3,244 research outputs found
Delayed soft X-ray emission lines in the afterglow of GRB 030227
Strong, delayed X-ray line emission is detected in the afterglow of GRB
030227, appearing near the end of the XMM-Newton observation, nearly twenty
hours after the burst. The observed flux in the lines, not simply the
equivalent width, sharply increases from an undetectable level (<1.7e-14
erg/cm^2/s, 3 sigma) to 4.1e-14 erg/cm^2/s in the final 9.7 ks. The line
emission alone has nearly twice as many detected photons as any previous
detection of X-ray lines. The lines correspond well to hydrogen and/or
helium-like emission from Mg, Si, S, Ar and Ca at a redshift z=1.39. There is
no evidence for Fe, Co or Ni--the ultimate iron abundance must be less than a
tenth that of the lighter metals. If the supernova and GRB events are nearly
simultaneous there must be continuing, sporadic power output after the GRB of a
luminosity >~5e46 erg/s, exceeding all but the most powerful quasars.Comment: Submitted to ApJL. 14 pages, 3 figures with AASLaTe
A Micro-Payment Scheme Encouraging Collaboration in Multi-Hop Cellular Networks
We propose a micro-payment scheme for multi-hop cellular networks that encourages collaboration in packet forwarding by letting users benefit from relaying others` packets. At the same time as proposing mechanisms for detecting and rewarding collaboration, we introduce appropriate mechanisms for detecting and punishing various forms of abuse. We show that the resulting scheme -- which is exceptionally light-weight -- makes collaboration rational and cheating undesirable
The host of the SN-less GRB 060505 in high resolution
The spiral host galaxy of GRB 060505 at z=0.089 was the site of a puzzling
long duration burst without an accompanying supernova. Studies of the burst
environment by Th\"one et al. (2008) suggested that this GRB came from the
collapse of a massive star and that the GRB site was a region with properties
different from the rest of the galaxy. We reobserved the galaxy in high spatial
resolution using the VIMOS integral-field unit (IFU) at the VLT with a spaxel
size of 0.67 arcsec. Furthermore, we use long slit high resolution data from
HIRES/Keck at two different slit positions covering the GRB site, the center of
the galaxy and an HII region next to the GRB region. We compare the properties
of different HII regions in the galaxy with the GRB site and study the global
and local kinematic properties of this galaxy. The resolved data show that the
GRB site has the lowest metallicity in the galaxy with around 1/3 Z_solar, but
its specific SFR (SSFR) of 7.4 M_solar/yr/L/L* and age (determined by the
Halpha EW) are similar to other HII regions in the host. The galaxy shows a
gradient in metallicity and SSFR from the bulge to the outskirts as it is
common for spiral galaxies. This gives further support to the theory that GRBs
prefer regions of higher star-formation and lower metallicity, which, in S-type
galaxies, are more easily found in the spiral arms than in the centre.
Kinematic measurements of the galaxy do not show evidence for large
perturbations but a minor merger in the past cannot be excluded. This study
confirms the collapsar origin of GRB060505 but reveals that the properties of
the HII region surrounding the GRB were not unique to that galaxy. Spatially
resolved observations are key to know the implications and interpretations of
unresolved GRB hosts observations at higher redshifts.Comment: 15 pages, 16 figures, 6 tables; resubmitted to MNRAS after minor
revision
Redshift distribution and luminosity function of long gamma-ray bursts from cosmological simulations
We study the luminosity function (LF), the comoving rate and the detection
rate of Long Gamma-Ray Burst (LGRBs) to high redshift, using galaxy catalogues
constructed by combining high-resolution N-body simulations with semi-analytic
models of galaxy formation. We assume the collapsar model and different
metallicity thresholds, and conclude that LGRBs are not good tracers of the
star formation history in the universe. Then using the log N-log P diagram for
BATSE bursts, we determine the LF (with and without evolution with redshift)
and the formation rate of LGRBs, obtaining constraints on the slope of the
power-law. We check the resulting redshift distribution with SWIFT data updated
to 2009 August, finding that models where LGRBs have as progenitors stars with
Z<0.3Z_sun and without evolution of the LF are in agreement with the data. We
also predict that there are about ~1% of GRBs at redshift z>6.Comment: The paper contains 5 figures and 3 tables. Accepted MNRA
Ukupni i specifični mortalitet u radnika izloženih azbestu od 1907. do 1985. godine
