Search

Infrared measurements of asteroids are crucial for the determination of physical and thermal properties of individual objects, and for the understanding of the small-body populations in the solar system as a whole. But standard radiometric methods can only be applied if the orbit of an object is known, hence its position at the time of the observation. We present MIRI observations of the outer-belt asteroid 10920 and an unknown object, detected in all 9 MIRI bands in close proximity to 10920. We developed a new method "STM-ORBIT" to interpret the multi-band measurements without knowing the object's true location. The method leads to a confirmation of radiometric size-albedo solution for 10920 and puts constraints on the asteroid's location and orbit in agreement with its true orbit. Groundbased lightcurve observations of 10920, combined with Gaia data, indicate a very elongated object (a/b >= 1.5), with a spin-pole at (l, b) = (178{\deg}, 81{\deg}), and a rotation period of 4.861191 h. A thermophysical study leads to a size of 14.5 - 16.5 km, a geometric albedo between 0.05 and 0.10, and a thermal inertia in the range 9 to 35 Jm-2s-0.5K-1. For the newly discovered MIRI object, the STM-ORBIT method revealed a size of 100-230 m. The new asteroid must be on a very low-inclination orbit and it was located in the inner main-belt region during JWST observations. A beaming parameter {\eta} larger than 1.0 would push the size even below 100 meter, a main-belt regime which escaped IR detections so far. These kind of MIRI observations can therefore contribute to formation and evolution studies via classical size-frequency studies which are currently limited to objects larger than about one kilometer in size. We estimate that MIRI frames with pointings close to the ecliptic and only short integration times of a few seconds will always include a few asteroids, most of them will be unknown objects., Comment: 17 pages, 10 figures, 4 tables, accepted for A&A publication on Nov 22, 2022

Full list of authors: Marciniak, A.; Ďurech, J.; Alí-Lagoa, V.; Ogłoza, W.; Szakáts, R.; Müller, T. G.; Molnár, L.; Pál, A.; Monteiro, F.; Arcoverde, P.; Behrend, R.; Benkhaldoun, Z.; Bernasconi, L.; Bosch, J.; Brincat, S.; Brunetto, L.; Butkiewicz-Bąk, M.; Del Freo, F.; Duffard, R.; Evangelista-Santana, M.; Farroni, G.; Fauvaud, S.; Fauvaud, M.; Ferrais, M.; Geier, S.; Golonka, J.; Grice, J.; Hirsch, R.; Horbowicz, J.; Jehin, E.; Julien, P.; Kalup, Cs.; Kamiński, K.; Kamińska, M. K.; Kankiewicz, P.; Kecskeméthy, V.; Kim, D. -H.; Kim, M. -J.; Konstanciak, I.; Krajewski, J.; Kudak, V.; Kulczak, P.; Kundera, T.; Lazzaro, D.; Manzini, F.; Medeiros, H.; Michimani-Garcia, J.; Morales, N.; Nadolny, J.; Oszkiewicz, D.; Pakštienė, E.; Pawłowski, M.; Perig, V.; Pilcher, F.; Pinel, P.; Podlewska-Gaca, E.; Polakis, T.; Richard, F.; Rodrigues, T.; Rondón, E.; Roy, R.; Sanabria, J. J.; Santana-Ros, T.; Skiff, B.; Skrzypek, J.; Sobkowiak, K.; Sonbas, E.; Stachowski, G.; Strajnic, J.; Trela, P.; Tychoniec, Ł.; Urakawa, S.; Verebelyi, E.; Wagrez, K.; Żejmo, M.; Żukowski, K., Context. Recent results for asteroid rotation periods from the TESS mission showed how strongly previous studies have underestimated the number of slow rotators, revealing the importance of studying those targets. For most slowly rotating asteroids (those with P > 12 h), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. Also, it is still unclear whether signatures of different surface material properties can be seen in thermal inertia determined from mid-infrared thermal flux fitting. Aims. We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. Our goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Methods. Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler and TESS spacecrafts. In addition to data in the visible range, we also use thermal data from infrared space observatories (mainly IRAS, Akari and WISE) in a combined optimisation process using the Convex Inversion Thermophysical Model. This novel method has so far been applied to only a few targets, and therefore in this work we further validate the method itself. Results. We present the models of 16 slow rotators, including two updated models. All provide good fits to both thermal and visible data.The obtained sizes are on average accurate at the 5% precision level, with diameters found to be in the range from 25 to 145 km. The rotation periods of our targets range from 11 to 59 h, and the thermal inertia covers a wide range of values, from 2 to, This work was was initiated with the support from the National Science Centre, Poland, through grant no. 2014/13/D/ST9/01818; and from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement no 687378 (SBNAF). The work of J.D. was supported by the grant 20-08218S of the Czech Science Foundation. A.P. and R.S. have been supported by the K-125015 grant of the National Research, Development and Innovation Office (NKFIH), Hungary. This project has been supported by the Lendulet grant LP2012-31 of the Hungarian Academy of Sciences. This project has been supported by the GINOP-2.3.2-15-2016-00003 grant of the Hungarian National Research, Development and Innovation Office (NKFIH). L.M. was supported by the Premium Postdoctoral Research Program of the Hungarian Academy of Sciences. The research leading to these results has received funding from the LP2018-7/2020 Lendulet grant of the Hungarian Academy of Sciences. The work of T.S.-R. was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain). This work was supported by the MINECO (Spanish Ministry of Economy) through grant RTI2018-095076-B-C21 (MINECO/FEDER, UE). E. P. acknowledges the Europlanet 2024 RI project funded by the European Union's Horizon 2020 Research and Innovation Programme (Grant agreement No. 871149). This article is based on observations obtained at the Observatorio Astronomico do Sertao de Itaparica (OASI, Itacuruba) of the Observatorio Nacional, Brazil. F.M. would like to thank the financial support given by FAPERJ (Process E-26/201.877/2020). E.R., P.A., H.M., M.E. and J.M. would like to thank CNPq and CAPES (Brazilian agencies) for their support through diverse fellowships. Support by CNPq (Process 305409/2016-6) and FAPERJ (Process E-26/202.841/2017) is acknowledged by D.L. The Joan Oro Telescope (TJO) of the Montsec Astronomical Observatory (OAdM) is owned by the Catalan Government and operated by the Institute for Space Studies of Catalonia (IEEC). This article is based on observations made in the Observatorios de Canarias del IAC with the 0.82 m IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofisica de Canarias (IAC) in the Observatorio del Teide. This article is based on observations made with the SARA telescopes (Southeastern Association for Research in Astronomy), whose nodes are located at the Observatorios de Canarias del IAC on the island of La Palma in the Observatorio del Roque de los Muchachos; Kitt Peak, AZ under the auspices of the National Optical Astronomy Observatory (NOAO); and Cerro Tololo Inter-American Observatory (CTIO) in La Serena, Chile. This project uses data from the SuperWASP archive. The WASP project is currently funded and operated by Warwick University and Keele University, and was originally set up by Queen's University Belfast, the Universities of Keele, St. Andrews, and Leicester, the Open University, the Isaac Newton Group, the Instituto de Astrofisica de Canarias, the South African Astronomical Observatory, and by STFC. TRAPPIST-South is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant PDR T.0120.21. TRAPPIST-North is a project funded by the University of Liege, in collaboration with the Cadi Ayyad University of Marrakech (Morocco). E. Jehin is FNRS Senior Research Associate. Funding for the Kepler and K2 missions are provided by the NASA Science Mission Directorate. The data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. 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. Data from Pic du Midi Observatory have been obtained with the 0.6-m telescope, a facility operated by Observatoire Midi Pyrenees and Association T60, an amateur association. We acknowledge the contributions of the occultation observers who have provided the observations in the dataset. Most of those observers are affiliated with one or more of: European Asteroidal Occultation Network (EAON), International Occultation Timing Association (IOTA), International Occultation Timing Association European Section (IOTA/ES), Japanese Occultation Information Network (JOIN), and Trans Tasman Occultation Alliance (TTOA)., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Context. Thanks to the Gaia mission, it will be possible to determine the masses of approximately hundreds of large main belt asteroids with very good precision. We currently have diameter estimates for all of them that can be used to compute their volume and hence their density. However, some of those diameters are still based on simple thermal models, which can occasionally lead to volume uncertainties as high as 20-30%. Aims. The aim of this paper is to determine the 3D shape models and compute the volumes for 13 main belt asteroids that were selected from those targets for which Gaia will provide the mass with an accuracy of better than 10%. Methods. We used the genetic Shaping Asteroids with Genetic Evolution (SAGE) algorithm to fit disk-integrated, dense photometric lightcurves and obtain detailed asteroid shape models. These models were scaled by fitting them to available stellar occultation and/or thermal infrared observations. Results. We determine the spin and shape models for 13 main belt asteroids using the SAGE algorithm. Occultation fitting enables us to confirm main shape features and the spin state, while thermophysical modeling leads to more precise diameters as well as estimates of thermal inertia values. Conclusions. We calculated the volume of our sample of main-belt asteroids for which the Gaia satellite will provide precise mass determinations. From our volumes, it will then be possible to more accurately compute the bulk density, which is a fundamental physical property needed to understand the formation and evolution processes of small Solar System bodies. © ESO 2020., The research leading to these results has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement no 687378 (SBNAF). Funding for the Kepler and K2 missions is provided by the NASA Science Mission directorate. L.M. was supported by the Premium Postdoctoral Research Program of the Hungarian Academy of Sciences. The research leading to these results has received funding from the LP2012-31 and LP2018-7 Lendulet grants of the Hungarian Academy of Sciences. This project has been supported by the Lendulet grant LP2012-31 of the Hungarian Academy of Sciences and by the GINOP-2.3.2-15-2016-00003 grant of the Hungarian National Research, Development and Innovation Office (NKFIH). TRAPPIST-South is a project funded by the Belgian Fonds de la Recherche Scientifique (F.R.S.-FNRS) under grant FRFC 2.5.594.09.F. TRAPPIST-North is a project funded by the University of Liege, and performed in collaboration with Cadi Ayyad University of Marrakesh. E.J. is a FNRS Senior Research Associate. "The Joan Oro Telescope (TJO) of the Montsec Astronomical Observatory (OAdM) is owned by the Catalan Government and operated by the Institute for Space Studies of Catalonia (IEEC)." "This article is based on observations made with the SARA telescopes (Southeastern Association for Research in Astronomy), whose node is located at the Kitt Peak National Observatory, AZ under the auspices of the National Optical Astronomy Observatory (NOAO)." "This project uses data from the SuperWASP archive. The WASP project is currently funded and operated by Warwick University and Keele University, and was originally set up by Queen's University Belfast, the Universities of Keele, St. Andrews, and Leicester, the Open University, the Isaac Newton Group, the Instituto de Astrofisica de Canarias, the South African Astronomical Observatory, and by STFC." "This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration." The work of TSR was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain)

