1,918 research outputs found
The profile of an emission line from relativistic outflows around a black hole
Recent observations show strong evidence for the presence of Doppler-shifted
emission lines in the spectrum of both black hole candidates and active
galactic nuclei. These lines are likely to originate from relativistic outflows
(or jets) in the vicinity of the central black hole. Consequently, the profile
of such a line should be distorted by strong gravitational effects near the
black hole, as well as special relativistic effects. In this paper, we present
results from a detailed study on how each process affects the observed line
profile. We found that the profile is sensitive to the intrinsic properties of
the jets (Lorentz factor, velocity profile, and emissivity law), as well as to
the spin of the black hole and the viewing angle (with respect to the axis of
the jets). More specifically, in the case of approaching jets, an intrisically
narrow line (blue-shifted) is seen as simply broadened at small viewing angles,
but it shows a doubly peaked profile at large viewing angles for extreme Kerr
black holes (due to the combination of gravitational focusing and Doppler
effects); the profile is always singly peaked for Schwarzschild black holes.
For receding jets, however, the line profile becomes quite complicated owing to
complicated photon trajectories. To facilitate comparison with observations, we
searched a large parameter space to derive representative line profiles. We
show the results and discuss how to use emission lines as a potential tool for
probing the inner region of a black hole jet system.Comment: 16 pages in emulateapj style, 11 figure
Tracing Ghost Cavities with Low Frequency Radio Observations
We present X-ray and multi-frequency radio observations of the central radio
sources in several X-ray cavity systems. We show that targeted radio
observations are key to determining if the lobes are being actively fed by the
central AGN. Low frequency observations provide a unique way to study both the
lifecycle of the central radio source as well as its energy input into the ICM
over several outburst episodes.Comment: 6 pages, 4 figures, To appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", eds. H. Boehringer, P.
Schuecker, G. W. Pratt & A. Finoguenov (ESO Astrophysics Symposia,
Springer-Verlag), Garching (Germany), August 200
A new structural model for the Si(331)-(12x1) reconstruction
A new structural model for the Si(331)-(12x1) reconstruction is proposed.
Based on scanning tunneling microscopy images of unprecedented resolution,
low-energy electron diffraction data, and first-principles total-energy
calculations, we demonstrate that the reconstructed Si(331) surface shares the
same elementary building blocks as the Si(110)-(16x2) surface, establishing the
pentamer as a universal building block for complex silicon surface
reconstructions
The Molecular Gas Reservoirs of Galaxies: A comparison of CO(1-0) and dust-based molecular gas masses
We test the use of long-wavelength dust continuum emission as a molecular gas
tracer at high redshift, via a unique sample of 12, z~2 galaxies with
observations of both the dust continuum and CO(1-0) line emission (obtained
with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array,
respectively). Our work is motivated by recent, high redshift studies that
measure molecular gas masses (\ensuremath{\rm{M}_{\rm{mol}}}) via a calibration
of the rest-frame m luminosity () against the
CO(1-0)-derived \ensuremath{\rm{M}_{\rm{mol}}}\ of star-forming galaxies. We
hereby test whether this method is valid for the types of high-redshift,
star-forming galaxies to which it has been applied. We recover a clear
correlation between the rest-frame m luminosity, inferred from the
single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent
with the samples used to perform the m calibration. The molecular gas
masses, derived from , agree to within a factor of
two with those derived from CO(1-0). We show that this factor of two
uncertainty can arise from the values of the dust emissivity index and
temperature that need to be assumed in order to extrapolate from the observed
frequency to the rest-frame at 850. The extrapolation to
850 therefore has a smaller effect on the accuracy of \Mmol\
derived via single-band dust-continuum observations than the assumed
CO(1-0)-to-\ensuremath{\rm{M}_{\rm{mol}}}\ conversion factor. We therefore
conclude that single-band observations of long-wavelength dust emission can be
used to reliably constrain the molecular gas masses of massive, star-forming
galaxies at
Compactness in Banach space theory - selected problems
We list a number of problems in several topics related to compactness in
nonseparable Banach spaces. Namely, about the Hilbertian ball in its weak
topology, spaces of continuous functions on Eberlein compacta, WCG Banach
spaces, Valdivia compacta and Radon-Nikod\'{y}m compacta
Physical parameters of a relativistic jet at very high redshift: the case of the blazar J1430+4204
Context. The high-redshift (z = 4.72) blazar J1430+4204 produced a major
radio outburst in 2005. Such outbursts are usually associated with the
emergence of a new component in the inner radio jet. Aims. We searched for
possible changes in the radio structure on milli-arcsecond angular scales, to
determine physical parameters that characterise the relativistic jet ejected
from the centre of this source. Methods. We analysed 15-GHz radio
interferometric images obtained with the Very Long Baseline Array (VLBA) before
and after the peak of the outburst. Results. We did not identify any
significant new jet component over a period of 569 days. We estimated the
Doppler factor, the Lorentz factor, and the apparent transverse speed of a
putative jet component using three different methods. The likely small jet
angle to the line of sight and our values of the apparent transverse speed are
consistent with not detecting a new jet feature.Comment: (6 pages, 4 figures) accepted for publication in Astronomy and
Astrophysic
Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events
A star orbiting a supermassive black hole can be tidally disrupted if the
black hole's gravitational tidal field exceeds the star's self gravity at
pericenter. Some of this stellar tidal debris can become gravitationally bound
to the black hole, leading to a bright electromagnetic flare with bolometric
luminosity proportional to the rate at which material falls back to pericenter.
