137 research outputs found
Direct Measurement of Neutron-Star Recoil in the Oxygen-Rich Supernova Remnant Puppis A
A sequence of three Chandra X-ray Observatory High Resolution Camera images
taken over a span of five years reveals arc-second-scale displacement of RX
J0822-4300, the stellar remnant (presumably a neutron star) near the center of
the Puppis A supernova remnant. We measure its proper motion to be
0.165+/-0.025 arcsec/yr toward the west-southwest. At a distance of 2 kpc, this
corresponds to a transverse space velocity of ~1600 km/s. The space velocity is
consistent with the explosion center inferred from proper motions of the
oxygen-rich optical filaments, and confirms the idea that Puppis A resulted
from an asymmetric explosion accompanied by a kick that imparted roughly
3*10^49 ergs of kinetic energy (some 3 percent of the kinetic energy for a
typical supernova) to the stellar remnant. We discuss constraints on
core-collapse supernova models that have been proposed to explain neutron star
kick velocities
Proper Motions of PSRs B1757-24 and B1951+32: Implications for Ages and Associations
Over the last decade, considerable effort has been made to measure the proper
motions of the pulsars B1757-24 and B1951+32 in order to establish or refute
associations with nearby supernova remnants and to understand better the
complicated geometries of their surrounding nebulae. We present proper motion
measurements of both pulsars with the Very Large Array, increasing the time
baselines of the measurements from 3.9 yr to 6.5 yr and from 12.0 yr to 14.5
yr, respectively, compared to previous observations. We confirm the
non-detection of proper motion of PSR B1757-24, and our measurement of (mu_a,
mu_d) = (-11 +/- 9, -1 +/- 15) mas yr^{-1} confirms that the association of PSR
B1757-24 with SNR G5.4-1.2 is unlikely for the pulsar characteristic age of
15.5 kyr, although an association can not be excluded for a significantly
larger age. For PSR B1951+32, we measure a proper motion of (mu_a, mu_d) =
(-28.8 +/- 0.9, -14.7 +/- 0.9) mas yr^{-1}, reducing the uncertainty in the
proper motion by a factor of two compared to previous results. After correcting
to the local standard of rest, the proper motion indicates a kinetic age of ~51
kyr for the pulsar, assuming it was born near the geometric center of the
supernova remnant. The radio-bright arc of emission along the pulsar proper
motion vector shows time-variable structure, but moves with the pulsar at an
approximately constant separation ~2.5", lending weight to its interpretation
as a shock structure driven by the pulsar.Comment: LaTeX file uses emulateapj.cls; 7 pages, 4 figures, to be published
ApJ February 10, 2008, v674 p271-278. Revision reflects journal formatting;
there are no substantial revision
Strategies for success: The use of social media in the marketing of professional services – evidence of a global case study
The aim of this qualitative case study was to address the problem that little research has specifically explored social media marketing in professional services firms. Many professional services firms do not know how to best use social media to achieve their business development goals. Some firms may believe social media entails a risk to their reputation, and improper use of social media could lead to negative business outcomes if time and resources are wasted. This is a problem because professional services firms are widely known to have unique characteristics differentiating them from other industries; therefore, general knowledge of social media marketing remains a challenge. To address this problem, this research sought to generate a rich description of the use of social media marketing by one global professional services firm. The research was guided by three research questions: How have social media affected the marketing of professional services in one professional services firm? How has one professional services firm responded to the rise of social media,and with what effects on its business outcomes? What lessons arise from the case of one professional services firm with regard to success strategies for leveraging social media in marketing? The study examined KPMG’s use of foursocial media platforms (blogs, Facebook, LinkedIn and Twitter) to enhance its brand, create a unified web identity, and drive traffic to its website. The study highlights the importance of using blogs, Facebook, LinkedIn and Twitter to address clients, as well as the business imperatives for successful planning, development and implementation
