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Register a new userRadio timing in a millisecond pulsar-extreme/intermediate mass ratio binary system
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Radio timing observations of a millisecond pulsar in orbit around the Galactic centre black hole (BH) or a BH at the centre of globular clusters could answer foundational questions in astrophysics and fundamental physics. Pulsar radio astronomy typically employs the post-Keplerian approximation to determine the system parameters. However, in the strong gravitational field around the central BH, higher order relativistic effects may become important. We compare the pulsar timing delays given by the post-Keplerian approximation with those given by a relativistic timing model. We find significant discrepancies between the solutions derived for the Einstein delay and the propagation delay (i.e. Roemer and Sharpiro delay) compared to the fully relativistic solutions. Correcting for these higher order relativistic effects is essential in order to construct accurate radio timing models for pulsar systems at the Galactic centre and the centre of globular clusters and informing issues related to their detection.
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The radio millisecond pulsar PSR J1023+0038 exhibits complex timing and eclipse behavior. Here we analyze four years worth of radio monitoring observations of this object. We obtain a long-term timing solution, albeit with large residual timing errors as a result of apparent orbital period variations. We also observe variable eclipses when the companion passes near our line of sight, excess dispersion measure near the eclipses and at random orbital phases, and short-term disappearances of signal at random orbital phases. We interpret the eclipses as possibly due to material in the companions magnetosphere supported by magnetic pressure, and the orbital period variations as possibly due to a gravitational quadrupole coupling mechanism. Both of these mechanisms would be the result of magnetic activity in the companion, in conflict with evolutionary models that predict it should be fully convective and hence non-magnetic. We also use our timing data to test for orbital and rotational modulation of the systems $gamma$-ray emission, finding no evidence for orbital modulation and $3.7sigma$ evidence for modulation at the pulsar period. The energetics of the system make it plausible that the $gamma$-ray emission we observe is entirely from the millisecond pulsar itself, but it seems unlikely for these $gamma$-rays to provide the irradiation of the companion, which we attribute instead to X-ray heating from a shock powered by a particle wind.
We present the orbital solution of a peculiar double-lined spectroscopic and eclipsing binary system, 2M17091769+3127589. This solution was obtained by a simultaneous fit of both APOGEE radial velocities and TESS and ASAS-SN light curves to determine masses and radii. This system consists of an $M=0.256^{+0.010}_{-0.006}$ $M_odot$, $R=3.961^{+0.049}_{-0.032}$ $R_{odot}$ red giant and a hotter $M=1.518 ^{+0.057}_{-0.031}$ $M_odot$, $R=2.608^{+0.034}_{-0.321}$ $R_{odot}$ subgiant. Modelling with the MESA evolutionary codes indicates that the system likely formed 5.26 Gyrs ago, with a $M=1.2$ $M_odot$ primary that is now the systems red giant and a $M=1.11$ $M_odot$ secondary that is now a more massive subgiant. Due to Roche-lobe overflow as the primary ascends the red giant branch, the more evolved primary (i.e., originally the more massive star of the pair) is now only one-sixth as massive as the secondary. Such a difference between the initial and the current mass ratio is one of the most extreme detected so far. Evolutionary modelling suggests the system is still engaged in mass transfer, at a rate of $dot{M} sim 10^{-9}$ $M_odot$ yr$^{-1}$, and it provides an example of a less evolved precursor to some of the systems that consist of white dwarfs and blue stragglers.
We present a study of PSR J1723-2837, an eclipsing, 1.86 ms millisecond binary radio pulsar discovered in the Parkes Multibeam survey. Radio timing indicates that the pulsar has a circular orbit with a 15 hr orbital period, a low-mass companion, and a measurable orbital period derivative. The eclipse fraction of ~15% during the pulsars orbit is twice the Roche lobe size inferred for the companion. The timing behavior is significantly affected by unmodeled systematics of astrophysical origin, and higher-order orbital period derivatives are needed in the timing solution to account for these variations. We have identified the pulsars (non-degenerate) companion using archival ultraviolet, optical, and infrared survey data and new optical photometry. Doppler shifts from optical spectroscopy confirm the stars association with the pulsar and indicate a pulsar-to-companion mass ratio of 3.3 +/- 0.5, corresponding to a companion mass range of 0.4 to 0.7 Msun and an orbital inclination angle range of between 30 and 41 degrees, assuming a pulsar mass range of 1.4-2.0 Msun. Spectroscopy indicates a spectral type of G for the companion and an inferred Roche-lobe-filling distance that is consistent with the distance estimated from radio dispersion. The features of PSR J1723-2837 indicate that it is likely a redback system. Unlike the five other Galactic redbacks discovered to date, PSR J1723-2837 has not been detected as a gamma-ray source with Fermi. This may be due to an intrinsic spin-down luminosity that is much smaller than the measured value if the unmeasured contribution from proper motion is large.
We report on the discovery and the timing analysis of the first eclipsing accretion-powered millisecond X-ray pulsar (AMXP): SWIFT J1749.4-2807. The neutron star rotates at a frequency of ~517.9 Hz and is in a binary system with an orbital period of 8.8 hrs and a projected semi-major axis of ~1.90 lt-s. Assuming a neutron star between 0.8 and 2.2 M_o and using the mass function of the system and the eclipse half-angle, we constrain the mass of the companion and the inclination of the system to be in the ~0.46-0.81 M_o and $sim74.4^o-77.3^o range, respectively. To date, this is the tightest constraint on the orbital inclination of any AMXP. As in other AMXPs, the pulse profile shows harmonic content up to the 3rd overtone. However, this is the first AMXP to show a 1st overtone with rms amplitudes between ~6% and ~23%, which is the strongest ever seen, and which can be more than two times stronger than the fundamental. The fact that SWIFT J1749.4-2807 is an eclipsing system which shows uncommonly strong harmonic content suggests that it might be the best source to date to set constraints on neutron star properties including compactness and geometry.
It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron stars rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.
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