3,862 research outputs found
ROSAT Results on Narrow-Line Seyfert 1 Galaxies
The excellent soft X-ray sensitivity of the PSPC detector onboard the ROSAT
satellite provided the first chance to study precisely the spectral and timing
properties of Narrow-Line Seyfert 1 galaxies. ROSAT observations of Narrow-Line
Seyfert 1 galaxies have revealed (1) the existence of a giant soft X-ray
excess, (2) a striking, clear correlation between the strength of the soft
X-ray excess emission and the FWHM of the H-beta line, (3) the general absence
of significant soft X-ray absorption by neutral hydrogen above the Galactic
column, (4) short doubling time scales down to about 1000 seconds, (5) the
existence of persistent giant (above a factor of 10), and rapid (less than 1
day) X-ray variability in extragalactic sources. The soft X-ray results on
Narrow-Line Seyfert 1 galaxies indicate that their black hole regions are
directly visible, further supporting the Seyfert 1 nature of these objects. The
extreme X-ray properties of Narrow-Line Seyfert 1 galaxies make them ideal
objects for understanding many of the problems raised generally by the Seyfert
phenomenon.Comment: Invited talk presented at the Joint MPE,AIP,ESO workshop on NLS1s,
Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at
http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
Investigating ionized disc models of the variable narrow-line Seyfert 1 PG 1404+226
We investigate the use of relativistically blurred photoionized disc models
on an XMM-Newton observation of the Narrow Line Seyfert 1 galaxy PG 1404+226.
The model is designed to reproduce the radiation from the inner accretion disc
around a Kerr black hole, and is more successful at fitting the spectrum than
models based on a thermal soft excess. The source varies strongly over the
course of the observation, and the disc model works over all observed flux
states. We conclude that it is a useful tool in the study of certain quasars.Comment: 6 pages, 3 figures. Accepted for publication in MNRA
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
An intense soft-excess and evidence for light bending in the luminous narrow-line quasar PHL 1092
The narrow-line quasar PHL 1092 was observed by XMM-Newton at two epochs
separated by nearly thirty months. Timing analyses confirm the extreme
variability observed during previous X-ray missions. A measurement of the
radiative efficiency is in excess of what is expected from a Schwarzschild
black hole. In addition to the rapid X-ray variability, the short UV light
curves (< 4 hours) obtained with the Optical Monitor may also show
fluctuations, albeit at much lower amplitude than the X-rays. In general, the
extreme variability is impressive considering that the broad-band (0.4-10 keV
rest-frame) luminosity of the source is ~10^45 erg/s. During at least one of
the observations, the X-ray and UV light curves show common trends, although
given the short duration of the OM observations, and low significance of the UV
light curves it is difficult to comment on the importance of this possible
correlation. Interestingly, the high-energy photons (> 2 keV) do not appear
highly variable. The X-ray spectrum resembles that of many narrow-line Seyfert
1 type galaxies: an intense soft-excess modelled with a multi-colour disc
blackbody, a power-law component, and an absorption line at ~1.4 keV. The ~1.4
keV feature is curious given that it was not detected in previous observations,
and its presence could be related to the strength of the soft-excess. Of
further interest is curvature in the spectrum above ~2 keV which can be
described by a strong reflection component. The strong reflection component,
lack of high-energy temporal variability, and extreme radiative efficiency
measurements can be understood if we consider gravitational light bending
effects close to a maximally rotating black hole.Comment: To appear in MNRAS. Submitted March 01, 2004. 9 page
Buckling instability in type-II superconductors with strong pinning
We predict a novel buckling instability in the critical state of thin type-II
superconductors with strong pinning. This elastic instability appears in high
perpendicular magnetic fields and may cause an almost periodic series of flux
jumps visible in the magnetization curve. As an illustration we apply the
obtained criteria to a long rectangular strip.Comment: Submitted to Phys. Rev. Let
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