With the aim of characterizing the dynamical processes involved in the formation of young protostars, we present high-angular-resolution ALMA dust polarization observations of the Class 0 protostellar cores Serpens SMM1, Emb 8(N), and Emb 8. With spatial resolutions ranging from 150 to 40 au at 870 μm, we find unexpectedly high values of the polarization fraction along the outflow cavity walls in Serpens Emb 8(N). We use 3 mm and 1 mm molecular tracers to investigate outflow and dense-gas properties and their correlation with the polarization. These observations allow us to investigate the physical processes involved in the radiative alignment torques (RATs) acting on dust grains along the outflow cavity walls, which experience irradiation from accretion processes and outflow shocks. The inner core of SMM1-a presents a polarization pattern with a poloidal magnetic field at the bases of the two lobes of the bipolar outflow. To the south of SMM1-a we see two polarized filaments, one of which seems to trace the redshifted outflow cavity wall. The other may be an accretion streamer of material infalling onto the central protostar. We propose that the polarized emission we see at millimeter wavelengths along the irradiated cavity walls can be reconciled with the expectations of RAT theory if the aligned grains present at μm size of dust grains in the interstellar medium. Our observations allow us to constrain the magnetic field morphologies of star-forming sources within the central cores, along the outflow cavity walls, and in possible accretion streamers.

The hot accretion flows upon black holes are usually optically thin two-temperature plasmas in which electrons can achieve temperatures up to , producing radiation via synchrotron, bremsstrahlung and inverse Compton, and the ions can reach temperatures up to . The hottest ions might produce gamma emission through proton-proton interactions. In this work, we considered a particular model of a hot accretion flow and estimate the spectral energy distributions produced by both species of particles. Fil: Gutiérrez, Eduardo Mario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina Fil: Vieyro, Florencia Laura. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina Fil: Romero, Gustavo Esteban. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina

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 ($t$). 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 $t>$3000 days can be due to a change in the mass-loss rate ($\dot M$) around $\sim$6500 years prior to the explosion of the SN. The exact epoch scales inversely with the assumed wind velocity of $v_{\rm w}=10~ km~s^{-1}$. 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 $\dot M$ can happen because of a change in the mass accretion efficiency ($\eta$) of the companion star. It is possible that before $\sim6500~(v_{\rm w}/10~km~s^{-1})^{-1}$years prior to the explosion, $\eta$ 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 $\dot M/v_{\rm w}=4\times10^{-6 }~M_{\odot}~ yr^{-1}/10 ~{km ~s^{-1}}$. 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 ApJ

Context: Radio continuum surveys of the Galactic plane are an excellent way to identify different source populations such as planetary nebulae, H Ⅱ regions, and radio stars and characterize their statistical properties. The Global View of Star Formation in the Milky Way (GLOSTAR) survey will study the star formation in the Galactic plane between −2° < ℓ < 85° and |b| < 1° with unprecedented sensitivity in both flux density (∼40 μJy beam⁻¹) and range ofangular scales (∼1″.5 to the largest radio structures in the Galaxy). Aims: In this paper we present the first results obtained from a radio continuum map of a 16-square-degree-sized region of the Galactic plane centered on ℓ = 32° and b = 0° (28° < ℓ < 36° and |b

Context.The near-Earth asteroid (1917) Cuyo was subject to radar and light curve observations during a close approach in 1989, and observed up until 2008. It was selected as one of our ESO Large Programme targets, aimed at observational detections of the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect through long-term light curve monitoring and physical modelling of near-Earth asteroids.Aims.We aim to constrain the physical properties of Cuyo: shape, spin-state, and spectroscopic and thermo-physical properties of the surface.Methods.We acquired photometric light curves of Cuyo spanning the period between 2010 and 2013, which we combined with published light curves from 1989 to 2008. Our thermal-infrared observations were obtained in 2011. Rotationally resolved optical spectroscopy data were acquired in 2011 and combined with all available published spectra to investigate any surface material variegation.Results.We developed a convex light curve-inversion shape of Cuyo that suggests the presence of an equatorial ridge, typical for an evolved system close to shedding mass due to fast rotation. We determine limits of YORP strength through light curve-based spin-state modelling, including both negative and positive acceleration values, between − 0.7 × 10−8and 1.7 × 10−8rad day−2. Thermo-physical modelling with the ATPM provides constraints on the geometric albedo,pV= 0.24 ± 0.07, the effective diameter,Deff= 3.15 ± 0.08km, the thermal inertia, Γ = 44 ± 9 J m−2s−1∕2K−1, and a roughness fraction of 0.52 ± 0.26. This enabled a YORP strength prediction ofν= (−6.39 ± 0.96) × 10−10rad day−2. We also see evidence of surface compositional variation.Conclusions.The low value of YORP predicted by means of thermo-physical analysis, consistent with the results of the light curve study, might be due to the self-limiting properties of rotational YORP, possibly involving movement of sub-surface and surface material. This may also be consistent with the surface compositional variation that we see. The physical model of Cuyo can be used to investigate cohesive forces as a way to explain why some targets survive rotation rates faster than the fission limit.

We report on the investigation of a very high-energy, Galactic γ-ray source recently discovered at >50 GeV using the Large Area Telescope on board Fermi. This object, 2FHL J0826.1-4500, displays one of the hardest >50 GeV spectra (photon index Γγ ∼ 1.6) in the 2FHL catalog, and a follow-up observation with XMM-Newton has uncovered diffuse, soft thermal emission at the position of the γ-ray source. A detailed analysis of the available multi-wavelength data shows that this source is located on the western edge of the Vela supernova remnant (SNR): the observations and the modeling of the spectral energy distribution support a scenario where this γ-ray source is the byproduct of the interaction between the SNR shock and a neutral hydrogen cloud. If confirmed, this shock-cloud interaction would make 2FHL J0826.1-4500 a promising candidate for efficient particle acceleration. Fil: Eagle, J.. Clemson University; Estados Unidos Fil: Marchesini Serres, Magdalena. Clemson University; Estados Unidos Fil: Castro, D.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos Fil: Ajello, M.. Clemson University; Estados Unidos Fil: Duvidovich, Laura Patricia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Tibaldo, L.. Observatoire Midi Pyrnes; Francia

Recent observations which resolved the mid-infrared (MIR) emission of nearby active galactic nuclei (AGN), surprisingly revealed that their dust emission appears prominently extended in the polar direction, at odds with the expectations from the canonical dusty torus. This polar dust, tentatively associated with dusty winds driven by radiation pressure, is found to have a major contribution to the MIR flux from scales of a few to hundreds of parsecs. When facing a potential change of paradigm, case studies of objects with the best intrinsic resolution are essential. One such source with a clear detection of polar dust is a nearby, well-known AGN in the Circinus galaxy. In the first paper, we successfully explained the peculiar MIR morphology of Circinus observed on large, tens of parsec scales with a model consisting of a compact dusty disc and an extended hollow dusty cone. In this work, we further refine the model on smaller, parsecs scales to test whether it can also explain the MIR interferometric data. We find that a model composed of a thin dusty disc seen almost edge-on and a polar outflow in the form of a hyperboloid shell can reproduce well the VLTI/MIDI observations at all wavelengths, baselines and position angles. In contrast, while providing a good fit to the integrated MIR spectrum, the dusty torus model fails to reproduce the spatially resolved interferometric data. We put forth the disc$+$hyperboloid wind model of Circinus AGN as a prototype for the dust structure in the AGN population with polar dust., Comment: MNRAS accepted

