Extreme-mass-ratio and intermediate-mass-ratio binaries with a millisecond pulsar are gravitational-wave sources that emit also electromagnetic radiation. The millisecond pulsars in these binaries ...have complex orbital and spin dynamics, which are observable because of spin–orbit and spin–spin coupling (through spin–curvature interaction). The strengths of the couplings generally depends on the mass ratio between the pulsar and the black hole. The narrow mass range of neutron stars gives an advantage in parameter extraction as it greatly reduces the search space, in particular, in the determination of the black-hole mass, in gravitational wave experiments and radio pulsar timing observations. Extreme-mass-ratio and intermediate-mass-ratio binaries with a millisecond pulsar will help to resolve the astrophysical problems, concerning the applicability of the M-σ relation for galactic spheroids extending to the very low-mass galaxies and whether or not low-mass dwarf galaxies and globular clusters would harbour a nuclear intermediate-mass black hole. The high-precision that can be achieved in gravitational wave experiments and radio pulsar timing observations will provide an opportunity to directly detect gravitational clock effects that are arisen from spin couplings. Radio monitoring of the orbital and spin evolution of the millisecond pulsar in an extreme-mass-ratio binary can be used as a bootstrap method for correcting the drifts in the phases in the gravitational waves from the extreme-mass-ratio and intermediate-mass-ratio binaries caused by self-force.
Abstract A firm establishment of the presence or the lack of periodicity in repeating fast radio bursts is crucial for determining their origins. Here, we compile 1145 radio bursts of FRB 20121102A ...with fluence larger than 0.15 Jy ms from observations using the Five-hundred-meter Aperture Spherical radio Telescope, the Arecibo Observatory, the Green Bank Telescope, the Effelsberg Telescope, the MeerKAT Telescope, the Lovell Telescope, the Deep Space Network 70 m radio telescopes, the Very Large Array, and the Westerbork Synthesis Radio Telescope, spanning the time interval of MJD 57175−58776. A quasi-period of 157.1 − 4.8 + 5.2 days and a candidate quasi-period of 4.605 − 0.010 + 0.003 days are found through the phase-folding probability binomial analysis. The former is consistent with previous findings and the latter is new. The 4.605 day periodicity is more obvious in high-energy bursts with fluence larger than 1 × 10 38 erg. The presence of these (candidate) quasi-periods, together with the corresponding width of burst accumulation in the phase space, are consistent with the bursts originating from a binary degenerate star system with a close-by planet around the primary neutron star.
We investigate emission signatures of binary compact star gravitational wave (GW) sources consisting of strongly magnetized neutron stars (NSs) and/or white dwarfs (WDs) in their late-time inspiral ...phase. Because of electromagnetic interactions between the magnetospheres of the two compact stars, a substantial amount of energy will be extracted, and the resultant power is expected to be ∼1038-1044 erg s−1 in the last few seconds before the two stars merge, when the binary system contains a NS with a surface magnetic field 1012 G. The induced electric field in the process can accelerate charged particles up to the EeV energy range. Synchrotron radiation is emitted from energetic electrons, with radiative energies reaching the GeV energy for binary NSs and the MeV energy for NS-WD or double WD binaries. In addition, a blackbody component is also presented, and it peaks at several to hundreds keV for binary NSs and at several keV for NS-WD or double WD binaries. The strong angular dependence of the synchrotron radiation and the isotropic nature of the blackbody radiation lead to distinguishable modulation patterns between the two emission components. If coherent curvature radiation is presented, fast radio bursts could be produced. These components provide unique simultaneous electromagnetic signatures as precursors of GW events associated with magnetized compact star mergers and short gamma-ray bursts (e.g., GRB 100717).
Abstract
We investigate ionization and heating of gas in the dense, shielded clumps/cores of molecular clouds bathed by an influx of energetic, charged cosmic rays (CRs). These molecular clouds have ...complex structures, with substantial variation in their physical properties over a wide range of length scales. The propagation and distribution of CRs is thus regulated accordingly, in particular, by the magnetic fields threaded through the clouds and into the dense regions within. We have found that a specific heating rate reaching 10
−26
erg cm
−3
s
−1
can be sustained in the dense clumps/cores for Galactic environments, and this rate increases with CR energy density. The propagation of CRs and heating rates in some star-forming filaments identified in IC 5146 are calculated, with the CR diffusion coefficients in these structures determined from magnetic field fluctuations inferred from optical and near-infrared polarizations of starlight, which is presumably a magnetic field tracer. Our calculations indicate that CR heating can vary by nearly three orders of magnitude between different filaments within a cloud due to different levels of CR penetration. The CR ionization rate among these filaments is similar. The equilibrium temperature that could be maintained by CR heating alone is of order 1 K in a Galactic environment, but this value would be higher in strongly star-forming environments, thus causing an increase in the Jeans mass of their molecular clouds.
Abstract
The routinely flaring events from Sgr A⋆ trace dynamic, high-energy processes in the immediate vicinity of the supermassive black hole. We statistically study temporal and spectral ...properties, as well as fluence and duration distributions, of the flares detected by the Chandra X-ray Observatory from 1999 to 2012. The detection incompleteness and bias are carefully accounted for in determining these distributions. We find that the fluence distribution can be well characterized by a power law with a slope of $1.73^{+0.20}_{-0.19}$, while the durations (τ in seconds) by a lognormal function with a mean $\log (\tau )=3.39^{+0.27}_{-0.24}$ and an intrinsic dispersion $\sigma =0.28^{+0.08}_{-0.06}$. No significant correlation between the fluence and duration is detected. The apparent positive correlation, as reported previously, is mainly due to the detection bias (i.e. weak flares can be detected only when their durations are short). These results indicate that the simple self-organized criticality model has difficulties in explaining these flares. We further find that bright flares usually have asymmetric light curves with no statistically evident difference/preference between the rising and decaying phases in terms of their spectral/timing properties. Our spectral analysis shows that although a power-law model with a photon index of 2.0 ± 0.4 gives a satisfactory fit to the joint spectra of strong and weak flares, there is weak evidence for a softer spectrum of weaker flares. This work demonstrates the potential to use statistical properties of X-ray flares to probe their trigger and emission mechanisms, as well as the radiation propagation around the black hole.
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