On understanding the lives of dead stars : Supernova Remnant N103B, radio pulsar B1951+32, and the Rabbit
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2003.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 87-98).Using the Chandra High Energy Transmission Grating Spectrometer, we observed the young Supernova Remnant N103B in the Large Magellanic Cloud as part of the Guaranteed Time Observation program. N103B has a small overall extent and shows substructure on arcsecond spatial scales. The spectrum, based on 116ks of data, reveals unambiguous Mg, Ne, and O emission lines. Due to the elemental abundances, we are able to tentatively reject suggestions that N103B arose from a Type Ia supernova, in favor of the massive progenitor, core-collapse hypothesis indicated by earlier radio and optical studies, and by some recent X-ray results. We present our latest two-temperature shock and two-dimensional spatial-spectral modeling of the remnant. If the massive progenitor conclusion holds true, it would significantly changes previous conceptions of the young SNR population in the LMC.(cont.) Using the Very Large Array and the Pie Town antenna, we have measured the position of the radio pulsar B1995+32 relative to nearby background radio sources at four epochs between 1989 and 2000. These data show a clear motion for the pulsar of (25 +/- 4) milliarcsec/yr at a position angle (252 +/- 7) degrees (north through east), corresponding to a transverse velocity (240 +/- 40) km/s for a distance to the source of 2 kpc. The measured direction of motion confirms that the pulsar is moving away from the center of its associated supernova remnant, the first time that such a result has been demonstrated. Independent of assumptions made about the pulsar birth-place, we show that the measured proper motion implies an age for the pulsar of (64 +/- 18) kyr, somewhat less than its characteristic age of 107 kyr. This discrepancy can be explained if the initial spin period of the pulsar was P0 = (27 +/- 6) ms.by Joshua Marc Migliazzo.S.M
Bow Shocks from Neutron Stars: Scaling Laws and HST Observations of the Guitar Nebula
The interaction of high-velocity neutron stars with the interstellar medium
produces bow shock nebulae, where the relativistic neutron star wind is
confined by ram pressure. We present multi-wavelength observations of the
Guitar Nebula, including narrow-band H-alpha imaging with HST/WFPC2, which
resolves the head of the bow shock. The HST observations are used to fit for
the inclination of the pulsar velocity vector to the line of sight, and to
determine the combination of spindown energy loss, velocity, and ambient
density that sets the scale of the bow shock. We find that the velocity vector
is most likely in the plane of the sky. We use the Guitar Nebula and other
observed neutron star bow shocks to test scaling laws for their size and
H-alpha emission, discuss their prevalence, and present criteria for their
detectability in targeted searches. The set of H-alpha bow shocks shows
remarkable consistency, in spite of the expected variation in ambient densities
and orientations. Together, they support the assumption that a pulsar's
spindown energy losses are carried away by a relativistic wind that is
indistinguishable from being isotropic. Comparison of H-alpha bow shocks with
X-ray and nonthermal, radio-synchrotron bow shocks produced by neutron stars
indicates that the overall shape and scaling is consistent with the same
physics. It also appears that nonthermal radio emission and H-alpha emission
are mutually exclusive in the known objects and perhaps in all objects.Comment: 12 pages, 7 figures (3 degraded), submitted to ApJ; minor revisions
and updates in response to referee report. (AASTeX, includes emulateapj5 and
onecolfloat5.
Birth Kick Distributions and the Spin-Kick Correlation of Young Pulsars
Evidence from pulsar wind nebula symmetry axes and radio polarization
observations suggests that pulsar motions correlate with the spin directions.
We assemble this evidence for young isolated pulsars and show how it can be
used to quantitatively constrain birth kick scenarios. We illustrate by
computing several plausible, but idealized, models where the momentum thrust is
proportional to the neutrino cooling luminosity of the proto-neutron star. Our
kick simulations include the effects of pulsar acceleration and spin-up and our
maximum likelihood comparison with the data constrains the model parameters.
