953 research outputs found
Black Hole Winds
We show that black holes accreting at or above the Eddington rate probably
produce winds which are optically thick in the continuum, whether in quasars or
X-ray binaries. The photospheric radius and outflow speed are proportional to
\mo^2 and \mo^-1 respectively, where \mo is the mass outflow rate. The outflow
momentum rate is always of order L_Edd/c. Blackbody emission from these winds
may provide the big blue bump in some quasars and AGN, as well as ultrasoft
X-ray components in ULXs.Comment: 3 pages, no figures; MNRAS, in press (with minor corrections applied
A Comparison Of Small Mammal Communities Among Three Habitats In Western North Dakota
There is recent oil and natural gas development within western North Dakota, which makes it imperative to update outdated and incomplete small mammal records. Small mammals are vital components to many ecosystems, including grasslands. Small mammals contribute to grazing, seed dispersal, and provide food for other animals. I surveyed small mammals in three habitats, grassland, badland, and wet meadow, in the summers of 2014 and 2015 in western North Dakota. In 2014, I surveyed in 8 badland and 10 grassland habitats and in 2015 I surveyed in 1 badland, 13 grassland, and 4 wet meadow habitats, with 1 transect per site. Each transect consisted of museum special snap traps and pitfall arrays with drift fencing. The resulting shape of the array was a ‘Y’. Each array had 10 pitfalls and 90 snap traps. Arrays were operated for 5 consecutive nights over 18 sampling periods during 20 May to 26 July 2014 and 19 May to 25 July 2015; 9 in 2014 and 9 in 2015, for a total of 18,000 trap nights. A total of 708 small mammals were collected in 2014 and 397 small mammals were collected in 2015, with an overall total of 1,105 small mammals for both years. These included 978 rodent and 127 insectivore individuals. There was no difference in species diversity across habitats in 2014 and 2015. There were higher captures of small mammals during the new moon phase. There were no distinct small mammal communities across the 3 habitats. Due to the recent oil boom in western North Dakota, it is critical to assess which small mammals inhabit the area before the effects of the oil boom potentially destroy small mammal habitats
AGN have Underweight Black Holes and Reach Eddington
Eddington outflows probably regulate the growth of supermassive black holes
(SMBH) in AGN. I show that effect of the Rayleigh--Taylor instability on these
outflows means that SMBH masses are likely to be a factor of a few below the relation in AGN. This agrees with the suggestion by Batcheldor (2010)
that the relation defines an upper limit to the black hole mass. I
further argue that observed AGN black holes must spend much of their lives
accreting at the Eddington rate. This is already suggested by the low observed
AGN fraction amongst all galaxies despite the need to grow to the masses
required by the Soltan relation, and is reinforced by the suggested low SMBH
masses. Most importantly, this is the simplest explanation of the recent
discovery by Tombesi et al (2010a, b) of the widespread incidence of massive
ultrafast X--ray outflows in a large sample of AGN.Comment: MNRAS, in pres
Evidence of a high velocity ionised outflow in a second narrow line quasar PG0844+349
Following the discovery of X-ray absorption in a high velocity outflow from
the bright quasar PG1211+143 we have searched for similar features in XMM
archival data of a second (high accretion rate) quasar PG0844+349. Evidence is
found for absorption lines in both the EPIC and RGS spectra, whose
identification with resonance transitions in H-like Fe, S, and Ne implies an
origin in highly ionised matter with an outflow velocity of order ~0.2c. The
line equivalent widths require a line-of-sight column density of N_H ~ 4 x
10^23 cm^-2, at an ionisation parameter of log(xi) ~ 3.7. Assuming a radial
outflow being driven by radiation pressure from the inner accretion disc, as
suggested previously for PG1211+143, the flow is again likely to be optically
thick, in this case within ~ 25 Schwarzschild radii. We suggest that a high
velocity, highly ionised outflow is likely to be a significant component in the
mass and energy budgets of many AGN accreting at or above the Eddington rate.Comment: 7 pages, 4 figures, accepted by MNRA
X-ray astronomy in the new Millenium. A Summary
Recent X-ray observations have had a major impact on topics ranging from
protostars to cosmology. They have also drawn attention to important and
general physical processes that currently limit our understanding of thermal
and nonthermal X-ray sources. These include unmeasured atomic astrophysics data
(wavelengths, oscillator strengths etc.), basic hydromagnetic processes (e.g.
