1,998 research outputs found
Periodic very high energy γ -Ray Emission from LS I +61◦303 Observed with the magic telescope
The MAGIC collaboration has recently reported the discovery of γ -ray emission from the binary system
LS I +61◦303 in the TeV energy region. Here we present new observational results on this source in the energy range
between 300 GeV and 3 TeV. In total, 112 hr of data were taken between 2006 September and December covering
four orbital cycles of this object. This large amount of data allowed us to produce an integral flux light curve covering
for the first time all orbital phases of LS I +61◦303. In addition, we also obtained a differential energy spectrum for
two orbital phase bins covering the phase range 0.5 < φ < 0.6 and 0.6 < φ < 0.7. The photon index in the two
phase bins is consistent within the errors with an average index Γ = 2.6±0.2stat ±0.2sys. LS I +61◦303 was found
to be variable at TeV energies on timescales of days. These new MAGIC measurements allowed us to search for
intranight variability of the very high energy emission; however, no evidence for flux variability on timescales down
to 30 min was found. To test for possible periodic structures in the light curve, we apply the formalism developed
by Lomb and Scargle to the LS I +61◦303 data taken in 2005 and 2006. We found the LS I +61◦303 data set to be
periodic with a period of (26.8 ± 0.2) days (with a post-trial chance probability of 10−7), close to the orbital period.Peer reviewe
Subarcsecond international LOFAR radio images of Arp 220 at 150 MHz: A kpc-scale star forming disk surrounding nuclei with shocked outflows
Context. Arp 220 is the prototypical ultra luminous infrared galaxy (ULIRG). Despite extensive studies, the structure at MHz-frequencies has remained unknown because of limits in spatial resolution. Aims. This work aims to constrain the flux and shape of radio emission from Arp 220 at MHz frequencies. Methods. We analyse new observations with the International Low Frequency Array (LOFAR) telescope, and archival data from the Multi-Element Radio Linked Interferometer Network (MERLIN) and the Karl G. Jansky Very Large Array (VLA). We model the spatially resolved radio spectrum of Arp 220 from 150 MHz to 33 GHz. Results. We present an image of Arp 220 at 150 MHz with resolution 0′. 65 × 0′. 35, sensitivity 0.15 mJy beam, and integrated flux density 394 ± 59 mJy. More than 80% of the detected flux comes from extended (6″∼ 2.2 kpc) steep spectrum (α = -0.7) emission, likely from star formation in the molecular disk surrounding the two nuclei. We find elongated features extending 0.3″ (110 pc) and 0.9″ (330 pc) from the eastern and western nucleus respectively, which we interpret as evidence for outflows. The extent of radio emission requires acceleration of cosmic rays far outside the nuclei. We find that a simple three component model can explain most of the observed radio spectrum of the galaxy. When accounting for absorption at 1.4 GHz, Arp 220 follows the FIR/radio correlation with q = 2.36, and we estimate a star formation rate of 220 M yr. We derive thermal fractions at 1 GHz of less than 1% for the nuclei, which indicates that a major part of the UV-photons are absorbed by dust. Conclusions. International LOFAR observations shows great promise to detect steep spectrum outflows and probe regions of thermal absorption. However, in LIRGs the emission detected at 150 MHz does not necessarily come from the main regions of star formation. This implies that high spatial resolution is crucial for accurate estimates of star formation rates for such galaxies at 150 MHz.A. A. and M.A.P.T. acknowledge support from the Spanish MINECO through grants AYA2012-38491-C02-02 and AYA2015-63939-C2-1-P, partially funded by FEDER funds.The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement No. 283393 (RadioNet3).Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts.Peer Reviewe
Evolution of the progenitors of SNe 1993J and 2011dh revealed through late time radio and X-ray studies
We perform hydrodynamical simulations of the interaction between supernova
(SN) ejecta and circumstellar medium (CSM) for SN 1993J and SN 2011dh, and
calculate the radio and X-ray emissions expected from the shocked gas at late
epochs (). Considering the ejecta structure from multi-group radiation
hydrodynamics simulation, we find that the observed rapid drop in radio and
X-ray light curves of SN 1993J at 3000 days can be due to a change in the
mass-loss rate () around 6500 years prior to the explosion of the
SN. The exact epoch scales inversely with the assumed wind velocity of . The progenitor of this SN very likely belonged to a binary
system, where, during its evolution, the primary had transferred material to
the secondary. It is argued in the paper that the change in can happen
because of a change in the mass accretion efficiency () of the companion
star. It is possible that before years
prior to the explosion, was high, thus the CSM was tenuous, which causes
the late time downturn in fluxes. In the case of SN 2011dh, the late time
evolution is found to be consistent with a wind medium with . It is difficult from
our analysis to predict whether the progenitor of this SN had a binary
companion, however, if future observations show similar decrease in radio and
X-ray fluxes, then that would give strong support to a scenario where both SNe
had undergone similar kind of binary evolution before explosion.Comment: 13 pages, 10 figures; Accepted for publication in Ap
Highly size-controlled synthesis of Au/Pd nanoparticles by inert-gas condensation
