2,627 research outputs found

    Non-tropical Cyclone Related Winter Heavy Rainfall Events over the Philippines: Climatology and Mechanisms

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    This study investigates non-tropical cyclone (TC) related boreal winter heavy rainfall events that lead to extensive flooding (HRF) over the Philippines through a case study and composite analysis. The HRF event examined occurred during January 16–22, 2017 over Cagayan de Oro City (CDO) in Mindanao Island (122–127°E, 5–10°N). The accumulated rainfall over CDO reached by about 180 mm from 00 UTC January 16 to 00 UTC January 17, 2017, exceeding the climatological maximum daily rainfall in January over this area. The interaction of a westward propagating cyclonic circulation over Mindanao Island (MCC) and a shearline that is associated with an eastward-propagating cyclonic and anticyclonic circulations along 20–40°N, led to enhanced moisture convergence and rainfall over CDO. The climatology of these non-TC related HRF events was examined through composite analysis of the HRF events documented in the Dartmouth Flood Observatory archive from 1979 to 2017. The authors identified 34 of such cases over the Philippines, in which 25 occurred over Mindanao Island. The composites of the circulation features of these 25 cases resemble those during the January 2017 case. A vorticity budget analysis was performed to explain the propagation tendency of the MCC. The results show that the MCC only propagated westward when the magnitudes of the stretching and advection terms of the vorticity tendency equation are almost comparable with each other, together with the weakening of the southerly winds around Mindanao Island. This study reveals how cold fronts over the north Pacific together with the MCC induces HRF events over the Philippines

    On the X-ray lines in the afterglows of GRBs

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    The observation of X-ray lines in the afterglow of GRB 011211 has been reported, and challenged. The lines were interpreted as blue-shifted X-rays characteristic of a set of photoionized ``metals'', located in a section of a supernova shell illuminated by a GRB emitted a couple of days after the supernova explosion. We show that the most prominent reported lines coincide with the ones predicted in the ``cannonball'' model of GRBs. In this model, the putative signatures are Hydrogen lines, boosted by the (highly relativistic) motion of the cannonballs (CBs). The corresponding Doppler boost can be extracted from the fit to the observed I-, R- and V-band light-curves of the optical afterglow of GRB 011211, so that, since the redshift is also known, the line energies are --in the CB model-- predicted. We also discuss other GRBs of known redshift which show spectral features generally interpreted as Fe lines, or Fe recombination edges. The ensemble of results is very encouraging from the CB-model's point of view, but the data on each individual GRB are not good enough to draw (any) objectively decisive conclusions. We outline a strategy for X-ray observers to search for lines which, in the CB model, move predictably from higher to lower energies.Comment: Accepted for publication in Ap

    Obstetric outcome of female genital mutilation in the Gambia – an observational study

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    Background: A 2010 survey in The Gambia among women of reproductive age put the prevalence rate of FGM/C at 76.3%. FGM/C was banned in 2015, but there is no real effort at enforcement of the ban. This study aimed to provide national data on obstetric outcomes to support advocacy and health education.A multicentre observational study to assess the obstetric and neonatal outcomes of parturient women with and without FGM/Cwas carried out across 4 healthcare facilities in The Gambia. The primary outcome was postpartum haemorrhage (>500ml) andsecondary outcomes were caesarean section, perineal tears (including episiotomy), neonatal resuscitation and perinatal death.Of the 1,569 participants recruited into the study, 23% had no FGM/C while 77% had FGM/C of varying severity. The riskof postpartum haemorrhage was doubled for women with type I FGM/C, tripled in type II FGM/C and increased by 5-foldfor those with type III and IV FGM/C. Caesarean section and perineal tears were also increased. FGM/C was associated withincreased risk for neonatal resuscitation and perinatal death.FGM/C is associated with poor obstetric and neonatal outcomes in the Gambia with degree of risk correlating with the severityof FGM/C. Keywords: Female genital mutilation; obstetric outcome; Gambia

    Wind Energy Projection for the Philippines based on Climate Change Modeling

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    To complement the existing method of wind energy assessment, this study presents wind energy projection by downscaling a regional climate model, RegCM3, which is also used in predicting rainfall and temperature changes, and using a conversion method using the Weibull distribution. A couple of papers which used long-term predicting models focused on two regions, China and the US High Plains, show a decrease of about 14% and 7%-17% respectively in wind power density due to global warming over the next century. This paper focuses on a smaller grid size of 10 km x 10 km to concentrate on a specific wind farm in Pililla, Rizal, Philippines which is considered as a commercially feasible site by wind developers. Wind energy projection that considers the effects of climate change for the expected period of operation of 25 years is used because this gives wind developers an outlook on the power production during the wind farm\u27s lifetime and would contribute in determining the wind farm\u27s potential for financial returns. Percentage difference of wind power density between the baseline period of 2008-2012 and five-year projection periods from 2013-2037 are presented. Contrary to the results of studies in China and western US, the results of this research show that there is an average five-year period increase of 6% in wind power density in Pililla, Rizal over the next 25 years

