28,502 research outputs found
The Pulsar B2224+65 and Its Jets: A Two Epoch X-ray Analysis
We present an X-ray morphological and spectroscopic study of the pulsar
B2224+65 and its apparent jet-like X-ray features based on two epoch Chandra
observations. The main X-ray feature, which shows a large directional offset
from the ram-pressure confined pulsar wind nebula (Guitar Nebula), is broader
in apparent width and shows evidence for spectral hardening (at 95 percent
confidence) in the second epoch compared to the first. Furthermore, the sharp
leading edge of the feature is found to have a proper motion consistent with
that of the pulsar (~180 mas yr-1). The combined data set also provides
evidence for the presence of a counter feature, albeit substantially fainter
and shorter than the main one. Additional spectral trends along the major and
minor axes of the feature are only marginally detected in the two epoch data,
including softening counter to the direction of proper motion. Possible
explanations for the X-ray features include diffuse energetic particles being
confined by an organized ambient magnetic field as well as a simple ballistic
jet interpretation; however, the former may have difficulty in explaining
observed spectral trends between epochs and along the feature's major axis
whereas the latter may struggle to elucidate its linearity. Given the low
counting statistics available in the two epoch observations, it remains
difficult to determine a physical production scenario for these enigmatic X-ray
emitting features with any certainty.Comment: 9 pages, 6 figures, submitted to MNRAS; updated as per reviewer
comment
Energetic Fermi/LAT GRB100414A: Energetic and Correlations
This study presents multi-wavelength observational results for energetic
GRB100414A with GeV photons. The prompt spectral fitting using Suzaku/WAM data
yielded spectral peak energies of E^src_peak of 1458.7 (+132.6, -106.6) keV and
Eiso of 34.5(+2.0, -1.8) x 10^52 erg with z=1.368. The optical afterglow light
curves between 3 and 7 days were effectively fitted according to a simple power
law with a temporal index of alpha=-2.6 +/- 0.1. The joint light curve with
earlier Swift/UVOT observations yields a temporal break at 2.3 +/- 0.2 days.
This was the first \fermi/LAT detected event that demonstrated the clear
temporal break in the optical afterglow. The jet opening angle derived from
this temporal break was 5.8 degree, consistent with those of other
well-observed long gamma-ray bursts (GRBs). The multi-wavelength analyses in
this study showed that GRB100414A follows E^src_peak-Eiso and
E^src_peak-E_gamma correlations. The late afterglow revealed a flatter
evolution with significant excesses at 27.2 days. The most straightforward
explanation for the excess is that GRB100414A was accompanied by a
contemporaneous supernova. The model light curve based on other GRB-SN events
is marginally consistent with that of the observed lightcurve.Comment: ApJL in press; 12 pages, 3 figures, 2 table
Colloquium: Multimessenger astronomy with gravitational waves and high-energy neutrinos
Many of the astrophysical sources and violent phenomena observed in our Universe are potential emitters of gravitational waves and high-energy cosmic radiation, including photons, hadrons, and presumably also neutrinos. Both gravitational waves (GW) and high-energy neutrinos (HEN) are cosmic messengers that may escape much denser media than photons. They travel unaffected over cosmological distances, carrying information from the inner regions of the astrophysical engines from which they are emitted (and from which photons and charged cosmic rays cannot reach us). For the same reasons, such messengers could also reveal new, hidden sources that have not been observed by conventional photon-based astronomy. Coincident observation of GWs and HENs may thus play a critical role in multimessenger astronomy. This is particularly true at the present time owing to the advent of a new generation of dedicated detectors: the neutrino telescopes IceCube at the South Pole and ANTARES in the Mediterranean Sea, as well as the GW interferometers Virgo in Italy and LIGO in the United States. Starting from 2007, several periods of concomitant data taking involving these detectors have been conducted. More joint data sets are expected with the next generation of advanced detectors that are to be operational by 2015, with other detectors, such as KAGRA in Japan, joining in the future. Combining information from these independent detectors can provide origin always of constraining the physical processes driving the sources and also help confirm the astrophysical origin of a GW or HEN signal in case of coincident observation. Given the complexity of the instruments, a successful joint analysis of this combined GW and HEN observational data set will be possible only if the expertise and knowledge of the data is shared between the two communities. This Colloquium aims at providing an overview of both theoretical and experimental state of the art and perspectives for GW and HEN multimessenger astronomy
A decametric wavelength radio telescope for interplanetary scintillation observations
A phased array, electrically steerable radio telescope (with a total collecting area of 18 acres), constructed for the purpose of remotely sensing electron density irregularity structure in the solar wind, is presented. The radio telescope is able to locate, map, and track large scale features of the solar wind, such as streams and blast waves, by monitoring a large grid of natural radio sources subject to rapid intensity fluctuation (interplanetary scintillation) caused by the irregularity structure. Observations verify the performance of the array, the receiver, and the scintillation signal processing circuitry of the telescope
Multi-Wavelength Observations of GRB 050820A: An Exceptionally Energetic Event Followed from Start to Finish
We present observations of the unusually bright and long gamma-ray burst GRB
050820A, one of the best-sampled broadband data sets in the Swift era. The
gamma-ray light curve is marked by a soft precursor pulse some 200 s before the
main event; the lack of any intervening emission suggests that it is due to a
physical mechanism distinct from the GRB itself. The large time lag between the
precursor and the main emission enabled simultaneous observations in the
gamma-ray, X-ray, and optical band-passes, something only achieved for a
handful of events to date. While the contemporaneous X-rays are the low-energy
tail of the prompt emission, the optical does not directly track the gamma-ray
flux. Instead, the early-time optical data appear mostly consistent with the
forward shock synchrotron peak passing through the optical, and are therefore
likely the beginning of the afterglow. On hour time scales after the burst, the
X-ray and optical light curves are inconsistent with an adiabatic expansion of
the shock into the surrounding region, but rather indicate that there is a
period of energy injection. Observations at late times allow us to constrain
the collimation angle of the relativistic outflow to theta = 6.8 - 9.3 degrees.
Our estimates of both the kinetic energy of the afterglow and the prompt
gamma-ray energy release make GRB 050820A one of the most energetic events for
which such values could be determined.Comment: Accepted to ApJ; 18 pages, 8 figures; High resolution version
available at http://www.srl.caltech.edu/~cenko/public/papers/grb050820a.p
A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment
The KATRIN experiment aims to determine the neutrino mass scale with a
sensitivity of 200 meV/c^2 (90% C.L.) by a precision measurement of the shape
of the tritium -spectrum in the endpoint region. The energy analysis of
the decay electrons is achieved by a MAC-E filter spectrometer. To determine
the transmission properties of the KATRIN main spectrometer, a mono-energetic
and angular-selective electron source has been developed. In preparation for
the second commissioning phase of the main spectrometer, a measurement phase
was carried out at the KATRIN monitor spectrometer where the device was
operated in a MAC-E filter setup for testing. The results of these measurements
are compared with simulations using the particle-tracking software
"Kassiopeia", which was developed in the KATRIN collaboration over recent
years.Comment: 19 pages, 16 figures, submitted to European Physical Journal
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