260 research outputs found
PSR J2032+4127, the counterpart of TeV J2032+4130? Multiwavelength Monitoring of the Approach to Periastron
PSR J2032+4127 has recently been identified as being in a long period (45-50
years) binary in a highly eccentric orbit with the Be star MT91 213. Periastron
is due to occur in November 2017 and this rare occurrence has prompted a
multiwavelength monitoring campaign to determine if the system is a gamma-ray
binary, and, if so, to study what would be only the second gamma-ray binary
with a known compact object. In the same direction as TeV J2032+4130, gamma-ray
emission from this binary system could be related to the extended very high
energy gamma-ray emission from that region. As part of this monitoring,
observations are being conducted by Swift, Fermi-LAT and VERITAS. We present
the status of those observations, preliminary results and the plan for
continued monitoring through periastron.Comment: 8 Pages, 4 figures, 1 table. In Proceedings of the 35th International
Cosmic Ray Conference (ICRC 2017), Busan (South Korea
VERITAS observations of the Cygnus Region
The Cygnus region of the galaxy is one of the richest regions of gas and star
formation and is the brightest region of diffuse GeV emission in the northern
sky. VERITAS has conducted deep observations (approximately 300 hours) in the
direction of Cygnus region, reaching an average sensitivity of a few percent of
the Crab nebula flux. We present the results of these observations and an
analysis of over seven years of Fermi-LAT data above 1 GeV. In addition to a
search for new sources in the region, we present updated spectra and
morphologies of the known TeV gamma-ray sources and a study of their
relationship with the GeV emission from the region. These results are discussed
in their multiwavelength context including the recently published HAWC
observatory gamma-ray catalog. A comparison is also made to the H.E.S.S.
galactic plane survey.Comment: 8 pages, 6 figures. In Proceedings of the 35th International Cosmic
Ray Conference (ICRC 2017), Busan (South Korea
Observing FRB 121102 with VERITAS; Searching for Associated TeV Emission
Fast radio bursts are bright, unresolved and short flashes of radio emission
originating from outside the Milky Way. The origin of these mysterious
outbursts is unknown, but their high luminosity and short duration has prompted
much speculation. The discovery that FRB 121102 repeats has enabled
multiwavelength follow up, which has identified the host galaxy. VERITAS has
observed the location of FRB 121102, including coincident observations with
Arecibo. We present the results of a search for steady very high energy
gamma-ray emission and the methodology for searching for short timescale,
transient optical and very high energy gamma-ray emission.Comment: 8 pages, 1 figure, 1 table. In Proceedings of the 35th International
Cosmic Ray Conference (ICRC 2017), Busan (South Korea
Initial Semantics for Strengthened Signatures
We give a new general definition of arity, yielding the companion notions of
signature and associated syntax. This setting is modular in the sense requested
by Ghani and Uustalu: merging two extensions of syntax corresponds to building
an amalgamated sum. These signatures are too general in the sense that we are
not able to prove the existence of an associated syntax in this general
context. So we have to select arities and signatures for which there exists the
desired initial monad. For this, we follow a track opened by Matthes and
Uustalu: we introduce a notion of strengthened arity and prove that the
corresponding signatures have initial semantics (i.e. associated syntax). Our
strengthened arities admit colimits, which allows the treatment of the
\lambda-calculus with explicit substitution.Comment: In Proceedings FICS 2012, arXiv:1202.317
Conductance of Open Quantum Billiards and Classical Trajectories
We analyse the transport phenomena of 2D quantum billiards with convex
boundary of different shape. The quantum mechanical analysis is performed by
means of the poles of the S-matrix while the classical analysis is based on the
motion of a free particle inside the cavity along trajectories with a different
number of bounces at the boundary. The value of the conductance depends on the
manner the leads are attached to the cavity. The Fourier transform of the
transmission amplitudes is compared with the length of the classical paths.
There is good agreement between classical and quantum mechanical results when
the conductance is achieved mainly by special short-lived states such as
whispering gallery modes (WGM) and bouncing ball modes (BBM). In these cases,
also the localization of the wave functions agrees with the picture of the
classical paths. The S-matrix is calculated classically and compared with the
transmission coefficients of the quantum mechanical calculations for five modes
in each lead. The number of modes coupled to the special states is effectively
reduced.Comment: 19 pages, 6 figures (jpg), 2 table
Formation and Evolution of the Disk System of the Milky Way: [alpha/Fe] Ratios and Kinematics of the SEGUE G-Dwarf Sample
We employ measurements of the [alpha/Fe] ratio derived from low-resolution
(R~2000) spectra of 17,277 G-type dwarfs from the SEGUE survey to separate them
into likely thin- and thick-disk subsamples. Both subsamples exhibit strong
gradients of orbital rotational velocity with metallicity, of opposite signs,
-20 to -30 km/s/dex for the thin-disk and +40 to +50 km/s/dex for the
thick-disk population. The rotational velocity is uncorrelated with
Galactocentric distance for the thin-disk subsample, and exhibits a small trend
for the thick-disk subsample. The rotational velocity decreases with distance
from the plane for both disk components, with similar slopes (-9.0 {\pm} 1.0
km/s/kpc). Thick-disk stars exhibit a strong trend of orbital eccentricity with
metallicity (about -0.2/dex), while the eccentricity does not change with
metallicity for the thin-disk subsample. The eccentricity is almost independent
of Galactocentric radius for the thin-disk population, while a marginal
gradient of the eccentricity with radius exists for the thick-disk population.
Both subsamples possess similar positive gradients of eccentricity with
distance from the Galactic plane. The shapes of the eccentricity distributions
for the thin- and thick-disk populations are independent of distance from the
plane, and include no significant numbers of stars with eccentricity above 0.6.
Among several contemporary models of disk evolution we consider, radial
migration appears to have played an important role in the evolution of the
thin-disk population, but possibly less so for the thick disk, relative to the
gas-rich merger or disk heating scenarios. We emphasize that more physically
realistic models and simulations need to be constructed in order to carry out
the detailed quantitative comparisons that our new data enable.Comment: Accepted for publication in ApJ, 18 pages, 12 figures, 2 tables,
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