We conduct forward-modeling analysis based on our 2.5 dimensional magnetohydrodynamics (MHD) simulation of magnetic flux rope (MFR) formation and eruption driven by photospheric converging motion. The current sheet (CS) evolution during the MFR formation and eruption process in our MHD simulation can be divided into four stages. The current sheet (CS) evolution during the MFR formation and eruption process in our MHD simulation can be divided into four stages. The first stage shows the CS forming and gradually lengthening. Resistive instabilities that disrupt the CS mark the beginning of the second stage. Magnetic islands disappear in the third stage and reappear in the fourth stage. Synthetic images and light curves of the seven Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) channels, i.e., 9.4 nm, 13.1 nm, 17.1 nm, 19.3 nm, 21.1 nm, 30.4 nm, and 33.5 nm, and the 3-25 keV thermal X-ray are obtained with forward-modeling analysis. The loop-top source and the coronal sources of the soft X-ray are reproduced in forward modeling. The light curves of the seven SDO/AIA channels start to rise once resistive instabilities develop. The light curve of the 3-25 keV thermal X-ray starts to go up when the reconnection rate reaches one of its peaks. Quasiperiodic pulsations (QPPs) appear twice in the SDO/AIA 17.1 nm, 21.1 nm, and 30.4 nm channels, corresponding to the period of chaotic (re)appearance and CS-guided displacements of the magnetic islands. QPPs appear once in the SDO/AIA 9.4 nm and 33.5 nm channels after the disruption of the CS by resistive instabilities and in the 19.3 nm channel when the chaotic motion of the magnetic islands reappears., The content of the paper has been published on ApJ. This version on arXiv is an improved version of the published one in ApJ, and some typos in the published one have been corrected

A large fraction of gamma-ray burst (GRB) spectra are very hard below the peak. Indeed, the observed distribution of sub-peak power-law indices, $\alpha$, has been used as an argument for a photospheric origin of GRB spectra. Here, we investigate what fraction of GRBs have spectra that are consistent with emission from a photopshere in a non-dissipative outflow. This is the simplest possible photospheric emission scenario. We create synthetic spectra, with a range of peak energies, by folding the theoretical predictions through the detector response of the FERMI/GBM detector. These simulated spectral data are fit with typically employed empirical models. We find that the low-energy photon indices obtain values ranging $-0.4 < \alpha < 0.0$, peaking at around $-0.1$, thus covering a non-negligible fraction of observed values. These values are significantly softer than the asymptotic value of the theoretical spectrum of $\alpha \sim 0.4$. The reason for the $\alpha$-values to be much softer than expected, is the limitation of the empirical functions to capture the true curvature of the theoretical spectrum. We conclude that more than a $1/4$ of the bursts in the GBM catalogue have at least one time-resolved spectrum, whose $\alpha$-values are consistent with a non-dissipative outflow, releasing its thermal energy at the photosphere. The fraction of spectra consistent with emission from the photosphere will increase even more if dissipation of kinetic energy in the flow occurs below the photosphere., Comment: Accepted; MNRAS

We present high-angular-resolution radio observations of the Arches cluster in the Galactic centre, one of the most massive young clusters in the Milky Way. The data were acquired in two epochs and at 6 and 10 GHz with the Karl G. Jansky Very Large Array. The rms noise reached is three to four times better than during previous observations and we have almost doubled the number of known radio stars in the cluster. Nine of them have spectral indices consistent with thermal emission from ionised stellar winds, one is a confirmed colliding wind binary, and two sources are ambiguous cases. Regarding variability, the radio emission appears to be stable on timescales of a few to ten years. Finally, we show that the number of radio stars can be used as a tool for constraining the age and/or mass of a cluster and also its mass function. © ESO 2021., Karl G. Jansky Very Large Array (JVLA) of the National Radio Astronomy Observatory (NRAO) is a facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities, Inc. A.T.G.-C., R.S., A.A. and B.S. acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). A.T.G.-C., R.S., and B.S. acknowledge financial support from national project PGC2018-095049-B-C21 (MCIU/AEI/FEDER, UE). A.A. acknowledges support from national project PGC2018-098915-B-C21 (MCIU/AEI/FEDER, UE). F.N. acknowledges financial support through Spanish grants ESP2017-86582-C4-1-R and PID2019-105552RB-C41 (MINECO/MCIU/AEI/FEDER) and from the Spanish State Research Agency (AEI) through the Unidad de Excelencia "Maria de Maeztu"-Centro de Astrobiologia (CSIC-INTA) project No. MDM-2017-0737. F.N.-L. gratefully acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project-ID 138713538 - SFB 881 ("The Milky Way System", subproject B8). The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no [614922].

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Jets and outflows are ubiquitous in the process of formation of stars since outflow is intimately associated with accretion. Free–free (thermal) radio continuum emission in the centimeter domain is associated with these jets. The emission is relatively weak and compact, and sensitive radio interferometers of high angular resolution are required to detect and study it. One of the key problems in the study of outflows is to determine how they are accelerated and collimated. Observations in the cm range are most useful to trace the base of the ionized jets, close to the young central object and the inner parts of its accretion disk, where optical or near-IR imaging is made difficult by the high extinction present. Radio recombination lines in jets (in combination with proper motions) should provide their 3D kinematics at very small scale (near their origin). Future instruments such as the Square Kilometre Array (SKA) and the Next Generation Very Large Array (ngVLA) will be crucial to perform this kind of sensitive observations. Thermal jets are associated with both high and low mass protostars and possibly even with objects in the substellar domain. The ionizing mechanism of these radio jets appears to be related to shocks in the associated outflows, as suggested by the observed correlation between the centimeter luminosity and the outflow momentum rate. From this correlation and that of the centimeter luminosity with the bolometric luminosity of the system it will be possible to discriminate between unresolved HII regions and jets, and to infer additional physical properties of the embedded objects. Some jets associated with young stellar objects (YSOs) show indications of non-thermal emission (negative spectral indices) in part of their lobes. Linearly polarized synchrotron emission has been found in the jet of HH 80–81, allowing one to measure the direction and intensity of the jet magnetic field, a key ingredient to determine the collimation and ejection mechanisms. As only a fraction of the emission is polarized, very sensitive observations such as those that will be feasible with the interferometers previously mentioned are required to perform studies in a large sample of sources. Jets are present in many kinds of astrophysical scenarios. Characterizing radio jets in YSOs, where thermal emission allows one to determine their physical conditions in a reliable way, would also be useful in understanding acceleration and collimation mechanisms in all kinds of astrophysical jets, such as those associated with stellar and supermassive black holes and planetary nebulae.© 2018, The Author(s). GA acknowledges support from MINECO (Spain) AYA2014-57369-C3-3-P and AYA2017-84390-C2-1-R grants (co-funded by FEDER). LFR acknowledges support from CONACyT, Mexico and DGAPA, UNAM. CC-G acknowledges support from UNAM-DGAPA-PAPIIT grant numbers IA102816 and IN108218. We thank an anonymous referee for his/her useful comments and suggestions.

Schindler, K. et. al., Context. A stellar occultation by a trans-Neptunian object (TNO) provides an opportunity to probe the size and shape of these distant solar system bodies. In the past seven years, several occultations by TNOs have been observed, but mostly from a single location. Only very few TNOs have been sampled simultaneously from multiple locations. Sufficient data that enable a robust estimation of shadow size through an ellipse fit could only be obtained for two objects. Aims. We present the first observation of an occultation by the TNO 2007 UK126 on 15 November 2014, measured by three observers, one nearly on and two almost symmetrical to the shadow's centerline. This is the first multi-chord dataset obtained for a so-called detached object, a TNO subgroup with perihelion distances so large that the giant planets have likely not perturbed their orbits. We also revisit Herschel/PACS far-infrared data, applying a new reduction method to improve the accuracy of the measured fluxes. Combining both datasets allows us to comprehensively characterize 2007 UK126. Methods. We use error-in-variable regression to solve the non-linear problem of propagating timing errors into uncertainties of the ellipse parameters. Based on the shadow's size and a previously reported rotation period, we expect a shape of a Maclaurin spheroid and derive a geometrically plausible size range. To refine our size estimate of 2007 UK126, we model its thermal emission using a thermophysical model code. We conduct a parametric study to predict far-infrared fluxes and compare them to the Herschel/PACS measurements. Results. The favorable geometry of our occultation chords, combined with minimal dead-time imaging, and precise GPS time measurements, allow for an accurate estimation of the shadow size (best-fitting ellipse with axes 645.80 +/- 5.68 km x 597.81 +/- 12.74 km) and the visual geometric albedo (p(V) = 15.0 +/- 1.6%). By combining our analyses of the occultation and the far-infrared data, we can constrain the effective diameter of 2007 UK126 to d(eff) = 599-629 km. We conclude that subsolar surface temperatures are in the order of approximate to 50 55 K., K.S. has been supported financially by a one-year fellowship from the German Academic Exchange Service (DAAD) during his stay at NASA Ames Research Center, CA as part of his Ph.D. research. K.S. would also like to thank the Universities Space Research Association (USRA) for their support throughout his thesis. T.M., C.K. and J.L.O. have received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378. C.K. has been supported by the PECS grant # 4000109997/13/NL/KML of the Hungarian Space Office and the European Space Agency, the K-104607 grant of the Hungarian Research Fund (OTKA), and the GINOP-2.3.2-15-2016 00003 grant of the National Research, Development and Innovation Office of Hungary (NKFIH). J.L.O. acknowledges support from Proyecto de Excelencia J.A. 2012-FQM1776.