Gold/Palladium nanoparticles were fabricated by inert-gas condensation on a sputtering reactor. With this method, by controlling both the atmosphere on the condensation chamber and the magnetron power, it was possible to produce nanoparticles with a high degree of monodispersity in size. The structure and size of the Au/Pd nanoparticles were determined by mass spectroscopy, and confirmed by atomic force microscopy and electron transmission microscopy measurements. The chemical composition was analyzed by X-ray microanalysis. From these measurements we confirmed that with the sputtering technique we are able to produce particles of 1, 3, and 5 nm on size, depending on the choice of the synthesis conditions. From TEM measurements made both in the regular HREM, as well as in STEM-HAADF mode, we found that the particles are icosahedral in shape, and the micrographs show no evidence of a core-shell structure, in contrast to what is observed in the case of nanoparticles prepared by chemical synthesis
Radio Emission from SN 2001gd in NGC 5033
We present the results of monitoring the radio emission from the Type IIb
supernova SN 2001gd between 2002 February 8 and 2002 October 28. Most of the
data were obtained using the Very Large Array at the five wavelengths of
1.3 cm (22.4 GHz), 2.0 cm (14.9 GHz), 3.6 cm (8.44 GHz), 6.2
cm (4.86 GHz), and 21 cm (1.4 GHz). Observations were also made with Giant
Meterwave Radio Telescope at 21 cm (1.4 GHz). The object was
discovered optically well after maximum light, making any determination of the
early radio evolution difficult. However, subsequent observations indicate that
the radio emission has evolved regularly in both time and frequency and is well
described by the SN shock/circumstellar medium interaction model.Comment: 16 pages 2 figures to appear in Astrophysical Journa
MAGIC observation of the GRB 080430 afterglow
6 páginas, 1 figura.-- El Pdf del artículo es la versión pre-print: arXiv:1004.3665v2.-- MAGIC Collaboration: et al.[Context]: Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the long-lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment.
[Aims]: Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, being satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ~100 GeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies.
[Methods]: We used the results of the MAGIC telescope observation of the moderate resdhift (z ~ 0.76) GRB 080430 at energies above about 80 GeV, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes.
[Results]: We obtained an upper limit of F95% CL = 5.5 × 10-11 erg cm-2 s-1 for the very-high energy emission of GRB 080430, which cannot set further constraints on the theoretical scenarios proposed for this object also due to the difficulties in modeling the low-energy afterglow. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z ≲ 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase.The support of the German BMBF and MPG,
the Italian INFN and Spanish MICINN is gratefully acknowledged. This work
was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW
Grant N N203 390834, and by the YIP of the Helmholtz Gemeinschaft.Peer reviewe
VLBI observations of young Type II supernovae
Abstract. We give an overview of circumstellar interaction in young Type II supernovae, as seen through the eyes of verylong-baseline interferometry (VLBI) observations. The resolution attained by such observations ( < ∼ 1 mas) is a powerful tool to probe the interaction that takes place after a supernova goes off. The direct imaging of a supernova permits, in principle, to estimate the deceleration of its expansion, and to obtain information on the ejecta and circumstellar density profiles, as well as estimates of the magnetic field intensity and relativistic particle energy density in the supernova. Unfortunately, only a handful of radio supernovae are close and bright enough as to permit their study with VLBI. We present results from our high-resolution observations of the nearby Type II radio supernovae SN 1986J and SN 2001gd
The far-infrared-radio correlation in galaxies
The tightness and universality of the far-infrared (FIR) to radio continuum (RC) correlation is still not completely understood. This correlation is followed by all star-forming galaxies not dominated by an Active Galactic Nucleus, both globally as well as locally within the disks. There is a general consensus that star formation (SF) is the ultimate driver of the relation, in the sense that the bulk of dust emission in the FIR is powered by young stars ending their lives as supernovae which are the main sites of Cosmic Ray (CR) acceleration. Although this simplistic view is correct, it neglects many of the additional parameters that affect the correlation. Thus, a detailed understanding is still missing which is crucial in order to correctly use the RC emission as a tracer of recent SF with the important advantage not to be affected by extinction. Furthermore, a detailed understanding of the correlation will lead to a deeper understanding of dust heating, the interstellar medium (ISM) and propagation of CRs. The capabilities of the SKA are needed to make progress in our understanding of the correlation. In particular, they will allow us to (i) extend the study of the correlation to low-luminosity dwarf galaxies which are expected not to follow the correlation so well, (ii) extend the correlation to high-z objects and test whether the correlation is still fulfilled, and (iii) study the properties of CR propagation in galactic halos via changes in the spectral
index in order to be able to compare the relative relevance of propagation, escape and
energy losses.UL acknowledges support by the research projects AYA2011-24728 from the Spanish Ministerio de Ciencia y Educación and the Junta de Andalucía (Spain) grants FQM108. MAPT and AA acknowledge support from the Spanish Ministerio de Economía y Competitividad (MINECO) through grant AYA2012-38491-C02-02. AAH acknowledges support from the Spanish Plan Nacional de Astronomia y Astrofisica under grant AYA2012-31447, and LC from grant LC from grant AYA2012-32295.Peer Reviewe
IAA : Información y actualidad astronómica (44)
Sumario : La importancia de los cometas.--
Gamow, Alpher y el ylem.--
DECONSTRUCCIÓN Y otros ENSAYOS. El universo molecular.--
EL “MOBY DICK” DE... Alberto Molino (IAG).--
CIENCIA EN HISTORIAS...Tras la estela de Plateau.--
ACTUALIDAD.--
SALA LIMPIA.--
CIENCIA: PILARES E INCERTIDUMBRES. Explosiones de rayos gamma.N
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