282 research outputs found
Herschel views on ultra-luminous X-ray sources
The nature of ultra-luminous X-ray sources (ULXs), which are off-nuclear
extragalactic X-ray sources that exceed the Eddington luminosity for a
stellar-mass black hole, is still largely unknown. They might be black hole
X-ray binaries in a super-Eddington accretion state, possibly with significant
beaming of their emission, or they might harbor a black hole of intermediate
mass (10^2 to 10^5 solar masses). Due to the enormous amount of energy
radiated, ULXs can have strong interactions with their environment,
particularly if the emission is not beamed and if they host a massive black
hole. We present early results of a project that uses archival Herschel
infrared observations of galaxies hosting bright ULXs in order to constrain the
nature of the environment surrounding the ULXs and possible interactions. We
already observe a spatial correlation between ULXs and dense clouds of cold
material, that will be quantified in subsequent work. Those observations will
allow us to test the similarities with the environment of Galactic high mass
X-ray binaries. This project will also shed light on the nature of the host
galaxies, and the possible factors that could favor the presence of a ULX in a
galaxy.Comment: Accepted for publication in Proceedings of Science (INTEGRAL 2012),
Eds. A. Goldwurm, F. Lebrun and C. Winkler, based on a presentation at the
9th INTEGRAL Workshop, October 15-19, 2012, Paris, Franc
Opening the 100-Year Window for Time Domain Astronomy
The large-scale surveys such as PTF, CRTS and Pan-STARRS-1 that have emerged
within the past 5 years or so employ digital databases and modern analysis
tools to accentuate research into Time Domain Astronomy (TDA). Preparations are
underway for LSST which, in another 6 years, will usher in the second decade of
modern TDA. By that time the Digital Access to a Sky Century @ Harvard (DASCH)
project will have made available to the community the full sky Historical TDA
database and digitized images for a century (1890--1990) of coverage. We
describe the current DASCH development and some initial results, and outline
plans for the "production scanning" phase and data distribution which is to
begin in 2012. That will open a 100-year window into temporal astrophysics,
revealing rare transients and (especially) astrophysical phenomena that vary on
time-scales of a decade. It will also provide context and archival comparisons
for the deeper modern surveysComment: 6 pages, 3 figures; invited talk at IAUS 28
Investigating the mass of the intermediate mass black hole candidate HLX-1 with the SLIMBH model
In this paper we present a comprehensive study of the mass of the
intermediate mass black hole candidate HLX-1 in the galaxy ESO 243-49. We
analyse the continuum X-ray spectra collected by Swift, XMM-Newton, and Chandra
with the slim disc model, SLIMBH, and estimate the black hole mass for the full
range of inclination (inc = 0{\deg} - 85{\deg}) and spin (a* = 0 - 0.998). The
relativistic SLIMBH model is particularly suited to study high luminosity disc
spectra as it incorporates the effects of advection, such as the shift of the
inner disc edge towards smaller radii and the increasing height of the disc
photosphere (including relativistic ray-tracing from its proper location rather
than the mid-plane of the disc). We find for increasing values of inclination
that a zero spin black hole has a mass range of 6,300 - 50,900 M_sun and a
maximally spinning black hole has a mass between 16,900 - 191,700 M_sun. This
is consistent with previous estimates and reinforces the idea that HLX-1
contains an intermediate mass black hole.Comment: updated version, published in Astronomy and Astrophysic
Measurement of the Radius of Neutron Stars with High S/N Quiescent Low-mass X-ray Binaries in Globular Clusters
This paper presents the measurement of the neutron star (NS) radius using the
thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular
clusters (GCs). Recent observations of NSs have presented evidence that cold
ultra dense matter -- present in the core of NSs -- is best described by
"normal matter" equations of state (EoSs). Such EoSs predict that the radii of
NSs, Rns, are quasi-constant (within measurement errors, of ~10%) for
astrophysically relevant masses (Mns > 0.5 Msun). The present work adopts this
theoretical prediction as an assumption, and uses it to constrain a single Rns
value from five qLMXB targets with available high signal-to-noise X-ray
spectroscopic data. Employing a Markov-Chain Monte-Carlo approach, we produce
the marginalized posterior distribution for Rns, constrained to be the same
value for all five NSs in the sample. An effort was made to include all
quantifiable sources of uncertainty into the uncertainty of the quoted radius
measurement. These include the uncertainties in the distances to the GCs, the
uncertainties due to the Galactic absorption in the direction of the GCs, and
the possibility of a hard power-law spectral component for count excesses at
high photon energy, which are observed in some qLMXBs in the Galactic plane.
