1,190 research outputs found
Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472
4U 1630-472 is a recurrent X-ray transient classified as a black-hole
candidate from its spectral and timing properties. One of the peculiarities of
this source is the presence of regular outbursts with a recurrence period
between 600 and 730 d that has been observed since the discovery of the source
in 1969. We report on a comparative study on the spectral and timing behaviour
of three consecutive outbursts occurred in 2006, 2008 and 2010. We analysed all
the data collected by the INTErnational Gamma-Ray Astrophysics Laboratory
(INTEGRAL) and the Rossi X-ray timing Explorer (RXTE) during these three years
of activity. We show that, in spite of having a similar spectral and timing
behaviour in the energy range between 3 and 30 keV, these three outbursts show
pronounced differences above 30 keV. In fact, the 2010 outburst extends at high
energies without any detectable cut-off until 150-200 keV, while the two
previous outbursts that occurred in 2006 and 2008 are not detected at all above
30 keV. Thus, in spite of a very similar accretion disk evolution, these three
outbursts exhibit totally different characteristics of the Compton electron
corona, showing a softening in their evolution rarely observed before in a low
mass X-ray binary hosting a black hole. We argue the possibility that the
unknown perturbation that causes the outbursts to be equally spaced in time
could be at the origin of this particular behaviour. Finally we describe
several possible scenarios that could explain the regularity of the outbursts,
identifying the most plausible, such as a third body orbiting around the binary
system.Comment: April 2015: accepted for publication in MNRAS. May 2015: in pres
Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472
4U 1630-472 is a recurrent X-ray transient classified as a black hole candidate from its spectral and timing properties. One of the peculiarities of this source is the presence of regular outbursts with a recurrence period between 600 and 730d that has been observed since the discovery of the source in 1969. We report on a comparative study of the spectral and timing behaviour of three consecutive outbursts that occurred in 2006, 2008 and 2010. We have analysed all the data collected by INTEGRAL and the Rossi X-ray Timing Explorer (RXTE) during these three years of activity. We show that, in spite of having a similar spectral and timing behaviour in the energy range between 3 and 30keV, these three outbursts show pronounced differences above 30keV. In fact, the 2010 outburst extends at high energies without any detectable cut-off until 150-200keV, while the two previous outbursts that occurred in 2006 and 2008 are not detected at all above 30keV. Thus, in spite of a very similar accretion disc evolution, these three outbursts exhibit totally different characteristics of the Compton electron corona, showing a softening in their evolution rarely observed before in a low-mass X-ray binary hosting a black hole. We argue the possibility that the unknown perturbation that causes the outbursts to be equally spaced in time could be at the origin of this particular behaviour. Finally, we describe several possible scenarios that could explain the regularity of the outbursts, identifying the most plausible, such as a third body orbiting around the binary syste
Decoupling social status and status certainty effects on health in macaques: a network approach.
BackgroundAlthough a wealth of literature points to the importance of social factors on health, a detailed understanding of the complex interplay between social and biological systems is lacking. Social status is one aspect of social life that is made up of multiple structural (humans: income, education; animals: mating system, dominance rank) and relational components (perceived social status, dominance interactions). In a nonhuman primate model we use novel network techniques to decouple two components of social status, dominance rank (a commonly used measure of social status in animal models) and dominance certainty (the relative certainty vs. ambiguity of an individual's status), allowing for a more complex examination of how social status impacts health.MethodsBehavioral observations were conducted on three outdoor captive groups of rhesus macaques (N = 252 subjects). Subjects' general physical health (diarrhea) was assessed twice weekly, and blood was drawn once to assess biomarkers of inflammation (interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and C-reactive protein (CRP)).ResultsDominance rank alone did not fully account for the complex way that social status exerted its effect on health. Instead, dominance certainty modified the impact of rank on biomarkers of inflammation. Specifically, high-ranked animals with more ambiguous status relationships had higher levels of inflammation than low-ranked animals, whereas little effect of rank was seen for animals with more certain status relationships. The impact of status on physical health was more straightforward: individuals with more ambiguous status relationships had more frequent diarrhea; there was marginal evidence that high-ranked animals had less frequent diarrhea.DiscussionSocial status has a complex and multi-faceted impact on individual health. Our work suggests an important role of uncertainty in one's social status in status-health research. This work also suggests that in order to fully explore the mechanisms for how social life influences health, more complex metrics of social systems and their dynamics are needed
Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939
We have searched and reviewed all multi- wavelength data available for the
region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain
its possible counterpart at lower energies. As a result, only a point-like
optical/infrared source with flat-spectrum radio emission is found to be
consistent with all X-ray and gamma-ray error circles. Its struc- ture is
marginally resolved at radio wavelengths at the sub-arcsecond level. An
extragalactic scenario appears to be the most likely interpretation for this
object.Comment: 5 pages, 3 figures, 1 tabl
Five new INTEGRAL unidentified hard X-Ray sources uncovered by Chandra
The IBIS imager on board INTEGRAL, with a sensitivity better than a mCrab in
deep observations and a point source location accuracy of the order of few
arcminutes, has localized so far 723 hard X-ray sources in the 17--100 keV
energy band, of which a fraction of about 1/3 are still unclassified. The aim
of this research is to provide sub-arcsecond localizations of the unidentified
sources, necessary to pinpoint the optical and/or infrared counterpart of those
objects whose nature is so far unknown. The cross-correlation between the new
IBIS sources published within the fourth INTEGRAL/IBIS Survey catalogue and the
CHANDRA/ACIS data archive resulted in a sample of 5 not yet identified objects.
