21 research outputs found
On the Role of the Accretion Disk in Black Hole Disk-Jet Connections
Models of jet production in black hole systems suggest that the properties of
the accretion disk - such as its mass accretion rate, inner radius, and
emergent magnetic field - should drive and modulate the production of
relativistic jets. Stellar-mass black holes in the "low/hard" state are an
excellent laboratory in which to study disk-jet connections, but few
coordinated observations are made using spectrometers that can incisively probe
the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1
made in the jet-producing low/hard state. Contemporaneous radio monitoring was
done using the Arcminute MicroKelvin Array radio telescope. Two important and
simple results are obtained: (1) the jet (as traced by radio flux) does not
appear to be modulated by changes in the inner radius of the accretion disk;
and (2) the jet is sensitive to disk properties, including its flux,
temperature, and ionization. Some more complex results may reveal aspects of a
coupled disk-corona-jet system. A positive correlation between the reflected
X-ray flux and radio flux may represent specific support for a plasma ejection
model of the corona, wherein the base of a jet produces hard X-ray emission.
Within the framework of the plasma ejection model, the spectra suggest a jet
base with v/c ~ 0.3, or the escape velocity for a vertical height of z ~ 20
GM/c^2 above the black hole. The detailed results of X-ray disk continuum and
reflection modeling also suggest a height of z ~ 20 GM/c^2 for hard X-ray
production above a black hole, with a spin in the range 0.6 < a < 0.99. This
height agrees with X-ray time lags recently found in Cygnus X-1. The overall
picture that emerges from this study is broadly consistent with some
jet-focused models for black hole spectral energy distributions in which a
relativistic plasma is accelerated at z = 10-100 GM/c^2.Comment: Accepted for publication in Ap
A Swift survey of accretion onto stellar-mass black holes
We present a systemic analysis of all of the stellar mass black hole binaries
(confirmed & candidate) observed by the Swift observatory up to June 2010. The
broad Swift bandpass enables a trace of disk evolution over an unprecedented
range in flux and temperature. The final data sample consists of 476 X-ray
spectra containing greater than 100 counts, in the 0.6 -- 10 keV band. This is
the largest sample of high quality CCD spectra of accreting black holes
published to date. In addition, strictly simultaneous data at optical/UV
wavelengths are available for 255 (54%) of these observations.
The data are modelled with a combination of an accretion disk and a hard
spectral component. For the hard component we consider both a simple power-law
and a thermal Comptonization model. An accretion disk is detected at greater
than the 5sigma confidence level in 61% of the observations. Lightcurves and
color-color diagrams are constructed for each system. Hardness luminosity and
disk fraction luminosity diagrams are constructed and are observed to be
consistent with those typically observed by RXTE, noting the sensitivity below
2 keV provided by Swift. The observed spectra have an average luminosity of ~
1% Eddington, though we are sensitive to accretion disks down to a luminosity
of 10^{-3} L_Edd. Thus this is also the largest sample of such cool accretion
disks studied to date. (abridged)Comment: 28 pages, 5 tables, 21 figures, Accepted for publication in ApJ. This
is the final revised versio
A census of X-ray nuclear activity in nearby galaxies
We have studied the X-ray nuclear activity of 187 nearby (distance < 15 Mpc)
galaxies observed with Chandra/ACIS. We found that 86 of them have a point-like
X-ray core, consistent with an accreting black hole (BH). We argue that the
majority of them are nuclear BHs, rather than X-ray binaries. The fraction of
galaxies with an X-ray detected nuclear BH is higher (~60 per cent) for
ellipticals and early-type spirals (E to Sb), and lower (~30 per cent) for
late-type spirals (Sc to Sm). There is no preferential association of X-ray
cores with a large-scale bar; in fact, strongly barred galaxies appear to have
slightly lower detection fraction and luminosity for their nuclear X-ray
sources, compared with non-barred or weakly barred galaxies of similar Hubble
types. The cumulative luminosity distribution of the nuclear sources in the
0.3-8 keV band is a power-law with slope ~-0.5, from ~2 x 10^{38} erg/s to
~10^{42} erg/s. The Eddington ratio is lower for ellipticals (L_{X}/L_{Edd} ~
10^{-8}) and higher for late-type spirals (up to L_{X}/L_{Edd} ~ 10^{-4}), but
in all cases, the accretion rate is low enough to be in the
radiatively-inefficient regime. The intrinsic NH is generally low, especially
for the less luminous sources: there appear to be no Type-2 nuclear BHs at
luminosities <~ 10^{39} erg/s. The lack of a dusty torus or of other sources of
intrinsic absorption (e.g., an optically-thick disk wind) may be directly
related to the lack of a standard accretion disk around those faint nuclear
BHs. The fraction of obscured sources increases with the nuclear BH luminosity:
2/3 of the sources with L_{X} > 10^{40} erg/s have a fitted NH > 10^{22}
cm^{-2}. This is contrary to the declining trend of the obscured fraction with
increasing luminosities, observed in more luminous AGN and quasars.Comment: 27 pages, 353 kB, accepted by Ap
Acetylsalicylic acid and ascorbic acid combination improves cognition; Via antioxidant effect or increased expression of NMDARs and nAChRs?
