756 research outputs found
The X-ray spectral properties of very-faint persistent neutron star X-ray binaries
AX J1754.2-2754, 1RXS J171824.2-402934 and 1RXH J173523.7-354013 are three
persistent neutron star low-mass X-ray binaries that display a 2--10 keV
accretion luminosity Lx of only (1-10)x1E34 erg s-1 (i.e., only ~0.005-0.05 %
of the Eddington limit). The phenomenology of accreting neutron stars which
accrete at such low accretion rates is not yet well known and the reason why
they have such low accretion rates is also not clear. Therefore, we have
obtained XMM-Newton data of these three sources and here we report our analysis
of the high-quality X-ray spectra we have obtained for them. We find that AX
J1754.2-2754 has Lx~1E35 erg s-1, while the other two have X-ray luminosities
about an order of magnitude lower. However, all sources have a similar,
relatively soft, spectrum with a photon index of 2.3-2.5, when the spectrum is
fitted with an absorbed power-law model. This model fits the data of AX
J1754.2-2754 adequately, but it cannot fit the data obtained for 1RXS
J171824.2-402934 and 1RXH J173523.7-354013. For those sources a clear soft
thermal component is needed to fit their spectra. This soft component
contributes 40% - 50% to the 0.5-10 keV flux of the sources. When including
this additional spectral component, the power-law photon indices are
significantly lower. It can be excluded that a similar component with similar
contributions to the 2-10 keV X-ray flux is present for AX J1754.2-2754,
indicating that the soft spectrum of this source is mostly due to the fact that
the power-law component itself is not hard. We note that we cannot excluded
that weaker soft component is present in the spectrum of this source which only
contributes up to ~25% to the 0.5-10 keV X-ray flux. We discuss our results in
the context of what is known of accreting neutron stars at very low accretion
rate.Comment: 9 pages, 2 tables, 1 figure. Aceppted for publication in MNRA
XMM-Newton and Swift spectroscopy of the newly discovered very-faint X-ray transient IGR J17494-3030
A growing group of low-mass X-ray binaries are found to be accreting at
very-faint X-ray luminosities of <1E36 erg/s (2-10 keV). Once such system is
the new X-ray transient IGR J17494-3030. We present Swift and XMM-Newton
observations obtained during its 2012 discovery outburst. The Swift
observations trace the peak of the outburst, which reached a luminosity of ~7
E35 (D/8 kpc)^2 erg/s (2-10 keV). The XMM-Newton data were obtained when the
outburst had decayed to an intensity of ~ 8 E34 (D/8 kpc)^2 erg/s. The spectrum
can be described by a power-law with an index of ~1.7 and requires an
additional soft component with a black-body temperature of ~0.37 keV
(contributing ~20% to the total unabsorbed flux in the 0.5-10 keV band). Given
the similarities with high-quality spectra of very-faint neutron star low-mass
X-ray binaries, we suggest that the compact primary in IGR J17494-3030 is a
neutron star. Interestingly, the source intensity decreased rapidly during the
~12 hr XMM-Newton observation, which was accompanied by a decrease in inferred
temperature. We interpret the soft spectral component as arising from the
neutron star surface due to low-level accretion, and propose that the observed
decline in intensity was the result of a decrease in the mass-accretion rate
onto the neutron star.Comment: 3 figures, 2 tables, accepted in MNRAS letter, in pres
An X-ray view of the very faint black hole X-ray transient Swift J1357.2-0933 during its 2011 outburst
We report on the X-ray spectral (using XMM-Newton data) and timing behavior
(using XMM-Newton and Rossi X-ray Timing Explorer [RXTE] data) of the very
faint X-ray transient and black hole system Swift J1357.2-0933 during its 2011
outburst. The XMM-Newton X-ray spectrum of this source can be adequately fitted
with a soft thermal component with a temperature of ~0.22 keV (using a disc
model) and a hard, non-thermal component with a photon index of ~1.6 when using
a simple power-law model. In addition, an edge at ~ 0.73 keV is needed likely
due to interstellar absorption. During the first RXTE observation we find a 6
mHz quasi-periodic oscillation (QPO) which is not present during any of the
later RXTE observations or during the XMM-Newton observation which was taken 3
days after the first RXTE observation. The nature of this QPO is not clear but
it could be related to a similar QPO seen in the black hole system H 1743-322
and to the so-called 1 Hz QPO seen in the dipping neutron-star X-ray binaries
(although this later identification is quite speculative). The observed QPO has
similar frequencies as the optical dips seen previously in this source during
its 2011 outburst but we cannot conclusively determine that they are due to the
same underlying physical mechanism. Besides the QPO, we detect strong
band-limited noise in the power-density spectra of the source (as calculated
from both the RXTE and the XMM-Newton data) with characteristic frequencies and
strengths very similar to other black hole X-ray transients when they are at
low X-ray luminosities. We discuss the spectral and timing properties of the
source in the context of the proposed very high inclination of this source. We
conclude that all the phenomena seen from the source cannot, as yet, be
straightforwardly explained neither by an edge-on configuration nor by any
other inclination configuration of the orbit.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in MNRA
Swift J1357.2-0933: the faintest black hole?
