137 research outputs found
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
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 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.
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
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
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