279 research outputs found
A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1
We present the results of a spectroscopic study of the Fe K{\alpha} emission
of the persistent neutron-star atoll low-mass X-ray binary and type I X-ray
burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux
modulation over several years and we observed it during its fainter phase,
which corresponds to an X-ray luminosity of Lx~10^37 ergs/s. When fitted with a
two-component model, the X-ray spectrum shows broad residuals at \sim6-7 keV
that can be ascribed to an iron K{\alpha} fluorescence line. In addition, lower
energy features are observed at \sim3.3 keV, \sim3.9 keV and might originate
from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a
relativistically smeared profile. This result is robust against possible
systematics caused by instrumental pile-up effects. Assuming that the line is
produced by reflection from the inner accretion disk, we infer an inner disk
radius of \sim25 Rg and a disk inclination of 35{\deg} < i < 44{\deg}.Comment: 4 pages, 3 figures Accepted for publication in Astronomy and
Astrophysic
Suzaku broad-band spectrum of 4U 1705-44: Probing the Reflection component in the hard state
Iron emission lines at 6.4-6.97 keV, identified with Kalpha radiative
transitions, are among the strongest discrete features in the X-ray band. These
are one of the most powerful probes to infer the properties of the plasma in
the innermost part of the accretion disk around a compact object. In this paper
we present a recent Suzaku observation, 100-ks effective exposure, of the atoll
source and X-ray burster 4U 1705-44, where we clearly detect signatures of a
reflection component which is distorted by the high-velocity motion in the
accretion disk. The reflection component consists of a broad iron line at about
6.4 keV and a Compton bump at high X-ray energies, around 20 keV. All these
features are consistently fitted with a reflection model, and we find that in
the hard state the smearing parameters are remarkably similar to those found in
a previous XMM-Newton observation performed in the soft state. In particular,
we find that the inner disk radius is Rin = 17 +/- 5 Rg (where Rg is the
Gravitational radius, GM/c^2), the emissivity dependence from the disk radius
is -2.5 +/- 0.5, the inclination angle with respect to the line of sight is i =
43 +/- 5 degrees, and the outer radius of the emitting region in the disk is
Rout > 200 Rg. We note that the accretion disk does not appear to be truncated
at large radii, although the source is in a hard state at about 3 % of the
Eddington luminosity for a neutron star. We also find evidence of a broad
emission line at low energies, at 3.03 +/- 0.03 keV, compatible with emission
from mildly ionized Argon (Ar XVI-XVII). Argon transitions are not included in
the self-consistent reflection models that we used and we therefore added an
extra component to our model to fit this feature. The low energy line appears
compatible with being smeared by the same inner disk parameters found for the
reflection component.Comment: 21 pages, 5 figures, 4 tables. To appear in Monthly Notices of the
Royal Astronomical Societ
Testing reflection features in 4U 1705-44 with XMM-Newton, BeppoSAX and RXTE in the hard and soft state
We use data of the bright atoll source 4U 1705-44 taken with XMM-Newton,
BeppoSAX and RXTE both in the hard and in the soft state to perform a
self-consistent study of the reflection component in this source. Although the
data from these X-ray observatories are not simultaneous, the spectral
decomposition is shown to be consistent among the different observations, when
the source flux is similar. We therefore select observations performed at
similar flux levels in the hard and soft state in order to study the spectral
shape in these two states in a broad band (0.1-200 keV) energy range, with good
energy resolution, and using self-consistent reflection models. These
reflection models provide a good fit for the X-ray spectrum both in the hard
and in the soft state in the whole spectral range. We discuss the differences
in the main spectral parameters we find in the hard and the soft state,
respectively, providing evidence that the inner radius of the optically thick
disk slightly recedes in the hard state.Comment: Accepted for publication in A&A, 20 pages, 12 figure
GRO J1744-28: an intermediate B-field pulsar in a low mass X-ray binary
The bursting pulsar, GRO J1744-28, went again in outburst after 18
years of quiescence in mid-January 2014. We studied the broad-band, persistent,
X-ray spectrum using X-ray data from a XMM-Newton observation, performed almost
at the peak of the outburst, and from a close INTEGRAL observation, performed 3
days later, thus covering the 1.3-70.0 keV band. The spectrum shows a complex
continuum shape that cannot be modelled with standard high-mass X-ray pulsar
models, nor by two-components models. We observe broadband and peaked residuals
from 4 to 15 keV, and we propose a self-consistent interpretation of these
residuals, assuming they are produced by cyclotron absorption features and by a
moderately smeared, highly ionized, reflection component. We identify the
cyclotron fundamental at 4.7 keV, with hints for two possible harmonics
at 10.4 keV and 15.8 keV. The position of the cyclotron fundamental allows an
estimate for the pulsar magnetic field of (5.27 0.06) 10
G, if the feature is produced at its surface. From the dynamical and
relativistic smearing of the disk reflected component, we obtain a lower limit
estimate for the truncated accretion disk inner radius, ( 100 R),
and for the inclination angle (18-48). We also detect the
presence of a softer thermal component, that we associate with the emission
from an accretion disk truncated at a distance from the pulsar of 50-115 R.