Swift J1357.2-0933 is the first confirmed very faint black hole X-ray
transient and has a short estimated orbital period of 2.8 hr. We observed Swift
J1357.2-0933 for ~50 ks with XMM-Newton in 2013 July during its quiescent
state. The source is clearly detected at a 0.5-10 keV unabsorbed flux of
~3x10^-15 erg cm-2 s-1. If the source is located at a distance of 1.5 kpc (as
suggested in the literature), this would imply a luminosity of ~8x10^29 erg
s-1, making it the faintest detected quiescent black hole LMXB. This would also
imply that there is no indication of a reversal in the quiescence X-ray
luminosity versus orbital period diagram down to 2.8 hr, as has been predicted
theoretically and recently supported by the detection of the 2.4 hr orbital
period black hole MAXI J1659-152 at a 0.5-10 keV X-ray luminosity of ~ 1.2 x
10^31 erg s-1. However, there is considerable uncertainty in the distance of
Swift J1357.2-0933 and it may be as distant as 6 kpc. In this case, its
quiescent luminosity would be Lx ~ 1.3 x 10^31 erg s-1, i.e., similar to MAXI
J1659-152 and hence it would support the existence of such a bifurcation
period. We also detected the source in optical at r' ~22.3 mag with the
Liverpool telescope, simultaneously to our X-ray observation. The X-ray/optical
luminosity ratio of Swift J1357.2-0933 agrees with the expected value for a
black hole at this range of quiescent X-ray luminosities.Comment: 5 pages, 3 figures, Accepted for publication in MNRA
Low-level accretion in neutron-star X-ray binaries
We search the literature for reports on the spectral properties of
neutron-star low-mass X-ray binaries when they have accretion luminosities
between 1E34 and 1E36 ergs/s. We found that in this luminosity range the photon
index (obtained from fitting a simple absorbed power-law in the 0.5-10 keV
range) increases with decreasing 0.5-10 keV X-ray luminosity (i.e., the
spectrum softens). Such behaviour has been reported before for individual
sources, but here we demonstrate that very likely most (if not all)
neutron-star systems behave in a similar manner and possibly even follow a
universal relation. When comparing the neutron-star systems with black-hole
systems, it is clear that most black-hole binaries have significantly harder
spectra at luminosities of 1E34 - 1E35 erg/s. Despite a limited number of data
points, there are indications that these spectral differences also extend to
the 1E35 - 1E36 erg/s range. This observed difference between the neutron-star
binaries and black-hole ones suggests that the spectral properties (between
0.5-10 keV) at 1E34 - 1E35 erg/s can be used to tentatively determine the
nature of the accretor in unclassified X-ray binaries. We discuss our results
in the context of properties of the accretion flow at low luminosities and we
suggest that the observed spectral differences likely arise from the
neutron-star surface becoming dominantly visible in the X-ray spectra. We also
suggest that both the thermal component and the non-thermal component might be
caused by low-level accretion onto the neutron-star surface for luminosities
below a few times 1E34 erg/s.Comment: Accepted for publication in MNRA
Multiwavelength spectral evolution during the 2011 outburst of the very faint X-ray transient Swift J1357.2-0933
We report our multiwavelength study of the 2011 outburst evolution of the
newly discovered black hole candidate X-ray binary Swift J1357.2-0933. We
analysed the Swift X-ray telescope and Ultraviolet/Optical telescope (UVOT)
data taken during the ~7 months duration of the outburst. It displayed a 2-10
keV X-ray peak luminosity of ~1E35(D/1.5 kpc)^2 erg s-1 which classifies the
source as a very faint X-ray transient. We found that the X-ray spectrum at the
peak was consistent with the source being in the hard state, but it softened
with decreasing luminosity, a common behaviour of black holes at low
luminosities or returning to quiescence from the hard state. The correlations
between the simultaneous X-ray and ultraviolet/optical data suggest a system
with a black hole accreting from a viscous disc that is not irradiated. The
UVOT filters provide the opportunity to study these correlations up to
ultraviolet wavelengths a regime so far unexplored. If the black hole nature is
confirmed, Swift J1357.2-0933 would be one of the very few established black
hole very-faint X-ray transients.Comment: 6 pages, 2 tables, 5 figures. Accepted by MNRA
Pengaruh Modal Sendiri dan Penerimaan Kredit terhadap Pendapatan Pedagang Kecil di Pasar Simpang Baru Panam Pekanbaru
What percentage of the influence of Equity and Acceptance Credit to Small Traders Revenue in Simpang Pasar Baru Panam Pekanbaru. This research was conducted in Pasar Baru Simpang Panam Pekanbaru in May-finished. The method used is descriptive quantitative method. The population in this study are all traders who trade in the market a new intersection panam pekanbaru totaling 320 traders and 10% of the population sampled is 32 respondents. The sampling based on purposive sampling. Data were collected through a questionnaire while analyzed using univariate and bivariate linear regression significant level of 0.05%. Based on the survey results revealed that the own capital and credit acceptance affect the income of traders, it is based on the results of the analysis using SPSS, showed simultannya calculation of F (9125)> F table (4.183) with Sig. (0.001) t table (2.045) and Sig. (0,023) t table (2.045) and Sig. (0.002) <0.05. So it can be concluded that there is significant influence from its own capital and acceptance of credit against the income of small traders in the market panam pekanbaru new intersection. The amount of contributions or donations of their own capital and acceptance of credit to traders income shown by the R Square of 0.386. What this means is that the contribution of the influence of their own capital and acceptance of credit againstincome amounted to 38.6% and the rest of 61.4% are not addressed in this stud
- …