10,540 research outputs found
Radiative pressure feedback by a quasar in a galactic bulge
We show that Eddington-limited black hole luminosities can be sufficient to
deplete a galaxy bulge of gas through radiation pressure, when the ionization
state of the gas and the presence of dust are properly taken into account. Once
feedback starts to be effective it can consistently drive all the gas out of
the whole galaxy. We estimate the amount by which the effect of radiation
pressure on dusty gas boosts the mass involved in the Eddington limit and
discuss the expected column density at which the gas is ejected. An example is
shown of the predicted observed nuclear spectrum of the system at the end of an
early, obscured phase of growth when the remaining column density NH ~ f * 1e24
cm^-2 where f is the gas fraction in the bulge.Comment: correct corrupted figures in pdf version, MNRAS accepted, 5 pages, 3
figure
XMM-Newton observations of GB B1428+4217: confirmation of intrinsic soft X-ray absorption
We report the results of XMM-Newton observations of the X-ray bright,
radio-loud blazar GB B1428+4217 at a redshift of z=4.72. We confirm the
presence of soft X-ray spectral flattening at energies <0.7 keV as reported in
previous ROSAT and BeppoSAX observations. At hard X-ray energies the spectrum
is consistent with a power-law although we find the spectral slope varied
between both XMM-Newton observations and is also significantly different from
that reported previously. Whilst we cannot rule-out intrinsic cold absorption
to explain the spectral depression, we favour a dust-free warm absorber. Cold
absorption requires a column density ~1.4-1.6 x 10^22 cm^-2 whilst a warm
absorber could have up to ~10^23 cm^-2 and an ionization parameter ~10^2. The
spectrum of GB B1428+4217 shows remarkable parallels with that of the z=4.4
blazar PMN J0525-3343, in which the available evidence is also most consistent
with a warm absorber model.Comment: 5 pages, 5 figures, MNRAS accepted. Minor changes to sections 3.1 and
ROSAT PSPC detection of soft X-ray absorption in GB 1428+4217: The most distant matter yet probed with X-ray spectroscopy
We report on a ROSAT PSPC observation of the highly-luminous z = 4.72
radio-loud quasar GB 1428+4217 obtained between 1998 December 11 and 17, the
final days of the ROSAT satellite. The low-energy sensitivity of the PSPC
detector was employed to constrain the intrinsic X-ray absorption of the
currently most distant X-ray detected object. Here we present the detection of
significant soft X-ray absorption towards GB 1428+4217, making the absorbing
material the most distant matter yet probed with X-ray spectroscopy. X-ray
variability by 25+-8 per cent is detected on a timescale of 6500 s in the rest
frame. The X-ray variation requires an unusually high radiative efficiency of
at least 4.2, further supporting the blazar nature of the source.Comment: 6 pages incl. 6 figures, accepted for publication in Monthly Notice
Limits from rapid TeV variability of Mrk 421
The extreme variability event in the TeV emission of Mrk 421, recently
reported by the Whipple team, imposes the tightest limits on the typical size
of the TeV emitting regions in Active Galactic Nuclei (AGN). We examine the
consequences that this imposes on the bulk Lorentz factor of the emitting
plasma and on the radiation fields present in the central region of this Active
Nucleus. No strong evidence is found for extreme Lorentz factors. However,
energetics arguments suggest that any accretion in Mrk 421 has to take place at
small rates, compatible with an advection-dominated regime.Comment: 5 pages (Latex MNRAS style), revised version, submitted to MNRA
Electric field control of spin lifetimes in Nb-SrTiO by spin-orbit fields
We show electric field control of the spin accumulation at the interface of
the oxide semiconductor Nb-SrTiO with Co/AlO spin injection
contacts at room temperature. The in-plane spin lifetime as
well as the ratio of the out-of-plane to in-plane spin lifetime
is manipulated by the built-in electric field at
the semiconductor surface, without any additional gate contact. The origin of
this manipulation is attributed to Rashba Spin-Orbit Fields (SOFs) at the
Nb-SrTiO surface and shown to be consistent with theoretical model
calculations based on SOF spin flip scattering. Additionally, the junction can
be set in a high or low resistance state, leading to a non-volatile control of
, consistent with the manipulation of the Rashba SOF
strength. Such room temperature electric field control over the spin state is
essential for developing energy-efficient spintronic devices and shows promise
for complex oxide based (spin)electronicsComment: 5 pages, 4 figure
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