We study the narrowest spectra expected from gamma-ray bursts. We present an analytical function for the spectrum that is emitted from the photosphere of a radiation-dominated flow that is under acceleration. This is the narrowest possible spectrum and it differs from a Planck function. We also present numerical spectra from photospheres occurring during the transition into the coasting phase of the flow. Using these spectral models, we reanalyse Fermi observations of GRB100507 and GRB101219, which both have been reported to have very narrow spectra. The bursts can be fitted by the spectral models: For GRB101219 the spectrum is consistent with the photosphere occurring below or close to the saturation radius, while for GRB100507 the photosphere position relative to the saturation radius can be determined as a function of time. In the latter case, we find that the photosphere initially occurs in the acceleration phase and thereafter transitions into the coasting phase. We also find that this transition occurs at the same time as the change in observed cooling behaviour: the temperature is close to constant before the break and decays after. We argue that such a transition can be explained by an increasing mass outflow rate. Both analysed bursts thus give strong evidence that the jets are (initially) radiation dominated., Comment: Accepted by MNRAS

Full list of authors: Höfner, S.; Vincent, J. -B.; Blum, J.; Davidsson, B. J. R.; Sierks, H.; El-Maarry, M. R.; Deller, J.; Hofmann, M.; Hu, X.; Pajola, M.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; A'Hearn, M. F.; Auger, A. -T.; Barucci, M. A.; Bertaux, J. -L. Bertini, I.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Fornasier, S.; Fulle, M.; Gicquel, A.; Groussin, O.; Gutiérrez, P. J.; Gutiérrez-Marqués, P.; Güttler, C.; Hviid, S. F.; Ip, W. -H.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J. -R.; Kührt, E.; Küppers, M.; La Forgia, F.; Lazzarin, M.; Lopez-Moreno, J. J.; Marzari, F.; Michalik, H.; Moissl-Fraund, R.; Moreno, F.; Mottola, S.; Naletto, G.; Oklay, N.; Preusker, F.; Scholten, F.; Shi, X.; Thomas, N.; Toth, I.; Tubiana, C.; Zitzmann, S., The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain. Aims. Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Observed temperatures and gas production rates can be explained or interpreted with the presence of fractures by applying appropriate modelling methods. Methods. We followed a transient thermophysical model approach that includes radiative, conductive, and water-ice sublimation fluxes by considering a variety of heliocentric distances, illumination conditions, and thermophysical properties for a set of characteristic fracture geometries on the nucleus of 67P. We computed diurnal temperatures, heat fluxes, and outgassing behaviour in order to derive and distinguish the influence of the mentioned parameters on fractured terrain. Results. Our analysis confirms that fractures, as already indicated by former studies about concavities, deviate from flat-terrain topographies with equivalent properties, mostly through the effect of self-heating. Compared to flat terrain, illuminated cometary fractures are generally warmer, with smaller diurnal temperature fluctuations. Maximum sublimation rates reach higher peaks, and dust mantle quenching effects on sublimation rates are weaker. Consequently, the rough structure of the fractured terrain leads to significantly higher inferred surface thermal inertia values than for flat areas with identical physical properties, which might explain the range of measured thermal inertia on 67P. Conclusions. At 3.5 AU heliocentric distance, sublimation heat sinks in fractures converge to maximum values >50 W / m2 and trigger dust activity that can be related mainly to H2O. Fractures are likely to grow through the erosive interplay of alternating sublimation and thermal fatigue. © ESO, 2017., OSIRIS was built by a consortium led by the Max-Planck-Institut fur Sonnensystemforschung, Gottingen, Germany, in collaboration with CISAS, University of Padova, Italy, the Laboratoire d'Astrophysique de Marseille, France, the Instituto de Astrofisica de Andalucia, CSIC, Granada, Spain, the Scientific Support OCE of the European Space Agency, Noordwijk, The Netherlands, the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain, the Universidad Politecnica de Madrid, Spain, the Department of Physics and Astronomy of Uppsala University, Sweden, and the Institut fur Datentechnik und Kommunikationsnetze der Technischen Universitat Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MINECO), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Mission Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission. The first author also wishes to thank the MPS for funding a research stipend, B. Gundlach for the helpful discussions of the application of his porous aggregate model, ITP Engines UK for providing a Ph.D. student research license of ESATAN-TMS (https://www.esatan-tms.com), which was used in this analysis, and the MPS Solar Orbiter Team for the funding of this licence. The authors gratefully acknowledge the referee work of Nalin Samarasinha, whose comments were very helpful in increasing the quality of this paper.

Radio observations of young stellar objects (YSOs) enable the study of ionised plasma outflows from young protostars via their free-free radiation. Previous studies of the low-mass young system T Tau have used radio observations to model the spectrum and estimate important physical properties of the associated ionised plasma (local electron density, ionised gas content and emission measure). However, without an indication of the low-frequency turnover in the free-free spectrum, these properties remain difficult to constrain. This paper presents the detection of T Tau at 149 MHz with the Low Frequency Array (LOFAR) - the first time a YSO has been observed at such low frequencies. The recovered total flux indicates that the free-free spectrum may be turning over near 149 MHz. The spectral energy distribution is fitted and yields improved constraints on local electron density ($(7.2 \pm 2.1)\times10^{3}$ cm$^{-3}$), ionised gas mass ($(1.0 \pm 1.8)\times10^{-6}$ M$_{\odot}$) and emission measure ($(1.67 \pm 0.14)\times10^5$ pc cm$^{-6}$)., Comment: 10 pages, accepted for publication in ApJ

Los blázares son un tipo de núcleo activo de galaxia (AGN, por sus siglas en inglés) que se encuentran entre los objetos astrofísicos más energéticos y violentos, a la par de los brotes de rayos gamma (GRB por sus siglas en inglés). Los procesos físicos y, en particular, el escenario del chorro relativista en el que se genera la radiación ultraenergética detectada por observatorios terrestres y en órbita, han conseguido atraer la atención e interés de los astrónomos y astrofísicos desde su descubrimiento. En la presente tesis investigamos el modelo de choques internos (IS) cuya hipótesis consta del choque de dos capas de plasma con geometría cilíndrica, formando dos ondas de choque que atraviesan las antedichas capas acelerando electrones a su paso: tanto térmicos como no térmicos. Dichos electrones interaccionan con el campo magnético presente en el chorro produciendo, de acuerdo con las observaciones, emisión magnetobremsstrahlung (MBS). En este modelo consideramos también que el chorro se encuentra envuelto en un ambiente de fotones monocromático, que equivaldría a la región de banda ancha (BLR) de un AGN. Ambos tipos de fotones, los del medio externo y los producidos in situ, eventualmente interaccionan con los electrones acelerados mediante la dispersión Compton inversa (IC). El objetivo básico de la presente tesis ha sido la búsqueda de algún indicio que pudiera revelar las huellas dejadas tanto por la magnetización de las capas como por la distribución energética de los electrones (EED) inyectados en el frente de choque en la distribución espectral de energía (SED). Nuestro enfoque ha sido numérico, lo cual significa que se desarrollaron herramientas numéricas sofisticadas, ampliando las ya existentes desarrolladas previamente y creando nuevas, que hemos usado sistemáticamente para simular el modelo de IS y reproducir las SEDs espectralmente amplias de los blázares. Entre estas mejoras se encuentra la manipulación adecuada de distribuciones híbridas (térmicas-no térmicas) de electrones, así como también el cómputo correcto de la emisión MBS de los electrones inmersos en el campo magnético amplificado en las regiones del plasma que las ondas de choque han atravesado. Datos observacionales fueron empleados para corroborar dichas simulaciones y delimitar el espacio de parámetros para, de esta forma, conseguir que nuestras SEDs sintéticas estuviesen en concordancia con las observaciones. Mostramos a partir de simulaciones que, si examinamos la dominancia Compton y el índice espectral de fotones en la banda de rayos gamma, una parte comsiderable de la secuencia de los blázares podría ser explicada por la magnetización de las capas; siendo las menos magnetizadas las que se encuentran en la región de los radiocuásares de espectro plano (FSRQs), mientras que las capas medianamente magnetizadas caen en la región de los objetos BL Lacertae (BL Lac). Por otra parte, al incluir electrones térmicos en la población inyectada y agregar la herramienta numérica que nos permite reproducir la emisión MBS de electrones poco energéticos, encontramos que el valle que separa las componentes sincrotrón e IC se hace más "profundo" cuando las distributiones inyectadas en el frente de choque son dominadas por electrones térmicos. Para estos casos descubrimos que el pico sincrotrón varía ligeramente entre modelos (10^11-10^13 Hz), al contrario de una componente IC sensible a la variación de parámetros. Este efecto induce una dispersión vertical en el plano dominancia Compton-pico sincrotrón, sugiriendo que quizá la proporción de electrones térmicos sobre los no térmicos está relacionada con la posición de los blázares en ese plano. Blazars are a type of active galactic nuclei (AGNs) which are among the most energetic and violent astrophysical objects, alongside γ-ray bursts (GRBs). The physical processes, and, in particular, the relativistic jet itself in which the high energy radiation detected by the terrestrial and space observatories is generated, has been attracting the attention and interest of astronomers and astrophysicists since their discovery. In the present thesis, we investigate the internal shock (IS) model in which two magnetized shells of plasma, with cylindrical geometry, collide forming shock waves, which propagate throughout the plasma accelerating electrons (thermal and nonthermal) in their wake. Those electrons interact with the magnetic field of the jet producing magnetobremsstrahlung emission, which is detected by observations. In this model we also consider that the surroundings of the jet in which this collision takes place are filled with a monochromatic photon field, which emulates the more complex broad line region (BLR) of the AGN. Both photons from the external field and those produced in situ are Compton upscattered by the accelerated electrons. The main work of the present thesis has been the search of signatures imprinted on the double bump spectral energy distribution (SED) of blazars that may uncover the degree of the shell magnetization and the profile of the electrons energy distribution (EED) injected at the shock front. We have approached the problem numerically, so that a fair fraction of the work has consisted on improving already existing sophisticated numerical tools or developing new ones from scratch. Among those improvements are the handling of hybrid distributions (thermal-nonthermal) of electrons, and the accurate computation of the magnetobremsstrahlung emission of the electrons immersed in the amplified magnetic field in the shocked region of the plasma shells. We have used these numerical tools to simulate the IS model and reproduce broadband SEDs of blazars. To validate our methodology and put bounds on the parameters of our model, observational data has been analyzed so that the generated SEDs are able to reproduce generic observational data and inferred physical trends. From the Compton dominance and the spectral index of γ-ray photons obtained in our models, we infer that a fair fraction of the blazar sequence could be explained by the shells magnetization; the negligibly magnetized models describing the Flat Spectrum Radio Quasars (FSRQs) region, whereas moderately magnetized shells fall into the BL Lacertae object (BL Lac) region. On the other hand, by including thermal electrons into the population of injected particles and using a numerical tool which reproduces the low energy region of the magnetobremsstrahlung (MBS) emission, we have found that the valley which separates the synchrotron and inverse-Compton (IC) components grows deeper when thermal dominated distributions are injected at the shock front. A slightly varying synchrotron peak between 1011–1013 Hz, in contrast with a parameters dependent IC component. These effects induce a scattering in the vertical direction of the Compton dominance-synchrotron peak plane. From this clear fact, we cautiously suggest that the proportions of the thermal/nonthermal electrons have a prominent role explaining the location of blazars in that plane.

