333 research outputs found
A Huge Drop in X-ray Luminosity of the Non-Active Galaxy RXJ1242.6-1119A, and First Post-Flare Spectrum - Testing the Tidal Disruption Scenario
It has been suggested that an unavoidable consequence of the existence of
supermassive black holes, and the best diagnostic of their presence in
non-active galaxies, would be occasional tidal disruption of stars captured by
the black holes. These events manifest themselves in form of luminous flares
powered by accretion of debris from the disrupted star into the black hole.
Candidate events among optically non-active galaxies emerged in the past few
years. For the first time, we have looked with high spatial and spectral
resolution at one of these most extreme variability events ever recorded among
galaxies. Here, we report measuring a factor ~200 drop in luminosity of the
X-ray source RXJ 1242-1119 with the X-ray observatories Chandra and XMM-Newton,
and perform key tests of the favored outburst scenario, tidal disruption of a
star by a supermassive black hole. We show that the detected `low-state'
emission has properties such that it must still be related to the flare. The
power-law shaped post-flare X-ray spectrum indicates a `hardening' compared to
outburst. The inferred black hole mass, the amount of liberated energy, and the
duration of the event favor an accretion event of the form expected from the
(partial or complete) tidal disruption of a star (abstract abbreviated).Comment: to appear in March 1 issue of ApJ Letters (submitted Nov. 10,
accepted in Dec. 2003); background information available at
http://www.xray.mpe.mpg.de/~skomossa
Comptonization in Super-Eddington Accretion Flow and Growth Timescale of Supermassive Black Holes
Super-Eddington accretion onto black holes (BHs) may occur at ultraluminous
compact X-ray sources in nearby galaxies, Galactic microquasars and narrow-line
Seyfert 1 galaxies (NLS1s). Effects of electron scattering (opacity and
Comptonization) and the relativistic correction (gravitational redshift and
transverse Doppler effect) on the emergent spectra from super-Eddington
accretion flows onto non-rotating BHs are examined for 10^{1.5} and 10^{6.5}
M_sun BH masses (M_BH). With mdot [= Mdot / (L_Edd / c^2), where Mdot is the
accretion rate] > 100, the spectral hardening factor via electron scattering is
\lesssim 2.3 - 6.5. Due to the mdot-sensitive hardening factor, the color
temperature of the innermost radiation is not proportional to L^{0.25},
differing from the simplest standard accretion disk. The model is applied to
optical--soft X-ray emission from NLS1s. We pick up one NLS1, namely PG
1448+273 with an inferred M_BH of 10^{6.4} M_sun, among the highest mdot
candidates. The broadband spectral distribution is successfully reproduced by
the model with an extremely high mdot (= 1000) and the viscosity parameter
alpha of 0.01. This implies that this object, as well as some other highest
mdot systems, is really young: the inferred age, M_BH / Mdot, is about 10^6
years. We also briefly discuss the distribution of mdot for transient and
highly variable NLS1s, finding that those are located at 3 \lesssim mdot
\lesssim 300. Such a moderately high accretion rate is indicative of thermal
instability. Furthermore, mdot for a possible type-2 counterpart of NLS1s, NGC
1068, is found to be similar to mdot for NLS1s.Comment: 16 pages (including 14 color figures), LaTeX emulateapj5.sty, The
Astrophysical Journal in press, corrected some typos and added reference
Physical education as Olympic education
Introduction
In a recent paper (Parry, 1998, p. 64), I argued that
the justification of PE activities lies in their capacity to facilitate the development of certain human excellences of a valued kind. Of course, the problem now lies in specifying those âhuman excellences of a valued kindâ, and (for anyone) this task leads us into the area of philosophical anthropology.
I suggested that the way forward for Physical Education lies in the philosophical anthropology (and the ethical ideals) of Olympism, which provide a specification of a variety of human values and excellences which:
âąhave been attractive to human groups over an impressive span of time and space
âąhave contributed massively to our historically developed conceptions of ourselves
âąhave helped to develop a range of artistic and cultural conceptions that have defined Western culture.
âąhave produced a range of physical activities that have been found universally satisfying and challenging.
Although physical activities are widely considered to be pleasurable, their likelihood of gaining wide acceptance lies rather in their intrinsic value, which transcends the simply hedonic or relative good. Their ability to furnish us with pleasurable experiences depends upon our prior recognition in them of opportunities for the development and expression of valued human excellences. They are widely considered to be such opportunities for the expression of valued human excellences because, even when as local instantiations, their object is to challenge our common human propensities and abilities.
I claimed that Olympic ideals may be seen not merely as inert âidealsâ, but living ideas which have the power to remake our notions of sport in education, seeing sport not as mere physical activity but as the cultural and developmental activity of an aspiring, achieving, well-balanced, educated and ethical individual.
