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Register a new userHydrodynamic simulations of pulsar glitch recovery
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Glitches are sudden jumps in the spin frequency of pulsars believed to originate in the superfluid interior of neutron stars. Superfluid flow in a model neutron star is simulated by solving the equations of motion of a two-component superfluid consisting of a viscous proton-electron plasma and an inviscid neutron condensate in a spherical Couette geometry. We examine the response of our model neutron star to glitches induced in three different ways: by instantaneous changes of the spin frequency of the inner and outer boundaries, and by instantaneous recoupling of the fluid components in the bulk. All simulations are performed with strong and weak mutual friction. It is found that the maximum size of a glitch that originates in the bulk decreases as the mutual friction strengthens. It is also found that mutual friction determines the fraction of the frequency jump which is later recovered, a quantity known as the healing parameter. These behaviours may explain some of the diversity in observed glitch recoveries.
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We present updated measurements of the Crab pulsar glitch of 2019 July 23 using a dataset of pulse arrival times spanning $sim$5 months. On MJD 58687, the pulsar underwent its seventh largest glitch observed to date, characterised by an instantaneous spin-up of $sim$1 $mu$Hz. Following the glitch the pulsars rotation frequency relaxed exponentially towards pre-glitch values over a timescale of approximately one week, resulting in a permanent frequency increment of $sim$0.5 $mu$Hz. Due to our semi-continuous monitoring of the Crab pulsar, we were able to partially resolve a fraction of the total spin-up. This delayed spin-up occurred exponentially over a timescale of $sim$18 hours. This is the sixth Crab pulsar glitch for which part of the initial rise was resolved in time and this phenomenon has not been observed in any other glitching pulsars, offering a unique opportunity to study the microphysical processes governing interactions between the neutron star interior and the crust.
A large number of binary black holes (BBHs) with longer orbital periods are supposed to exist as progenitors of BBH mergers recently discovered with gravitational wave (GW) detectors. In our previous papers, we proposed to search for such BBHs in triple systems through the radial-velocity modulation of the tertiary orbiting star. If the tertiary is a pulsar, high precision and cadence observations of its arrival time enable an unambiguous characterization of the pulsar -- BBH triples located at several kpc, which are inaccessible with the radial velocity of stars. The present paper shows that such inner BBHs can be identified through the short-term R{o}mer delay modulation, on the order of $10$ msec for our fiducial case, a triple consisting of $20~M_odot$ BBH and $1.4~M_odot$ pulsar with $P_mathrm{in}=10$ days and $P_mathrm{out}=100$ days. If the relativistic time delays are measured as well, one can determine basically all the orbital parameters of the triple. For instance, this method is applicable to inner BBHs of down to $sim 1$ hr orbital periods if the orbital period of the tertiary pulsar is around several days. Inner BBHs with $lesssim 1$ hr orbital period emit the GW detectable by future space-based GW missions including LISA, DECIGO, and BBO, and very short inner BBHs with sub-second orbital period can be even probed by the existing ground-based GW detectors. Therefore, our proposed methodology provides a complementary technique to search for inner BBHs in triples, if exist at all, in the near future.
The collapse of a massive stars core, followed by a neutrino-driven, asymmetric supernova explosion, can naturally lead to pulsar recoils and neutron star kicks. Here, we present a two-dimensional, radiation-hydrodynamic simulation in which core collapse leads to significant acceleration of a fully-formed, nascent neutron star (NS) via an induced, neutrino-driven explosion. During the explosion, a ~10% anisotropy in the low-mass, high-velocity ejecta lead to recoil of the high-mass neutron star. At the end of our simulation, the NS has achieved a velocity of ~150 km s$^{-1}$ and is accelerating at ~350 km s$^{-2}$, but has yet to reach the ballistic regime. The recoil is due almost entirely to hydrodynamical processes, with anisotropic neutrino emission contributing less than 2% to the overall kick magnitude. Since the observed distribution of neutron star kick velocities peaks at ~300-400 km s$^{-1}$, recoil due to anisotropic core-collapse supernovae provides a natural, non-exotic mechanism with which to obtain neutron star kicks.
We report the discovery of PSR J1757$-$1854, a 21.5-ms pulsar in a highly-eccentric, 4.4-h orbit around a neutron star (NS) companion. PSR J1757$-$1854 exhibits some of the most extreme relativistic parameters of any known pulsar, including the strongest relativistic effects due to gravitational-wave (GW) damping, with a merger time of 76 Myr. Following a 1.6-yr timing campaign, we have measured five post-Keplerian (PK) parameters, yielding the two component masses ($m_text{p}=1.3384(9),text{M}_odot$ and $m_text{c}=1.3946(9),text{M}_odot$) plus three tests of general relativity (GR), which the theory passes. The larger mass of the NS companion provides important clues regarding the binary formation of PSR J1757$-$1854. With simulations suggesting 3-$sigma$ measurements of both the contribution of Lense-Thirring precession to the rate of change of the semi-major axis and the relativistic deformation of the orbit within $sim7-9$ years, PSR J1757$-$1854 stands out as a unique laboratory for new tests of gravitational theories.
We present evidence for a small glitch in the spin evolution of the millisecond pulsar J0613$-$0200, using the EPTA Data Release 1.0, combined with Jodrell Bank analogue filterbank TOAs recorded with the Lovell telescope and Effelsberg Pulsar Observing System TOAs. A spin frequency step of 0.82(3) nHz and frequency derivative step of ${-1.6(39) times 10^{-19},text{Hz} text{s}^{-1}}$ are measured at the epoch of MJD 50888(30). After PSR B1821$-$24A, this is only the second glitch ever observed in a millisecond pulsar, with a fractional size in frequency of ${Delta u/ u=2.5(1) times 10^{-12}}$, which is several times smaller than the previous smallest glitch. PSR J0613$-$0200 is used in gravitational wave searches with pulsar timing arrays, and is to date only the second such pulsar to have experienced a glitch in a combined 886 pulsar-years of observations. We find that accurately modelling the glitch does not impact the timing precision for pulsar timing array applications. We estimate that for the current set of millisecond pulsars included in the International Pulsar Timing Array, there is a probability of $sim 50$% that another glitch will be observed in a timing array pulsar within 10 years.
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