We present new 3D numerical simulations for Kepler´s supernova remnant. In this work we revisit the possibility that the asymmetric shape of the remnant in X-rays is the product of a type Ia supernova explosion which occurs inside the wind bubble previously created by an AGB companion star. Due to the large peculiar velocity of the system, the interaction of the strong AGB wind with the interstellar medium results in a bow shock structure. In this new model we propose that the AGB wind is anisotropic, with properties such as mass-loss rate and density having a latitude dependence, and that the orientation of the polar axis of the AGB star is not aligned with the direction of motion. The ejecta from the type Ia supernova explosion is modeled using a power-law density prole, and we let the remnant evolve for 400 yr. We computed synthetic X-ray maps from the numerical results. We find that the estimated size and peculiar X-ray morphology of Kepler´s SNR are well reproduced by considering an AGB mass-loss rate of 10-5 M_sol yr-1, a wind terminal velocity of 10 km s-1, an ambient medium density of 10-3 cm^3 and an explosion energy of 7x10^50 erg. The obtained total X-ray luminosity of the remnant in this model reaches 6x10^50 erg, which is within a factor of two of the observed value, and the time evolution of the luminosity shows a rate of decrease in recent decades of ~2.4% yr-1 that is consistent with the observations. Fil: Toledo Roy, J. C.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; México Fil: Esquivel, A.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; México Fil: Velazquez, P. F.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; México Fil: Reynoso, Estela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

The near-Earth asteroid (NEA) 2015 TB had a very close encounter with Earth at 1.3 lunar distances on October 31, 2015. We obtained 3-band mid-infrared observations of this asteroid with the ESO VLT-VISIR instrument covering approximately four hours in total. We also monitored the visual lightcurve during the close-encounter phase. The NEA has a (most likely) rotation period of 2.939 ± 0.005 h and the visual lightcurve shows a peak-to-peak amplitude of approximately 0.12 ± 0.02 mag. A second rotation period of 4.779 ± 0.012 h, with an amplitude of the Fourier fit of 0.10 ± 0.02 mag, also seems compatible with the available lightcurve measurements. We estimate a V-R colour of 0.56 ± 0.05 mag from different entries in the MPC database. A reliable determination of the object's absolute magnitude was not possible. Applying different phase relations to the available R-/V-band observations produced H = 18.6 mag (standard H-G calculations) or H = 19.2 mag and H = 19.8 mag (via the H-G procedure for sparse and low-quality data), with large uncertainties of approximately 1 mag. We performed a detailed thermophysical model analysis by using spherical and partially also ellipsoidal shape models. The thermal properties are best explained by an equator-on (± 30°) viewing geometry during our measurements with a thermal inertia in the range 250-700 J m s K (retrograde rotation) or above 500 J m s K (prograde rotation). We find that the NEA has a minimum size of approximately 625 m, a maximum size of just below 700 m, and a slightly elongated shape with a/b 1.1. The best match to all thermal measurements is found for: (i) thermal inertia Γ = 900 J m s K; D = 644 m, p = 5.5% (prograde rotation with 2.939 h); regolith grain sizes of 50-100 mm; (ii) thermal inertia Γ = 400 J m s K; D = 667 m, p = 5.1% (retrograde rotation with 2.939 h); regolith grain sizes of 10-20 mm. A near-Earth asteroid model (NEATM) confirms an object size well above 600 m (best NEATM solution at 690 m, beaming parameter η = 1.95), significantly larger than early estimates based on radar measurements. In general, a high-quality physical and thermal characterisation of a close-encounter object from two-week apparition data is not easily possible. We give recommendations for improved observing strategies for similar events in the future. © ESO, 2017., The research leading to these results has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378. Funding from Spanish grant AYA-2014-56637-C2-1-P is acknowledged. Hungarian funding from the NKFIH grant GINOP-2.3.2-15-2016-00003 is also acknowledged. R.D. acknowledges the support of MINECO for his Ramon y Cajal Contract.

We study the correlation between far-infared/submm dust emission and atomic gas column density in order to derive the properties of the high Galactic latitude, low density, Milky Way cirrus in the foreground of the Virgo cluster of galaxies. Dust emission maps from 60 to 850 um are obtained from SPIRE observations carried out within the Herschel Virgo Cluster Survey, complemented by IRAS-IRIS and Planck-HFI maps. Data from the Arecibo legacy Fast ALFA Survey is used to derive atomic gas column densities for two broad velocity components, low and intermediate velocity clouds. Dust emissivities are derived for each gas component and each far-infared/submm band. For the low velocity clouds, we measure an average emissivity 0.79 +/- 0.08 times 1E-20 MJy sr^-1 cm^2 at 250 um. After fitting a modified blackbody to the available bands, we estimated a dust absorption cross-section 0.49 +/- 0.13 times 1E-25 cm^2 H^-1 at 250 um (with dust temperature T = 20.4 +/- 1.5 K and spectral index beta = 1.53 +/- 0.17). The results are in excellent agreement with those obtained by Planck over a much larger coverage of the high Galactic latitude cirrus (50% of the sky vs 0.2% in our work). For dust associated with intermediate velocity gas, we confirm earlier Planck results and find a higher temperature and lower emissivity and cross-section. After subtracting the modelled components, we find regions at scales smaller than 20' where the residuals deviate significantly from the average, cosmic-infrared-background dominated, scatter. These large residuals are most likely due to local variations in the cirrus dust properties (and/or the dust/atomic-gas correlation) or to high-latitude molecular clouds with average N_H2, Comment: 25 pages, 19 figures, A&A accepted

Aims. We aim to study the spatial distribution of the physical and chemical properties of the X-ray emitting plasma of the supernova remnant (SNR) G306.3-0.9 in detail to obtain constraints on its ionization stage, the progenitor supernova explosion, and the age of the remnant. Methods. We used combined data from XMM-Newton and Chandra observatories to study the X-ray morphology of G306.3-0.9 in detail. A spatially resolved spectral analysis was used to obtain physical and geometrical parameters of different regions of the remnant. Spitzer infrared observations, available in the archive, were also used to constrain the progenitor supernova and study the environment in which the remnant evolved. Results. 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 (VAPEC) with a mean temperature of ∼0.19 keV, and another out of equilibrium ionization (VNEI) 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 remnant, a result that is also supported by an independent morphological analysis using the X-ray and 24 μm IR data., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

""

Aims. 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. Methods. The morphology and spectral properties of the X-ray SNR were studied using a single full frame XMM-Netwon observation in the 0.3 to 10.0 keV energy band. Archival infrared WISE observations at 8, 12 and 24 μm were also used to investigate the properties of the source and its surroundings at different wavelengths. Results. 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., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

12 pages, 10 figures, 3 tables.-- ISI Article Identifier: 000250480600041.-- ArXiv pre-print available at: http://arxiv.org/abs/0706.1302, We present broadband (3-500 keV) INTEGRAL X-ray spectra and X-ray/optical light curves of the luminous black hole X-ray transient and relativistic jet source GRO J1655-40. Our analysis covers four Target of Opportunity observations of the outburst that started in 2005 February. We find that the high-energy emission of GRO J1655-40 can be modeled well with an unbroken power law (with photon indices Γ of 1.72 ± 0.03 and 2.21 ± 0.04 for the first and second observations). These correspond to hard and thermal-dominant states, respectively. In contrast to many other black hole spectra, high-energy complexity in the form of a break or cutoff is not required for the hard state, contrary to previous expectations. We show for the first time that Comptonization by nonthermal electrons is the dominant process behind the high-energy emission in the hard state. We discuss our results in terms of models for broadband emission and accretion flows in stellar-mass black holes., MDCG is a MEC funded PhD student supported under grants PNE2003-04352+ESP2005-07714-C03-03. This work is based on observations made with INTEGRAL, an ESA science mission with instruments and science data centre funded by ESA member states and with the participation of Russia and the USA.

