116 research outputs found
X-ray Periodicity in AGN
Significant (marginal) detections of periodic signals have been recently
reported in 3 (4) Active Galactic Nuclei. Three of the detections were obtained
from long EUVE light curves of moderate-luminosity Seyfert galaxies; the fourth
was discovered in Chandra data from the low-luminosity Seyfert 1 galaxy NGC
4395. When compared with Cyg X-1, I find that the period is related to the
luminosity as rather than the expected one-to-one
relationship. This result might be explained if the QPO is associated with the
inner edge of the optically thick accretion disk, and the inner edge radius
depends on the source luminosity (or black hole mass). A discussion of
uncertainties in the period detection methodology is also discussed.Comment: To appear in From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales, eds. T. J. Maccarone, R. P. Fender, and L. C. Ho (Dordrecht:
Kluwer
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Weighing black holes with warm absorbers
We present a new technique for determining an upper limit for the mass of the
black hole in active galactic nuclei showing warm absorption features. The
method relies on the balance of radiative and gravitational forces acting on
outflowing warm absorber clouds. It has been applied to 6 objects: five Seyfert
1 galaxies: IC 4329a, MCG-6-30-15, NGC 3516, NGC 4051 and NGC 5548; and one
radio-quiet quasar: MR 2251-178. We discuss our result in comparison with other
methods. The procedure could also be applied to any other radiatively driven
optically thin outflow in which the spectral band covering the major absorption
is directly observed.Comment: 13 pages, 6 figures, 7 tables. MNRAS accepte
Mass Spectra of Supersymmetric Yang-Mills Theories in 1+1 Dimensions
Physical mass spectra of supersymmetric Yang-Mills theories in 1+1 dimensions
are evaluated in the light-cone gauge with a compact spatial dimension. The
supercharges are constructed and the infrared regularization is unambiguously
prescribed for supercharges, instead of the light-cone Hamiltonian. This
provides a manifestly supersymmetric infrared regularization for the
discretized light-cone approach. By an exact diagonalization of the supercharge
matrix between up to several hundred color singlet bound states, we find a
rapidly increasing density of states as mass increases.Comment: LaTeX file, 32 page, 7 eps figure
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
Human surface anatomy terminology for dermatology: a Delphi consensus from the International Skin Imaging Collaboration
BackgroundThere is no internationally vetted set of anatomic terms to describe human surface anatomy.ObjectiveTo establish expert consensus on a standardized set of terms that describe clinically relevant human surface anatomy.MethodsWe conducted a Delphi consensus on surface anatomy terminology between July 2017 and July 2019. The initial survey included 385 anatomic terms, organized in seven levels of hierarchy. If agreement exceeded the 75% established threshold, the term was considered - accepted- and included in the final list. Terms added by the participants were passed on to the next round of consensus. Terms with <75% agreement were included in subsequent surveys along with alternative terms proposed by participants until agreement was reached on all terms.ResultsThe Delphi included 21 participants. We found consensus (- ÂĽ75% agreement) on 361/385 (93.8%) terms and eliminated one term in the first round. Of 49 new terms suggested by participants, 45 were added via consensus. To adjust for a recently published International Classification of Diseases- Surface Topography list of terms, a third survey including 111 discrepant terms was sent to participants. Finally, a total of 513 terms reached agreement via the Delphi method.ConclusionsWe have established a set of 513 clinically relevant terms for denoting human surface anatomy, towards the use of standardized terminology in dermatologic documentation.Linked Commentary: R.J.G. Chalmers. J Eur Acad Dermatol Venereol 2020; 34: 2456- 2457. https://doi.org/10.1111/jdv.16978.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163915/1/jdv16855_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163915/2/jdv16855-sup-0001-FigS1-S3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163915/3/jdv16855.pd
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Anthropogenic natal environmental effects on life histories in a wild bird population
Recent work suggests that the environment experienced in early life can alter life histories in wild populations [1, 2, 3, 4 and 5], but our understanding of the processes involved remains limited [6 and 7]. Since anthropogenic environmental change is currently having a major impact on wild populations [8], this raises the possibility that life histories may be influenced by human activities that alter environmental conditions in early life. Whether this is the case and the processes involved remain unexplored in wild populations. Using 23 years of longitudinal data on the Mauritius kestrel (Falco punctatus), a tropical forest specialist, we found that females born in territories affected by anthropogenic habitat change shifted investment in reproduction to earlier in life at the expense of late life performance. They also had lower survival rates as young adults. This shift in life history strategy appears to be adaptive, because fitness was comparable to that of other females experiencing less anthropogenic modification in their natal environment. Our results suggest that human activities can leave a legacy on wild birds through natal environmental effects. Whether these legacies have a detrimental effect on populations will depend on life history responses and the extent to which these reduce individual fitness
2022 Upgrade and Improved Low Frequency Camera Sensitivity for CMB Observation at the South Pole
Constraining the Galactic foregrounds with multi-frequency Cosmic Microwave
Background (CMB) observations is an essential step towards ultimately reaching
the sensitivity to measure primordial gravitational waves (PGWs), the sign of
inflation after the Big-Bang that would be imprinted on the CMB. The BICEP
Array telescope is a set of multi-frequency cameras designed to constrain the
energy scale of inflation through CMB B-mode searches while also controlling
the polarized galactic foregrounds. The lowest frequency BICEP Array receiver
(BA1) has been observing from the South Pole since 2020 and provides 30 GHz and
40 GHz data to characterize the Galactic synchrotron in our CMB maps. In this
paper, we present the design of the BA1 detectors and the full optical
characterization of the camera including the on-sky performance at the South
Pole. The paper also introduces the design challenges during the first
observing season including the effect of out-of-band photons on detectors
performance. It also describes the tests done to diagnose that effect and the
new upgrade to minimize these photons, as well as installing more dichroic
detectors during the 2022 deployment season to improve the BA1 sensitivity. We
finally report background noise measurements of the detectors with the goal of
having photon noise dominated detectors in both optical channels. BA1 achieves
an improvement in mapping speed compared to the previous deployment season.Comment: Proceedings of SPIE Astronomical Telescopes + Instrumentation 2022
(AS22
Track D Social Science, Human Rights and Political Science
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138414/1/jia218442.pd
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