118 research outputs found
Time properties of the the rho-class burst of the microquasar GRS 1915+105 observed with BeppoSAX in April 1999
We present a temporal analysis of a BeppoSAX observation of GRS 1915+105
performed on April 13, 1999 when the source was in the rho class, which is
characterised by quasi-regular bursting activity. The aim of the present work
is to confirm and extend the validity of the results obtained with a BeppoSAX
observation performed on October 2000 on the recurrence time of the burst and
on the hard X-ray delay. We divided the entire data set into several series,
each corresponding to a satellite orbit, and performed the Fourier and wavelet
analysis and the limit cycle mapping technique using the count rate and the
average energy as independent variables. We found that the count rates
correlate with the recurrence time of bursts and with hard X-ray delay,
confirming the results previously obtained. In this observation, however, the
recurrence times are distributed along two parallel branches with a constant
difference of 5.2+/-0.5 s.Comment: Accepted for publication in Section 7. Stellar structure and
evolution of Astronomy and Astrophysic
Discovery of periodic dips in the light curve of GX 13+1: the X-ray orbital ephemeris of the source
The bright low-mass X-ray binary (LMXB) GX 13+1 is one of the most peculiar
Galactic binary systems. A periodicity of 24.27 d with a formal statistical
error of 0.03 d was observed in its power spectrum density obtained with RXTE
All Sky Monitor (ASM) data spanning 14 years. Starting from a recent study,
indicating GX 13+1 as a possible dipping source candidate, we systematically
searched for periodic dips in the X-ray light curves of GX 13+1 from 1996 up to
2013 using RXTE/ASM, and MAXI data to determine for the first time the X-ray
orbital ephemeris of GX 13+1. We searched for a periodic signal in the ASM and
MAXI light curves, finding a common periodicity of 24.53 d. We folded the 1.3-5
keV and 5-12.1 keV ASM light curves and the 2-4 and 4-10 keV MAXI light curves
at the period of 24.53 d finding a periodic dip. To refine the value of the
period we used the timing technique dividing the ASM light curve in eight
intervals and the MAXI light curve in two intervals, obtaining four and two dip
arrival times from the ASM and MAXI light curves, respectively. We improved the
X-ray position of GX 13+1 using a recent Chandra observation. The new X-ray
position is discrepant by \sim 7\arcsec from the previous one, while it is
compatible with the infrared and radio counterpart positions. We detected an
X-ray dip, that is totally covered by the Chandra observation, in the light
curve of GX 13+1 and showed, a-posteriori, that it is a periodic dip. We
obtained seven dip arrival times from ASM, MAXI, and Chandra light curves. We
calculated the delays of the detected dip arrival times with respect to the
expected times for a 24.52 d periodicity. Fitting the delays with a linear
function we find that the orbital period and the epoch of reference of GX 13+1
are 24.5274(2) days and 50,086.79(3) MJD, respectively.(Abridged)Comment: 12 pages, including 16 figures. Accepted for publication in A&
Broadband observations of the X-ray burster 4U 1705-44 with BeppoSAX
4U 1705-44 is one of the most-studied type I X-ray burster and Atoll sources.
This source represents a perfect candidate to test different models proposed to
self-consistently track the physical changes occurring between different
spectral states because it shows clear spectral state transitions. The
broadband coverage, the sensitivity and energy resolution of the BeppoSAX
satellite offers the opportunity to disentangle the components that form the
total X-ray spectrum and to study their changes according to the spectral
state. Using two BeppoSAX observations carried out in August and October 2000,
respectively, for a total effective exposure time of about 100 ks, we study the
spectral evolution of the source from a soft to hard state. Energy spectra are
selected according to the source position in the color-color diagram (CCD)
Results. We succeeded in modeling the spectra of the source using a physical
self-consistent scenario for both the island and banana branches (the double
Comptonization scenario). The components observed are the soft Comptonization
and hard Comptonization, the blackbody, and a reflection component with a broad
iron line. When the source moves from the banana state to the island state, the
parameters of the two Comptonization components change significantly and the
blackbody component becomes too weak to be detected. We interpret the soft
Comptonization component as emission from the hot plasma surrounding the
neutron star, hard Comptonization as emission from the disk region, and the
blackbody component as emission from the inner accretion disk. The broad
feature in the iron line region is compatible with reflection from the inner
accretion disk.Comment: 8 pages, 10 figures, accepted for publication by A&
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
A self-consistent approach to the reflection component in 4U 1705-44
High-resolution spectroscopy has recently revealed in many neutron-star Low-Mass X-ray binaries that the shape of the broad iron line observed in the 6.4-6.97 keV range is consistently well fitted by a relativistically smeared line profile. We show here spectral fitting results using a newly developed self-consistent reflection model on XMM-Newton data of the LMXB 4U 1705-44 during a period when the source was in a bright soft state. This reflection model adopts a blackbody prescription for the shape of the impinging radiation field, that we physically associate with the boundary layer emission. \ua9 2010 American Institute of Physics
The near-IR counterpart of IGR J17480-2446 in Terzan 5
Some globular clusters in our Galaxy are noticeably rich in low-mass X-ray
binaries. Terzan 5 has the richest population among globular clusters of X- and
radio-pulsars and low-mass X-ray binaries. The detection and study of
optical/IR counterparts of low-mass X-ray binaries is fundamental to
characterizing both the low-mass donor in the binary system and investigating
the mechanisms of the formation and evolution of this class of objects. We aim
at identifying the near-IR counterpart of the 11 Hz pulsar IGRJ17480-2446
discovered in Terzan 5. Adaptive optics (AO) systems represent the only
possibility for studying the very dense environment of GC cores from the
ground. We carried out observations of the core of Terzan 5 in the near-IR
bands with the ESO-VLT NAOS-CONICA instrument. We present the discovery of the
likely counterpart in the Ks band and discuss its properties both in outburst
and in quiescence. Archival HST observations are used to extend our discussion
to the optical bands. The source is located at the blue edge of the turn-off
area in the color-magnitude diagram of the cluster. Its luminosity increase
from quiescence to outburst, by a factor 2.5, allows us to discuss the nature
of the donor star in the context of the double stellar generation population of
Terzan 5 by using recent stellar evolution models.Comment: 7 pages, 4 figure
Chandra Observation of the Big Dipper X 1624-490
We present the results of a 73 ks long Chandra observation of the dipping source X 1624-490. During the observation a complex dip lasting 4 hours is observed. We analyse the persistent emission detecting, for the first time in the 1st-order spectra of X 1624-490, an absorption line associated to \ion{Ca}{xx}. We confirm the presence of the \ion{Fe}{xxv} K and \ion{Fe}{xxvi} K absorption lines with a larger accuracy with respect to a previous XMM observation. Assuming that the line widths are due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines have been produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk
Relativistically Smeared Iron Lines in the Spectra of Bright NS LMXB
We present preliminary results of a study on three bright accreting low-mass X-ray binaries hosting a neutron star, based on XMM-Newton observations. These sources (GX 340+0, GX 349+2 and SAX J1808.4-3658) show a broad Fe K alpha iron line in their spectra. This feature can be well described by relativistic line profile in each case; the good spectral resolution of the EPIC/PN and the high statistics spectra allow to put very good constraints on the disk geometry and ionization stage of the reflecting matter
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