988 research outputs found
CTA and cosmic-ray diffusion in molecular clouds
Molecular clouds act as primary targets for cosmic-ray interactions and are
expected to shine in gamma-rays as a by-product of these interactions. Indeed
several detected gamma-ray sources both in HE and VHE gamma-rays (HE: 100 MeV <
E 100 GeV) have been directly or indirectly associated with
molecular clouds. Information on the local diffusion coefficient and the local
cosmic-ray population can be deduced from the observed gamma-ray signals. In
this work we concentrate on the capability of the forthcoming Cherenkov
Telescope Array Observatory (CTA) to provide such measurements. We investigate
the expected emission from clouds hosting an accelerator, exploring the
parameter space for different modes of acceleration, age of the source, cloud
density profile, and cosmic ray diffusion coefficient. We present some of the
most interesting cases for CTA regarding this science topic. The simulated
gamma-ray fluxes depend strongly on the input parameters. In some cases, from
CTA data it will be possible to constrain both the properties of the
accelerator and the propagation mode of cosmic rays in the cloud.Comment: In Proceedings of the 2012 Heidelberg Symposium on High Energy
Gamma-Ray Astronomy. All CTA contributions at arXiv:1211.184
Determination of the Night Sky Background around the Crab pulsar using its optical pulsation
The poor angular resolution of imaging gamma-ray telescopes is offset by the
large reflector areas of next generation telescopes such as MAGIC (17~m
diameter), which makes the study of optical emission associated with some
gamma-ray sources feasible. Furthermore, the extremely fast time response of
photomultipliers (PMs) makes them ideal detectors for fast (subsecond) optical
transients and periodic sources like pulsars. The optical pulse of the Crab
pulsar was detected with the HEGRA CT1 central pixel using a modified PM,
similar to the future MAGIC camera PMs. The purpose of these periodic
observations was to determine the light of the night sky (LONS) for the
galactic anticenter Crab region.Our results are between 2.5 and 3 times larger
than the previously measured LONS (outside the galactic plane), as expected
since the Crab pulsar is in the galactic plane, which implies a slightly higher
energy threshold for Crab observations, if the higher value of CT1 measured
LONS rate for galactic sources is used.Comment: 19 pages, 6 figures, accepted by Astroparticle Physic
H.E.S.S. observations of the Large Magellanic Cloud
The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way at a
distance of approximately 48 kpc. Despite its distance it harbours several
interesting targets for TeV gamma-ray observations. The composite supernova
remnant N 157B/PSR J05367-6910 was discovered by H.E.S.S. being an emitter of
very high energy (VHE) gamma-rays. It is the most distant pulsar wind nebula
ever detected in VHE gamma-rays. Another very exciting target is SN 1987A, the
remnant of the most recent supernova explosion that occurred in the
neighbourhood of the Milky Way. Models for Cosmic Ray acceleration in this
remnant predict gamma-ray emission at a level detectable by H.E.S.S. but this
has not been detected so far. Fermi/LAT discovered diffuse high energy (HE)
gamma-ray emission from the general direction of the massive star forming
region 30 Doradus but no clear evidence for emission from either N 157B or SN
1987A has been published. The part of the LMC containing these objects has been
observed regularly with the H.E.S.S. telescopes since 2003. With deep
observations carried out in 2010 a very good exposure of this part of the sky
has been obtained. The current status of the H.E.S.S. LMC observations is
reported along with new results on N 157B and SN 1987A.Comment: 4 pages, 3 figures, proceedings of the 32nd Internatioal Cosmic Ray
Conference, Beijing 201
Observations of one young and three middle-aged -ray pulsars with the Gran Telescopio Canarias
We used the 10.4m Gran Telescopio Canarias to search for the optical
counterparts to four isolated -ray pulsars, all detected in the X-rays
by either \xmm\ or \chan\ but not yet in the optical. Three of them are
middle-aged pulsars -- PSR\, J1846+0919 (0.36 Myr), PSR\, J2055+2539 (1.2 Myr),
PSR\, J2043+2740 (1.2 Myr) -- and one, PSR\, J1907+0602, is a young pulsar
(19.5 kyr). For both PSR\, J1907+0602 and PSR\, J2055+2539 we found one object
close to the pulsar position. However, in both cases such an object cannot be a
viable candidate counterpart to the pulsar. For PSR\, J1907+0602, because it
would imply an anomalously red spectrum for the pulsar and for PSR\, J2055+2539
because the pulsar would be unrealistically bright () for the
assumed distance and interstellar extinction. For PSR\, J1846+0919, we found no
object sufficiently close to the expected position to claim a possible
association, whereas for PSR\, J2043+2740 we confirm our previous findings that
the object nearest to the pulsar position is an unrelated field star. We used
our brightness limits (), the first obtained with a
large-aperture telescope for both PSR\, J1846+0919 and PSR\, J2055+2539, to
constrain the optical emission properties of these pulsars and investigate the
presence of spectral turnovers at low energies in their multi-wavelength
spectra.Comment: 10 pages, 11 figures, accpted for publication in MNRA
Observations of three young gamma-ray pulsars with the Gran Telescopio Canarias
We report the analysis of the first deep optical observations of three
isolated -ray pulsars detected by the {\em Fermi Gamma-ray Space
Telescope}: the radio-loud PSR\, J0248+6021 and PSR\, J0631+1036, and the
radio-quiet PSR\, J0633+0632. The latter has also been detected in the X rays.
