508 research outputs found
Radio and IR study of the massive star-forming region IRAS 16353-4636
Context. With the latest infrared surveys, the number of massive protostellar
candidates has increased significantly. New studies have posed additional
questions on important issues about the formation, evolution, and other
phenomena related to them. Complementary to infrared data, radio observations
are a good tool to study the nature of these objects, and to diagnose the
formation stage. Aims. Here we study the far-infrared source IRAS 16353-4636
with the aim of understanding its nature and origin. In particular, we search
for young stellar objects (YSOs), possible outflow structure, and the presence
of non-thermal emission. Methods. Using high-resolution, multi-wavelength radio
continuum data obtained with the Australia Telescope Compact Array, we image
IRAS 16353-4636 and its environment from 1.4 to 19.6 GHz, and derive the
distribution of the spectral index at maximum angular resolution. We also
present new JHKs photometry and spectroscopy data obtained at ESO NTT. 13 CO
and archival HI line data, and infrared databases (MSX, GLIMPSE, MIPSGal) are
also inspected. Results. The radio continuum emission associated with IRAS
16353-4636 was found to be extended (~10 arcsec), with a bow-shaped morphology
above 4.8 GHz, and a strong peak persistent at all frequencies. The NIR
photometry led us to identify ten near-IR sources and classify them according
to their color. We used the HI line data to derive the source distance, and
analyzed the kinematical information from the CO and NIR lines detected.
Conclusions. We have identified the source IRAS 16353-4636 as a new
protostellar cluster. In this cluster we recognized three distinct sources: a
low-mass YSO, a high-mass YSOs, and a mildly confined region of intense and
non-thermal radio emission. We propose the latter corresponds to the terminal
part of an outflow.Comment: To appear in A&A. 10 pages, 8 figure
On the origin of the various types of radio emission in GRS 1915+105
We investigate the association between the radio ``plateau'' states and the
large superluminal flares in GRS 1915+105 and propose a qualitative scenario to
explain this association. We identify several candidate superluminal flare
events from available monitoring data on this source and analyze the
contemporaneous RXTE pointed observations. We detect a strong correlation
between the average X-ray flux during the ``plateau'' state and the total
energy emitted in radio during the subsequent radio flare. We find that the
sequence of events is similar for all large radio flares with a fast rise and
exponential decay morphology. Based on these results, we propose a qualitative
scenario in which the separating ejecta during the superluminal flares are
observed due to the interaction of the matter blob ejected during the X-ray
soft dips, with the steady jet already established during the ``plateau''
state. This picture can explain all types of radio emission observed from this
source in terms of its X-ray emission characteristics.Comment: Corrected typo in the author names, contents unchanged, accepted in
Ap
TYC 2675-663-1: A newly discovered W UMa system in an active state
The recently discovered eclipsing binary system TYC 2675-663-1 is a X-ray
source, and shows properties in the optical that are similar to the W UMa
systems, but are somewhat unusual compared to what is seen in other contact
binary systems. The goal of this work is to characterize its properties and
investigate its nature by means of detailed photometric and spectroscopic
observations. We have performed extensive V-band photometric measurements with
the INTEGRAL satellite along with ground-based multi-band photometric
observations, as well as high-resolution spectroscopic monitoring from which we
have measured the radial velocities of the components. These data have been
analysed to determine the stellar properties, including the absolute masses and
radii. Additional low-resolution spectroscopy was obtained to investigate
spectral features. From the measured eclipse timings we determine an orbital
period for the binary of P=0.4223576+-0.0000009 days. The light-curve and
spectroscopic analyses reveal the observations to be well represented by a
model of an overcontact system composed of main-sequence F5 and G7 stars
(temperature difference of nearly 1000 K), with the possible presence of a
third star. Low-resolution optical spectroscopy reveals a complex H alpha
emission, and other features that are not yet understood. The unusually large
mass ratio of q=0.81+-0.05 places it in the rare "H" (high mass ratio) subclass
of the W UMa systems, which are presumably on their way to coalescence.Comment: 12 pages in double column format. Accepted for publication in
Astronomy and Astrophysic
Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from the
INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large
neutral hydrogen column density and are likely members of an emerging class of
heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL
observations. Two of the sources in our sample are approximately constant flux
sources, one source shows periodic variation and one source exhibited a short,
bright X-ray outburst. The periodicity is transient, suggesting it is produced
by a neutron star in an elliptical orbit around a stellar wind source. We
analyze the flaring source in several segments to look for spectral variation
and discuss the implications of the findings for the nature of the source. We
conclude that all four sources in our sample can be identified with the
emerging class of highly absorbed HMXBs, that one is a newly identified
transient X-ray pulsar and that at least one is a newly identified supergiant
