76 research outputs found
A model-independent comparison of the variability of accreting neutron stars and black holes
We use Rossi X-ray Timing Explorer observations to conduct a population study
of the timing properties of accretion-powered neutron star Low Mass X-ray
Binaries (LMXBs), following a model-independent approach that was originally
applied to black hole systems. The ratios of integrated power in four equally
spaced Fourier frequency bands allow power spectral shapes to be parameterised
with two `power colour' values, providing a simple way of tracking the
evolution in timing properties across observations. We show that neutron star
LMXBs follow a remarkably similar power spectral evolution to black hole LMXBs,
confirming that the broadband noise variability seen in both types of system
has a common origin in the accretion flow. Both neutron stars and black holes
follow a similar clear track in the power colour-colour diagram as they
transition from the hard through soft states. Quantifying the position on this
oval track using a single parameter, the power-spectral `hue', we find that the
transition in X-ray spectral shape occurs at the same hue for both neutron star
and black hole systems. The power colours of Z sources map on to those of soft
state black holes, while those of atoll sources correspond to all spectral
states. There is no clear dependence of power colour on neutron star spin, or
on whether the neutron star is clearly magnetised (determined by ms X-ray
pulsations).Comment: 21 pages, 19 figures, accepted for publication in MNRA
Multi-dimensional population modelling using frbpoppy: magnetars can produce the observed Fast Radio Burst sky
Fast Radio Bursts (FRBs) are energetic, short, bright transients that occur
frequently over the entire radio sky. The observational challenges following
from their fleeting, generally one-off nature have prevented identification of
the underlying sources producing the bursts. As the population of detected FRBs
grows, the observed distributions of brightness, pulse width and dispersion
measure now begin to take shape. Meaningful direct interpretation of these
distributions is, however, made impossible by the selection effects that
telescope and search pipelines invariably imprint on each FRB survey. Here we
show that multi-dimensional FRB population synthesis can find a single,
self-consistent population of FRB sources that can reproduce the real-life
results of the major ongoing FRB surveys. This means that individual observed
distributions can now be combined to derive the properties of the intrinsic FRB
source population. The characteristics of our best-fit model for one-off FRBs
agree with a population of magnetars. We extrapolate this model and predict the
number of FRBs future surveys will find. For surveys that have commenced, the
method we present here can already determine the composition of the FRB source
class, and potentially even its subpopulations.Comment: 12 pages, 4 figures, accepted by Astronomy & Astrophysic
Captain Baby Bunting : Of The Rocking-Horse Brigade
https://digitalcommons.library.umaine.edu/mmb-vp/1148/thumbnail.jp
Correlating spectral and timing properties in the evolving jet of the micro blazar MAXI J1836-194
During outbursts, the observational properties of black hole X-ray binaries
(BHXBs) vary on timescales of days to months. These relatively short timescales
make these systems ideal laboratories to probe the coupling between accreting
material and outflowing jets as a the accretion rate varies. In particular, the
origin of the hard X-ray emission is poorly understood and highly debated. This
spectral component, which has a power-law shape, is due to Comptonisation of
photons near the black hole, but it is unclear whether it originates in the
accretion flow itself, or at the base of the jet, or possibly the interface
region between them. In this paper we explore the disk-jet connection by
modelling the multi-wavelength emission of MAXI J1836-194 during its 2011
outburst. We combine radio through X-ray spectra, X-ray timing information, and
a robust joint-fitting method to better isolate the jet's physical properties.
Our results demonstrate that the jet base can produce power-law hard X-ray
emission in this system/outburst, provided that its base is fairly compact and
that the temperatures of the emitting electrons are sub-relativistic. Because
of energetic considerations, our model favours mildly pair-loaded jets carrying
at least 20 pairs per proton. Finally, we find that the properties of the X-ray
power spectrum are correlated with the jet properties, suggesting that an
underlying physical process regulates both.Comment: 17 pages, 10 figures, accepted for publication on MNRA
Correlating spectral and timing properties in the evolving jet of the microblazar MAXI J1836-194
During outbursts, the observational properties of black hole X-ray binaries vary on time-scales of days to months. These relatively short time-scales make these systems ideal laboratories to probe the coupling between accreting material and outflowing jets as the accretion rate varies. In particular, the origin of the hard X-ray emission is poorly understood and highly debated. This spectral component, which has a power-law shape, is due to Comptonization of photons near the black hole, but it is unclear whether it originates in the accretion flow itself, or at the base of the jet, or possibly the interface region between them. In this paper, we explore the disc-jet connection by modelling the multiwavelength emission of MAXI J1836-194 during its 2011 outburst. We combine radio through X-ray spectra, X-ray timing information, and a robust joint-fitting method to better isolate the jet\u27s physical properties. Our results demonstrate that the jet base can produce power-law hard X-ray emission in this system/outburst, provided that its base is fairly compact and that the temperatures of the emitting electrons are subrelativistic. Because of energetic considerations, our model favours mildly pair-loaded jets carrying at least 20 pairs per proton. Finally, we find that the properties of the X-ray power spectrum are correlated with the jet properties, suggesting that an underlying physical process regulates both
A bright, high rotation-measure FRB that skewers the M33 halo
We report the detection of a bright fast radio burst, FRB\,191108, with
Apertif on the Westerbork Synthesis Radio Telescope (WSRT). The interferometer
allows us to localise the FRB to a narrow 5\arcsec\times7\arcmin ellipse by
employing both multibeam information within the Apertif phased-array feed (PAF)
beam pattern, and across different tied-array beams. The resulting sight line
passes close to Local Group galaxy M33, with an impact parameter of only
18\,kpc with respect to the core. It also traverses the much larger
circumgalactic medium of M31, the Andromeda Galaxy. We find that the shared
plasma of the Local Group galaxies could contribute 10\% of its
dispersion measure of 588\,pc\,cm. FRB\,191108 has a Faraday rotation
measure of +474\,\,rad\,m, which is too large to be explained by
either the Milky Way or the intergalactic medium. Based on the more moderate
RMs of other extragalactic sources that traverse the halo of M33, we conclude
that the dense magnetised plasma resides in the host galaxy. The FRB exhibits
frequency structure on two scales, one that is consistent with quenched
Galactic scintillation and broader spectral structure with
\,MHz. If the latter is due to scattering in the shared
M33/M31 CGM, our results constrain the Local Group plasma environment. We found
no accompanying persistent radio sources in the Apertif imaging survey data
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