Binary MSPs

The Double Pulsar, PSR J0737-3039A/B, is the only binary pulsar system in which both neutron stars have been detected as radio pulsars.

This is a rare situation as it requires the electromagnetic beam from both pulsars to intercept our line of sight at the same time. The Double Pulsar was discovered in late 2003 by an international team of astronomers with the 64-m Parkes radio telescope in Australia as part of a high-latitude multibeam survey of the Southern sky. Double Pulsars are one of the research topics of the Pulsars and Time Domain Astrophysics group.

Radio emission at 607 MHz
The left panel shows the orbital phase coverage, where thick lines indicates detections. Red and magenta symbols correspond to GMRT observations at 607MHz and 322MHz respectively and green for Parkes observations at 1.4GHz. The eclipse region is shaded and the superior conjunction is marked by the dotted line. The right panel shows the pulse profiles at three observing frequencies with vertical offsets added for clarity. GMRT- Parkes time-offset and the profile evolution can make the profile alignment covariant with DM.
  • Double Pulsar

    Double Pulsar System showing the interaction of the two radio beams

    Artist's impression of the Double Pulsar system 
    showing the interaction of two radio beams.

    The Double Pulsar provides an amazing laboratory for the study of relativistic gravity and the most precise test to date of General Relativity in the strong-field regime3. The two pulsars orbit each other in a 2.4-hr orbit, the shortest of any observed double neutron star systems, with moderate orbital eccentricity of 0.088. The first-born pulsar, pulsar A, has a short spin period of 23 ms and the second-born companion, pulsar B, spins with a longer 2.8 s period. Due to almost edge-on orbital plane of the system, the eclipses of pulsar A by pulsar B have been detected. Also, the strong stellar wind produced by the high energy loss from pulsar A distorts the magnetosphere of its companion pulsar B4,5,14. Thus, the Double Pulsar offers a unique opportunity to probe directly the magnetospheric structures and the plasma properties of pulsars in general.

    With strong gravitational fields and rapid motions of the two pulsars in a tight binary, the system is expected to show large relativistic effects. The required parameters to explain the Keplerian orbits of the system and their relativistic corrections have been measured through pulsar timing3. Due to relativistic spin precession, the spin axis of the pulsar precesses around the orbital angular momentum of the system. This results a modulation in observed radio emission properties, namely pulse profiles and flux densities. As a result, the radio emission from pulsar B disappeared in 2008 towards our line of sight6. Based on geometry models, the reappearance of B's radio emission is expected to happen between 2014 and 2024. We here at JBCA use the Lovell Telescope to monitor the system since its discovery.

  • Transitioning MSPs (1023, 1227)

    Neutron star low-mass X-ray binaries (LMXBs) and radio millisecond pulsars (MSPs) are evolutionarily linked, where MSPs are the end products of an episode of accretion of mat- ter and angular momentum from the binary companion to the neutron star (Bhattacharya et al. 1991). Recent observations of PSR J1023+0038 (Stappers et al. 2014; Takata et al. 2013; Patruno et al. 2014) and PSR J1824−2452I (Papitto et al. 2013) have directly shown transitions from LMXB to MSP states and vice versa. Such systems in tight orbits (1 day) around main-sequence-like companions (with typical mass 0.2–0.3 Msun called “red- backs” (Roberts 2011), similar to another class of eclipsing systems, called “black-widows”, containing MSPs that are ablating their very-low-mass (<0.05 Msun) systems will help to determine whether they are on the way to becoming canonical MSPs with white dwarf companions, or whether they are a sub-class of MSPs that will continue to transition back-and-forth between the two states.
    PSR J1023+0038 was the first such system seen to transition from an LMXB to an eclipsing binary radio MSP (Archibald et al. 2009). PSR J1023+0038 disappeared as an observable radio MSP sometime in 2013 June (Stappers et al. 2014) suggesting a return to the LMXB state. Patruno et al. (2014) reported that an accretion disc has recently formed in the system and also reported the detection of fast X-ray changes spanning about two orders of magnitude in luminosity. PSR J1023+0038 has also brightened by a factor of ∼5 in gamma-rays since the radio pulsations disappeared (Stappers et al. 2014).

    XSS J12270-4859 is an X-ray binary associated with the Fermi Large Area Telescope gamma-ray source 1FGL J1227.9-4852. In 2012 December, this source underwent a transition where the X-ray and optical luminosity dropped and the spectral signatures of an accretion disk disappeared. We report the discovery of a 1.69 millisecond pulsar (MSP), PSR J1227-4853, at a dispersion measure of 43.4 pc cm-3 associated with this source, using the Giant Metrewave Radio Telescope (GMRT) at 607 MHz. This demonstrates that, post-transition, the system hosts an active radio MSP. This is the third system after PSR J1023+0038 and PSR J1824-2452I showing evidence of state switching between radio MSP and low-mass X-ray binary states. We report timing observations of PSR J1227-4853 with the GMRT and Parkes, which give a precise determination of the rotational and orbital parameters of the system. The companion mass measurement of 0.17-0.46 M⊙ suggests that this is a redback system. PSR J1227-4853 is eclipsed for about 40% of its orbit at 607 MHz with additional short-duration eclipses at all orbital phases. We also find that the pulsar is very energetic, with a spin-down luminosity of ˜1035 erg s-1. We report simultaneous imaging and timing observations with the GMRT, which suggests that eclipses are caused by absorption rather than dispersion smearing or scattering.

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