fast X-ray transient (SFXT).Comment: 22 pages, 5 figures, submitted to Ap
The masses of the neutron and donor star in the high mass X-ray binary IGR J18027-2016
We report near-infrared observations of the supergiant donor to the eclipsing
high mass X-ray binary pulsar IGR J18027-2016. We aim to determine its spectral
type and measure its radial velocity curve and hence determine the stellar
masses of the components. ESO/VLT observations of the donor utilising the NIR
spectrograph ISAAC were obtained in the H and K bands. The multi-epoch H band
spectra were cross-correlated with RV templates in order to determine a radial
solution for the system. The spectral type of the donor was confirmed as B0-1
I. The radial velocity curve constructed has a semi-amplitude of
km s. Combined with other measured system parameters, a dynamically
determined neutron star mass of 1.4 0.2 - 1.6 0.3 M is
found. The mass range of the B0-B1 I donor was 18.6 0.8 - 21.8 2.4
~M. These lower and upper limits were obtained under the assumption
that the system is viewed edge-on (i = 90 with = 0.89) for the
lower limit and the donor fills its Roche lobe ( with i =
73.1) for the upper limit respectively.Comment: 5 pages, 4 figures, Accepted for publication in A&
Sources of Relativistic Jets in the Galaxy
Black holes of stellar mass and neutron stars in binary systems are first
detected as hard X-ray sources using high-energy space telescopes. Relativistic
jets in some of these compact sources are found by means of multiwavelength
observations with ground-based telescopes. The X-ray emission probes the inner
accretion disk and immediate surroundings of the compact object, whereas the
synchrotron emission from the jets is observed in the radio and infrared bands,
and in the future could be detected at even shorter wavelengths. Black-hole
X-ray binaries with relativistic jets mimic, on a much smaller scale, many of
the phenomena seen in quasars and are thus called microquasars. Because of
their proximity, their study opens the way for a better understanding of the
relativistic jets seen elsewhere in the Universe. From the observation of
two-sided moving jets it is inferred that the ejecta in microquasars move with
relativistic speeds similar to those believed to be present in quasars. The
simultaneous multiwavelength approach to microquasars reveals in short
timescales the close connection between instabilities in the accretion disk
seen in the X-rays, and the ejection of relativistic clouds of plasma observed
as synchrotron emission at longer wavelengths. Besides contributing to a deeper
comprehension of accretion disks and jets, microquasars may serve in the future
to determine the distances of jet sources using constraints from special
relativity, and the spin of black holes using general relativity.Comment: 39 pages, Tex, 8 figures, to appear in vol. 37 (1999) of Annual
Reviews of Astronomy and Astrophysic
Simultaneous multi-wavelength observations of GRS 1915+105
We present the result of multi-wavelength observations of the microquasar GRS
1915+105 in a plateau state with a luminosity of ~7.5x10^{38) erg s-1 (~40%
L_Edd), conducted simultaneously with the INTEGRAL and RXTE satellites, the
ESO/NTT, the Ryle Telescope, the NRAO VLA and VLBA, in 2003 April 2-3. For the
first time were observed concurrently in GRS 1915+105 all of the following
properties: a strong steady optically thick radio emission corresponding to a
powerful compact jet resolved with the VLBA, bright near-IR emission, a strong
QPO at 2.5 Hz in the X-rays and a power law dominated spectrum without any
cutoff in the 3-400 keV range.Comment: 5 pages, 5 figures (4 colour figures), accepted by A&A Letter
Initial low/hard state, multiple jet ejections and X-ray/radio correlations during the outburst of XTE J1859+226
We have studied the 1999 soft X-ray transient outburst of XTE J1859+226 at
radio and X-ray wavelengths. The event was characterised by strong variability
in the disc, corona and jet - in particular, a number of radio flares
(ejections) took place and seemed well-correlated with hard X-ray events.
Apparently unusual for the `canonical soft' X-ray transient, there was an
initial period of low/hard state behaviour during the rise from quiescence but
prior to the peak of the main outburst - we show that not only could this
initial low/hard state be an ubiquitous feature of soft X-ray transient
outbursts but that it could also be extremely important in our study of
outburst mechanisms.Comment: 12 pages, Accepted for publication in MNRA
Fitting the Gamma-Ray Spectrum from Dark Matter with DMFIT: GLAST and the Galactic Center Region
We study the potential of GLAST to unveil particle dark matter properties
with gamma-ray observations of the Galactic center region. We present full
GLAST simulations including all gamma-ray sources known to date in a region of
4 degrees around the Galactic center, in addition to the diffuse gamma-ray
background and to the dark matter signal. We introduce DMFIT, a tool that
allows one to fit gamma-ray emission from pair-annihilation of generic particle
dark matter models and to extract information on the mass, normalization and
annihilation branching ratios into Standard Model final states. We assess the
impact and systematic effects of background modeling and theoretical priors on
the reconstruction of dark matter particle properties. Our detailed simulations
demonstrate that for some well motivated supersymmetric dark matter setups with
one year of GLAST data it will be possible not only to significantly detect a
dark matter signal over background, but also to estimate the dark matter mass
and its dominant pair-annihilation mode.Comment: 37 pages, 16 figures, submitted to JCA
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