Total and cause-specific mortality data for the 1907 -1985 period were compared between cohorts of male asbestos-cement workers (N = 1908) and referents (N = 726), using Poisson regression modelling. The rate ratio (RR) for total mortality was significantly increased (1.3) among the exposed workers, as was mortality from non-malignant respiratory disease (RR= 2.2). Numerically, but not statistically significantly, raised ratios were found for respiratory (RR= 1.6) and gastrointestinal (RR= 1.3) cancers. The trend in the rate ratio for total mortality with time was better fitted with a curved line, than with a monotonic one, because of a period of increased risk up to the 1950s, and another one starting after 1970.Ukupni i specifični mortalitet za razdoblje od 1907. do 1985. godine uspoređen je u kohortama muških radnika koji su bili izloženi azbestu (N = 1908) s kontrolama (N = 726) pomoću Poissonove regresijske analize. Koeficijent regresije (RR) za ukupni mortalitet, kao i mortalitet od nemalignih respiratornih bolesti bio je statistički značajno viši i iznosio je 1,3, odnosno 2,2. Povećanje ovog koeficijenta nađeno je i za plućni (1,6) i gastrointestinalni karcinom (1,3), ali vrijednosti nisu statistički značajne
The genetic variation of lactase persistence alleles in northeast Africa
Lactase persistence (LP) is a well-studied example of a Mendelian trait under selection in some human groups due to gene-culture co-evolution. We investigated the frequencies of genetic variants linked to LP in Sudanese and South Sudanese populations. These populations have diverse subsistence patterns, and some are dependent on milk to various extents, not only from cows, but also from other livestock such as camels and goats. We sequenced a 316bp region involved in regulating the expression of the LCT gene on chromosome 2, which encompasses five polymorphisms that have been associated with LP. Pastoralist populations showed a higher frequency of LP-associated alleles compared to non-pastoralist groups, hinting at positive selection also in northeast African pastoralists. There was no incidence of the East African LP allele (−14010:C) in the Sudanese groups, and only one heterozygote individual for the European LP allele (−13910:T), suggesting limited recent admixture from these geographic regions. Among the LP variants, the −14009:G variant occurs at the highest frequency among the investigated populations, followed by the −13915:G variant, which is likely of Middle Eastern origin, consistent with Middle Eastern gene-flow to the Sudanese populations. The Beja population of the Beni Amer show three different LP-variants at substantial and similar levels, resulting in one of the greatest frequencies of LP-variants among all populations across the world.Competing Interest StatementThe authors have declared no competing interest.Introduction Results and Discussion - Allele frequencies - Haplotype Structure - Selection Scan Conclusion Materials and Methods - Phasing and imputation to analyze haplotype structure - Locus specific branch length (LSBL
Testing the E_p,i - L_p,iso - T_0.45 correlation on a BeppoSAX and Swift sample of gamma-ray bursts
Using a sample of 14 BeppoSAX and 74 Swift GRBs with measured redshift we
tested the correlation between the intrinsic peak energy of the time-integrated
spectrum, E_p,i, the isotropic-equivalent peak luminosity, L_p,iso, and the
duration of the most intense parts of the GRB computed as T_0.45 ("Firmani
correlation"). For 41 out of 88 GRBs we could estimate all of the three
required properties. Apart from 980425, which appears to be a definite outlier
and notoriously peculiar in many respects, we used 40 GRBs to fit the
correlation with the maximum likelihood method discussed by D'Agostini,
suitable to account for the extrinsic scatter in addition to the intrinsic
uncertainties affecting every single GRB. We confirm the correlation. However,
unlike the results by Firmani et al., we found that the correlation does have a
logarithmic scatter comparable with that of the E_p,i-E_iso ("Amati")
correlation. We also find that the slope of the product L_p,iso T_0.45 is equal
to ~0.5, which is consistent with the hypothesis that the E_p,i-L_p,iso-T_0.45
correlation is equivalent to the E_p,i-E_iso correlation (slope ~0.5). We
conclude that, based on presently available data, there is no clear evidence
that the E_p,i-L_p,iso-T_0.45 correlation is different (both in terms of slope
and dispersion) from the E_p,i-E_iso correlation.Comment: 9 pages, 4 figures, revised version submitted to MNRA
Deep-water flow over the Lomonosov Ridge in the Arctic Ocean
Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 1489–1493, doi:10.1175/JPO2765.1.The Arctic Ocean likely impacts global climate through its effect on the rate of deep-water formation and the subsequent influence on global thermohaline circulation. Here, the renewal of the deep waters in the isolated Canadian Basin is quanitified. Using hydraulic theory and hydrographic observations, the authors calculate the magnitude of this renewal where circumstances have thus far prevented direct measurements. A volume flow rate of Q = 0.25 ± 0.15 Sv (Sv ≡ 106 m3s−1) from the Eurasian Basin to the Canadian Basin via a deep gap in the dividing Lomonosov Ridge is estimated. Deep-water renewal time estimates based on this flow are consistent with 14C isolation ages. The flow is sufficiently large that it has a greater impact on the Canadian Basin deep water than either the geothermal heat flux or diffusive fluxes at the deep-water boundaries.Financial
support was provided to P. Winsor from NSF OPP-
0352628
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