The pulsars are very similar in their spin-down age (40--60 kyrs),
spin-down energy ( erg s), and dipolar surface
magnetic field (-- G). These pulsars are promising
targets for multi-wavelength observations, since they have been already
detected in rays and in radio or X-rays. None of them has been
detected yet in the optical band. We observed the three pulsar fields in 2014
with the Spanish 10.4m Gran Telescopio Canarias (GTC). We could not find any
candidate optical counterpart to the three pulsars close to their most recent
radio or {\em Chandra} positions down to limits of ,
, for PSR\, J0248+6021, J0631+1036, and J0633+0632,
respectively. From the inferred optical upper limits and estimated distance and
interstellar extinction, we derived limits on the pulsar optical luminosity. We
also searched for the X-ray counterpart to PSR\, J0248+6021 with \chan\ but we
did not detect the pulsar down to a 3 flux limit of
erg cm s (0.3--10 keV). For all these pulsars, we compared the
optical flux upper limits with the extrapolations in the optical domain of the
-ray spectra and compared their multi-wavelength properties with those
of other -ray pulsars of comparable age.Comment: 12 pages, 5 figures, accepted for publication in MNRA
A Population of Teraelectronvolt Pulsar Wind Nebulae in the H.E.S.S. Galactic Plane Survey
The most numerous source class that emerged from the H.E.S.S. Galactic Plane
Survey are Pulsar Wind Nebulae (PWNe). The 2013 reanalysis of this survey,
undertaken after almost 10 years of observations, provides us with the most
sensitive and most complete census of gamma-ray PWNe to date. In addition to a
uniform analysis of spectral and morphological parameters, for the first time
also flux upper limits for energetic young pulsars were extracted from the
data. We present a discussion of the correlation between energetic pulsars and
TeV objects, and their respective properties. We will put the results in
context with the current theoretical understanding of PWNe and evaluate the
plausibility of previously non-established PWN candidates.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil
Results of the Third High Protein-High Lysine Wheat Observation Nursery Grown in 1977
This is the third report of results from a high protein-high lysine (HP-HL) wheat observation nursery organized in 1974 by the Nebraska Agricultural Experiment Station and the Science and Education Administration, U.S. Department of Agriculture, under a contract with the Agency for International Development, U.S. Department of State. Advanced experimental lines distributed to breeders and cooperators in the 3rd HP-HL nursery were selected from numerous hybrid combinations of both spring and winter types. All exhibited elevated protein and/or lysine in nursery trials in Nebraska or Arizona
Results of the Second High Protein-High Lysine Wheat Observation Nursery Grown in 1976
This is the second report of results from a high protein-high lysine (HP-HL) observation nursery organized in 1974 by the Nebraska Agricultural Experiment Station and the Science and Education Administration, U. S. Department of Agriculture, under a contract with the Agency for International Development, U. S. Department of State. Primary objectives of this nursery are to: (1) Systematically provide breeders and cooperators with superior genetic germplasm for elevated levels of protein and/or lysine. (2) Test the degree of expression of the high protein and high lysine traits in a diverse array of environments. Funding from USAID has permitted the Nebraska wheat program to establish breeding nurseries at Lincoln, Nebraska, for evaluation of winter genotypes and at Yuma, Arizona, for both spring and winter wheats. Advanced experimental lines distributed to breeders and cooperators in the 2nd HP-HL nursery were selected from numerous hybrid combinations of both spring and winter types. All exhibited elevated protein and/or elevated lysine in nursery trials at Nebraska and Arizona. The lines were screened for growth habit at Nebraska, and were assigned to the designated spring or winter sections of the 2nd HP-HL nursery
Results of the Second High Protein-High Lysine Wheat Observation Nursery Grown in 1976
This is the second report of results from a high protein-high lysine (HP-HL) observation nursery organized in 1974 by the Nebraska Agricultural Experiment Station and the Science and Education Administration, U. S. Department of Agriculture, under a contract with the Agency for International Development, U. S. Department of State. Primary objectives of this nursery are to: (1) Systematically provide breeders and cooperators with superior genetic germplasm for elevated levels of protein and/or lysine. (2) Test the degree of expression of the high protein and high lysine traits in a diverse array of environments. Funding from USAID has permitted the Nebraska wheat program to establish breeding nurseries at Lincoln, Nebraska, for evaluation of winter genotypes and at Yuma, Arizona, for both spring and winter wheats. Advanced experimental lines distributed to breeders and cooperators in the 2nd HP-HL nursery were selected from numerous hybrid combinations of both spring and winter types. All exhibited elevated protein and/or elevated lysine in nursery trials at Nebraska and Arizona. The lines were screened for growth habit at Nebraska, and were assigned to the designated spring or winter sections of the 2nd HP-HL nursery
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