487 research outputs found
The HI absorption distance of HESS J1943+213 favours its extragalactic nature
The H.E.S.S. collaboration (Abramowski et al. 2011) dicovered a new TeV
point-like source HESS J1943+213 in the Galactic plane and suggested three
possible low-energy-band counterparts: a -ray binary, a pulsar wind
nebula (PWN), or a BL Lacertae object. We measure the distance to the radio
counterpart G57.76-1.29 of HESS J1943+213. We analyze Very Large Array
observations to obtain a reliable HI absorption spectrum.The resulting distance
limit is 16 kpc. This distance strongly supports that HESS J1943+213 is
an extragalactic source, consistent with the preferred counterpart of the HESS
collaboration.Comment: 3 figures, 2 pages, A&A accepte
Time-dependent absorption of very high-energy gamma-rays from the Galactic center by pair-production
Very high energy (VHE) gamma-rays have been detected from the direction of
the Galactic center. The H.E.S.S. Cherenkov telescopes have located this
gamma-ray source with a preliminary position uncertainty of 8.5" per axis (6"
statistic + 6" sytematic per axis). Within the uncertainty region several
possible counterpart candidates exist: the Super Massive Black Hole Sgr A*, the
Pulsar Wind Nebula candidate G359.95-0.04, the Low Mass X-Ray Binary-system
J174540.0-290031, the stellar cluster IRS 13, as well as self-annihilating dark
matter. It is experimentally very challenging to further improve the positional
accuracy in this energy range and therefore, it may not be possible to clearly
associate one of the counterpart candidates with the VHE-source. Here, we
present a new method to investigate a possible link of the VHE-source with the
near environment of Sgr A* (within approximately 1000 Schwarzschild radii).
This method uses the time- and energy-dependent effect of absorption of
gamma-rays by pair-production (in the following named pair-eclipse) with
low-energy photons of stars closely orbiting the SMBH Sgr A*.Comment: 4 pages, 6 figures, Published in Proceedings of the 4th International
Meeting on High Energy Gamma-Ray Astronomy (Gamma 08), Heidelber
Can children with autism read emotions from the eyes? The eyes test revisited
This study aimed to test two new, simplified tasks related to the eye-test, targeting children with Autism Spectrum Disorder (ASD) and typically developing controls (TD). Test-1 assessed the recognition of emotion/mental states with displays using one word and two eye-pictures, whereas Test-2 presented displays using two words and one eye-picture. Black and white photographs of children were used as materials. A cross-cultural study (Caucasian/East-Asian) with adults was initially carried out to verify generalizability across different ethnic groups. Cross-sectional trajectory analyses were used to compare emotion recognition from the eyes in the two tests. Trajectories were constructed linking performance on both tests either to chronological age or to different measures of mental age (receptive vocabulary based on the BPVS, CARS or ASQ for the ASD group). Performance improved with chronological age in both the ASD and TD groups of children. However, performance in Test-1 was significantly superior in children with ASD, who showed delayed onset and slower rate of improvement than TD children in Test-2. In both the ASD and TD groups the lowest error rate was recorded for the item âangerâ, suggesting that threat-detection cue mechanisms may be intact in Autism. In general, all children showed good performance on our novel tests, thus making them good candidates for assessing younger children and those with lower general abilities
Detailed spectral and morphological analysis of the shell type supernova remnant RCW 86
Aim. We aim for an understanding of the morphological and spectral properties of the supernova remnant RCW 86 and for insights into the production mechanism leading to the RCW 86 very high-energy Îł-ray emission. Methods. We analyzed High Energy Spectroscopic System (H.E.S.S.) data that had increased sensitivity compared to the observations presented in the RCW 86 H.E.S.S. discovery publication. Studies of the morphological correlation between the 0.5â1 keV X-ray band, the 2â5 keV X-ray band, radio, and Îł-ray emissions have been performed as well as broadband modeling of the spectral energy distribution with two different emission models. Results. We present the first conclusive evidence that the TeV Îł-ray emission region is shell-like based on our morphological studies. The comparison with 2â5 keV X-ray data reveals a correlation with the 0.4â50 TeV Îł-ray emission. The spectrum of RCW 86 is best described by a power law with an exponential cutoff at Ecut = (3.5 ± 1.2stat) TeV and a spectral index of Î â 1.6 ± 0.2. A static leptonic one-zone model adequately describes the measured spectral energy distribution of RCW 86, with the resultant total kinetic energy of the electrons above 1 GeV being equivalent to ~0.1% of the initial kinetic energy of a Type Ia supernova explosion (1051 erg). When using a hadronic model, a magnetic field of B â 100 ÎŒG is needed to represent the measured data. Although this is comparable to formerly published estimates, a standard Eâ2 spectrum for the proton distribution cannot describe the Îł-ray data. Instead, a spectral index of Îp â 1.7 would be required, which implies that âŒ7 Ă 1049/ncmâ3 has been transferred into high-energy protons with the effective density ncmâ3 = n/1 cmâ3. This is about 10% of the kinetic energy of a typical Type Ia supernova under the assumption of a density of 1 cmâ3
Very-high energy gamma-ray astronomy: A 23-year success story in high-energy astroparticle physics
Very-high energy (VHE) gamma quanta contribute only a minuscule fraction -
below one per million - to the flux of cosmic rays. Nevertheless, being neutral
particles they are currently the best "messengers" of processes from the
relativistic/ultra-relativistic Universe because they can be extrapolated back
to their origin. The window of VHE gamma rays was opened only in 1989 by the
Whipple collaboration, reporting the observation of TeV gamma rays from the
Crab nebula. After a slow start, this new field of research is now rapidly
expanding with the discovery of more than 150 VHE gamma-ray emitting sources.