We present here the results of CHANDRA X-ray Observatory observations of these
five hard X-ray sources discovered by the INTEGRAL satellite. We associated IGR
J10447-6027 with IR source 2MASSJ10445192-6025115, IGR J16377-6423 with the
cluster CIZA J1638.2-6420, IGR J14193-6048 with the pulsar with nebula PSR
J1420-6048 and IGR J12562+2554 with the Quasar SDSSJ125610.42+260103.5. We
suggest that the counterpart of IGR J12288+0052 may be an AGN/QSO type~2 at a
confidence level of 90%.Comment: ApJ accepte
GMRT observations of the field of INTEGRAL X-ray sources- II (newly discovered hard X-ray sources)
We have conducted low-frequency radio observations with the Giant Metrewave
Radio Telescope (GMRT) of 40 new hard X-ray sources discovered by the INTEGRAL
satellite. This survey was conducted in order, to study radio emissions from
these sources, to provide precise position and to identify new microquasar
candidates. From our observations we find that 24 of the X-ray sources have
radio candidates within the INTEGRAL error circle. Based on the radio
morphology, variability and information available from different wavelengths,
we categorize them as seventeen Galactic sources (4 unresolved, 7 extended, 6
extended sources in diffuse region) and seven extragalactic sources (2
unresolved, 5 extended). Detailed account for seventeen of these sources was
presented in earlier paper. Based on the radio data for the remaining sources
at 0.61 GHz, and the available information from NVSS, DSS, 2MASS and NED, we
have identified possible radio counterparts for the hard X-ray sources. The
three unresolved sources, viz IGR J173030601, IGR J174643213, and IGR
J184060539 are discussed in detail. These sources have been identified as
X-ray binaries with compact central engine and variable in X-ray and in the
radio, and are most likely microquasar candidates. The remaining fourteen
sources have extended radio morphology and are either diffuse Galactic regions
or extragalactic in origin.Comment: 9 pages, 7 figures, submitted to A&A. submitted to A&
Targeting Endoplasmic Reticulum and/or Mitochondrial Ca2+ Fluxes as Therapeutic Strategy for HCV Infection.
Chronic hepatitis C is characterized by metabolic disorders and by a microenvironment in the liver dominated by oxidative stress, inflammation and regeneration processes that can in the long term lead to liver cirrhosis and hepatocellular carcinoma. Several lines of evidence suggest that mitochondrial dysfunctions play a central role in these processes. However, how these dysfunctions are induced by the virus and whether they play a role in disease progression and neoplastic transformation remains to be determined. Most javax.xml.bind.JAXBElement@5b15fc8d studies performed so far have shown that several of the hepatitis C virus (HCV) proteins also localize to mitochondria, but the consequences of these interactions on mitochondrial functions remain contradictory and need to be confirmed in the context of productively replicating virus and physiologically relevant javax.xml.bind.JAXBElement@5e13485c and javax.xml.bind.JAXBElement@73aee95e model systems. In the past decade we have been proposing a temporal sequence of events in the HCV-infected cell whereby the primary alteration is localized at the mitochondria-associated ER membranes and causes release of Ca javax.xml.bind.JAXBElement@476155bf from the ER, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen and nitrogen species and a progressive metabolic adaptive response consisting in decreased oxidative phosphorylation and enhanced aerobic glycolysis and lipogenesis. Here we resume the major results provided by our group in the context of HCV-mediated alterations of the cellular inter-compartmental calcium flux homeostasis and present new evidence suggesting targeting of ER and/or mitochondrial calcium transporters as a novel therapeutic strategy
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