963 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
The accretion environment of Supergiant Fast X-ray Transients probed with XMM-Newton
Supergiant fast X-ray transients (SFXTs) are characterized by a remarkable
variability in the X-ray domain, widely ascribed to the accretion from a clumpy
stellar wind. In this paper we performed a systematic and homogeneous analysis
of sufficiently bright X-ray flares from the SFXTs observed with XMM-Newton to
probe spectral variations on timescales as short as a few hundred of seconds.
Our ultimate goal is to investigate if SFXT flares and outbursts are triggered
by the presence of clumps and eventually reveal whether strongly or mildly
dense clumps are required. For all sources, we employ a technique developed by
our group, making use of an adaptive rebinned hardness ratio to optimally
select the time intervals for the spectral extraction. A total of twelve
observations performed in the direction of five SFXTs are reported. We show
that both strongly and mildly dense clumps can trigger these events. In the
former case, the local absorption column density may increase by a factor of
>>3, while in the latter case, the increase is only by a factor of 2-3 (or
lower). Overall, there seems to be no obvious correlation between the dynamic
ranges in the X-ray fluxes and absorption column densities in SFXTs, with an
indication that lower densities are recorded at the highest fluxes. This can be
explained by the presence of accretion inhibition mechanism(s). We propose a
classification of the flares/outbursts from these sources to drive future
observational investigations. We suggest that the difference between the
classes of flares/outbursts is related to the fact that the mechanism(s)
inhibiting accretion can be overcome more easily in some sources compared to
others. We also investigate the possibility that different stellar wind
structures, rather than clumps, could provide the means to temporarily overcome
the inhibition of accretion in SFXTs.Comment: Accepted for publication on A&
The first outburst of the black hole candidate MAXI J1836-194 observed by INTEGRAL, Swift, and RXTE
MAXI J1836-194 is a transient black-hole candidate discovered in outburst by
MAXI on 30 August 2011. We report on the available INTEGRAL, Swift, and RXTE
observations performed in the direction of the source during this event before
55 864 MJD. Combining the broad band (0.6-200 keV) spectral and timing
information obtained from these data with the results of radio observations, we
show that the event displayed by MAXI J1836-194 is another example of "failed"
outburst. During the first ~20 days after the onset of the event, the source
underwent a transition from the canonical low/hard to the hard intermediate
state, while reaching the highest X-ray flux. In the ~40 days following the
peak of the outburst, the source displayed a progressive spectral hardening and
a decrease of the X-ray flux, thus it entered again the low/hard state and
began its return to quiescence.Comment: Accepted for A&A Letters on 22 Dec. 201
Broad-band characteristics of seven new hard X-ray selected cataclysmic variables
Indexación: Web of Science; Scopus.We present timing and spectral analysis of a sample of seven hard X-ray selected cataclysmic
variable candidates based on simultaneous X-ray and optical observations collected
with XMM–Newton, complemented with Swift/BAT and INTEGRAL /IBIS hard X-ray data
and ground-based optical photometry. For six sources, X-ray pulsations are detected for the
first time in the range of ∼296–6098 s, identifying them as members of the magnetic class.