Progress is intimately related with the steady improvement of detectors and
rapidly increasing computing power. We give an overview of the early attempts
before and around 1989 and the progress after the pioneering work of the
Whipple collaboration. The main focus of this article is on the development of
experimental techniques for Earth-bound gamma-ray detectors; consequently, more
emphasis is given to those experiments that made an initial breakthrough rather
than to the successors which often had and have a similar (sometimes even
higher) scientific output as the pioneering experiments. The considered energy
threshold is about 30 GeV. At lower energies, observations can presently only
be performed with balloon or satellite-borne detectors. Irrespective of the
stormy experimental progress, the success story could not have been called a
success story without a broad scientific output. Therefore we conclude this
article with a summary of the scientific rationales and main results achieved
over the last two decades.Comment: 45 pages, 38 figures, review prepared for EPJ-H special issue "Cosmic
rays, gamma rays and neutrinos: A survey of 100 years of research
Interpretation of the flares of M87 at TeV energies in the cloud-jet interaction scenario
Active galactic nuclei with misaligned jets have been recently established as
a class of high-energy gamma-ray sources. M87, a nearby representative of this
class, shows fast TeV variability on timescales less than one day. We present
calculations performed in the framework of the scenario in which gamma-ray
flares in non-blazar active galactic nuclei are produced by a red giant or a
gas cloud interacting with the jet. We show that both the light curve and
energy spectrum of the spectacular April 2010 flare can be reproduced by this
model, assuming that a relatively massive cloud of approx 1.e29 g penetrates
into the jet at few tens of Schwarzschild radii from the super-massive black
hole.Comment: 8 pages, 8 figures, accepted by Ap
Locating the VHE source in the Galactic Centre with milli-arcsecond accuracy
Very high-energy gamma-rays (VHE; E>100 GeV) have been detected from the
direction of the Galactic Centre up to energies E>10 TeV. Up to now, the origin
of this emission is unknown due to the limited positional accuracy of the
observing instruments. One of the counterpart candidates is the super-massive
black hole (SMBH) Sgr A*. If the VHE emission is produced within ~10^{15} cm
~1000 r_G (r_G=G M/c^2 is the Schwarzschild radius) of the SMBH, a decrease of
the VHE photon flux in the energy range 100--300 GeV is expected whenever an
early type or giant star approaches the line of sight within ~ milli-arcseconds
(mas). The dimming of the flux is due to absorption by pair-production of the
VHE photons in the soft photon field of the star, an effect we refer to as
pair-production eclipse (PPE). Based upon the currently known orbits of stars
in the inner arcsecond of the Galaxy we find that PPEs lead to a systematic
dimming in the 100--300 GeV band at the level of a few per cent and lasts for
several weeks. Since the PPE affects only a narrow energy band and is well
correlated with the passage of the star, it can be clearly discriminated
against other systematic or even source-intrinsic effects. While the effect is
too small to be observable with the current generation of VHE detectors,
upcoming high count-rate experiments like the Cherenkov telescope array (CTA)
will be sufficiently sensitive. Measuring the temporal signature of the PPE
bears the potential to locate the position and size of the VHE emitting region
within the inner 1000 r_G or in the case of a non-detection exclude the
immediate environment of the SMBH as the site of gamma-ray production
altogether.Comment: 7 pages, published in MNRAS 402, pg. 1342-134
Galactic Structure Toward the Carina Tangent
This investigation presents a photometric study of the Galactic structure
toward the Carina arm tangent. The field is located between 280 deg and 286 deg
galactic longitude and -4 deg to 4 deg galactic latitude. All currently
available uvbybeta data is used to obtain homogeneous color excesses and
distances for more than 260 stars of spectral types O to G. We present revised
distances and average extinction for the open clusters and cluster candidates
NGC 3293, NGC 3114, Loden 46 and Loden 112. The cluster candidate Loden 112
appears to be a very compact group at a true distance modulus of 11.06 +\- 0.11
(s.e.) (1629 +84,-80 pc), significantly closer than previous estimates. We
found other OB stars at that same distance and, based on their proper motions,
suggest a new OB association at coordinates 282 deg < l < 285 deg, -2 deg < b <
2 deg. Utilizing BV photometry and spectral classification of the known O-type
stars in the very young open cluster Wd 2 we provide a new distance estimate of
14.13 +\-0.16 (s.e.) (6698 +512,-475 pc), in excellent agreement with recent
distance determinations to the giant molecular structures in this direction. We
also discuss a possible connection between the HII region RCW 45 and the
highly-reddened B+ star CPD -55 3036 and provide a revised distance for the
luminous blue variable HR Car.Comment: accepted to PAS
- âŠ