10,909 research outputs found
ROSAT monitoring of persistent giant and rapid variability in the narrow-line Seyfert 1 galaxy IRAS 13224-3809
We report evidence for persistent giant and rapid X-ray variability in the
radio-quiet, ultrasoft, strong Fe II, narrow-line Seyfert 1 galaxy IRAS
13224-3809. Within a 30 day ROSAT High Resolution Imager (HRI) monitoring
observation at least five giant amplitude count rate variations are visible,
with the maximum observed amplitude of variability being about a factor of 60.
We detect a rise by a factor of about 57 in just two days. IRAS 13224-3809
appears to be the most X-ray variable Seyfert known, and its variability is
probably nonlinear. We carefully check the identification of the highly
variable X-ray source with the distant galaxy, and it appears to be secure. We
examine possible explanations for the giant variability. Unusually strong
relativistic effects and partial covering by occulting structures on an
accretion disc can provide plausible explanations of the X-ray data, and we
explore these two scenarios. Relativistic boosting effects may be relevant to
understanding the strong X-ray variability of some steep spectrum Seyferts more
generally.Comment: 14 pages, submitted to MNRA
Soft X--Ray Properties of Seyfert Galaxies in the Rosat All--Sky Survey
We present the results of ROSAT All-Sky Survey observations of Seyfert and
IR-luminous galaxies from the Extended 12 Micron Galaxy Sample and the
optically-selected CfA Sample. Roughly half of the Seyferts (mostly Seyfert 1s)
have been fitted to an absorbed power-law model, yielding an average gamma of
2.26+-0.11 for 43 Seyfert 1s and 2.45+-0.18 for 10 Seyfert 2s, with both types
having a median value of 2.3.
The soft X-ray (SXR) luminosity correlates with the 12um luminosity, with
Seyfert 1s having relatively more SXR emission than Seyfert 2s of similar
mid-infrared luminosities, by a factor of 1.6+-0.3. Several physical
interpretations of these results are discussed, including the standard unified
model for Seyfert galaxies. Infrared-luminous non-Seyferts are shown to have
similar distributions of SXR luminosity and X-ray-to-IR slope as Seyfert 2s,
suggesting that some of them may harbor obscured active nuclei (as has already
been shown to be true for several objects) and/or that the soft X-rays from
some Seyferts 2s may be non-nuclear.
A SXR luminosity function (XLF) is calculated for the 12um sample, which is
well described by a single power-law with a slope of -1.75. The normalization
of this XLF agrees well with that of a HXR selected sample. Several of our
results, related to the XLF and the X-ray-to-IR relation are shown to be
consistent with the HXR observations of the 12um sample by Barcons et al.Comment: AASTeX, 40 pages. Text and Table 2 only. PostScript versions of this
file, figures, and Table 1, and a latex version of Table 1 are available by
ftp://ftp.astro.ucla.edu/pub/rush/papers, get rmfv*. Accepted by ApJ ~1996
May 10. Should be published in late 199
Autowaves in a dc complex plasma confined behind a de Laval nozzle
Experiments to explore stability conditions and topology of a dense
microparticle cloud supported against gravity by a gas flow were carried out.
By using a nozzle shaped glass insert within the glass tube of a dc discharge
plasma chamber a weakly ionized gas flow through a de Laval nozzle was
produced. The experiments were performed using neon gas at a pressure of 100 Pa
and melamine-formaldehyde particles with a diameter of 3.43 {\mu}m. The
capturing and stable global confining of the particles behind the nozzle in the
plasma were demonstrated. The particles inside the cloud behaved as a single
convection cell inhomogeneously structured along the nozzle axis in a tube-like
manner. The pulsed acceleration localized in the very head of the cloud
mediated by collective plasma-particle interactions and the resulting wave
pattern were studied in detail.Comment: 6 pages, 4 figure
Exact time-reversal focusing of acoustic and quantum excitations in open cavities: The perfect inverse filter
The time-reversal mirror (TRM) prescribes the reverse playback of a signal to
focalize an acoustic excitation as a Loschmidt echo. In the quantum domain, the
perfect inverse filter (PIF) processes this signal to ensure an exact reversion
provided that the excitation originated outside the cavity delimited by the
transducers. We show that PIF takes a simple form when the initial excitation
is created inside this cavity. This also applies to the acoustical case, where
it corrects the TRM and improves the design of an acoustic bazooka. We solve an
open chaotic cavity modeling a quantum bazooka and a simple model for a
Helmholtz resonator, showing that the PIF becomes decisive to compensate the
group velocities involved in a highly localized excitation and to achieve
subwavelength resolution.Comment: 6 pages, 2 figure
Bare electron dispersion from photoemission experiments
Performing an in-depth analysis of the photoemission spectra along the nodal
direction of the high temperature superconductor Bi-2212 we have developed a
procedure to determine the underlying electronic structure and established a
precise relation of the measured quantities to the real and imaginary parts of
the self-energy of electronic excitations. The self-consistency of the
procedure with respect to the Kramers-Kronig transformation allows us to draw
conclusions on the applicability of the spectral function analysis and on the
existence of well defined quasiparticles along the nodal direction even for the
underdoped Bi-2212 in the pseudogap state.Comment: 4 pages 3 figures revtex, corrected misprint
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