330 research outputs found
On the origin of \gamma-ray emission in \eta\ Carina
\eta\ Car is the only colliding-wind binary for which high-energy \gamma\
rays are detected. Although the physical conditions in the shock region change
on timescales of hours to days, the variability seen at GeV energies is weak
and on significantly longer timescales. The \gamma-ray spectrum exhibits two
features that can be interpreted as emission from the shocks on either side of
the contact discontinuity. Here we report on the first time-dependent modelling
of the non-thermal emission in \eta\ Car. We find that emission from primary
electrons is likely not responsible for the \gamma-ray emission, but
accelerated protons interacting with the dense wind material can explain the
observations. In our model, efficient acceleration is required at both shocks,
with the primary side acting as a hadron calorimeter, whilst on the companion
side acceleration is limited by the flow time out of the system, resulting in
changing acceleration conditions. The system therefore represents a unique
laboratory for the exploration of hadronic particle acceleration in
non-relativistic shocks.Comment: 5 pages, 4 figures, 1 table, accepted for publication in MNRAS
Letter
VHE observations of the gamma-ray binary system LS 5039 with H.E.S.S
LS 5039 is a gamma-ray binary system observed in a broad energy range, from
radio to TeV energies. The binary system exhibits both flux and spectral
modulation as a function of its orbital period. The X-ray and very-high-energy
(VHE, E > 100 GeV) gamma-ray fluxes display a maximum/minimum at
inferior/superior conjunction, with spectra becoming respectively
harder/softer, a behaviour that is completely reversed in the high-energy
domain (HE, 0.1 < E < 100 GeV). The HE spectrum cuts off at a few GeV, with a
new hard component emerging at E > 10 GeV that is compatible with the
low-energy tail of the TeV emission. The low 10 - 100 GeV flux, however, makes
the HE and VHE components difficult to reconcile with a scenario including
emission from only a single particle population. We report on new observations
of LS 5039 conducted with the High Energy Stereoscopic System (H.E.S.S.)
telescopes from 2006 to 2015. This new data set enables for an
unprecedentedly-deep phase-folded coverage of the source at TeV energies, as
well as an extension of the VHE spectral range down to ~120 GeV, which makes LS
5039 the first gamma-ray binary system in which a spectral overlap between
satellite and ground-based gamma-ray observatories is obtained.Comment: Proceeding for ICRC 201
H.E.S.S. observations of PSR B1259-63 during its 2014 periastron passage
An extended observation campaign of the gamma-ray binary system PSR
B125963 has been conducted with the H.E.S.S. (High Energy Stereoscopic
System) II 5-telescope array during the system's periastron passage in 2014. We
report on the outcome of this campaign, which consists of more than 85 h of
data covering both pre- and post-periastron orbital phases. The lower energy
threshold of the H.E.S.S. II array allows very-high-energy (VHE; GeV) gamma-ray emission from PSR B125963 to be studied for the first
time down to 200 GeV. The new dataset partly overlaps with and extends in phase
previous H.E.S.S. campaigns on this source in 2004, 2007 and 2011, allowing for
a detailed long-term characterisation of the flux level at VHEs. In addition,
the 2014 campaign reported here includes VHE observations during the exact
periastron time, , as well as data taken simultaneously to the
gamma-ray flare detected with the Fermi-LAT. Our results will be discussed in a
multiwavelength context, thanks to the dense broad-band monitoring campaign
conducted on the system during this last periastron passage.Comment: 8 pages, 5 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherland
Slow and Fast Neocortical Oscillations in the Senescence-Accelerated Mouse Model SAMP8
The senescence-accelerated mouse prone 8 (SAMP8) model is characterized by accelerated, progressive cognitive decline as well as Alzheimer's disease (AD)-like neurodegenerative changes, and resembles the etiology of multicausal, sporadic late-onset/age-related AD in humans. Our aim was to find whether these AD-like pathological features, together with the cognitive deficits present in the SAMP8 strain, are accompanied by disturbances in cortical network activity with respect to control mice (SAM resistance 1, SAMR1) and, if so, how the alterations in cortical activity progress with age. For this purpose, we characterized the extracellular spontaneous oscillatory activity in different regions of the cerebral cortex of SAMP8 and SAMR1 mice under ketamine anesthesia at 5 and 7 months of age. Under these conditions, slow oscillations and fast rhythms generated in the cortical network were recorded and different parameters of these oscillations were quantified and compared between SAMP8 and their control, SAMR1 mice. The average frequency of slow oscillations in SAMP8 mice was decreased with respect to the control mice at both studied ages. An elongation of the silent periods or Down states was behind the decreased slow oscillatory frequency while the duration of active or Up states remained stable. SAMP8 mice also presented increased cycle variability and reduced high frequency components during Down states. During Up states, the power peak in the gamma range was displaced towards lower frequencies in all the cortical areas of SAMP8 with respect to control mice suggesting that the spectral profile of SAMP8 animals is shifted towards lower frequencies. This shift is reminiscent to one of the principal hallmarks of electroencephalography (EEG) abnormalities in patients with Alzheimer's disease, and adds evidence in support of the suitability of the SAMP8 mouse as a model of this disease. Although some of the differences between SAMP8 and control mice were emphasized with age, the evolution of the studied parameters as SAMR1 mice got older indicates that the SAMR1 phenotype tends to converge with that of SAMP8 animals. To our knowledge, this is the first systematic characterization of the cortical slow and fast rhythms in the SAMP8 strain and it provides useful insights about the cellular and synaptic mechanisms underlying the reported alterations
Candidate counterparts to the soft gamma-ray flare in the direction of LS i +61 303
Context. A short duration burst reminiscent of a soft gamma-ray repeater/anomalous X-ray pulsar behaviour was detected in the direction of LS I +61 303 by the Swift satellite. While the association with this well known gamma-ray binary is likely, a different origin cannot be excluded.
Aims. We explore the error box of this unexpected flaring event and establish the radio, near-infrared and X-ray sources in our search for any peculiar alternative counterpart.
Methods. We carried out a combined analysis of archive Very Large Array radio data of LS I +61 303 sensitive to both compact and extended emission. We also reanalysed previous near infrared observations with the 3.5 m telescope of the Centro Astronómico Hispano Alemn and X-ray observations with the Chandra satellite.
Results. Our deep radio maps of the LS I +61 303 environment represent a significant advancement on previous work and 16 compact radio sources in the LS I +61 303 vicinity are detected. For some detections, we also identify near infrared and X-ray counterparts. Extended emission features in the field are also detected and confirmed. The possible connection of some of these sources with the observed flaring event is considered. Based on these data, we are unable to claim a clear association between the Swift-BAT flare and any of the sources reported here. However, this study represents the most sophisticated attempt to determine possible alternative counterparts other than LS I +61 303.Facultad de Ciencias Astronómicas y Geofísica
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