shock structure, reconnection), plasma processes (such as electron-ion
equipartition and heat conduction) and radiative transfer (in disks and
accretion columns). Progress on these problems will probably come from
integrative studies that draw upon observations, throughout the electromagnetic
spectrum, of different classes of source. X-ray observations are also giving a
new perspective on astronomical subjects, like the nature of galactic nuclei
and the evolution of stellar populations. They are contributing to answering
central cosmological questions including the measurement of the matter content
of the universe, understanding its overall luminosity density, describing its
chemical evolution and locating the first luminous objects. X-ray astronomy has
a healthy future with several international space missions under construction
and in development.Comment: 12 page
The End of the Black Hole Dark Ages, and Warm Absorbers
We consider how the radiation pressure of an accreting supermassive hole
(SMBH) affects the interstellar medium around it. Much of the gas originally
surrounding the hole is swept into a shell with a characteristic radius
somewhat larger than the black hole's radius of influence ( 1-100 pc).
The shell has a mass directly comparable to the () mass the hole
will eventually reach, and may have a complex topology. We suggest that
outflows from the central supermassive black holes are halted by collisions
with the shell, and that this is the origin of the warm absorber components
frequently seen in AGN spectra. The shell may absorb and reradiate some of the
black hole accretion luminosity at long wavelengths, implying both that the
bolometric luminosities of some known AGN may have been underestimated, and
that some accreting SMBH may have escaped detection entirely.Comment: accepted for MNRAS Letter
A simultaneous XMM-Newton and BeppoSAX observation of the archetypal Broad Line Seyfert 1 galaxy NGC 5548
We report the spectral analysis of a long XMM-Newton observation of the
well-studied, moderate luminosity Broad Line Seyfert 1 galaxy NGC 5548. The
source was at an historically average brightness and we find the hard (3-10
keV) spectrum can be well fitted by a power law of photon index gamma ~ 1.75,
together with reflection. The only feature in the hard X-ray spectrum is a
narrow emission line near 6.4 keV, with an equivalent width of ~ 60 eV. The
energy and strength of this line is consistent with fluorescence from `neutral'
iron distant from the central continuum source. We find no evidence for a broad
Fe K line, with an upper limit well below previous reports, suggesting the
inner accretion disc is now absent or highly ionised. The addition of
simultaneous BeppoSAX data allows the analysis to be extended to 200 keV,
yielding important constraints on the total reflection. Extrapolation of the
hard X-ray power law down to 0.3 keV shows a clear `soft excess' below ~ 0.7
keV. After due allowance for the effects of a complex warm absorber, measured
with the XMM-Newton RGS, we find the soft excess is better described as a
smooth upward curvature in the continuum flux below ~ 2 keV. The soft excess
can be modelled either by Comptonised thermal emission or by enhanced
reflection from the surface of a highly ionised disc.Comment: 9 pages, 11 figures, accepted by MNRAS; minor changes to text and
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A high velocity ionised outflow and XUV photosphere in the narrow emission line quasar PG1211+143
We report on the analysis of a ~60 ksec XMM observation of the bright, narrow
emission line quasar PG 1211+143. Absorption lines are seen in both EPIC and
RGS spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C.
The observed line energies indicate an ionised outflow velocity of ~24000 km
s^-1. The highest energy lines require a column density of N_H ~ 5 x 10^23
cm^-2, at an ionisation parameter of log(xi) ~ 3.4. If the origin of this high
velocity outflow lies in matter being driven from the inner disc, then the flow
is likely to be optically thick within a radius ~130 Schwarzschild radii,
providing a natural explanation for the Big Blue Bump (and strong soft X-ray)
emission in PG 1211+143.Comment: Accepted by MNRAS; Table 1 correcte
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