11,797 research outputs found
The multi-wavelength polarization of Cygnus X-1
Polarization measurements of the microquasar Cygnus X-1 exist at gamma-ray,
X-ray, UV, optical and radio frequencies. The gamma-ray emission has been shown
to be highly linearly polarized. Here, we present new infrared polarimetric
data of Cygnus X-1 taken with the 10.4-m Gran Telescopio Canarias and the 4.2-m
William Herschel Telescope. We show that the broadband, radio to gamma-ray flux
spectrum and polarization spectrum in the hard state are largely consistent
with a simple phenomenological model of a strongly polarized synchrotron jet,
an unpolarized Comptonized corona and a moderately polarized interstellar dust
component. In this model, the origin of the gamma-ray, X-ray and some of the
infrared polarization is the optically thin synchrotron power law from the
inner regions of the jet. The model requires the magnetic field in this region
to be highly ordered and perpendicular to the axis of the resolved radio jet.
This differs to studies of some other X-ray binaries, in which the magnetic
field is turbulent, variable and aligned with the jet axis. The model is able
to explain the approximate polarization strength and position angle at all
wavelengths including the detected X-ray (3 - 5 keV) polarization, except the
observed position angle of the gamma-ray polarization, which differs to the
model by ~ 60 degrees. Past numerical modelling has shown that a curved
synchrotron spectrum can produce a shift in position angle by ~ 60 degrees,
which may account for this.Comment: Accepted in MNRA
LGBT Equality and Sexual Racism
Bigots such as the trial judge in Loving have long invoked religion to justify discrimination. We agree with other scholars that neither religion nor artistic freedom justifies letting businesses discriminate. However, we also want to make manifest the tension between the public posture of LGBT-rights litigants and the practices of some LGBT people who discriminate based on race in selecting partners. We argue that some white people’s aversion to dating and forming relationships with people of color is a form of racism, and this sexual racism is inconsistent with the spirit of Loving. Part I provides a review of empirical literature on the prevalence of racial preferences in intimate relationships and shows that racial preferences are particularly pronounced among gay men. Part II supplements this overview with a qualitative exploration of how race informed the intimate experiences of people who sat for interviews as part of our ongoing study, LGBT Relationships and Well-Being. We also offer a theory that may partially explain sexual racism in the LGBT community. Specifically, exposure to mainstream gay culture may teach sexual minority men that race and desire are closely intertwined. In Part III, we propose ideas for further research, including a study that would test our theory
Polarized synchrotron emission in quiescent black hole X-ray transients
We present near-infrared polarimetric observations of the black hole X-ray
binaries Swift J1357.2-0933 and A0620-00. In both sources, recent studies have
demonstrated the presence of variable infrared synchrotron emission in
quiescence, most likely from weak compact jets. For Swift J1357.2-0933 we find
that the synchrotron emission is polarized at a level of 8.0 +- 2.5 per cent (a
3.2 sigma detection of intrinsic polarization). The mean magnitude and rms
variability of the flux (fractional rms of 19-24 per cent in K_s-band) agree
with previous observations. These properties imply a continuously launched
(stable on long timescales), highly variable (on short timescales) jet in the
Swift J1357.2-0933 system in quiescence, which has a moderately tangled
magnetic field close to the base of the jet. We find that for A0620-00, there
are likely to be three components to the optical-infrared polarization;
interstellar dust along the line of sight, scattering within the system, and an
additional source that changes the polarization position angle in the reddest
(H and K_s) wave-bands. We interpret this as a stronger contribution of
synchrotron emission, and by subtracting the line-of-sight polarization, we
measure an excess of ~ 1.25 +- 0.28 per cent polarization and a position angle
of the magnetic field vector that is consistent with being parallel with the
axis of the resolved radio jet. These results imply that weak jets in low
luminosity accreting systems have magnetic fields which possess similarly
tangled fields compared to the more luminous, hard state jets in X-ray
binaries.Comment: Accepted to MNRA
Optical/infrared polarised emission in X-ray binaries
Recently, evidence for synchrotron emission in both black hole and neutron
star X-ray binaries has been mounting, from optical/infrared spectral,
polarimetric, and fast timing signatures. The synchrotron emission of jets can
be highly linearly polarised, depending on the configuration of the magnetic
field. Optical and infrared (OIR) polarimetric observations of X-ray binaries
are presented in this brief review. The OIR polarimetric signature of
relativistic jets is detected at levels of ~ 1-10 %, similar to AGN cores. This
reveals that the magnetic geometry in the compact jets may be similar for
supermassive and stellar-mass BHs. The magnetic fields near the jet base in
most of these systems appear to be turbulent, variable and on average, aligned
with the jet axis, although there are some exceptions. These measurements probe
the physical conditions in the accretion (out)flow and demonstrate a new way of
connecting inflow and outflow, using both rapid timing and polarisation.
Variations in polarisation could be due to rapid changes of the ordering of the
magnetic field in the emitting region, or in one case, flares from individual
ejections or collisions between ejecta. It is predicted that in some cases,
variable levels of X-ray polarisation from synchrotron emission originating in
jets will be detected from accreting Galactic black holes with upcoming
spaceborne X-ray polarimeters.Comment: 6 pages short review; Accepted by MDPI Galaxies; Conference
Proceedings for 'Polarised Emission from Astrophysical Jets', June 12-16,
2017, Ierapetra, Greece http://www.mdpi.com/2075-4434/6/1/
Introducing the Spatial Conflict Dynamics indicator of political violence
Modern armed conflicts have a tendency to cluster together and spread
geographically. However, the geography of most conflicts remains under-studied.
To fill this gap, this article presents a new indicator that measures two key
geographical properties of subnational political violence: the conflict
intensity within a region on the one hand, and the spatial distribution of
conflict within a region on the other. We demonstrate the indicator in North
and West Africa between 1997 to 2019 to show that it can clarify how conflicts
can spread from place to place and how the geography of conflict changes over
time
Robotic Astronomy with the Faulkes Telescopes and Las Cumbres Observatory Global Telescope
We present results from ongoing science projects conducted by members of the
Faulkes Telescope (FT) team and Las Cumbres Observatory Global Telescope
(LCOGT). Many of these projects incorporate observations carried out and
analysed by FT users, comprising amateur astronomers and schools.
We also discuss plans for the further development of the LCOGT network.Comment: 8 pages, 2 figures, conference proceedings from "Workshop on Robotic
Autonomous Observatories", held at Malaga, Spain from 18-21 May 2009,
acccepted for publication in Advances in Astronom
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