A condensate cloud on Titan identified by its 220 cm (sup -1) far-infrared signature continues to undergo seasonal changes at both the north and south poles. In the north the cloud, which extends from 55 North to the pole, has been gradually decreasing in emission intensity since the beginning of the Cassini mission with a half-life of 3.8 years. The cloud in the south did not appear until 2012 but its intensity has increased rapidly, doubling every year. The shape of the cloud at the South Pole is very different from that in the north. Mapping in December 2013 showed that the condensate emission was confined to a ring with a maximum at 80 South. The ring was centered 4 degrees from Titan's pole. The pattern of emission from stratospheric trace gases like nitriles and complex hydrocarbons (mapped in January 2014) was also offset by 4 degrees, but had a central peak at the pole and a secondary maximum in a ring at about 70 South with a minimum at 80 South. The shape of the gas emissions distribution can be explained by abundances that are high at the atmospheric pole and diminish toward the equator, combined with correspondingly increasing temperatures. We discuss possible causes for the condensate ring. The present rapid build up of the condensate cloud at the South Pole is likely to transition to a gradual decline during 2015-16.

Much evidence points towards that the photosphere in the relativistic outflow in GRBs plays an important role in shaping the observed MeV spectrum. However, it is unclear whether the spectrum is fully produced by the photosphere or whether a substantial part of the spectrum is added by processes far above the photosphere. Here we make a detailed study of the $\gamma-$ray emission from single pulse GRB110920A which has a spectrum that becomes extremely narrow towards the end of the burst. We show that the emission can be interpreted as Comptonisation of thermal photons by cold electrons in an unmagnetised outflow at an optical depth of $\tau \sim 20$. The electrons receive their energy by a local dissipation occurring close to the saturation radius. The main spectral component of GRB110920A and its evolution is thus, in this interpretation, fully explained by the emission from the photosphere including localised dissipation at high optical depths., Comment: 14 pages, 11 figures, accepted to MNRAS

Context. Recent NuSTAR observations revealed a somewhat unexpected increase in the X-ray flux of the nucleus of NGC 1068. We expect the infrared emission of the dusty torus to react on the intrinsic changes of the accretion disk. Aims. We aim to investigate the origin of the X-ray variation by investigating the response of the mid-infrared environment. Methods. We obtained single-aperture and interferometric mid-infrared measurements and directly compared the measurements observed before and immediately after the X-ray variations. The average correlated and single-aperture fluxes as well as the differential phases were directly compared to detect a possible change in the structure of the nuclear emission on scales of $\sim$ 2 pc. Results. The flux densities and differential phases of the observations before and during the X-ray variation show no significant change over a period of ten years. Possible minor variations in the infrared emission are $\lesssim$ 8 %. Conclusions. Our results suggest that the mid-infrared environment of NGC 1068 has remained unchanged for a decade. The recent transient change in the X-rays did not cause a significant variation in the infrared emission. This independent study supports previous conclusions that stated that the X-ray variation detected by NuSTAR observations is due to X-ray emission piercing through a patchy section of the dusty region., 6 pages, 5 figures, 3 tables. Accepted for publication on A&A

One of the key open question in the study of jets in general, and jets in gamma-ray bursts (GRBs) in particular, is the magnetization of the outflow. Here we consider the photospheric emission of Poynting flux dominated outflows, when the dynamics is mediated by magnetic reconnection. We show that thermal three-particle processes, responsible for the thermalization of the plasma, become inefficient at a radius $r_{\rm sup} \sim 10^{9.5}$~cm, far below the photosphere, at $\sim 10^{11.5}$~cm. Conservation of the total photon number above $r_{\rm sup}$ combined with Compton scattering below the photosphere enforces kinetic equilibrium between electrons and photons. This, in turn, leads to an increase in the observed photon temperature, which reaches $\gtrsim 8$~MeV (observed energy) when decoupling the plasma at the photosphere. This result is weakly dependent on the free model parameters. We show that in this case, the expected thermal luminosity is a few \% of the total luminosity, and could therefore be detected. The predicted peak energy is more than an order of magnitude higher than the observed peak energy of most GRBs, which puts strong constraints on the magnetization of these outflows., Comment: submitted for publication in Ap.J

We present a comprehensive spectral and morphological analysis of the remnant of Supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the radio emission are investigated in images from 94 to 672 GHz ($\lambda$ 3.2 mm to 450 $\mu$m), with the assistance of a high-resolution 44 GHz synchrotron template from the ATCA, and a dust template from ALMA observations at 672 GHz. An analysis of the emission distribution over the equatorial ring in images from 44 to 345 GHz highlights a gradual decrease of the east-to-west asymmetry ratio with frequency. We attribute this to the shorter synchrotron lifetime at high frequencies. Across the transition from radio to far infrared, both the synchrotron/dust-subtracted images and the spectral energy distribution (SED) suggest additional emission beside the main synchrotron component ($S_{\nu}\propto\nu^{-0.73}$) and the thermal component originating from dust grains at $T\sim22$ K. This excess could be due to free-free flux or emission from grains of colder dust. However, a second flat-spectrum synchrotron component appears to better fit the SED, implying that the emission could be attributed to a pulsar wind nebula (PWN). The residual emission is mainly localised west of the SN site, as the spectral analysis yields $-0.4\lesssim\alpha\lesssim-0.1$ across the western regions, with $\alpha\sim0$ around the central region. If there is a PWN in the remnant interior, these data suggest that the pulsar may be offset westward from the SN position., Comment: ApJ accepted. 21 pages, emulateapj. References updated

Since the Voyager 1 (V1) flyby in 1980, Titan's exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titanian year or 29.5 Earth years had elapsed in 2010 May). In this study, we search for temporal variations affecting Titan's atmospheric thermal and chemical structure within that year. We process Cassini/CIRS data taken during the Titan flybys from 2006-2013 and find a rather uneventful equatorial evolution. Conversely, at northern latitudes, we found enhanced abundances around the period of the northern spring equinox in mid-2009, which subsequently decreased (from 2010 to 2012), returning to values similar to those found in the V1 epoch, one Titanian year before. In the southern latitudes, since 2012, we see a trend for an increase of several trace gases (C4H2, C3H4, and HCN), indicative of a seasonal atmospheric reversal setting in. When we compare the CIRS 2010 and the 1980 V1/IRIS spectra (reanalyzed here), we find limited inter-annual variations. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50 degrees N to 50 degrees S, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by general circulation and photochemical models. Exceptions concern the most complex hydrocarbons (C4H2 and C3H4). We also consider data from ground-based and Earth-orbiting observatories (such as from the Infrared Space Observatory, revisited here) and discuss possible atmospheric composition trends during a Titanian year.

Aims. We aim to study the spatial distribution of the physical and chemical properties of the X-ray emitting plasma of the supernova remnant G272.2-3.2 in order to obtain important constraints on its ionization stage, the progenitor supernova explosion, and the age of the remnant. Methods. We report on combined XMM-Newton and Chandra images, median photon energy maps, silicon and sulfur equivalent width maps, and a spatially resolved spectral analysis for a set of regions of the remnant. Complementary radio and Hα observations, available in the literature, are also used to study the multi-wavelength connection of all detected emissions. Results. The X-ray morphology of the remnant displays an overall structure with an almost circular appearance and a centrally brightened hard region with a peculiar elongated hard structure oriented along the northwest-southeast direction of the central part. The X-ray spectral study of the regions shows distinct Kα emission-line features of metal elements, confirming the thermal origin of the emission. The X-ray spectra are well represented by an absorbed variable abundance non-equilibrium ionization thermal plasma model, which produces elevated abundances of Si, S, and Fe in the circular central region, typical of ejecta material. The values of abundances found in the central region of the supernova remnant favor a Type Ia progenitor for this remnant. The outer region shows abundances below the solar value, to be expected if the emission arises from the shocked interstellar medium. The relatively low ionization timescales suggest non-equilibrium ionization. We identify the location of the contact discontinuity. Its distance to the outer shock is higher than expected for expansion in a uniform media, which suggests that the remnant spent most of its time in more dense medium., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

Context. Simple models fail to describe the observed spectra of X-ray-dim isolated neutron stars (XDINSs). Interpretating these spectra requires detailed studies of radiative properties in the outermost layers of neutron stars with strong magnetic fields. Previous studies have shown that the strongly magnetized plasma in the outer envelopes of a neutron star may exhibit a phase transition to a condensed form. In this case thermal radiation can emerge directly from the metallic surface without going through a gaseous atmosphere, or alternatively, it may pass through a "thin" atmosphere above the surface. The multitude of theoretical possibilities complicates modeling the spectra and makes it desirable to have analytic formulae for constructing samples of models without going through computationally expensive, detailed calculations. Aims. The goal of this work is to develop a simple analytic description of the emission properties (spectrum and polarization) of the condensed, strongly magnetized surface of neutron stars. Methods. We have improved our earlier work for calculating the spectral properties of condensed magnetized surfaces. Using the improved method, we calculated the reflectivity of an iron surface at magnetic field strengths B ∼ 10 12 G-10 14 G, with various inclinations of the magnetic field lines and radiation beam with respect to the surface and each other. We constructed analytic expressions for the emissivity of this surface as functions of the photon energy, magnetic field strength, and the three angles that determine the geometry of the local problem. Using these expressions, we calculated X-ray spectra for neutron stars with condensed iron surfaces covered by thin partially ionized hydrogen atmospheres. Results. We develop simple analytic descriptions of the intensity and polarization of radiation emitted or reflected by condensed iron surfaces of neutron stars with the strong magnetic fields typical of isolated neutron stars. This description provides boundary conditions at the bottom of a thin atmosphere, which are more accurate than previously used approximations. The spectra calculated with this improvement show different absorption features from those in simplified models. Conclusions. The approach developed in this paper yields results that can facilitate modeling and interpretation of the X-ray spectra of isolated, strongly magnetized, thermally emitting neutron stars. © 2012 ESO.

