406 research outputs found
Orbital Period Determinations for Four SMC Be/X-ray Binaries
We present an optical and X-ray study of four Be/X-ray binaries located in
the Small Magellanic Cloud (SMC). OGLE I-band data of up to 11 years of
semi-continuous monitoring has been analysed for SMC X-2, SXP172 and SXP202B,
providing both a measurement of the orbital period (Porb = 18.62, 68.90, and
229.9 days for the pulsars respectively) and a detailed optical orbital profile
for each pulsar. For SXP172 this has allowed a direct comparison of the optical
and X-ray emission seen through regular RXTE monitoring, revealing that the
X-ray outbursts precede the optical by around 7 days. Recent X-ray studies by
XMM-Newton have identified a new source in the vicinity of SXP15.3 raising
doubt on the identification of the optical counterpart to this X-ray pulsar.
Here we present a discussion of the observations that led to the proposal of
the original counterpart and a detailed optical analysis of the counterpart to
the new X-ray source, identifying a 21.7 d periodicity in the OGLE I-band data.
The optical characteristics of this star are consistent with that of a SMC
Be/X-ray binary. However, this star was rejected as the counterpart to SXP15.3
in previous studies due to the lack of H{\alpha} emission.Comment: Accepted for publication in MNRAS, 11 pages, 17 figure
Rapid N_H changes in NGC 4151
We have analyzed the two longest (elapsed time > 3 days) BeppoSAX
observations of the X-ray brightest Seyfert galaxy, NGC 4151, to search for
spectral variability on time-scales from a few tens of ksec to years. We found
in both cases highly significant spectral variability below ~ 6 keV down to the
shortest time-scales investigated. These variations can be naturally explained
in terms of variations in the low energy cut-off due to obscuring matter along
the line of sight. If the cut-off is modeled by two neutral absorption
components, one fully covering the source and the second covering only a
fraction of the source, the shortest time-scale of variability of a few days
constrains the location of the obscuring matter to within 3.4 X 10^4
Schwarzschild radii from the central X-ray source. This is consistent with the
distance of the Broad Emission Line Region, as inferred from reverberation
mapping, and difficult to reconcile with the parsec scale dusty molecular torus
of Krolik & Begelman (1988). We have also explored a more complex absorption
structure, namely the presence of an ionized absorber. Although the behaviour
of the ionization parameter is nicely consistent with the expectations, the
results are not completely satisfactory from the statistical point of view.
The overall absorption during the 2001 December observation is lower than in
all other historical observations with similar 2-10 keV flux. This suggests
that absorption variability plays a crucial role in the observed flux
variability of this source.Comment: Added references, corrected typos. 21 pages, 9 figures; accepted for
publication in Monthly Notices of the Royal Astronomical Society Main Journa
The Orbital Solution and Spectral Classification of the High-Mass X-Ray Binary IGR J01054-7253 in the Small Magellanic Cloud
We present X-ray and optical data on the Be/X-ray binary (BeXRB) pulsar IGR
J01054-7253 = SXP11.5 in the Small Magellanic Cloud (SMC). Rossi X-ray Timing
Explorer (RXTE) observations of this source in a large X-ray outburst reveal an
11.483 +/- 0.002s pulse period and show both the accretion driven spin-up of
the neutron star and the motion of the neutron star around the companion
through Doppler shifting of the spin period. Model fits to these data suggest
an orbital period of 36.3 +/- 0.4d and Pdot of (4.7 +/- 0.3) x 10^{-10}
ss^{-1}. We present an orbital solution for this system, making it one of the
best described BeXRB systems in the SMC. The observed pulse period, spin-up and
X-ray luminosity of SXP11.5 in this outburst are found to agree with the
predictions of neutron star accretion theory. Timing analysis of the long-term
optical light curve reveals a periodicity of 36.70 +/- 0.03d, in agreement with
the orbital period found from the model fit to the X-ray data. Using blue-end
spectroscopic observations we determine the spectral type of the counterpart to
be O9.5-B0 IV-V. This luminosity class is supported by the observed V-band
magnitude. Using optical and near-infrared photometry and spectroscopy, we
study the circumstellar environment of the counterpart in the months after the
X-ray outburst.Comment: 12 pages, 13 figures and 3 tables. This paper has been accepted for
publication in MNRA
An X-ray view of absorbed INTEGRAL AGN
Aims. We present a 0.2--200 keV broad-band study of absorbed AGN observed
with INTEGRAL, XMM-Newton, Chandra and ASCA to investigate the continuum shape
and the absorbing/reflecting medium properties. Methods. The sources are
selected in the INTEGRAL AGN sample to have a 20--100 keV flux below
8 \flux (5 mCrab), and are characterized by a 2--10 keV flux
in the range (0.8--10) \flux. The good statistics allow us a
detailed study of the intrinsic and reflected continuum components. In
particular, the analysis performed on the combined broad-band spectra allow us
to investigate the presence of Compton reflection features and high energy
cut-off in these objects. Results. The column density of the absorbing gas
