430 research outputs found
Evidence of coupling between the thermal and nonthermal emission in the gamma-ray binary LS I +61 303
The gamma-ray binary LS I +61 303 is composed of a Be star and a compact
companion orbiting in an eccentric orbit. Variable flux modulated with the
orbital period of ~26.5 d has been detected from radio to very high-energy
gamma rays. In addition, the system presents a superorbital variability of the
phase and amplitude of the radio outburst with a period of ~4.6 yr. We present
optical photometric observations of LS I +61 303 spanning ~1.5 yr and
contemporaneous Halpha equivalent width (EW Halpha) data. The optical
photometry shows, for the first time, that the known orbital modulation suffers
a positive orbital phase shift and an increase in flux for data obtained 1-yr
apart. This behavior is similar to that already known at radio wavelengths,
indicating that the optical flux follows the superorbital variability as well.
The orbital modulation of the EW Halpha presents the already known superorbital
flux variability but shows, also for the first time, a positive orbital phase
shift. In addition, the optical photometry exhibits a lag of ~0.1-0.2 in
orbital phase with respect to the EW Halpha measurements at similar
superorbital phases, and presents a lag of ~0.1 and ~0.3 orbital phases with
respect noncontemperaneous radio and X-ray outbursts, respectively. The phase
shifts detected in the orbital modulation of thermal indicators, such as the
optical flux and the EW Halpha, are in line with the observed behavior for
nonthermal indicators, such as X-ray or radio emission. This shows that there
is a strong coupling between the thermal and nonthermal emission processes in
the gamma-ray binary LS I +61 303. The orbital phase lag between the optical
flux and the EW Halpha is naturally explained considering different emitting
regions in the circumstellar disk, whereas the secular evolution might be
caused by the presence of a moving one-armed spiral density wave in the disk.Comment: 4 pages, 3 figures, accepted for publication in A&A (this version
matches the published version
Transport of cattle in Spain. Technical, administrative and welfare aspects according to the destination.
To obtain a thorough description of how are cattle transported in Spain with respect to the journey destination a survey was performed in 2004 and 2005. Information was obtained by means of a 119-parameters questionnaire, and 44 transport operators representative of the sector (27 slaughterhouses, 10 traders, and 7 cattle markets) were interviewed. Over 80% of journeys transported growing-finishing/finished animals, and about 3% of journeys transported both growing-finishing/finished and reproductive animals. With respect to farm transports, slaughter transports loaded in fewer farms (1.2 vs. 1.4 farms; pPara conocer en detalle como se transporta el ganado vacuno en España según el destino del viaje, entre los años 2004 y 2005 se entrevistaron 44 operadores representativos del sector (27 mataderos, 10 comerciantes y 7 mercados) mediante cuestionarios que recogían información relativa a 119 parámetros. Más del 80% de los viajes fueron de animales cebados/para cebo, y algo más de un 3% de los viajes transportaban animales cebados/para cebo y reproductores. Los transportes a matadero cargaron en un menor número de explotaciones (1,2 vs. 1,4 granjas;
Gamma rays from microquasars Cygnus X-1 and Cygnus X-3
Gamma-ray observations of microquasars at high and very-high energies can
provide valuable information of the acceleration processes inside the jets, the
jet-environment interaction and the disk-jet coupling. Two high-mass
microquasars have been deeply studied to shed light on these aspects: Cygnus
X-1 and Cygnus X-3. Both systems display the canonical hard and soft X-ray
spectral states of black hole transients, where the radiation is dominated by
non-thermal emission from the corona and jets and by thermal emission from the
disk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeV
using 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. A
hint of orbital flux modulation was also found, as the source is only detected
in phases around the compact object superior conjunction. We conclude that the
high-energy gamma-ray emission from Cygnus X-1 is most likely associated with
jets and its detection allow us to constrain the production site. Moreover, we
include in the discussion the final results of a MAGIC long-term campaign on
Cygnus X-1 that reaches almost 100 hr of observations at different X-ray
states. On the other hand, during summer 2016, Cygnus X-3 underwent a flaring
activity period in radio and high-energy gamma rays, similar to the one that
led to its detection in the high-energy regime in 2009. MAGIC performed
comprehensive follow-up observations for a total of about 70 hr. We discuss our
results in a multi-wavelength context.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Small grid embeddings of 3-polytopes
We introduce an algorithm that embeds a given 3-connected planar graph as a
convex 3-polytope with integer coordinates. The size of the coordinates is
bounded by . If the graph contains a triangle we can
bound the integer coordinates by . If the graph contains a
quadrilateral we can bound the integer coordinates by . The
crucial part of the algorithm is to find a convex plane embedding whose edges
can be weighted such that the sum of the weighted edges, seen as vectors,
cancel at every point. It is well known that this can be guaranteed for the
interior vertices by applying a technique of Tutte. We show how to extend
Tutte's ideas to construct a plane embedding where the weighted vector sums
cancel also on the vertices of the boundary face
LS 5039: a runaway microquasar ejected from the galactic plane
We have compiled optical and radio astrometric data of the microquasar LS
5039 and derived its proper motion. This, together with the distance and radial
velocity of the system, allows us to state that this source is escaping from
its own regional standard of rest, with a total systemic velocity of about 150
km/s and a component perpendicular to the galactic plane larger than 100 km/s.
