Identifying the counterpart of HESS J1858+020

HESS J1858+020 is a weak gamma-ray source that does not have any clear cataloged counterpart at any wavelengths. Recently, the source G35.6-0.4 was re-identified as a SNR. The HESS source lies towards the southern border of this remnant. The purpose of this work is to investigate the interstellar medium around the mentioned sources in order to look for possible counterparts of the very-high energy emission. Using the 13CO J=1-0 line from the Galactic Ring Survey and mid-IR data from GLIMPSE we analyze the environs of HESS J1858+020 and SNR G35.6-0.4. The 13CO data show the presence of a molecular cloud towards the southern border of SNR G35.6-0.4 and at the same distance as the remnant. This cloud is composed by two molecular clumps, one, over the SNR shell and the other located at the center of HESS J1858+020. We estimate a molecular mass and a density of ~ 5 X 10^{3} Msun and ~ 500 cm^{-3}, respectively for each clump. Considering the gamma-ray flux observed towards HESS J1858+020, we estimate that a molecular cloud with a density of at least 150 cm^{-3} could explain the very-high energy emission hadronically. Thus, we suggest that the gamma-ray emission detected in HESS J1858+020 is due to hadronic mechanism. Additionally, analyzing mid-IR emission, we find that the region is active in star formation, which could be considered as an alternative or complementary possibility to explain the very-high energy emission.Comment: 6 pages, 3 figures, accepted for publication in A&A Lette

Galactic Supernova Remnants: From radio frequencies to TeV

Supernova remnants are among the most valuable astrophysical laboratory to study numerous physical processes involved in their evolution and interaction with the surrounding interstellar medium. These objects are one of the most important sources of injection of mechanic energy and chemical enrichment of the interstellar mediumi, accelerate cosmic rays and generate strong shock waves in such conditions that cannot be reproduced in a terrestrial laboratory. The remnants can emit radiation from radio to gamma ray bands. In this report I describe the relevant radiation processes in the different spectral regimes and the information obtained by multifrequency observations of supernova remnants, including some recent results.Los remanentes de supernovas constituyen un laboratorio astrofısico muy valioso para estudiar los numerosos procesos fısicos que se desencadenan durante su evolucion y en la interaccion con el medio interestelar circundante. Ellos son una de las principales fuentes de inyeccion de energıa mecanica y enriquecimiento quımico del medio interestelar, aceleran rayos cosmicos y generan fuertes ondas de choque en condiciones que no se reproducen en un laboratorio terrestre. Los remanentes pueden emitir radiacion desde el rango de radio hasta los rayos gamma. En este informe describo los procesos fısicos generadores de la radiacion en las distintas bandas del espectro electromagnetico y la informacion brindada por las observaciones en cada una de esas bandas, incluyendo algunos resultados recientes.Fil: Giacani, Elsa Beatriz. 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; Argentin

e-MERLIN observations of the puzzling TeV source HESS J1943+213

HESS J1943+213 is a TeV source close to the Galactic plane proposed to be a BL Lac object. Our high resolution EVN observation failed to recover two thirds of the source flux density detected simultaneously by the WSRT. Our recent e-MERLIN observations in L and C bands show only a point source with flux density comparable to the EVN detection. Thus the structure responsible for the missing flux density has to be larger than 2". It may be related to the presumed extragalactic source (thus would have a kpc-scale size), or to the Galactic foreground material close to the line of sight to the source.Comment: 4 pages, 1 figure, appears in the proceedings of the 12th European VLBI Network Symposium and Users Meeting (7-10 October 2014, Cagliari, Italy), eds. A. Tarchi, M. Giroletti & L. Feretti. Proceedings of Science, PoS(EVN 2014)07

VLBI search for the radio counterpart of HESS J1943+213

HESS J1943+213, a TeV point source close to the Galactic plane recently discovered by the H.E.S.S. collaboration, was proposed to be an extreme BL Lacertae object, though a pulsar wind nebula (PWN) nature could not be completely discarded. To investigate its nature, we performed high-resolution radio observations with the European Very Long Baseline Interferometry Network (EVN) and reanalyzed archival continuum and H {\sc i} data. The EVN observations revealed a compact radio counterpart of the TeV source. The low brightness temperature and the resolved nature of the radio source are indications against the beamed BL Lacertae hypothesis. The radio/X-ray source appears immersed in a $\sim$ 1\arcmin elliptical feature suggesting a possible galactic origin (PWN nature) for the HESS source. We found that HESS\,J1943+213 is located in the interior of a \sim1\degr diameter H {\sc i} feature, and explored the possibility of they being physically related.Comment: Significantly revised and extended. Accepted for publication in ApJ (ApJ, 762, 63). (4 figures.

Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1

We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and G352.7-0.1, to understand the causes of such morphology. The research was carried out based on new and reprocessed archival VLA observations and XMM-Newton archival data. The surrounding was investigated based on data extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring Survey and the HI Southern Galactic Plane Survey. The present study revealed that the overall morphology of both SNRs is the result of the mass-loss history of their respective progenitor stars. Kes79 would be the product of the gravitational collapse of a massive O9 star evolving near a molecular cloud and within the precursor's wind-driven bubble, while G352.7-0.1 would be the result of interactions of the SNR with an asymmetric wind from the progenitor together with projection effects. No radio point source or pulsar wind nebula was found associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray radiation completely fills in the interior of the remnant and originates in heated ejecta. Characteristic parameters, like radio flux, radio spectral index, age, distance, shock velocity, initial energy and luminosity, were estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and Astrophysic

Evolving supernova remnants in multiphase interstellar media

We performed three-dimensional magnetohydrodynamic simulations to study the evolution of a supernova remnant (SNR) in a turbulent neutral atomic interstellar medium. The media used as background shares characteristics with the Solar neighbourhood and the SNR has mass and energy similar to those of a Type Ia object. Our initial conditions consist of dense clouds in a diluted medium, with the main difference between simulations being the average magnitude of the magnetic field. We measured amplifications of the magnetic energy of up to 34 per cent, and we generated synthetic maps that illustrate how the same object can show different apparent geometries and physical properties when observed through different lines of sight.Fil: Villagran Azuara, Marco Adrian. 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; ArgentinaFil: Velazquez, Paula Florencia. Universidad Nacional Autónoma de México; MéxicoFil: Gomez, Daniel Osvaldo. 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. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Giacani, Elsa Beatriz. Universidad de Buenos Aires. Facultad de Arquitectura, Diseño y Urbanismo; Argentina. 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; Argentin

The neutral gas in the environs of the Geminga gamma-ray pulsar

We present a high-resolution (24 arcsec) study of the HI interstellar gas distribution around the radio-quiet neutron star Geminga. Based on Very Large Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field around Geminga. These observations have revealed the presence of a neutral gas shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which surrounds Geminga at a radial velocity compatible with the kinematical distance of the neutron star. In addition, morphological agreement is observed between the internal face of the HI shell and the brightest structure of Geminga's tail observed in X-rays.We explore the possibility that this morphological agreement is the result of a physical association.Comment: One tarfile including a Latex file (7 pages) and two figures. Paper accepted for publication in Advances in Space Research; typos corrected; changes in section Results and Discussion after referee's suggestions. S. Johnston's affilation correcte