400 research outputs found
Detection of a new, low-brightness supernova remnant possibly associated with EGRET sources
We report on the discovery of a shell-type supernova remnant in the southern
sky. It is a large (8*8), low-brightness source with a nonthermal radio
spectrum, which requires background filtering to isolate it from the diffuse
background emission of the Galaxy. Three 3EG gamma-ray sources are spatially
correlated with the radio structure. We have made 21-cm line observations of
the region and found that two of these sources are coincident with HI clouds.
We propose that the gamma-ray emission is the result of hadronic interactions
between high-energy protons locally accelerated at the remnant shock front and
atomic nuclei in the ambient clouds.Comment: 6 pages, 5 figure
New evidence on the origin of the microquasar GRO J1655-40
Aims. Motivated by the new determination of the distance to the microquasar
GRO J1655-40 by Foellmi et al. (2006), we conduct a detailed study of the
distribution of the atomic and molecular gas, and dust around the open cluster
NGC 6242, the possible birth place of the microquasar. The proximity and
relative height of the cluster on the galactic disk provides a unique
opportunity to study SNR evolution and its possible physical link with
microquasar formation. Methods. We search in the interstellar atomic and
molecular gas around NGC 6242 for traces that may have been left from a
supernova explosion associated to the formation of the black hole in GRO
J1655-40. Furthermore, the 60/100 mu IR color is used as a tracer of
shocked-heated dust. Results. At the kinematical distance of the cluster the
observations have revealed the existence of a HI hole of 1.5*1.5 degrees in
diameter and compressed CO material acumulated along the south-eastern internal
border of the HI cavity. In this same area, we found extended infrared emission
with characteristics of shocked-heated dust. Based on the HI, CO and FIR
emissions, we suggest that the cavity in the ISM was produced by a supernova
explosion occured within NGC 6242. The lower limit to the kinematic energy
transferred by the supernova shock to the surrounding interstellar medium is ~
10^{49} erg and the atomic and molecular mass displaced to form the cavity of ~
16.500 solar masses. The lower limit to the time elapsed since the SN explosion
is ~ 2.2*10^{5} yr, which is consistent with the time required by GRO J1655-40
to move from the cluster up to its present position. The observations suggest
that GRO J1655-40 could have been born inside NGC 6242, being one of the
nearest microquasars known so far.Comment: 6 pages, 6 figures. Accepted for publication in Astronomy &
Astrophysic
The runaway black hole GRO J1655-40
We have used the Hubble Space Telescope to measure the motion in the sky and
compute the galactocentric orbit of the black hole X-ray binary GRO J1655-40.
The system moves with a runaway space velocity of km s in a
highly eccentric () orbit. The black hole was formed in the
disk at a distance greater than 3 kpc from the Galactic centre and must have
been shot to such an eccentric orbit by the explosion of the progenitor star.
The runaway linear momentum and kinetic energy of this black hole binary are
comparable to those of solitary neutron stars and millisecond pulsars. GRO
J1655-40 is the first black hole for which there is evidence for a runaway
motion imparted by a natal kick in a supernova explosion.Comment: Published in Astronomy and Astrophysics. 5 pages, 2 color figures.