From these estimates, we derive the magneto-spheric radius for disk accretion
to be 0.2 times the classical Alfv\'en radius for radial accretion.Comment: Accepted for publication in MNRA
The reflection component in NS LMXBs
Thanks to the good spectral resolution and large effective area of the EPIC/PN instrument on board of XMM-Newton, we have at hand a large number of observations of accreting low-mass X-ray binaries, that allow for the fist time a comprehensive view on the characteristics of the reflection component at different accretion regimes and to probe the effects of a magnetosphere on its formation. We focus here on a comparative analysis of the reflection component from a series of spectroscopic studies on selected sources: 4U 1705-44, observed both in the soft and hard state, the pulsating ms pulsars SAX J1808.4-3658 and IGR J17511-3057, and the intermittent pulsar HETE J1900-2455. Although the sources can present very similar accretion rates and continuum shapes, the reflection parameters do not generally result the same, moreover the effect of a magnetosphere on the formation of the reflection component appears elusive. \ua9 2014 Owned by the authors
L-functions of Symmetric Products of the Kloosterman Sheaf over Z
The classical -variable Kloosterman sums over the finite field
give rise to a lisse -sheaf on , which we call the Kloosterman
sheaf. Let be the
-function of the -fold symmetric product of . We
construct an explicit virtual scheme of finite type over such that the -Euler factor of the zeta function of coincides with
. We also prove
similar results for and .Comment: 16 page
Study of the temporal behavior of 4U 1728-34 as a function of its position in the color-color diagram
We study the timing properties of the bursting atoll source 4U 1728-34 as a function of its position in the X-ray color-color diagram. In the island part of the color-color diagram (corresponding to the hardest energy spectra), the power spectrum of 4U 1728-34 shows several features such as a band-limited noise component present up to a few tens of Hz, a low-frequency quasi-periodic oscillation (LFQPO) at frequencies between 20 and 40 Hz, a peaked noise component around 100 Hz, and one or two QPOs at kHz frequencies. In addition to these, in the lower banana (corresponding to softer energy spectra) we also find a very low frequency noise (VLFN) component below ∼1 Hz. In the upper banana (corresponding to the softest energy spectra), the power spectra are dominated by the VLFN, with a peaked noise component around 20 Hz. We find that the frequencies of the kHz QPOs are well correlated with the position in the X-ray color-color diagram. For the frequency of the LFQPO and the break frequency of the broadband noise component, the relation appears more complex. Both of these frequencies increase when the frequency of the upper kHz QPO increases from 400 to 900 Hz, but at this frequency a jump in the values of the parameters occurs. We interpret this jump in terms of the gradual appearance of a QPO at the position of the break at high inferred mass accretion rate, while the previous LFQPO disappears. Simultaneously, another kind of noise appears with a break frequency of ∼7 Hz, similar to the NBO of Z sources. The 100 Hz peaked noise does not seem to correlate with the position of the source in the color-color diagram but remains relatively constant in frequency. This component may be similar to several 100 Hz QPOs observed in black hole binaries.Facultad de Ciencias Astronómicas y Geofísica
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