The fit to the pulsar spin and velocity measurements suggests that: i) the
anisotropic momentum required amounts to ~10% of the neutrino flux, ii) while a
pre-kick spin of the star is required, the preferred magnitude is small
10-20rad/s, so that for the best-fit models iii) the bulk of the spin is
kick-induced with ~120rad/s and iv) the models suggest that the
anisotropy emerges on a timescale ~1-3s.Comment: 37 pages, 13 figures, ApJ accepte
Herramientas estratégicas específicas para Startups tecnológicos: Cameo LLC
Fil: Migliazzo, Oscar Andrés. Universidad Católica de Córdoba. Instituto de Ciencias de la Administración; Argentin
The Radial Structure of SNR N103B
We report on the results from a Chandra ACIS observation of the young,
compact, supernova remnant N103B. The unprecedented spatial resolution of
Chandra reveals sub-arcsecond structure, both in the brightness and in spectral
variations. Underlying these small-scale variations is a surprisingly simple
radial structure in the equivalent widths of the strong Si and S emission
lines. We investigate these radial variations through spatially resolved
spectroscopy using a plane-parallel, non-equilibrium ionization model with
multiple components. The majority of the emission arises from components with a
temperature of 1 keV: a fully ionized hydrogen component; a high ionization
timescale (n_e*t > 10^12 s cm^-3) component containing Si, S, Ar, Ca, and Fe;
and a low ionization timescale (n_e*t ~ 10^{11} s cm^-3) O, Ne, and Mg
component. To reproduce the strong Fe Kalpha line, it is necessary to include
additional Fe in a hot (> 2 keV), low ionization (n_e*t ~ 10^10.8 s cm^-3)
component. This hot Fe may be in the form of hot Fe bubbles, formed in the
radioactive decay of clumps of 56Ni. We find no radial variation in the
ionization timescales or temperatures of the various components. Rather, the Si
and S equivalent widths increase at large radii because these lines, as well as
those of Ar and Ca, are formed in a shell occupying the outer half of the
remnant. A shell of hot Fe is located interior to this, but there is a large
region of overlap between these two shells. In the inner 30% of the remnant,
there is a core of cooler, 1 keV Fe. We find that the distribution of the
ejecta and the yields of the intermediate mass species are consistent with
model prediction for Type Ia events.Comment: 34 pages, including 7 tables and 7 figures, Accepted by Ap
MOLECULAR CHARACTERIZATION OF K26 GENE OF LEISHMANIA INFANTUM, ISOLATE BY HUMAN PATIENTS FROM SICILY REGION
Human Leishmaniasis is an emerging problem in Italy and increase in the Sicily region.
In the present work, we explored the genetic polymorphism of Leishmania isolates from twenty-five cases of human
Leishmaniasis: two cases of visceral Leishmaniasis (VL) and twenty-three of cutaneous Leishmaniasis (CL). The
characterization is carried out in comparison with twenty five human isolates of leishmania and one reference strain, L.
infantum MHOM/TN/80IPT1 (MON-1). MON-1 is the most common zymodeme responsible for Leishmaniasis in Italy.
The aim of the study is to genotype Leishmania isolates from Sicily by PCR ,analyzing size polymorphism of K26 gene
to discriminate between MON-1 and non MON-1 zymodemes. K26 is a protein belonging to the Hydrofilic acylated
surface protein B (HASPB) family. It is characterized by repeated aminoacidal domains and shows polymorphisms. The
k26 polymorphism of MON-1 zymodeme is determinate in the size of 626 bp. The analysis show that all the 25 isolates
belong to the L. infantum species, in particular the product size of 626 bp is detect in six patients affected by cutaneous
Leishmaniasis. The molecular tools applied in this study can constitute a helpful support for parasite tracking and for a
better understanding of the epidemiological evolution of Leishmaniasis
Precision Southern Hemisphere pulsar VLBI astrometry: techniques and results for PSR J1559-4438
We describe a data reduction pipeline for VLBI astrometric observations of
pulsars, implemented using the ParselTongue AIPS interface. The pipeline
performs calibration (including ionosphere modeling), phase referencing with
proper accounting of reference source structure, amplitude corrections for
pulsar scintillation, and position fitting to yield the position, proper motion
and parallax. The optimal data weighting scheme to minimize the total error
budget of a parallax fit, and how this scheme varies with pulsar parameters
such as flux density, is also investigated. The robustness of the techniques
employed are demonstrated with the presentation of the first results from a two
year astrometry program using the Australian Long Baseline Array (LBA). The
parallax of PSR J1559-4438 is determined to be 0.384 +- 0.081 mas (1 sigma),
resulting in a distance estimate of 2600 pc which is consistent with earlier DM
and HI absorption estimates.Comment: 30 pages, 8 figures, submitted to Ap
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