Color figure and animation can be found at
http://www.iafe.uba.ar/astronomia/mirabel/mirabel.html or
ftp://ftp.cea.fr/incoming/y2k01/mirabe
Detailed study of SNR G306.3-0.9 using XMM-Newton and Chandra observations
We used combined data from XMM-Newton and Chandra observatories to study the
X-ray morphology of SNR G306.3-0.9. A spatially-resolved spectral analysis was
used to obtain physical and geometrical parameters of different regions of the
remnant. Spitzer infrared observations were also used to constrain the
progenitor supernova and study the environment in which the SNR evolved. The
X-ray morphology of the remnant displays a non-uniform structure of
semi-circular appearance, with a bright southwest region and very weak or
almost negligible X-ray emission in its northern part. These results indicate
that the remnant is propagating in a non-uniform environment as the shock
fronts are encountering a high-density medium, where enhanced infrared emission
is detected. The X-ray spectral analysis of the selected regions shows distinct
emission-line features of several metal elements, confirming the thermal origin
of the emission. The X-ray spectra are well represented by a combination of two
absorbed thermal plasma models: one in equilibrium ionization with a mean
temperature of ~0.19 keV, and another out of equilibrium ionization at a higher
temperature of ~1.1 or 1.6-1.9 keV. For regions located in the northeast,
central, and southwest part of the SNR, we found elevated abundances of Si, S,
Ar, Ca, and Fe, typical of ejecta material. The outer regions located northwest
and south show values of the abundances above solar but lower than to those
found in the central regions. This suggests that the composition of the
emitting outer parts of the SNR is a combination of ejecta and shocked material
of the interstellar medium. The comparison between the S/Si, Ar/Si, and Ca/Si
abundances ratios (1.75, 1.27, and 2.72 in the central region, respectively),
favor a Type Ia progenitor for this SNR, a result that is also supported by an
independent morphological analysis using X-ray and IR data.Comment: 8 pages, 7 figures. Accepted by Astronomy and Astrophysic
Swift UVOT Grism Spectroscopy of Comets: A First Application to C/2007 N3 (Lulin)
We observed comet C/2007 N3 (Lulin) twice on UT 28 January 2009, using the UV
grism of the Ultraviolet and Optical Telescope (UVOT) on board the Swift Gamma
Ray Burst space observatory. Grism spectroscopy provides spatially resolved
spectroscopy over large apertures for faint objects. We developed a novel
methodology to analyze grism observations of comets, and applied a Haser comet
model to extract production rates of OH, CS, NH, CN, C3, C2, and dust. The
water production rates retrieved from two visits on this date were and 7.9 0.7 x 1E28 molecules s-1, respectively. Jets were sought
(but not found) in the white-light and `OH' images reported here, suggesting
that the jets reported by Knight and Schleicher (2009) are unique to CN. Based
on the abundances of its carbon-bearing species, comet Lulin is `typical'
(i.e., not `depleted') in its composition
Chandra X-ray counterpart of KS 1741-293
We aim to investigate the nature of the high energy source KS 1741-293 by
revisiting the radio and infrared associations proposed in the early 1990s. Our
work is mostly based on the analysis of modern survey and archive data,
including the NRAO, MSX, 2MASS and Chandra archives, and catalogues. We also
have obtained deep CCD optical observations by ourselves. The coincidence of KS
1741-293 with an extended radio and far-infrared source, tentatively suggested
in 1994, is no longer supported by modern observational data. Instead, a
Chandra source is the only peculiar object found to be consistent with all
high-energy error circles of KS 1741-293 and we propose it to be its most
likely X-ray counterpart. We also report the existence of a non-thermal radio
nebula in the vicinity of the KS 1741-293 position with the appearance of a
supernova remnant. The possibility of being associated to this X-ray binary is
discussed.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in Astronomy &
Astrophysic
High energy protons from PKS 1333-33
In this letter we give an account of the possible acceleration of protons in
the outer radio lobes of the active galaxy PKS 1333-33. We also make estimates
of the arrival energy spectrum.Comment: 3 pages revtex, two figures, to appear in Mod. Phys. Lett.
A multiwavelength study of the supernova remnant G296.8-0.3
We report XMM-Newton observations of the Galactic supernova remnant
G296.8-0.3, together with complementary radio and infrared data. The spatial
and spectral properties of the X-ray emission, detected towards G296.8-0.3, was
investigated in order to explore the possible evolutionary scenarios and the
physical connexion with its unusual morphology detected at radio frequencies.
G296.8-0.3 displays diffuse X-ray emission correlated with the peculiar radio
morphology detected in the interior of the remnant and with the shell-like
radio structure observed to the northwest side of the object. The X-ray
emission peaks in the soft/medium energy range (0.5-3.0 keV). The X-ray
spectral analysis confirms that the column density is high (NH \sim 0.64 x
10^{22} cm^{-2}) which supports a distant location (d>9 kpc) for the SNR. Its
X-ray spectrum can be well represented by a thermal (PSHOCK) model, with kT
\sim 0.86 keV, an ionization timescale of 6.1 x 10^{10} cm^{-3} s, and low
abundance (0.12 Z_sun). The 24 microns observations show shell-like emission
correlated with part of the northwest and southeast boundaries of the SNR. In
addition a point-like X-ray source is also detected close to the geometrical
center of the radio SNR. The object presents some characteristics of the
so-called compact central objects (CCO). Its X-ray spectrum is consistent with
those found at other CCOs and the value of NH is consistent with that of
G296.8-0.3, which suggests a physical connexion with the SNR.Comment: Accepted for publication in Astrophysics & Space Scienc
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