This is probably the result of an acceleration obtained during the supernova
event that created the compact object in this binary system. We have computed
the trajectory of LS 5039 in the past, and searched for OB associations and
supernova remnants in its path. In particular, we have studied the possible
association between LS 5039 and the supernova remnant G016.8-01.1, which,
despite our efforts, remains dubious. We have also discovered and studied an HI
cavity in the ISM, which could have been created by the stellar wind of LS 5039
or by the progenitor of the compact object in the system. Finally, in the
symmetric supernova explosion scenario, we estimate that at least 17 solar
masses were lost in order to produce the high eccentricity observed. Such a
mass loss could also explain the observed runaway velocity of the microquasar.Comment: 12 pages, 5 figures, LaTeX, uses aa.cls. Accepted for publication in
A&
3.9 day orbital modulation in the TeV gamma-ray flux and spectrum from the X-ray binary LS 5039
New observations of LS 5039, a High Mass X-ray Binary comprising a massive
star and compact object, were carried out with the High Energy Stereoscopic
System of Cherenkov Telescopes (H.E.S.S.) in 2005 at very high energy (VHE)
gamma-ray energies. These observations reveal that its flux and energy spectrum
are modulated with the 3.9 day orbital period of the binary system. This is the
first time in gamma-ray astronomy that orbital modulation has been observed,
and periodicity clearly established using ground-based gamma-ray detectors. The
VHE gamma-ray emission is largely confined to half of the orbit, peaking around
the inferior conjunction epoch of the compact object. For this epoch, there is
also a hardening of the energy spectrum in the energy range between 0.2 TeV and
a few TeV. The flux vs. orbital phase profile provides the first clear
indication of gamma-ray absorption via pair production within an astrophysical
source, a process which is expected to occur if the gamma-ray production site
is situated within ~1 AU of the compact object. Moreover the production region
size must be not significantly greater than the binary separation (~0.15 AU).
