17,711 research outputs found
Comment on "Nucleon elastic form factors and local duality"
We comment on the papers "Nucleon elastic form factors and local duality"
[Phys. Rev. {\bf D62}, 073008 (2000)] and "Experimental verification of
quark-hadron duality" [Phys. Rev. Lett. {\bf 85}, 1186 (2000)]. Our main
comment is that the reconstruction of the proton magnetic form factor, claimed
to be obtained from the inelastic scaling curve thanks to parton-hadron local
duality, is affected by an artifact.Comment: to appear in Phys. Rev.
Multi-color Optical and NIR Light Curves of 64 Stripped-Envelope Core-Collapse Supernovae
We present a densely-sampled, homogeneous set of light curves of 64 low
redshift (z < 0.05) stripped-envelope supernovae (SN of type IIb, Ib, Ic and
Ic-bl). These data were obtained between 2001 and 2009 at the Fred L. Whipple
Observatory (FLWO) on Mt. Hopkins in Arizona, with the optical FLWO 1.2-m and
the near-infrared PAIRITEL 1.3-m telescopes. Our dataset consists of 4543
optical photometric measurements on 61 SN, including a combination of UBVRI,
UBVr'i', and u'BVr'i', and 2142 JHKs near-infrared measurements on 25 SN. This
sample constitutes the most extensive multi-color data set of stripped-envelope
SN to date. Our photometry is based on template-subtracted images to eliminate
any potential host galaxy light contamination. This work presents these
photometric data, compares them with data in the literature, and estimates
basic statistical quantities: date of maximum, color, and photometric
properties. We identify promising color trends that may permit the
identification of stripped-envelope SN subtypes from their photometry alone.
Many of these SN were observed spectroscopically by the CfA SN group, and the
spectra are presented in a companion paper (Modjaz et al. 2014). A thorough
exploration that combines the CfA photometry and spectroscopy of
stripped-envelope core-collapse SN will be presented in a follow-up paper.Comment: 26 pages, 17 figures, 8 tables. Revised version resubmitted to ApJ
Supplements after referee report. Additional online material is available
through http://cosmo.nyu.edu/SNYU
Discovery of a supernova associated with GRB 031203: SMARTS Optical-Infrared Lightcurves from 0.2 to 92 days
Optical and infrared monitoring of the afterglow site of gamma-ray burst
(GRB) 031203 has revealed a brightening source embedded in the host galaxy,
which we attribute to the presence of a supernova (SN) related to the GRB ("SN
031203"). We present details of the discovery and evolution of SN 031203 from
0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I
and J bands. A template type Ic lightcurve, constructed from SN 1998bw
photometry, is consistent with the peak brightness of SN 031203 although the
lightcurves are not identical. Differential astrometry reveals that the SN, and
hence the GRB, occurred less than 300 h_71^-1 pc (3-sigma) from the apparent
galaxy center. The peak of the supernova is brighter than the optical afterglow
suggesting that this source is intermediate between a strong GRB and a
supernova.Comment: 11 pages, 3 figures, submitted to ApJ Letter
Tuning the electron energy by controlling the density perturbation position in laser plasma accelerators
A density perturbation produced in an underdense plasma was used to improve
the quality of electron bunches produced in the laser-plasma wakefield
acceleration scheme. Quasi-monoenergetic electrons were generated by controlled
injection in the longitudinal density gradients of the density perturbation. By
tuning the position of the density perturbation along the laser propagation
axis, a fine control of the electron energy from a mean value of 60 MeV to 120
MeV has been demonstrated with a relative energy-spread of 15 +/- 3.6%,
divergence of 4 +/- 0.8 mrad and charge of 6 +/- 1.8 pC.Comment: 7 pages, 8 figure
On the Nature of Velocity Fields in High z Galaxies
We analyze the gas kinematics of damped Lya systems (DLAs) hosting high z
gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs) focusing on
threestatistics: (1) dv, the velocity interval encompassing 90% of the
totaloptical depth, (2,3) Wsi and Wciv, the rest equivalent widths of the
SiII1526 and CIV1548 transitions. The dv distributions of the GRB-DLAs and
QSO-DLAs are similar, each has median dv~80km/s and a significant tail to
several hundred km/s. This suggests comparable galaxy masses for the parent
populations of GRB-DLAs and QSO-DLAs and we infer the average dark matter halo
mass of GRB galaxies is <~10^{12} Msol. The unique configuration of GRB-DLA
sightlines and the presence (and absence) of fine-structure absorption together
give special insight into the nature of high z, protogalactic velocity fields.
The data support a scenario where the dv statistic reflects dynamics in the
interstellar medium (ISM) and Wsi traces motions outside the ISM (e.g. halo
gas, galactic-scale winds). The Wsi statistic and gas metallicity [M/H] are
tightly correlated, especially for the QSO-DLAs: [M/H]=a + b log(Wsi/1A) with
a=-0.92+/-0.05 and b=-1.41+/-0.10. We argue that the Wsi statistic primarily
tracks dynamical motions in the halos of high z galaxies and interpret this
correlation as a mass-metallicity relation with very similar slope to the trend
observed in local, low-metallicity galaxies. Finally, the GRB-DLAs exhibit
systematically larger Wsi values (>0.5A) than the QSO-DLAs (~ 0.5A) which
may suggest galactic-scale outflows contribute to the largest observed velocity
fields.Comment: 14 pages, 9 figures. Submitted to Ap
Dust and dark Gamma-Ray Bursts: mutual implications
In a cosmological context dust has been always poorly understood. That is
true also for the statistic of GRBs so that we started a program to understand
its role both in relation to GRBs and in function of z. This paper presents a
composite model in this direction. The model considers a rather generic
distribution of dust in a spiral galaxy and considers the effect of changing
some of the parameters characterizing the dust grains, size in particular. We
first simulated 500 GRBs distributed as the host galaxy mass distribution,
using as model the Milky Way. If we consider dust with the same properties as
that we observe in the Milky Way, we find that due to absorption we miss about
10% of the afterglows assuming we observe the event within about 1 hour or even
within 100s. In our second set of simulations we placed GRBs randomly inside
giants molecular clouds, considering different kinds of dust inside and outside
the host cloud and the effect of dust sublimation caused by the GRB inside the
clouds. In this case absorption is mainly due to the host cloud and the
physical properties of dust play a strong role. Computations from this model
agree with the hypothesis of host galaxies with extinction curve similar to
that of the Small Magellanic Cloud, whereas the host cloud could be also
characterized by dust with larger grains. To confirm our findings we need a set
of homogeneous infrared observations. The use of coming dedicated infrared
telescopes, like REM, will provide a wealth of cases of new afterglow
observations.Comment: 16 pages, 8 figures, accepted by A&
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