Using conservative assumptions,we found that the radius, common to the five
qLMXBs and constant for a wide range of masses, lies in the low range of
possible NS radii, Rns=9.1(+1.3)(-1.5) km (90%-confidence). Such a value is
consistent with low-res equations of state. We compare this result with
previous radius measurements of NSs from various analyses of different types of
systems. In addition, we compare the spectral analyses of individual qLMXBs to
previous works.Comment: Accepted to Apj. 31 pages, 17 figures, 8 table
DASCH 100-yr light curves of high-mass X-ray binaries
We analyzed the 100-yr light curves of Galactic high-mass X-ray binaries
using the Harvard photographic plate collection, made accessible through the
DASCH project (Digital Access to a Sky Century at Harvard). As scanning is
still in progress, we focus on the four objects that are currently well
covered: the supergiant X-ray binary Cyg X-1 (V1357 Cyg), and the Be X-ray
binaries 1H 1936+541 (BD+53 2262), RX J1744.7-2713 (HD 161103), and RX
J2030.5+4751 (SAO 49725), the latter two objects being similar to gamma Cas.
The star associated with Cyg X-1 does not show evidence for variability with an
amplitude higher than 0.3 magnitude over a hundred years. We found significant
variability of one magnitude with timescales of more than 10 years for SAO
49725, as well as a possible period of 500-600 days and an amplitude of 0.05
magnitude that might be the orbital, or super-orbital period of the system. The
data is insufficient to conclude for HD 161103 but suggests a similar long-term
variability. We thus observe an additional characteristic of gamma Cas-like
objects: their long-term variability. This variability seems to be due to the
slow evolution of a decretion disk around the Be star, but may be triggered by
the presence of a compact object in the system, possibly a white dwarf. This
characteristic could be used to identify further similar objects otherwise
difficult to detect.Comment: Accepted for publication in Proceedings of Science (INTEGRAL 2012),
Eds. A. Goldwurm, F. Lebrun and C. Winkler, based on a presentation at the
9th INTEGRAL Workshop "An INTEGRAL view of the high-energy sky (the first 10
years)", October 15-19, 2012, Paris, Franc
Herschel observations of INTEGRAL supergiant High Mass X-ray Binaries
We present preliminary results on Herschel/PACS mid/far-infrared photometric
observations of INTEGRAL supergiant High Mass X-ray Binaries (HMXBs), with the
aim of detecting the presence and characterizing the nature of absorbing
material (dust and/or cold gas), either enshrouding the whole binary systems,
or surrounding the sources within their close environment. These unique
observations allow us to better characterize the nature of these HMXBs, to
constrain the link with their environment (impact and feedback), and finally to
get a better understanding of the formation and evolution of such rare and
short-living supergiant HMXBs in our Galaxy.Comment: Proceedings of the 9th INTEGRAL Workshop and celebration of the 10th
anniversary of the launch "An INTEGRAL view of the high-energy sky (the first
10 years)", accepted for publication in Proceedings of Science (editors: F.
Lebrun, A. Goldwurm and C. Winkler), 4 pages, 2 figure
IVOA Provenance data model: hints from the CTA Provenance prototype
We present the last developments on the IVOA Provenance data model, mainly
based on the W3C PROV concept. In the context of the Cherenkov astronomy, the
data processing stages imply both assumptions and comparison to dedicated
simulations. As a consequence, Provenance information is crucial to the end
user in order to interpret the high level data products. The Cherenkov
Telescope Array (CTA), currently in preparation, is thus a perfect test case
for the development of an IVOA standard on Provenance information. We describe
general use-cases for the computational Provenance in the CTA production
pipeline and explore the proposed W3C notations like PROV-N formats, as well as
Provenance access solutions.Comment: 4 pages, 3 figures, to appear in ADASS XXV proceedings, edited by N.
P. F. Lorente, & K. Shortridge (San Francisco: ASP), ASP Conf. Se
Discovery of a Significant Magnetic CV Population in the Limiting Window
[Abridged] We have discovered 10 periodic X-ray sources from the 1 Ms Chandra
ACIS observation of the Limiting Window (LW), a low extinction region (A_V~3.9)
at 1.4 Deg south of the Galactic center. The observed periods (~1.3 to 3.4
hours) and the X-ray luminosities (10^{31.8-32.9} erg s^-1 at 8 kpc) of the 10
periodic sources, combined with the lack of bright optical counterparts and
thus high X-ray-to-optical flux ratios, suggest that they are likely accreting
binaries, in particular, magnetic cataclysmic variables (MCVs). All of the 10
sources exhibit a relatively hard X-ray spectrum (PLI<2 for a power law model)
and X-ray spectra of at least five show an extinction larger than the field
average expected from the interstellar medium in the region. The discovery of
these periodic X-ray sources in the LW further supports the current view that
MCVs constitute the majority of low luminosity hard X-ray sources (~10^{30-33}
erg s^-1) in the Bulge. The period distribution of these sources resembles
those of polars, whereas the relatively hard spectra suggest that they could be
intermediate polars (IPs). These puzzling properties can be explained by
unusual polars with buried magnetic fields or a rare sub-class of MCVs, nearly
synchronous MCVs. These unusual MCVs may provide important clues in the
evolutionary path of MCVs from IPs to polars. The completeness simulation
indicates >~40% of the hard X-ray sources in the LW are periodic. Therefore,
this discovery provides a first direct evidence of a large MCV population in
the Bulge.Comment: 15 pages, 10 figures, 5 tables, submitted to ApJ, revised in response
to the referee's revie
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