57 research outputs found
Remanentes de supernova que brillan en rayos-X
Los remanentes de supernova (RSN), restos gaseosos de la explosión de una estrella (fenómeno comúnmente conocido como supernova - SN), se forman por la propagación de una onda de choque a través del medio interestelar circundante a donde se produjo dicha explosión.
A las SN se las puede clasificar en dos clases bien diferentes: las SN del tipo I y las SN del tipo II. Cada clase se caracteriza por su historia evolutiva y la masa inicial de la estrella que muere. Las del tipo I se originan por la explosión termonuclear de estrellas con unas pocas masas solares. En cambio las del tipo II, son el resultado del colapso gravitacional de estrellas masivas de varias masas solares. En estas explosiones, se pueden producir destellos de radiación intensísimos a lo largo de todo el espectro electromagnético, que pueden durar desde varias semanas a varios meses. Se caracterizan por un rápido aumento de la intensidad hasta alcanzar un máximo determinado, para luego decrecer en brillo de forma más o menos suave hasta desaparecer completamente
Extreme photo-polarimetric behaviour of the blazar AO 0235+164
We present optical photo-polarimetric observations with high temporal
resolution of the blazar AO 0235+164. Our data, the first to test the
photo-polarimetric behaviour of this object at very short time-scales, show
significant micro-variability in total flux, colour index, linear polarization
degree, and position angle. Strong inter-night variations are also detected for
these parameters. Although no correlation between colour index and total flux
was found, our data seem to support the general bluer-when-brighter trend
already known for this object. The polarization degree, in turn, shows no
correlation with total flux, but a clear trend in the sense that colour index
is redder (the spectrum is softer) when the measured polarization is higher.Comment: Accepted by MNRAS (Letters), 5 page
On the origin of two unidentified radio/X-ray sources discovered with XMM-Newton
We aim at clarifying the nature of the emission of two spatially related
unidentified X-ray sources detected with XMM-Newton telescope at
intermediate-low Galactic latitude. Observations reveal a point-like source
aligned with elongated diffuse emission. The X-ray spectra are best-fitted by
absorbed power laws with photon indices ~1.7 for the point-like and ~2.0 for
the extended one. Both sources show nonthermal radio-continuum counterparts
that might indicate a physical association. From the available data, we did not
detect variability on the point-like source in several timescales. Two possible
scenarios are analyzed: first, based on HI line absorption, assuming a Galactic
origin, we infer a distance upper bound of <2 kpc, which poses a constraint on
the height over the Galactic plane of <200 pc and on the linear size of the
system of 10^32 erg/s and
>7.5 x 10^32 erg/s, for the point-like and extended sources, respectively;
second, an extra-Galactic nature is discussed, where the point-like source
might be the core of a radio galaxy and the extended source its lobe. In this
case, we compare derived fluxes, spectral indices, and spatial correlation with
those typical from the radio galaxy population, showing the feasibility of this
alternative astrophysical scenario. From the available observational evidence,
we suggest that the most promising scenario to explain the nature of these
sources is a system consisting of a one-sided radio galaxy, where the
point-like source is an active galactic nucleus and the extended source
corresponds to the emission from its lobe. Other possibilities include a
PSR/PWN origin, where the radio/X-ray emission originates from the synchrotron
cooling of relativistic particles in the PSR magnetic field or a casual
alignment between two unrelated sources, such as an AGN core and a Galactic
X-ray blob.Comment: 6 pages, 2 figures. Accepted for publication in Astronomy and
Astrophysics (A&A
Variable gamma-ray emission from the Be/X-ray transient A0535+26?