著者人数: 111名, Accepted: 2012-08-29, 資料番号: SA1004199000

X-ray selected galaxy group samples are usually generated by searching for extended X-ray sources that reflect the thermal radiation of the intragroup medium. On the other hand, large radio galaxies that regularly occupy galaxy groups also emit in the X-ray window, and their contribution to X-ray selected group samples is still not well understood. In order to investigate their relative importance, we have carried out a systematic search for non- thermal extended X-ray sources in the Cosmic Evolution Survey (COSMOS) field. Based on the morphological coincidence of X-ray and radio extensions, out of 60 radio galaxies, and ˜300 extended X-ray sources, we find only one candidate where the observed extended X-ray emission arises from non-thermal processes related to radio galaxies. We present a detailed analysis of this source, and its environment. Our results yield that external inverse Compton emission of the lobes is the dominant process that generates the observed X-ray emission of our extended X-ray candidate, with a minor contribution from the gas of the galaxy group hosting the radio galaxy. Finally, we show that finding only one potential candidate in the COSMOS field (in a redshift range 0 < z < 6 and with radio luminosity between 1025 and 1030 W Hz- 1) is consistent with expected X-ray counts arising from synchrotron lobes. This implies that these sources are not a prominent source of contamination in samples of X-ray selected clusters/groups, but they could potentially dominate the z > 1 cluster counts at the bright end (SX > 7 × 10-15 erg s-1 cm2).

All the neutron star (NS) atmosphere models published so far have been calculated in the "cold plasma approximation," which neglects the relativistic effects in the radiative processes, such as cyclotron emission/absorption at harmonics of cyclotron frequency. Here, we present new NS atmosphere models which include such effects. We calculate a set of models for effective temperatures T eff = 1-3 MK and magnetic fields B 10 10-1011 G, typical for the so-called central compact objects (CCOs) in supernova remnants, for which the electron cyclotron energy E c, e and its first harmonics are in the observable soft X-ray range. Although the relativistic parameters, such as kT eff/mec 2 and E c, e/mec 2, are very small for CCOs, the relativistic effects substantially change the emergent spectra at the cyclotron resonances, E sE c, e (s = 1, 2, ...). Although the cyclotron absorption features can form in a cold plasma due to the quantum oscillations of the free-free opacity, the shape and depth of these features change substantially if the relativistic effects are included. In particular, the features acquire deep Doppler cores, in which the angular distribution of the emergent intensity is quite different from that in the cold plasma approximation. The relative contributions of the Doppler cores to the equivalent widths of the features grow with increasing quantization parameter b eff ≡ E c, e/kT eff and harmonic number s. The total equivalent widths of the features can reach 150-250 eV; they increase with growing b eff and are smaller for higher harmonics. © 2012. The American Astronomical Society. All rights reserved..

The emission from a gamma-ray burst (GRB) photosphere can give rise to a variety of spectral shapes. The spectrum can retain the shape of a Planck function or it can be broadened and have the shape of a Band function. This fact is best illustrated by studying GRB090902B: The main gamma-ray spectral component is initially close to a Planck function, which can only be explained by emission from the jet photosphere. Later, the same component evolves into a broader Band function. This burst thus provides observational evidence that the photosphere can give rise to a non-thermal spectrum. We show that such a broadening is most naturally explained by subphotospheric dissipation in the jet. The broadening mainly depends on the strength and location of the dissipation, on the magnetic field strength, and on the relation between the energy densities of thermal photons and of the electrons. We suggest that the evolution in spectral shape observed in GRB090902B is due to a decrease of the bulk Lorentz factor of the flow, leading to the main dissipation becoming subphotospheric. Such a change in the flow parameters can also explain the correlation observed between the peak energy of the spectrum and low-energy power law slope, alpha, a correlation commonly observed in GRBs. We conclude that photospheric emission could indeed be a ubiquitous feature during the prompt phase in GRBs and play a decisive role in creating the diverse spectral shapes and spectral evolutions that are observed., Submitted to MNRAS, 14 pages, 7 figures

The jets in a microquasar are modelled using a three-dimensional relativistic hydrocode (PLUTO), with the aim of investigating the appearance of equatorial radio emission. A dynamical mechanism is explored whereby the bow shocks of the jets strongly affect the equatorial regions. The presence of an extended disc is assumed and its role proves to be important in producing equatorial emission. As a concrete example, we focus on the SS 433 microquasar, one of the most intensively studied objects in the Galaxy, for which equatorial emission has been repeatedly detected during the last decade. Monthly Notices of the Royal Astronomical Society

Discerning the radiative dissipation mechanism for prompt emission in gamma-ray bursts (GRBs) requires detailed spectroscopic modeling that straddles the {nu}F{sub {nu}} peak in the 100 keV-1 MeV range. Historically, empirical fits such as the popular Band function have been employed with considerable success in interpreting the observations. While extrapolations of the Band parameters can provide some physical insight into the emission mechanisms responsible for GRBs, these inferences do not provide a unique way of discerning between models. By fitting physical models directly, this degeneracy can be broken, eliminating the need for empirical functions; our analysis here offers a first step in this direction. One of the oldest, and leading, theoretical ideas for the production of the prompt signal is the synchrotron shock model. Here we explore the applicability of this model to a bright Fermi gamma-ray burst monitor (GBM) burst with a simple temporal structure, GRB 090820A. Our investigation implements, for the first time, thermal and non-thermal synchrotron emissivities in the RMFIT forward-folding spectral analysis software often used in GBM burst studies. We find that these synchrotron emissivities, together with a blackbody shape, provide at least as good a match to the data as the Band GRB spectral fitting function. more » This success is achieved in both time-integrated and time-resolved spectral fits. « less

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2010 RAS © 2010 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved., Using analytical models and cosmological N-body simulations, we study the free-free radio emission from ionized gas in clusters and groups of galaxies. The results obtained with the simulations are compared with analytical predictions based on the mass function and scaling relations. Earlier works based on analytical models have shown that the average free-free signal from small haloes (galaxies) during and after the reionization time could be detected with future experiments as a distortion of the cosmic microwave background (CMB) spectrum at low frequencies (ν < 5 GHz). We focus on the period after the reionization time (from redshift z= 0 to 7) and on haloes that are more massive than in previous works (groups and clusters). We show how the average signal from haloes with M > 10 13 h -1 M Ȯ is less than 10 per cent the signal from the more abundant and colder smaller mass haloes. However, the individual signal from the massive haloes could be detected with future experiments opening the door for a new window to study the intracluster medium, We acknowledge partial financial support from the Ministerio de Ciencia e Innovación project AYA2007-68058-C03-02. PPP acknowledges support from the Spanish Ministerio de Educación y Ciencia and CSIC for an I3P grant. PPP also acknowledges support from the programme of ‘Estancias Breves’, grants 22007ESTI3P-00493 and 009ESTCSIC-01386. CBacknowledges partial support for this work by the AS/INAF agreement I/072/09/0 for the Planck LFI Activity of Phase E2 and the ASI contract I/016/07/0 COFIS. RKS acknowledges the support of grant NFS-AST 0908241. SRK acknowledges support by the MICINN under the Consolider-Ingenio, SyeC projectCSD-2007-00050.YAacknowledges financial support from project AYA2007-67965-C03-03

Observations of GRB 100724B with the Fermi Gamma-Ray Burst Monitor (GBM) find that the spectrum is dominated by the typical Band functional form, which is usually taken to represent a non-thermal emission component, but also includes a statistically highly significant thermal spectral contribution. The simultaneous observation of the thermal and non-thermal components allows us to confidently identify the two emission components. The fact that these seem to vary independently favors the idea that the thermal component is of photospheric origin while the dominant non-thermal emission occurs at larger radii. Our results imply either a very high efficiency for the non-thermal process, or a very small size of the region at the base of the flow, both quite challenging for the standard fireball model. These problems are resolved if the jet is initially highly magnetized and has a substantial Poynting flux., 6 pages, 3 figures, 1 table, Accepted for publication in the Astrophysical Journal Letters November, 23 2010 (Submitted October, 20 2010)

Aims. We report the first detailed X-ray study of the supernova remnant (SNR) G304.6+0.1, achieved with the XMM-Newton mission. Methods. The powerful imaging capability of XMM-Newton was used to study the X-ray characteristics of the remnant at different energy ranges. The X-ray morphology and spectral properties were analyzed. In addittion, radio and mid-infrared data obtained with the Molonglo Observatory Synthesis Telescope and the Spitzer Space Telescope were used to study the association with the detected X-ray emission and to understand the structure of the SNR at differents wavelengths. Results. The SNR shows an extended and arc-like internal structure in the X-ray band with out a compact point-like source inside the remnant. We find a high column density of NH in the range 2.5-3.5x1022 cm-2, which supports a relatively distant location (d $\geq$ 9.7 kpc). The X-ray spectrum exhibits at least three emission lines, indicating that the X-ray emission has a thin thermal plasma origin, although a non-thermal contribution cannot be discarded. The spectra of three different regions (north, center and south) are well represented by a combination of a non-equilibrium ionization (PSHOCK) and a power-law (PL) model. The mid-infrared observations show a bright filamentary structure along the north-south direction coincident with the NW radio shell. This suggests that Kes 17 is propagating in a non-uniform environment with high density and that the shock front is interacting with several adjacent massive molecular clouds. The good correspondence of radio and mid-infrared emissions suggests that the filamentary features are caused by shock compression. The X-ray characteristics and well-known radio parameters indicate that G304.6+0.1 is a middle-aged SNR (2.8-6.4)x104 yr old and a new member of the recently proposed group of mixed-morphology SNRs., 5 pages, 2 figures; Accepted for publication in Astronomy & Astrophysics

