5,526 research outputs found
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
The distances of short-hard GRBs and the SGR connection
We present a search for nearby (D<100 Mpc) galaxies in the error boxes of six
well-localized short-hard gamma-ray bursts (GRBs). None of the six error boxes
reveals the presence of a plausible nearby host galaxy. This allows us to set
lower limits on the distances and, hence, the isotropic-equivalent energy of
these GRBs. Our lower limits are around erg (at
confidence level); as a consequence, some of the short-hard GRBs we examine
would have been detected by BATSE out to distances greater than 1 Gpc and
therefore constitute a bona fide cosmological population. Our search is
partially motivated by the December 27, 2004 hypergiant flare from SGR 1806-20,
and the intriguing possibility that short-hard GRBs are extragalactic events of
a similar nature. Such events would be detectable with BATSE to a distance of
\~50 Mpc, and their detection rate should be comparable to the actual BATSE
detection rate of short-hard GRBs. The failure of our search, by contrast,
suggests that such flares constitute less than 15% of the short-hard GRBs (<40%
at 95% confidence). We discuss possible resolutions of this discrepancy.Comment: Enlarged sample of bursts; ApJ in pres
X-Ray Light Curves of Gamma-ray Bursts Detected with the All-Sky Monitor on RXTE
We present X-ray light curves (1.5-12 keV) for fifteen gamma-ray bursts
(GRBs) detected by the All-Sky Monitor on the Rossi X-ray Timing Explorer. We
compare these soft X-ray light curves with count rate histories obtained by the
high-energy (>12 keV) experiments BATSE, Konus-Wind, the BeppoSAX Gamma-Ray
Burst Monitor, and the burst monitor on Ulysses. We discuss these light curves
within the context of a simple relativistic fireball and synchrotron shock
paradigm, and we address the possibility of having observed the transition
between a GRB and its afterglow. The light curves show diverse morphologies,
with striking differences between energy bands. In several bursts, intervals of
significant emission are evident in the ASM energy range with little or no
corresponding emission apparent in the high-energy light curves. For example,
the final peak of GRB 970815 as recorded by the ASM is only detected in the
softest BATSE energy bands. We also study the duration of bursts as a function
of energy. Simple, singly-peaked bursts seem consistent with the E^{-0.5} power
law expected from an origin in synchrotron radiation, but durations of bursts
that exhibit complex temporal structure are not consistent with this
prediction. Bursts such as GRB 970828 that show many short spikes of emission
at high energies last significantly longer at low energies than the synchrotron
cooling law would predict.Comment: 15 pages with 20 figures and 2 tables. In emulateapj format. Accepted
by ApJ
A pertubative approach to the Kondo effect in magnetic atoms on nonmagnetic substrates
Recent experimental advances in scanning tunneling microscopy make the
measurement of the conductance spectra of isolated and magnetically coupled
atoms on nonmagnetic substrates possible. Notably these spectra are
characterized by a competition between the Kondo effect and spin-flip inelastic
electron tunneling. In particular they include Kondo resonances and a
logarithmic enhancement of the conductance at voltages corresponding to
magnetic excitations, two features that cannot be captured by second order
perturbation theory in the electron-spin coupling. We have now derived a third
order analytic expression for the electron-spin self-energy, which can be
readily used in combination with the non-equilibrium Green's function scheme
for electron transport at finite bias. We demonstrate that our method is
capable of quantitative description the competition between Kondo resonances
and spin-flip inelastic electron tunneling at a computational cost
significantly lower than that of other approaches. The examples of Co and Fe on
CuN are discussed in detail
De-blending Deep Herschel Surveys: A Multi-wavelength Approach
Cosmological surveys in the far infrared are known to suffer from confusion.
