分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Advanced LIGO and Virgo gravitational wave observatories have opened a new window with which to study the inspiral and mergers of binary compact objects. These observations are most powerful when coordinated with multi-messenger observations. This was underlined by the first observation of a binary neutron star merger GW170817, coincident with a short Gamma-ray burst, GRB170817A, and the identification of the host galaxy NGC~4993 from the optical counterpart AT~2017gfo. Finding the fast-fading optical counterpart critically depends on the rapid production of a sky-map based on LIGO/Virgo data. Currently, a rapid initial sky map is produced followed by a more accurate, high-latency, $\gtrsim{12}{\rm{hr}}$ sky map. We study optimization choices of the Bayesian prior and signal model which can be used alongside other approaches such as reduced order quadrature. We find these yield up to a $60\%$ reduction in the time required to produce the high-latency localisation for binary neutron star mergers.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： It is believed that millisecond pulsars attain their fast spins by accreting matter and angular momentum from companion stars. Theoretical modelling of the accretion process suggests a spin-up line in the period-period derivative ($P$-$\dot{P}$) diagram of millisecond pulsars, which plays an important role in population studies of radio millisecond pulsars and accreting neutron stars in X-ray binaries. Here we present observational evidence for such a spin-up line using a sample of 143 radio pulsars with $P$ < 30 ms. We also find that PSRs~J1823$-$3021A and J1824$-$2452A, located near the classic spin-up line, are consistent with the broad population of millisecond pulsars. Finally, we show that our approach of Bayesian inference can probe accretion physics, allowing constraints to be placed on the accretion rate and the disk-magnetosphere interaction.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Małgorzata Curyło
Timothy T. Pennucci
Matthew Bailes
N. D. Ramesh Bhat
Andrew D. Cameron
Shi Dai
George Hobbs
Agastya Kapur
Richard N. Manchester
Rami Mandow
Matthew T. Miles
Christopher J. Russell
Daniel J. Reardon
Ryan M. Shannon
Renée Spiewak
Andrew Zic
Xing-Jiang Zhu
摘要： In 2018 an ultra-wide-bandwidth low-frequency (UWL) receiver was installed on the 64-m Parkes Radio Telescope enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here, we present the analysis of a three-year data set of 35 millisecond pulsars observed with the UWL by the Parkes Pulsar Timing Array (PPTA), using wideband timing methods. The two key differences compared to typical narrow-band methods are, firstly, generation of two-dimensional templates accounting for pulse shape evolution with frequency and, secondly, simultaneous measurements of the pulse time-of-arrival (ToA) and dispersion measure (DM). This is the first time that wideband timing has been applied to a uniform data set collected with a single large-fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions including initial noise analysis. Precision of our ToA and DM measurements is in the range of 0.005 $-$ 2.08 $\mu$s and (0.043$-$14.24)$\times10^{-4}$ cm$^{-3}$ pc, respectively, with 94% of the pulsars achieving a median ToA uncertainty of less than 1 $\mu$s.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： GW200115 is one of the first two confidently detected gravitational-wave events of neutron star-black hole mergers. An interesting property of this merger is that the black hole, if spinning rapidly, has its spin axis negatively aligned (with a misalignment angle $> 90^{\circ}$) with the binary orbital angular momentum vector. Although such a large spin-orbit misalignment angle naturally points toward a dynamical origin, the measured neutron star-black hole merger rate exceeds theoretical predictions of the dynamical formation channel. In the canonical isolated binary formation scenario, the immediate progenitor of GW200115 is likely to be a binary consisting of a black hole and a helium star, with the latter forming a neutron star during a supernova explosion. Since the black hole is generally expected to spin along the pre-supernova binary orbital angular momentum axis, a large neutron star natal kick is required to produce the observed misalignment angle. Using simple kinematic arguments, we find that a misalignment angle $> 90^{\circ}$ in GW200115-like systems implies a kick velocity $\sim 600\, \text{km/s}$ and a kick direction within $\approx 30 ^{\circ}$ of the pre-supernova orbital plane. We discuss different interpretations of the large apparent black hole spin-orbit misalignment angle, including a non-spinning black hole.
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