We present a study of the unidentified gamma-ray source 3EG J0542+2610. This
source is spatially superposed to the supernova remnant G180.0-1.7, but its
time variability makes unlikely a physical link. We have searched into the
EGRET location error box for compact radio sources that could be the low energy
counterpart of the gamma-ray source. Although 29 point-like radio sources were
detected and measured, none of them is strong enough as to be considered the
counterpart of a background gamma-ray emitting AGN. We suggest that the only
object within the 95 % error box capable of producing the required gamma-ray
flux is the X-ray transient A0535+26. We show that this Be/accreting pulsar can
produce variable hadronic gamma-ray emission through the mechanism originally
proposed by Cheng & Ruderman (1989), where a proton beam accelerated in a
magnetospheric electrostatic gap impacts the transient accretion disk.Comment: 6 pages, 3 figures, Astronomy & Astrophysics in pres
Supernova remnants and gamma-ray sources
A review of the possible relationship between gamma-ray sources and supernova
remnants (SNRs) is presented. Particular emphasis is given to the analysis of
the observational status of the problem of cosmic ray acceleration at SNR shock
fronts. All positional coincidences between SNRs and unidentified gamma-ray
sources listed in the Third EGRET Catalog at low Galactic latitudes are
discussed on a case by case basis. For several coincidences of particular
interest, new CO(J=1-0) and radio continuum maps are shown, and the mass
content of the SNR surroundings is determined. The contribution to the
gamma-ray flux observed that might come from cosmic ray particles (particularly
nuclei) locally accelerated at the SNR shock fronts is evaluated. We discuss
the prospects for future research in this field and remark on the possibilities
for observations with forthcoming gamma-ray instruments.Comment: Final version of a review article, to appear in the Physics Reports
(82 pages, 31 figures). Figures requiring high quality are just too large and
too many to be included here. Please download them from
http://www.angelfire.com/id/dtorres/down3.htm
An X-ray characterization of the central region of the SNR G332.5-5.6
We present an X-ray analysis of the central region of supernova remnant (SNR)
G332.5-5.6 through an exhaustive analysis of XMM-Netwon observations with
complementary infrared observations. We characterize and discuss the origin of
the observed X-ray morphology, which presents a peculiar plane edge over the
west side of the central region. The morphology and spectral properties of the
X-ray supernova remnant were studied using a single full frame XMM-Newton
observation in the 0.3 to 10.0 keV energy band. Archival infrared WISE
observations at 8, 12 and 24 \mu m were also used to investigate the properties
of the source and its surroundings at different wavelengths. The results show
that the extended X-ray emission is predominantly soft (0.3-1.2 keV) and peaks
around 0.5 keV, which shows that it is an extremely soft SNR. X-ray emission
correlates very well with central regions of bright radio emission. On the west
side the radio/X-ray emission displays a plane-like feature with a terminal
wall where strong infrared emission is detected. Our spatially resolved X-ray
spectral analysis confirms that the emission is dominated by weak atomic
emission lines of N, O, Ne, and Fe, all of them undetected in previous X-ray
studies. These characteristics suggest that the X-ray emission is originated in
an optically thin thermal plasma, whose radiation is well fitted by a
non-equilibrium ionization collisional plasma (VNEI) X-ray emission model. Our
study favors a scenario where G332.5-5.6 is expanding in a medium with an
abrupt density change (the wall), likely a dense infrared emitting region of
dust on the western side of the source.Comment: 7 pages, 5 figures and 2 tables. Accepted for publication in A&
Study of the luminous blue variable star candidate G26.47+0.02 and its environment
Aims. The luminous blue variable (LBV) stars are peculiar very massive stars. The study of these stellar objects and their surroundings is important for understanding the evolution of massive stars and its effects on the interstellar medium. We study the LBV star candidate G26.47+0.02.
Methods. Using several large-scale surveys in different frequencies we performed a multiwavelength study of G26.47+0.02 and its surroundings.
Results. We found a molecular shell (seen in the 13CO J = 1-0 line) that partially surrounds the mid-infrared nebula of G26.47+0.02, which suggests an interaction between the strong stellar winds and the molecular gas. From the HI absorption and the molecular gas study we conclude that G26.47+0.02 is located at a distance of ~4.8 kpc. The radio continuum analysis shows both thermal and non-thermal emission toward this LBV candidate, pointing to wind-wind collision shocks from a binary system. This hypothesis is supported by a search of near-IR sources and the Chandra X-ray analysis. Additional multiwavelength and long-term observations are needed to detect some possible variable behavior, and if that is found, to confirm the binary nature of the system.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí
On the origin of the jet-like radio/X-ray morphology of G290.1-0.8
The origin and evolution of supernova remnants of the mixed-morphology class
is not well understood. Several remnants present distorted radio or X-ray
shells with jet-like structures. G290.1-0.8 (MSH 11-61A) belongs to this class.
We aim to investigate the nature of this supernova remnant in order to unveil
the origin of its particular morphology. We based our work on the study of the
X-ray emitting plasma properties and the conditions imposed by the cold
interstellar medium where the remnant expanded. We use archival radio, HI line
data and X-ray observations from XMM-Newton and Chandra observatories, to study
G290.1-0.8 and its surrounding medium. Spatially resolved spectral analysis and
mean photon energy maps are used to obtain physical and geometrical parameters
of the source. Radio continuum and HI line maps give crucial information to
understand the radio/X-ray morphology. The X-ray images show that the remnant
presents two opposite symmetric bright spots on a symmetry axis running towards
the NW-SE direction. Spectral analysis and mean photon energy maps confirm that
the physical conditions of the emitting plasma are not homogeneous throughout
the remnant. In fact, both bright spots have higher temperatures than the rest
of the plasma and its constituents have not reached ionization equilibrium yet.
HI line data reveal low density tube-like structures aligned along the same
direction. This evidence supports the idea that the particular X-ray morphology
observed is a direct consequence of the structure of the interstellar medium
where the remnant evolved. However, the possibility that an undetected
point-like object, as a neutron star, exists within the remnant and contributes
to the X-ray emission cannot be discarded. Finally, we suggest that a supernova
explosion due to the collapse of a high-mass star with a strong bipolar wind
can explain the supernova remnant morphology.Comment: 8 pages, 6 figures. Accepted for publication in A&
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