This paper seeks to make good that claim by trying to develop a case for Physical Education as Olympic Education. I begin by setting out various accounts and conceptions of the Olympic Idea; then I suggest a unifying and organising account of the philosophical anthropology of Olympism; and this is followed by the practical application of that account in two examples of current ethical issues. Finally, I seek to present an account of Physical Education as Olympic Education
The first gamma-ray outburst of a Narrow-Line Seyfert 1 Galaxy: the case of PMN J0948+0022 in July 2010
We report on a multiwavelength campaign on the radio-loud Narrow-Line Seyfert
1 (NLS1) Galaxy PMN J0948+0022 (z=0.5846) performed in 2010 July-September and
triggered by a high-energy gamma-ray outburst observed by the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. The peak flux in
the 0.1-100 GeV energy band exceeded, for the first time in this type of
source, the value of 10^-6 ph cm^-2 s^-1, corresponding to an observed
luminosity of 10^48 erg s^-1. Although the source was too close to the Sun
position to organize a densely sampled follow-up, it was possible to gather
some multiwavelength data that confirmed the state of high activity across the
sampled electromagnetic spectrum. The comparison of the spectral energy
distribution of the NLS1 PMN J0948+0022 with that of a typical blazar - like 3C
273 - shows that the power emitted at gamma rays is extreme.Comment: 8 pages, 7 figures, 2 tables. Accepted for the publication on MNRAS
Main Journal. Typo in bibliography correcte
XMM-Newton spectroscopy of high redshift quasars
We present XMM-Newton X-ray spectra and optical photometry of four high
redshift (z=2.96-3.77) quasars, [HB89] 0438-436, [HB89] 2000-330, [SP89]
1107+487 and RX J122135.6+280613; of these four objects the former two are
radio-loud, the latter two radio-quiet. Model fits require only a power law
with Galactic absorption in each case; additional intrinsic absorption is also
needed for [HB89] 0438-436 and RX J122135.6+280613. The spectra are hard (Gamma
\~1.7 for [HB89] 0438-436, [HB89] 2000-330 and ~1.4 for RX J122135.6+280613)
with the exception of [SP89]~1107+487 which is softer (Gamma ~2.0); the
combined Galactic and intrinsic absorption of lower energy X-rays in the latter
source is much less significant than in the other three. The two intrinsically
unabsorbed sources have greater optical fluxes relative to the X-ray
contributions at the observed energies. While there is no need to include
reflection or iron line components in the models, our derived upper limits (99%
confidence) on these parameters are not stringent; the absence of these
features, if confirmed, may be explained in terms of the high power law
contribution and/or a potentially lower albedo due to the low disc temperature.
However, we note that the power-law spectrum can be produced via mechanisms
other than the Comptonization of accretion disc emission by a corona; given
that all four of these quasars are radio sources at some level we should also
consider the possibility that the X-ray emission originates, at least
partially, in a jet.Comment: Accepted for publication in MNRA
Broad-band properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
We report about recent updates of broad-band properties of radio-loud
narrow-line Seyfert 1 galaxies.Comment: 5 pages, no figures. Proceedings 28th Texas Symposium on Relativistic
Astrophysics, Geneva (Switzerland), 13-18 December 201
RXTE and XMM observations of intermediate polar candidates
Aims. To determine the credentials of nine candidate intermediate polars in order to confirm whether or not they are magnetic cataclysmic variables.
Methods. Frequency analysis of RXTE and XMM data was used to search for temporal variations which could be associated with the spin period of the magnetic white dwarf. X-ray spectral analysis was carried out to characterise the emission and absorption properties of each target.
Results. The hard X-ray light curve of V2069 Cyg shows a pulse period of 743.2 s, and its spectrum is fit by an absorbed bremsstrahlung model with an iron line, confirming this to be a genuine intermediate polar. The hard X-ray light curve of the previously confirmed intermediate polar IGR J00234+6141 is shown to be consistent with the previous low energy X-ray detection of a 563.5 s pulse period. The likely polar IGR J14536-5522 shows no coherent modulation at the previously identified period of 3.1 hr, but does exhibit a clear signal at periods likely to be harmonically related to it. Whilst our RXTE observations of RX J0153.3+7447, Swift J061223.0+701243.9, V436 Car and DD Cir are largely too faint to give any definitive results, the observation of IGR J16167-4957 and V2487 Oph show some characteristics of intermediate polars and these objects remain good candidates.
Conclusions. We confirmed one new hard X-ray selected intermediate polar from our sample, V2069 Cyg
The Spectral Energy Distribution and Emission-Line properties of the NLS1 Galaxy Arakelian 564
We present the intrinsic spectral energy distribution (SED) of the NLS1
Arakelian 564, constructed with contemporaneous data obtained during a
multi-wavelength, multi-satellite observing campaign in 2000 and 2001. We
compare it with that of the NLS1 Ton S180 and with those obtained for BLS1s to
infer how the relative accretion rates vary among the Sy1 population. Although
the peak of the SED is not well constrained, most of the energy is emitted in
the 10-100 eV regime, constituting roughly half of the emitted energy in the
optical/X-ray ranges. This is consistent with a primary spectral component
peaking in the extreme UV/soft X-ray band, and disk-corona models, hence high
accretion rates. Indeed, we estimate that \dot{m}~1. We examine the emission
lines in its spectrum, and we constrain the physical properties of the
line-emitting gas through photoionization modeling. The line-emitting gas is
characterized by log n~11 and log U~0, and is stratified around log U~0. Our
estimate of the radius of the H\beta-emitting region ~10 \pm 2 lt-days is
consistent with the radius-luminosity relationships found for Sy1 galaxies. We
also find evidence for super-solar metallicity in this NLS1. We show that the
emission lines are not good diagnostics for the underlying SEDs and that the
absorption line studies offer a far more powerful tool to determine the
ionizing continuum of AGNs, especially if comparing the lower- and
higher-ionization lines.Comment: 15 pages, 10 figures; accepted for publication in The Astrophysical
Journal, LaTeX emulateapj.st
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