Swift J0927.7−6945, Swift J0958.0−4208, Swift J1701.3−4304, Swift J2113.5+5422 and
possibly PBC J0801.2−4625 are intermediate polars (IPs), while Swift J0706.8+0325 is a
short (1.7 h) orbital period polar, the 11th hard X-ray-selected identified so far. X-ray orbital
modulation is also observed in Swift J0927.7−6945 (5.2 h) and Swift J2113.5+5422
(4.1 h). Swift J1701.3−4304 is discovered as the longest orbital period (12.8 h) deep eclipsing
IP. The spectra of the magnetic systems reveal optically thin multitemperature emission
between 0.2 and 60 keV. Energy-dependent spin pulses and the orbital modulation in
Swift J0927.7−6945 and Swift J2113.5+5422 are due to intervening local high-density absorbing
material (NH ∼ 1022 − 23 cm−2). In Swift J0958.0−4208 and Swift J1701.3−4304, a
soft X-ray blackbody (kT ∼ 50 and ∼80 eV) is detected, adding them to the growing group
of ‘soft’ IPs. White dwarf masses are determined in the range of ∼0.58–1.18 M, indicating
massive accreting primaries in five of them. Most sources accrete at rates lower than the
expected secular value for their orbital period. Formerly proposed as a long-period (9.4 h)
nova-like CV, Swift J0746.3−1608 shows peculiar spectrum and light curves suggesting either
an atypical low-luminosity CV or a low-mass X-ray binary.https://academic.oup.com/mnras/article/470/4/4815/390658
Textiles, body care products, amenity horticulture and energy production
Food production is the most evident result of Organic Farming. However, farm products are used for other human needs. Some of those Organic sectors beyond food, e.g. the amenity horticulture are in an early stage of development, but have big potentials. Awareness inside and outside of the Organic world and development of the value chain need to be further developed. Other Organic sectors beyond food, e.g. Organic cotton have made impressive progress during the past few years
IGRJ17361-4441: a possible new accreting X-ray binary in NGC6388
IGRJ17361-4441 is a newly discovered INTEGRAL hard X-ray transient, located
in the globular cluster NGC6388. We report here the results of the X-ray and
radio observations performed with Swift, INTEGRAL, RXTE, and the Australia
Telescope Compact Array (ATCA) after the discovery of the source on 2011 August
11. In the X-ray domain, IGRJ17361-4441 showed virtually constant flux and
spectral parameters up to 18 days from the onset of the outburst. The
broad-band (0.5-100 keV) spectrum of the source could be reasonably well
described by using an absorbed power-law component with a high energy cut-off
(N_H\simeq0.8x10^(22) cm^(-2), {\Gamma}\simeq0.7-1.0, and E_cut\simeq25 keV)
and displayed some evidence of a soft component below \sim2 keV. No coherent
timing features were found in the RXTE data. The ATCA observation did not
detect significant radio emission from IGRJ17361-4441, and provided the most
stringent upper limit (rms 14.1 {\mu}Jy at 5.5 GHz) to date on the presence of
any radio source close to the NGC6388 center of gravity. The improved position
of IGRJ17361-4441 in outburst determined from a recent target of opportunity
observation with Chandra, together with the X-ray flux and radio upper limits
measured in the direction of the source, argue against its association with the
putative intermediate-mass black hole residing in the globular cluster and with
the general hypothesis that the INTEGRAL source is a black hole candidate.
IGRJ17361-4441 might be more likely a new X-ray binary hosting an accreting
neutron star. The ATCA radio non-detection also permits us to derive an upper
limit to the mass of the suspected intermediate massive black hole in NGC6388
of <600 M\odot. This is a factor of 2.5 lower than the limit reported
previously.Comment: Accepted for publication on A&A lette
Quantitative dominances of taxa structuring the macrozoobenthic communities living in different coastal habitats.
The aim of this study was to quantify the dominance of macrozoobenthic taxa structuring the benthic assemblages associated to 6 coastal habitats, which occur from the mesolittoral to the circalittoral zone of the Campania coast. Crustaceans, polychaetes and molluscs were the main taxonomic groups structuring all the benthic assemblages, representing an average of 89.20% of the total taxa. However, each habitat showed the dominance of only one peculiar taxon
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
Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
In this paper, we report on the analysis of the peculiar X-ray variability
displayed by the accreting millisecond X-ray pulsar IGR J00291+5934 in a 80
ks-long joint NuSTAR and XMM-Newton observation performed during the source
outburst in 2015. The light curve of the source was characterized by a
flaring-like behavior, with typical rise and decay time scales of ~120 s. The
flares are accompanied by a remarkable spectral variability, with the X-ray
emission being generally softer at the peak of the flares. A strong quasi
periodic oscillation (QPO) is detected at ~8 mHz in the power spectrum of the
source and clearly associated with the flaring-like behavior. This feature has
the strongest power at soft X-rays (<3 keV). We carried out a dedicated
hardness-ratio resolved spectral analysis and a QPO phase-resolved spectral
analysis, together with an in-depth study of the source timing properties, to
investigate the origin of this behavior. We suggest that the unusual
variability of IGR J00291+5934 observed by XMM-Newton and NuSTAR could be
produced by an heartbeat-like mechanism, similar to that operating in
black-hole X-ray binaries. The possibility that this variability, and the
associated QPO, are triggered by phases of quasi-stable nuclear burning, as
suggested in the literature for a number of other neutron star binaries
displaying a similar behavior, cannot be solidly tested in the case of IGR
J00291+5934 due to the paucity of type-I X-ray bursts observed from this
source.Comment: Submitted to MNRAS on 23 Sept 2016. Modified according to the
referee's suggestions. Comments are welcomed. One reference updated in this
versio
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