Chronic inflammation occurs systematically in the central nervous system during ageing, it has been shown that neuroinflammation plays an important role in the pathogenesis of many neurodegenerative disorders. Aspirin, a nonselective COX inhibitor, as well as ascorbic acid, has been purported to protect cerebral tissue. We investigated the effects of subchronic aspirin and ascorbic acid usage on spatial learning, oxidative stress and expressions of NR2A, NR2B, nAChR alpha 7, alpha 4 and beta 2. Forty male rats (16-18 months) were divided into 4 groups, namely, control, aspirin-treated, ascorbic acid-treated, aspirin + ascorbic acid-treated groups. Following 10-weeks administration period, rats were trained and tested in the Morris water maze. 8-Hydroxy-2-deoxyguanosine and malondialdehyde were evaluated by ELISA and HPLC, respectively. Receptor expressions were assessed by western blotting of hippocampi. Spatial learning performance improved partially in the aspirin group, but significant improvement was seen in the aspirin + ascorbic acid group (p < 0.05). While 8-hydroxy-2-deoxyguanosine and malondialdehyde levels were significantly decreased, NR2B and nAChRa7 expressions were significantly increased in the aspirin + ascorbic acid group as compared to the control group (p < 0.05). Subchronic treatment with aspirin + ascorbic acid in aged rats was shown to enhance cognitive performance and increase the expressions of several receptors related to learning and memory process. (C) 2014 Elsevier B.V. All rights reserved
Effects of maternally exposed coloring food additives on receptor expressions related to learning and memory in rats
Exposure to artificial food colors and additives (AFCAs) has been implicated in the induction and severity of some childhood behavioral and learning disabilities. N-methyl-D-aspartate receptors (NMDARs) and nicotinic acetylcholine receptors (nACHRs) are thought to be effective in the learning and memory-generating process. In this study, we investigated the effects of intrauterine exposure to AFCAs on subunit concentrations of NMDARs and nAChRs isoforms in rats. We administered a mixture of AFCAs (Eritrosin, Ponceau 4R, Allura Red AC, Sunset Yellow FCF, Tartrazin, Amaranth, Brilliant Blue, Azoruhin and Indigotin) to female rats before and during gestation. The concentration of NR2A and NR2B subunits and nAChR alpha 7, alpha 4 beta 2 isoforms in their offspring's hippocampi were measured by Western Blotting. Expressions of NR2B and nAChR beta 2 were significantly increased (17% and 6.70%, respectively), whereas expression of nAChR alpha 4 was significantly decreased (5.67%) in male experimental group compared to the male control group (p < 0.05). In the female experimental group, AFCAs caused a 14% decrease in NR2B expression when compared to the female control group (p < 0.05). Our results indicate that exposure to AFCAs during the fetal period may lead to alterations in expressions of NMDARs and nAChRs in adulthood. These alterations were different between male and female genders. (C) 2013 Elsevier Ltd. All rights reserved
Effects of maternally exposed coloring food additives on receptor expressions related to learning and memory in rats
Exposure to artificial food colors and additives (AFCAs) has been implicated in the induction and severity of some childhood behavioral and learning disabilities. N-methyl-D-aspartate receptors (NMDARs) and nicotinic acetylcholine receptors (nACHRs) are thought to be effective in the learning and memory-generating process. In this study, we investigated the effects of intrauterine exposure to AFCAs on subunit concentrations of NMDARs and nAChRs isoforms in rats. We administered a mixture of AFCAs (Eritrosin, Ponceau 4R, Allura Red AC, Sunset Yellow FCF, Tartrazin, Amaranth, Brilliant Blue, Azoruhin and Indigotin) to female rats before and during gestation. The concentration of NR2A and NR2B subunits and nAChR alpha 7, alpha 4 beta 2 isoforms in their offspring's hippocampi were measured by Western Blotting. Expressions of NR2B and nAChR beta 2 were significantly increased (17% and 6.70%, respectively), whereas expression of nAChR alpha 4 was significantly decreased (5.67%) in male experimental group compared to the male control group (p < 0.05). In the female experimental group, AFCAs caused a 14% decrease in NR2B expression when compared to the female control group (p < 0.05). Our results indicate that exposure to AFCAs during the fetal period may lead to alterations in expressions of NMDARs and nAChRs in adulthood. These alterations were different between male and female genders. (C) 2013 Elsevier Ltd. All rights reserved
Are there any remarkable effects of prenatal exposure to food colourings on neurobehaviour and learning process in rat offspring?
Objective: Artificial food colourings and additives (AFCAs) have long been discussed to have adverse effects on cognition and behaviour in children. In this study, our aim was to assess the probable side effects of prenatal exposure to colouring food additives on neurobehaviour and spatial learning process
Prenatal exposure to artificial food colorings alters NMDA receptor subunit concentrations in rat hippocampus
Exposure to artificial food color additives (AFCAs) has been implicated in the etiology of certain childhood hyperactivity and learning disabilities. N-methyl-D-aspartate receptors and alpha-7 nicotinic acetylcholine receptor (alpha 7 nAChR) are involved in learning and memory. We administered a mixture of AFCAs (erythrosine, ponceau 4R, allura red AC, sunset yellow FCF, tartrazine, amaranth, brilliant blue, azorubine, and indigotine) to female rats during gestation to investigate the effects of prenatal exposure to AFCAs on neurobehavior, spatial learning, and memory in their offspring. We also investigated whether AFCAs modulate NR2A, NR2B, and alpha 7 nAChR protein levels in their offsprings' hippocampi. Although spatial learning and memory were not altered, the offspring of rats exposed to AFCAs exhibited decreased motivation and increased despair-related behavior. NR2A and NR2B protein levels were significantly reduced in female offspring in the experimental group (p < 0.05), whereas alpha 7 nAChR level was not significantly altered. Our results suggest that prenatal exposure to AFCAs may lead to sex-dependent alterations in glutamatergic signaling which may continue into adolescence