The Bayesian de-blending tool, XID+, currently provides one of the best ways to
de-confuse deep Herschel SPIRE images, using a flat flux density prior. This
work is to demonstrate that existing multi-wavelength data sets can be
exploited to improve XID+ by providing an informed prior, resulting in more
accurate and precise extracted flux densities. Photometric data for galaxies in
the COSMOS field were used to constrain spectral energy distributions (SEDs)
using the fitting tool CIGALE. These SEDs were used to create Gaussian prior
estimates in the SPIRE bands for XID+. The multi-wavelength photometry and the
extracted SPIRE flux densities were run through CIGALE again to allow us to
compare the performance of the two priors. Inferred ALMA flux densities
(F), at 870m and 1250m, from the best fitting SEDs from the
second CIGALE run were compared with measured ALMA flux densities (F) as an
independent performance validation. Similar validations were conducted with the
SED modelling and fitting tool MAGPHYS and modified black body functions to
test for model dependency. We demonstrate a clear improvement in agreement
between the flux densities extracted with XID+ and existing data at other
wavelengths when using the new informed Gaussian prior over the original
uninformed prior. The residuals between F and F were calculated. For
the Gaussian prior, these residuals, expressed as a multiple of the ALMA error
(), have a smaller standard deviation, 7.95 for the Gaussian
prior compared to 12.21 for the flat prior, reduced mean, 1.83
compared to 3.44, and have reduced skew to positive values, 7.97
compared to 11.50. These results were determined to not be significantly model
dependent. This results in statistically more reliable SPIRE flux densities.Comment: 8 pages, 7 figures, 3 tables. Accepted for publication in A&
Raman Spectroscopy Characterization of Aqueous Vanadate Species Interaction with Aluminum Alloy 2024-T3 Surfaces
Raman spectroscopy and electrochemical techniques were used to characterize the interactions of aqueous NaVO_3/NaCl and NH_4VO_3/oxalic acid with AA 2024-T3. The interaction of aqueous NaVO_3 with Cu^0 and Cu_2O was characterized. At potential values similar to the OCP of AA 2024-T3 in dilute NaCl, aqueous NaVO_3 formed a polyvanadate film on Cu_2O and formed little or no vanadate film on Cu^0. Treatment of AA 2024-T3 with basic, aqueous NaVO_3/NaCl resulted in a polyvanadate film on copper-rich intermetallic particles and the formation of monovanadates on the matrix. Treatment of AA 2024-T3 with acidic, aqueous NH_4VO_3/oxalic resulted in the formation of monovanadates on the matrix and provided no evidence of vanadate species on copper-rich particles. AA 2024-T3 samples pretreated with either aqueous vanadate salt solution displayed modest cathodic inhibition soon after treatment but inhibition degraded with aging. The formation of polymerized vanadates species on copper-rich particles supports the cathodic inhibition mechanism. The presence of vanadate species on copper-rich particles pretreated with aqueous NaVO_3/NaCl containing predominantly tetrahedral vanadates versus the lack of evidence for similar species on particles treated with aqueous NH_4VO_3/oxalic acid containing predominantly octahedral vanadates supports the importance of tetrahedrally coordinated vanadate species for corrosion inhibition
Detailed transonic flow field measurements about a supercritical airfoil section
The transonic flow field about a Whitcomb-type supercritical airfoil profile was measured in detail. In addition to the usual surface pressure distributions and wake surveys, schlieren photographs were taken and velocity vector profiles were determined in the upper surface boundary layer and in the near wake. Spanwise variations in the measured pressures were also determined. The data are analyzed with the aid of an inviscid transonic finite-difference computer program as well as with boundary layer modeling and calculation schemes
Quiet but still bright: XMM-Newton observations of the soft gamma-ray repeater SGR 0526-66
SGR 0526-66 was the first soft gamma-ray repeater (SGR) from which a giant
flare was detected in March 1979, suggesting the existence of magnetars, i.e.
neutron stars powered by the decay of their extremely strong magnetic field.
Since then, very little information has been obtained on this object, mainly
because it has been burst-inactive since 1983 and the study of its persistent
X-ray emission has been hampered by its large distance and its location in a
X-ray bright supernova remnant in the Large Magellanic Cloud. Here we report on
a comprehensive analysis of all the available XMM-Newton observations of SGR
0526-66. In particular, thanks to a deep observation taken in 2007, we measured
its pulsation period (P = 8.0544 +/- 0.0002 s) 6 years after its latest
detection by Chandra. This allowed us to detect for the first time a
significant reduction of its spin-down rate. From a comparison with two shorter
XMM-Newton observations performed in 2000 and 2001, we found no significant
changes in the spectrum, which is well modelled by an absorbed power-law with
nH = 4.6E+21 cm^-2 and photon index = 3.27. The high luminosity (about 4E+35
erg/s, in the 1-10 keV energy band) still observed about 25 years after the
latest detection of bursting activity places SGR 0526-66 in the group of bright
and persistent magnetar candidates.Comment: 5 pages, 3 figures (1 color) and 2 tables; Accepted for publication
in MNRAS Letter
Unusual Burst Emission from the New Soft Gamma Repeater SGR1627-41
In June-July,1998 the Konus-Wind burst spectrometer observed a series of
bursts from the new soft gamma repeater SGR1627-41. Time histories and energy
spectra of the bursts have been studied, revealing fluences and peak fluxes in
the ranges of 3x10^{-7} - 7.5x10^{-6} erg cm^{-2} and 10^{-5} - 10^{-4}erg
cm^{-2}/s respectively. One event, 18 June 6153.5sUT stands out dramatically
from this series. Its fluence is ~7x10^{-4} erg cm^{-2} and peak flux
~2x10^{-2} erg cm^{-2}/s. These values from a source at a distance of 5.8 kpc
yield an energy output of ~3x10^{42}erg and maximum luminosity of ~8x10^{43}
erg/s, similar to the values for the famous March 5, 1979 and August27,1998
events. In terms of energy, this event is another giant outburst seen in a
third SGR! However, this very energetic burst differs significantly from the
other giant outbursts. It exhibits no separate initial pulse with a fast rise
time, no extended tail, and no pulsations. It is rather similar to ordinary
repeated bursts but is a few hundred times stronger in intensity. According to
the magnetar model by Thompson and Duncan (1995) such a burst may be initiated
by a strong starquake when a crust fracture propagates over the whole surface
of a neutron star.Comment: 7 pages, 5 figures. To be appeared in ApJ
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