24,176 research outputs found
A Multiwavelength Investigation of Unidentified EGRET Sources
Statistical studies indicate that the 271 point sources of high-energy gamma
rays belong to two groups: a Galactic population and an isotropic extragalactic
population. Many unidentified extragalactic sources are certainly blazars, and
it is the intention of this work to uncover gamma-ray blazars missed by
previous attempts. Until recently, searches for blazar counterparts to
unidentified EGRET sources have focused on finding AGN that have 5-GHz radio
flux densities S_5 near or above 1 Jy. However, the recent blazar
identification of 3EG J2006-2321 (S_5 = 260 mJy) and other work suggest that
careful studies of weaker flat-spectrum sources may be fruitful. In this
spirit, error circles of 4 high-latitude unidentified EGRET sources have been
searched for 5-GHz sources. The gamma-ray sources are 3EG J1133+0033, 3EG
J1212+2304, 3EG J1222+2315, and 3EG J1227+4302. Within the error contours of
each of the four sources are found 6 radio candidates; by observing the
positions of the radio sources with the 0.81-m Tenagra II telescope it is
determined that 14 of these 24 radio sources have optical counterparts with R <
22. Eight of these from two different EGRET sources have been observed in the
B, V, and R bands in more than one epoch and the analysis of these data is
ongoing. Any sources that are found to be variable will be the objects of
multi-epoch polarimetry studies.Comment: 6 pages, 2 tables. To appear in Astrophysics & Space Scienc
The impact of health on professionally active people's incomes in Poland. Microeconometric analysis
The outcome of the research confirms the occurrence of positive interaction between professionally active people's incomes and the self-assessed state of health. People declaring a bad state of health have incomes by 20% on average lower than people who enjoy good health (assuming that the remaining characteristics of the surveyed person are the same). In case of men, the impact of health state on incomes is slightly greater than in case of women.Wyniki badań potwierdzają istnienie pozytywnej zależności dochodów osób aktywnych zawodowo od stanu zdrowia mierzonego jego samooceną. Osoby deklarujące zły stan zdrowia osiągają dochody przeciętnie o 20% niższe niż osoby, które cieszą się dobrym stanem zdrowia (przy założeniu, że pozostałe charakterystyki badanej osoby są takie same). W przypadku mężczyzn zależność dochodów od stanu zdrowia jest nieznacznie silniejsza niż w przypadku kobiet
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
Deposition of general ellipsoidal particles
We present a systematic overview of granular deposits composed of ellipsoidal
particles with different particle shapes and size polydispersities. We study
the density and anisotropy of such deposits as functions of size polydispersity
and two shape parameters that fully describe the shape of a general ellipsoid.
Our results show that, while shape influences significantly the macroscopic
properties of the deposits, polydispersity plays apparently a secondary role.
The density attains a maximum for a particular family of non-symmetrical
ellipsoids, larger than the density observed for prolate or oblate ellipsoids.
As for anisotropy measures, the contact forces show are increasingly preferred
along the vertical direction as the shape of the particles deviates for a
sphere. The deposits are constructed by means of an efficient molecular
dynamics method, where the contact forces are efficiently and accurately
computed. The main results are discussed in the light of applications for
porous media models and sedimentation processes.Comment: 7 pages, 8 figure
Convergence of random zeros on complex manifolds
We show that the zeros of random sequences of Gaussian systems of polynomials
of increasing degree almost surely converge to the expected limit distribution
under very general hypotheses. In particular, the normalized distribution of
zeros of systems of m polynomials of degree N, orthonormalized on a regular
compact subset K of C^m, almost surely converge to the equilibrium measure on K
as the degree N goes to infinity.Comment: 16 page
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&
GRB Energetics and the GRB Hubble Diagram: Promises and Limitations
We present a complete sample of 29 GRBs for which it has been possible to
determine temporal breaks (or limits) from their afterglow light curves. We
interpret these breaks within the framework of the uniform conical jet model,
incorporating realistic estimates of the ambient density and propagating error
estimates on the measured quantities. In agreement with our previous analysis
of a smaller sample, the derived jet opening angles of those 16 bursts with
redshifts result in a narrow clustering of geometrically-corrected gamma-ray
energies about E_gamma = 1.33e51 erg; the burst-to-burst variance about this
value is a factor of 2.2. Despite this rather small scatter, we demonstrate in
a series of GRB Hubble diagrams, that the current sample cannot place
meaningful constraints upon the fundamental parameters of the Universe. Indeed
for GRBs to ever be useful in cosmographic measurements we argue the necessity
of two directions. First, GRB Hubble diagrams should be based upon fundamental
physical quantities such as energy, rather than empirically-derived and
physically ill-understood distance indicators. Second, a more homogeneous set
should be constructed by culling sub-classes from the larger sample. These
sub-classes, though now first recognizable by deviant energies, ultimately must
be identifiable by properties other than those directly related to energy. We
identify a new sub-class of GRBs (``f-GRBs'') which appear both underluminous
by factors of at least 10 and exhibit a rapid fading at early times. About
10-20% of observed long-duration bursts appear to be f-GRBs.Comment: Accepted to the Astrophysical Journal (20 May 2003). 19 pages, 3
Postscript figure
On the Conditions for Neutron-Rich Gamma-Ray Burst Outflows
We calculate the structure and neutron content of neutrino-heated MHD winds
driven from the surface of newly-formed magnetars (``proto-magnetars'') and
from the midplane of hyper-accreting disks, two of the possible central engines
for gamma-ray bursts (GRBs) and hyper-energetic supernovae (SNe). Both the
surface of proto-magnetars and the midplane of neutrino-cooled accretion flows
(NDAFs) are electron degenerate and neutron-rich (neutron-to-proton ratio n/p
>> 1). If this substantial free neutron excess is preserved to large radii in
ultra-relativistic outflows, several important observational consequences may
result. Weak interaction processes, however, can drive n/p to ~1 in the
nondegenerate regions that obtain just above the surfaces of NDAFs and
proto-magnetars. Our calculations show that mildly relativistic neutron-rich
outflows from NDAFs are possible in the presence of a strong poloidal magnetic
field. However, we find that neutron-rich winds possess a minimum mass-loss
rate that likely precludes simultaneously neutron-rich and ultra-relativistic
(Lorentz factor > 100) NDAF winds accompanying a substantial accretion power.
In contrast, proto-magnetars are capable of producing neutron-rich
long-duration GRB outflows ~10-30 seconds following core bounce for
sub-millisecond rotation periods; such outflows would, however, accompany only
extremely energetic events, in which the GRB + SN energy budget exceeds ~ 4e52
ergs. Neutron-rich highly relativistic outflows may also be produced during
some short-duration GRBs by geometrically thick accretion disks formed from
compact object mergers. The implications for r-process nucleosynthesis, optical
transients due to non-relativistic neutron-rich winds, and Nickel production in
proto-magnetar and NDAF winds are also briefly discussed.Comment: 24 pages, 7 figures, submitted to Ap
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