The origin of the far-infrared emission from the nearby radio galaxy M87 remains a matter of debate. Some studies find evidence of a far-infrared excess due to thermal dust emission, whereas others propose that the far-infrared emission can be explained by synchrotron emission without the need for an additional dust emission component. We present Herschel PACS and SPIRE observations of M87, taken as part of the science demonstration phase observations of the Herschel Virgo Cluster Survey. We compare these data with a synchrotron model based on mid-infrared, far-infrared, submm and radio data from the literature to investigate the origin of the far-infrared emission. Both the integrated SED and the Herschel surface brightness maps are adequately explained by synchrotron emission. At odds with previous claims, we find no evidence of a diffuse dust component in M87, which is not unexpected in the harsh X-ray environment of this radio galaxy sitting at the core of the Virgo Cluster., Letter accepted for publication in A&A (Herschel special issue)

Aims. We report results of an X-ray study of the supernova remnant (SNR) G344.7-0.1 and the point-like X-ray source located at the geometrical center of the SNR radio structure. Methods. The morphology and spectral properties of the remnant and the central X-ray point-like source were studied using data from the XMM-Newton and Chandra satellites. Archival radio data and infrared Spitzer observations at 8 and 24 $\mu$m were used to compare and study its multi-band properties at different wavelengths. Results. The XMM-Newton and Chandra observations reveal that the overall X-ray emission of G344.7-0.1 is extended and correlates very well with regions of bright radio and infrared emission. The X-ray spectrum is dominated by prominent atomic emission lines. These characteristics suggest that the X-ray emission originated in a thin thermal plasma, whose radiation is represented well by a plane-parallel shock plasma model (PSHOCK). Our study favors the scenario in which G344.7-0.1 is a 6 x 10^3 year old SNR expanding in a medium with a high density gradient and is most likely encountering a molecular cloud on the western side. In addition, we report the discovery of a soft point-like X-ray source located at the geometrical center of the radio SNR structure. The object presents some characteristics of the so-called compact central objects (CCO). However, its neutral hydrogen absorption column (N_{H}) is inconsistent with that of the SNR. Coincident with the position of the source, we found infrared and optical objects with typical early-K star characteristics. The X-ray source may be a foreground star or the CCO associated with the SNR. If this latter possibility were confirmed, the point-like source would be the farthest CCO detected so far and the eighth member of the new population of isolated and weakly magnetized neutron stars., Comment: 9 pages, 8 figures, accepted for publication in Astronomy and Astrophysics. Higher resolution figures can be seen on A&A

We report observations with the Chandra X-ray Observatory of the single, cool, magnetic white dwarf GD 356. For consistent comparison with other X-ray observations of single white dwarfs, we also re-analyzed archival ROSAT data for GD 356 (GJ 1205), G99-47(GR 290 = V1201 Ori), GD 90, G195-19 (EG 250 = GJ 339.1), and WD 2316+123, and archival Chandra data for LHS 1038 (GJ 1004) and GD 358 (V777 Her). Our Chandra observation detected no X-rays from GD 356, setting the most restrictive upper limit to the X-ray luminosity from any cool white dwarf: LX < 6.0 × 1025 ergs s-1, at 99.7% confidence, for a 1 keV thermal bremsstrahlung spectrum. The corresponding limit to the electron density is n0 < 4.4 × 10-1 cm-3. Our re-analysis of the archival data confirmed the nondetections reported by the original investigators. We discuss the implications of our and prior observations for models of coronal emission from white dwarfs. For magnetic white dwarfs, we emphasize the more stringent constraints imposed by cyclotron radiation. In addition, we describe (in an Appendix) a statistical methodology for detecting a source and for constraining the strength of a source, which applies even when the number of source or background events is small. © 2007. The American Astronomical Society. All rights reserved.

We investigate the diffuse absolute calibration of the Infrared Array Camera (IRAC) on the Spitzer Space Telescope (SST) at 8.0 mu m using a sample of 43 H II regions with a wide range of morphologies near l = 312 degrees. For each region we carefully measure sky-subtracted, point-source-subtracted, areally integrated IRAC 8.0-mu m fluxes and compare these with Midcourse Space eXperiment (MSX) 8.3-mu m images at two different spatial resolutions, and with radio continuum maps. We determine an accurate median ratio of IRAC 8.0-mu m/MSX 8.3-mu m fluxes, of 1.55 +/- 0.15. From robust spectral energy distributions of these regions we conclude that the present 8.0-mu m diffuse calibration of the SST is 36 per cent too high compared with the MSX validated calibration, perhaps due to scattered light inside the camera. This is an independent confirmation of the result derived for the diffuse calibration of IRAC by the Spitzer Science Centre (SSC). From regression analyses we find that 843-MHz radio fluxes of H II regions and mid-infrared (MIR) fluxes are linearly related for MSX at 8.3 mu m and Spitzer at 8.0 mu m, confirming the earlier MSX result by Cohen & Green. The median ratio of MIR/843-MHz diffuse continuum fluxes is 600x smaller in non-thermal than thermal regions, making it a sharp discriminant. The ratios are largely independent of morphology up to a size of similar to 24 arcmin. We provide homogeneous radio and MIR morphologies for all sources. MIR morphology is not uniquely related to radio structure. Compact regions may have MIR filaments and/or diffuse haloes, perhaps infrared counterparts to weakly ionized radio haloes found around compact H II regions. We offer two IRAC colour-colour plots as quantitative diagnostics of diffuse H II regions.

We define an appropriate problem for benchmarking dust emissivity calculations in the context of radiative transfer (RT) simulations, specifically including the emission from stochastically heated dust grains. Our aim is to provide a self-contained guide for implementors of such functionality, and to offer insights in the effects of the various approximations and heuristics implemented by the participating codes to accelerate the calculations. The benchmark problem definition includes the optical and calorimetric material properties, and the grain size distributions, for a typical astronomical dust mixture with silicate, graphite and PAH components; a series of analytically defined radiation fields to which the dust population is to be exposed; and instructions for the desired output. We process this problem using six RT codes participating in this benchmark effort, and compare the results to a reference solution computed with the publicly available dust emission code DustEM. The participating codes implement different heuristics to keep the calculation time at an acceptable level. We study the effects of these mechanisms on the calculated solutions, and report on the level of (dis)agreement between the participating codes. For all but the most extreme input fields, we find agreement within 10% across the important wavelength range from 3 to 1000 micron. We conclude that the relevant modules in RT codes can and do produce fairly consistent results for the emissivity spectra of stochastically heated dust grains., 22 pages, 9 figures, accepted for publication in A&A

We report spectroscopic observations in the wavelength region 0.8–2.4 μm aimed at detecting near-infrared coronal lines in a sample of five narrow-line and one broad-line Seyfert 1 galaxies. Our measurements show that [Si vI] 1.963 μm, [S Ix] 1.252 μm, and [S vIII] 0.991 μm are present in most of the objects and are useful tracers of nuclear activity. Line ratios between coronal and low-ionization forbidden lines are larger in narrow-line Seyfert 1 galaxies. A positive correlation between FHWMand ionization potential of the forbidden lines is observed. Some coronal lines have widths similar to those of lines emitted in the broad-line region (BLR), indicating that part of their flux originates in gas close to the outer portions of the BLR. Most coronal lines are blueshifted relative to the systemic velocity of the galaxy, and this shift increases with the increase in line width. Asymmetries toward the blue are observed in the profiles of high-ionization Fe lines, suggesting that the emitting gas is related to winds or outflows, most probably originating in material that is being evaporated from the torus. This scenario is supported by models that combine the effects of shock ionization and photoionization by a central continuum source in the gas clouds. The agreement between the coronal line emission predicted by the models and the observations is satisfactory; the models reproduced the whole range of coronal line intensities observed. We also report the detection of [Fe xIII] 1.074, 1.079 μm in three of our objects and the first detection of [P II] 1.188 μm and [Ni II] 1.191 μm in a Seyfert 1 galaxy, Ark 564. Using the ratio [P II]/[Fe II], we deduced that most Fe present in the outer narrow-line region of Ark 564 is locked up in grains and that the influence of shocks is negligible.

We explore the spectral and polarization properties of photospheric emissions from stratified jets in which multiple components, separated by a sharp velocity shear regions, are distributed in lateral direction. Propagation of thermal photons injected at high optical depth region are calculated until they escape from the photosphere. It is found that presence of the lateral structure within the jet leads to non-thermal feature of the spectra and significant polarization signal in the resulting emission. The deviation from thermal spectra as well as the polarization degree tends to be enhanced as the velocity gradient in the shear region increases. In particular, we show that emissions from multi-component jet can reproduce the typical observed spectra of gamma-ray bursts (GRBs) irrespective to the position of the observer when a velocity shear region is closely spaced in various lateral ($\theta$) positions. The degree of polarization associated in the emission is significant (> few%) at wide range of observer angles and can be higher than 30%., Comment: 21 pages, 12 figures, accepted for publication in ApJ