expanded the number of known galactic-field “black widow” and “redback” millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase centering of the double-peaked X-ray orbital modulation originating from mildly relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock standoff R {sub 0}. We develop synthetic X-ray synchrotron orbital light curves and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the standoff is R {sub 0} ∼ 0.15–0.3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R {sub 0} ≲ 0.4, while X-ray light curves suggest 0.1 ≲ R {sub 0} ≲ 0.3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy dependence in the shape of light curves, motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein.},
doi = {10.3847/1538-4357/AA69BF},
journal = {Astrophysical Journal},
number = 2,
volume = 839,
place = {United States},
year = {Thu Apr 20 00:00:00 EDT 2017},
month = {Thu Apr 20 00:00:00 EDT 2017}
}
  • We report radio polarization observations of G319.9-0.7 (MSC 319.9-0.7) at 3 and 6 cm obtained with the Australia Telescope Compact Array. The source shows a highly elongated morphology with the energetic pulsar J1509-5850 located at the tip. We found a flat radio spectrum of index alpha = -0.26 +- 0.04 and a high degree of linear polarization. These results confirm G319.9-0.7 as a bow-shock pulsar wind nebula. The polarization maps suggest a helical magnetic field trailing the pulsar, with the symmetry axis parallel to the system's inferred direction of motion. This is the first time such a field geometry hasmore » been seen in a bow-shock nebula, and it may be the result of an alignment between the pulsar spin axis and its space velocity. Compared to other bow-shock examples, G319.9-0.7 exhibits very different properties in the field structure and surface brightness distribution, illustrating the large diversity of the population.« less
  • According to the recycling scenario, millisecond pulsars (MSPs) have evolved from low-mass X-ray binaries (LMXBs). Their orbits are expected to be circular due to tidal interactions during binary evolution, as observed in most binary MSPs. There are some peculiar systems that do not fit this picture. Three recent examples are the PSRs J2234+06, J1946+3417, and J1950+2414, all of which are MSPs in eccentric orbits but with mass functions compatible with expected He white dwarf (WD) companions. It has been suggested these MSPs may have formed from delayed accretion-induced collapse of massive WDs, or the eccentricity may be induced by dynamicalmore » interaction between the binary and a circumbinary disk. Assuming that the core density of accreting neutron stars (NSs) in LMXBs may reach the density of quark deconfinement, which can lead to phase transition from NSs to strange quark stars, we show that the resultant MSPs are likely to have an eccentric orbit, due to the sudden loss of the gravitational mass of the NS during the transition. The eccentricities can be reproduced with a reasonable estimate of the mass loss. This scenario might also account for the formation of the youngest known X-ray binary Cir X–1, which also possesses a low-field compact star in an eccentric orbit.« less
  • The heating associated with the deposition of {gamma}-rays in an accretion disk is proposed as a mechanism to facilitate the transformation of a low-mass X-ray binary to the radio millisecond pulsar (MSP) phase. The {gamma}-ray emission produced in the outer gap accelerator in the pulsar magnetosphere likely irradiates the surrounding disk, resulting in its heating and the possible escape of matter from the system. We apply the model to PSR J1023+0038, which has recently been discovered as a newly born rotation-powered MSP. The predicted {gamma}-ray luminosity {approx}6 x 10{sup 34} erg s{sup -1} can be sufficient to explain the disappearancemore » of the truncated disk existing during the 8 month-2 yr period prior to the 2002 observations of J1023+0038 and the energy input required for the anomalously bright optical emission of its companion star.« less
  • The Rossi X-ray Timing Explorer has observed five outbursts from the transient 2.5 ms accretion-powered pulsar SAX J1808.4-3658 during 1998-2008. We present a pulse timing study of the most recent outburst and compare it with the previous timing solutions. The spin frequency of the source continues to decrease at a rate of (-5.5 {+-} 1.2) x 10{sup -18} Hz s{sup -1}, which is consistent with the previously determined spin derivative. The spin down occurs mostly during quiescence, and is most likely due to the magnetic dipole torque from a B = 1.5 x 10{sup 8} G dipolar field at themore » neutron star surface. We also find that the 2 hr binary orbital period is increasing at a rate of (3.80 {+-} 0.06) x 10{sup -12} s s{sup -1}, also consistent with previous measurements. It remains uncertain whether this orbital change reflects secular evolution or short-term variability.« less
  • The Fermi Large Area Telescope has revealed that rotation powered millisecond pulsars (MSPs) are a major contributor to the Galactic {gamma}-ray source population. Such pulsars may also be important in modeling the quiescent state of several low-mass X-ray binaries (LMXBs), where optical observations of the companion star suggest the possible existence of rotation powered MSPs. To understand the observational properties of the different evolutionary stages of MSPs, the X-ray and {gamma}-ray emissions associated with the outer gap model are investigated. For rotation powered MSPs, the size of the outer gap and the properties of the high-energy emission are controlled bymore » either the photon-photon pair-creation process or magnetic pair-creation process near the surface. For these pulsars, we find that the outer gap model controlled by the magnetic pair-creation process is preferable in explaining the possible correlations between the {gamma}-ray luminosity or non-thermal X-ray luminosity versus the spin-down power. For the accreting MSPs in quiescent LMXBs, the thermal X-ray emission at the neutron star (NS) surface resulting from deep crustal heating can control the conditions in the outer gap. We argue that the optical modulation observed in the quiescent state of several LMXBs originates from the irradiation of the donor star by {gamma}-rays from the outer gap. In these systems, the irradiation luminosity required for the optical modulation of the source such as SAX J1808.4-3658 can be achieved for a NS of high mass. Finally, we discuss the high-energy emission associated with an intra-binary shock in black widow systems, e.g., PSR B1957+20.« less