establishes the Compton thin nature for three sources in which a measure of the
absorption was still missing. The Compton thin nature of all the sources in
this small sample is also confirmed by the diagnostic ratios F$x/F[OIII]. The
Compton reflection components we measure, reflection continuum and iron line,
are not immediately compatible with a scenario in which the absorbing and
reflecting media are one and the same, i.e. the obscuring torus. A possible
solution is that the absorption is more effective than reflection, e.g. under
the hypothesis that the absorbing/reflecting medium is not uniform, like a
clumpy torus, or that the source is observed through a torus with a very
shallow opening angle. The high energy cut-off (a lower limit in two cases) is
found in all sources of our sample and the range of values is in good agreement
with that found in type 1 Seyfert galaxies. At lower energies there is clear
evidence of a soft component (reproduced with a thermal and/or scattering
model), in six objects.Comment: Accepted for publication in Astronomy and Astrophysic
Multiwavelength Properties of the X-ray Sources in the Groth-Westphal Strip Field
We summarize the multiwavelength properties of X-ray sources detected in the
80 ks XMM-Newton observation of the Groth-Westphal Strip. We find 23 XMM-Newton
sources within the WFPC2 fields. Ten spectroscopic redshifts are available from
the DEEP and CFRS projects and 4 of these show broad Mg II emission (type 1
AGNs). Two of those without any broad lines, nevertheless, have [NeV] emission
which is an unambiguous signature of AGN activity, one of which is a
narrow-line Seyfert 1 and the other a type 2 AGN. We have made near-infrared
(NIR) spectroscopic observations using the Subaru OHS/CISCO spectrometer for
five of the X-ray sources for which we found no indication of an AGN activity
in the optical spectrum. We have detected H-alpha+[NII] emission in four of
them. A broad H-alpha component and/or a large [NII]/H-alpha ratio is seen,
suggestive of AGN activity. Nineteen sources have been detected in the Ks band
and four of these are extremely red objects (I814-Ks>4). The optical
counterparts for the majority of the X-ray sources are bulge-dominated with
colors consistent with evolving elliptical galaxies, with starburst/AGN
contamination. Assuming that the known local relations among the bulge
luminosity,central velocity dispersion, and the mass of the central blackhole
hold at about z=1, the AGN bolometric luminosity to Eddington luminosity ratio
ranges from 0.3% to 10%. (abridged)Comment: 18 pages, 6 figures, accepted for publication in Astronomical Journa
INTEGRAL deep observations of the Small Magellanic Cloud
Deep observations of the Small Magellanic Cloud (SMC) and region were carried
out in the hard X-ray band by the INTEGRAL observatory in 2008-2009. The field
of view of the instrument permitted simultaneous coverage of the entire SMC and
the eastern end of the Magellanic Bridge. In total, INTEGRAL detected seven
sources in the SMC and five in the Magellanic Bridge; the majority of the
sources were previously unknown systems. Several of the new sources were
detected undergoing bright X- ray outbursts and all the sources exhibited
transient behaviour except the supergiant system SMC X-1. They are all thought
to be High Mass X-ray Binary (HMXB) systems in which the compact object is a
neutron star.Comment: 7 pages, 10 figures Accepted for publication in MNRA
Improved annotation of 3' untranslated regions and complex loci by combination of strand-specific direct RNA sequencing, RNA-seq and ESTs
The reference annotations made for a genome sequence provide the framework
for all subsequent analyses of the genome. Correct annotation is particularly
important when interpreting the results of RNA-seq experiments where short
sequence reads are mapped against the genome and assigned to genes according to
the annotation. Inconsistencies in annotations between the reference and the
experimental system can lead to incorrect interpretation of the effect on RNA
expression of an experimental treatment or mutation in the system under study.
Until recently, the genome-wide annotation of 3-prime untranslated regions
received less attention than coding regions and the delineation of intron/exon
boundaries. In this paper, data produced for samples in Human, Chicken and A.
thaliana by the novel single-molecule, strand-specific, Direct RNA Sequencing
technology from Helicos Biosciences which locates 3-prime polyadenylation sites
to within +/- 2 nt, were combined with archival EST and RNA-Seq data. Nine
examples are illustrated where this combination of data allowed: (1) gene and
3-prime UTR re-annotation (including extension of one 3-prime UTR by 5.9 kb);
(2) disentangling of gene expression in complex regions; (3) clearer
interpretation of small RNA expression and (4) identification of novel genes.
While the specific examples displayed here may become obsolete as genome
sequences and their annotations are refined, the principles laid out in this
paper will be of general use both to those annotating genomes and those seeking
to interpret existing publically available annotations in the context of their
own experimental dataComment: 44 pages, 9 figure
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