Notably, these constraints are also considerably smaller than the collimated
outflows or jets (extending out to ~1000 AU) observed in LS 5039. The spectral
hardening could arise from variations with phase in the maximum electron
energies, and/or the dominant VHE gamma-ray production mechanism.Comment: 8 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
The Cherenkov Telescope Array Large Size Telescope
The two arrays of the Very High Energy gamma-ray observatory Cherenkov
Telescope Array (CTA) will include four Large Size Telescopes (LSTs) each with
a 23 m diameter dish and 28 m focal distance. These telescopes will enable CTA
to achieve a low-energy threshold of 20 GeV, which is critical for important
studies in astrophysics, astroparticle physics and cosmology. This work
presents the key specifications and performance of the current LST design in
the light of the CTA scientific objectives.Comment: 4 pages, 5 figures, In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at
arXiv:1307.223
An intermittent extreme BL Lac: MWL study of 1ES 2344+514 in an enhanced state
Extreme high-frequency BL Lacs (EHBL) feature their synchrotron peak of the broad-band spectral energy distribution (SED) at vs ≥ 1017 Hz. The BL Lac object 1ES 2344+514 was included in the EHBL family because of its impressive shift of the synchrotron peak in 1996. During the following years, the source appeared to be in a low state without showing any extreme behaviours. In 2016 August, 1ES 2344+514 was detected with the groundbased γ -ray telescope FACT during a high γ -ray state, triggering multiwavelength (MWL) observations. We studied the MWL light curves of 1ES 2344+514 during the 2016 flaring state, using data from radio to very-high-energy (VHE) γ -rays taken with OVRO, KAIT, KVA, NOT, some telescopes of the GASP-WEBT collaboration at the Teide, Crimean, and St. Petersburg observatories, Swift-UVOT, Swift-XRT, Fermi-LAT, FACT, and MAGIC. With simultaneous observations of the flare, we built the broad-band SED and studied it in the framework of a leptonic and a hadronic model. The VHE γ -ray observations show a flux level of 55 per cent of the Crab Nebula flux above 300 GeV, similar to the historical maximum of 1995. The combination of MAGIC and Fermi-LAT spectra provides an unprecedented characterization of the inverse-Compton peak for this object during a flaring episode. The _ index of the intrinsic spectrum in the VHE γ -ray band is 2.04 ± 0.12stat ± 0.15sys.We find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to 1018 Hz.The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2017-87859-P, FPA2017-85668-P, FPA2017-82729-C6-2-R, FPA2017-82729-C6-6-R, FPA2017-82729-C6-5-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2017-87055-C2-2-P, and FPA2017-90566-REDC), the Indian Department of Atomic Energy, the Japanese JSPS and MEXT, the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-153/28.08.2018, and the Academy of Finland grant no. 320045 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia ‘Severo Ochoa’ SEV-2016-0588 and SEV-2015-0548, and Unidad de Excelencia ‘María de Maeztu’ MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382 and by the Brazilian MCTIC, CNPq, and FAPERJ. The FACT collaboration acknowledges the important contributions from ETH Zurich grants ETH-10.08-2 and ETH-27.12-1 as well as the funding by the Swiss SNF and the German BMBF (Verbundforschung Astro- und Astroteilchenphysik) and HAP (Helmoltz Alliance for Astroparticle Physics) are gratefully acknowledged. Part of this work is supported by Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Center SFB 876 ‘Providing Information by Resource-Constrained Analysis’, project C3
Long-term multi-wavelength variability and correlation study of Markarian 421 from 2007 to 2009
We study the multi-band variability and correlations of the TeV blazar Mrk
421 on year time scales, which can bring additional insight on the processes
responsible for its broadband emission. We observed Mrk 421 in the very high
energy (VHE) gamma-ray range with the Cherenkov telescope MAGIC-I from March
2007 to June 2009 for a total of 96 hours of effective time after quality cuts.
The VHE flux variability is quantified with several methods, including the
Bayesian Block algorithm, which is applied to data from Cherenkov telescopes
for the first time. The 2.3 year long MAGIC light curve is complemented with
data from the Swift/BAT and RXTE/ASM satellites and the KVA, GASP-WEBT, OVRO,
and Mets\"ahovi telescopes from February 2007 to July 2009, allowing for an
excellent characterisation of the multi-band variability and correlations over
year time scales. Mrk 421 was found in different gamma-ray emission states
during the 2.3 year long observation period. Flares and different levels of
variability in the gamma-ray light curve could be identified with the Bayesian
Block algorithm. The same behaviour of a quiet and active emission was found in
the X-ray light curves measured by Swift/BAT and the RXTE/ASM, with a direct
correlation in time. The behaviour of the optical light curve of GASP-WEBT and
the radio light curves by OVRO and Mets\"ahovi are different as they show no
coincident features with the higher energetic light curves and a less variable
emission. The fractional variability is overall increasing with energy. The
comparable variability in the X-ray and VHE bands and their direct correlation
during both high- and low-activity periods spanning many months show that the
electron populations radiating the X-ray and gamma-ray photons are either the
same, as expected in the Synchrotron-Self-Compton mechanism, or at least
strongly correlated, as expected in electromagnetic cascades.Comment: Corresponding authors: Ann-Kristin Overkemping
([email protected]), Marina Manganaro
([email protected]), Diego Tescaro ([email protected]), To be published
in Astronomy&Astrophysics (A&A), 12 pages, 9 figure
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