In the Newtonian limit, this flare will have a light curve that scales as
t^-5/3 if the tidal debris has a flat distribution in binding energy. We
investigate the time dependence of the black-hole mass accretion rate when
tidal disruption occurs close enough the black hole that relativistic effects
are significant. We find that for orbits with pericenters comparable to the
radius of the marginally bound circular orbit, relativistic effects can double
the peak accretion rate and halve the time it takes to reach this peak
accretion rate. The accretion rate depends on both the magnitude of the
black-hole spin and its orientation with respect to the stellar orbit; for
orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal
black-hole spin anti-aligned with the orbital angular momentum leads to the
largest peak accretion rate.Comment: 16 pages, 15 figures, 1 table, PRD published versio
Implications of the PSR 1257+12 Planetary System for Isolated Millisecond Pulsars
The first extrasolar planets were discovered in 1992 around the millisecond
pulsar PSR 1257+12. We show that recent developments in the study of accretion
onto magnetized stars, plus the existence of the innermost, moon-sized planet
in the PSR 1257+12 system, suggest that the pulsar was born with approximately
its current rotation frequency and magnetic moment. If so, this has important
implications for the formation and evolution of neutron star magnetic fields as
well as for the formation of planets around pulsars. In particular, it suggests
that some and perhaps all isolated millisecond pulsars may have been born with
high spin rates and low magnetic fields instead of having been recycled by
accretion.Comment: 17 pages including one figure, uses aaspp4, accepted by Ap
Number, frequency and time interval of examinations under anesthesia in bilateral retinoblastoma
PURPOSE: Current practice in retinoblastoma (Rb) has transformed this malignancy into a curable disease. More attention should therefore be given to quality of life considerations, including measures related to examinations under anesthesia (EUAs). We aimed to investigate EUA measures in bilateral Rb patients and compare the findings to EUAs in unilateral Rb. METHODS: A retrospective analysis of bilateral Rb patients that presented to the London Rb service from 2006 to 2013, were treated and had long-term follow-up. RESULTS: A total of 62 Rb patients, 15 (24.2%) of which had International Intraocular Retinoblastoma Classification (IIRC) group A/B/no Rb at presentation, 26 (41.9%) C/D, and 21 (33.9%) were E in at least one eye. The mean number of EUAs was 35.8 ± 21.5, mean time from first to last EUA was 50.6 ± 19.9 months, and mean EUA frequency was 0.715 ± 0.293 EUAs/month. IIRC group was found not to correlate with any of the EUA measures. Age at presentation inversely correlated with time interval from first to last EUA and to EUA frequency (p ≤ 0.029). Rb family history correlated with the latter measure (p = 0.005) and intraophthalmic artery chemotherapy and brachytherapy correlated with all EUA measures (p ≤ 0.029). Mean follow-up time was 80.1 ± 24.3 months. When compared with a previously reported cohort of unilateral Rb, the present group underwent 3× more EUAs (p < 0.001) over nearly double the time (p < 0.001). CONCLUSIONS: Families should be counselled on anticipated EUA burden associated with bilateral Rb. In this respect, age at presentation and family history were found to have a predictive role, whereas IIRC group did not
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