    Optical Behavior of GRB 061121 around its X-Ray Shallow Decay Phase

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    Aims. We report on a detailed study of the optical afterglow of GRB 061121 with our original time-series photometric data. In conjunction with X-ray observations, we discuss the origin of its optical and X-ray afterglows. Methods. We observed the optical afterglow of Swift burst GRB 061121 with the Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers a period just after an X-ray plateau phase. We also performed deep imaging with the Subaru telescope in 2010 in order to estimate the contamination of the host galaxy. Results. In the light curve, we find that the optical afterglow also exhibited a break as in the X-ray afterglow. However, our observation suggests a possible hump structure or a flattening period before the optical break in the light curve. There is no sign of such a hump in the X-ray light curve. Conclusions. This implies that the emitting region of optical was distinct from that of X-rays. The hump in the optical light curve was possibly caused by the passage of the typical frequency of synchrotron emission from another forward shock distinct from the early afterglow. The observed decay and spectral indices are inconsistent with the standard synchrotron-shock model. Hence, the observation requires a change in microphysical parameters in the shock region or a prior activity of the central engine. Alternatively, the emission during the shallow decay phase may be a composition of two forward shock emissions, as indicated by the hump structure in the light curve.Comment: 8 pages, including 4 figures and 2 tables. Accepted to A&

    Two types of softening detected in X-ray afterglows of Swift bursts: internal and external shock origins?

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    The softening process observed in the steep decay phase of early X-ray afterglows of Swift bursts has remained a puzzle since its discovery. The softening process can also be observed in the later phase of the bursts and its cause has also been unknown. Recently, it was suggested that, influenced by the curvature effect, emission from high latitudes would shift the Band function spectrum from higher energy band to lower band, and this would give rise to the observed softening process accompanied by a steep decay of the flux density. The curvature effect scenario predicts that the terminating time of the softening process would be correlated with the duration of the process. In this paper, based on the data from the UNLV GRB group web-site, we found an obvious correlation between the two quantities. In addition, we found that the softening process can be divided into two classes: the early type softening (ts,max"4000"st_{s,max}\leq "4000"s) and the late type softening (ts,max>"4000"st_{s,max} > "4000"s). The two types of softening show different behaviors in the duration vs. terminating time plot. In the relation between the variation rates of the flux density and spectral index during the softening process, a discrepancy between the two types of softening is also observed. According to their time scales and the discrepancy between them, we propose that the two types are of different origins: the early type is of internal shock origin and the late type is of external shock origin. The early softening is referred to the steep decay just following the prompt emission, whereas the late decay typically conceives the transition from flat decay to late afterglow decay. We suspect that there might be a great difference of the Lorentz factor in two classes which is responsible for the observed discrepancy.Comment: 20 pages, 5 figures, 2 tables, Accepted for Publication to Journal of Cosmology and Astroparticle Physics (JCAP

    The electromagnetic model of Gamma Ray Bursts

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    I describe electromagnetic model of gamma ray bursts and contrast its main properties and predictions with hydrodynamic fireball model and its magnetohydrodynamical extension. The electromagnetic model assumes that rotational energy of a relativistic, stellar-mass central source (black-hole--accretion disk system or fast rotating neutron star) is converted into magnetic energy through unipolar dynamo mechanism, propagated to large distances in a form of relativistic, subsonic, Poynting flux-dominated wind and is dissipated directly into emitting particles through current-driven instabilities. Thus, there is no conversion back and forth between internal and bulk energies as in the case of fireball model. Collimating effects of magnetic hoop stresses lead to strongly non-spherical expansion and formation of jets. Long and short GRBs may develop in a qualitatively similar way, except that in case of long bursts ejecta expansion has a relatively short, non-relativistic, strongly dissipative stage inside the star. Electromagnetic and fireball models (as well as strongly and weakly magnetized fireballs) lead to different early afterglow dynamics, before deceleration time. Finally, I discuss the models in view of latest observational data in the Swift era.Comment: solicited contribution to Focus Issue of New Journal of Physics, 27 pages, 4 figure

    GRB Fireball Physics: Prompt and Early Emission

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    We review the fireball shock model of gamma-ray burst prompt and early afterglow emission in light of rapid follow-up measurements made and enabled by the multi-wavelength Swift satellite. These observations are leading to a reappraisal and expansion of the previous standard view of the GRB and its fireball. New information on the behavior of the burst and afterglow on minutes to hour timescales has led, among other results, to the discovery and follow-up of short GRB afterglows, the opening up of the z>6 redshift range, and the first prompt multi-wavelength observations of a long GRB-supernova. We discuss the salient observational results and some associated theoretical issues.Comment: 23 pages. Published in the New Journal of Physics Focus Issue, "Focus on Gamma-Ray Bursts in the Swift Era" (Eds. D. H. Hartmann, C. D. Dermer & J. Greiner). V2: Minor change

    Absolute electron and positron fluxes from PAMELA/Fermi and Dark Matter

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    We extract the positron and electron fluxes in the energy range 10 - 100 GeV by combining the recent data from PAMELA and Fermi LAT. The {\it absolute positron and electron} fluxes thus obtained are found to obey the power laws: E2.65E^{-2.65} and E3.06E^{-3.06} respectively, which can be confirmed by the upcoming data from PAMELA. The positron flux appears to indicate an excess at energies E\gsim 50 GeV even if the uncertainty in the secondary positron flux is added to the Galactic positron background. This leaves enough motivation for considering new physics, such as annihilation or decay of dark matter, as the origin of positron excess in the cosmic rays.Comment: Accepted by JCA

    The Spectrum of Electromagnetic Jets from Kerr Black Holes and Naked Singularities in the Teukolsky Perturbation Theory

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    We give a new theoretical basis for examination of the presence of the Kerr black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of different astrophysical objects around which astrophysical jets are typically formed: X-ray binary systems, gamma ray bursts (GRBs), active galactic nuclei (AGN), etc. Our method is based on the study of the exact solutions of the Teukolsky master equation for electromagnetic perturbations of the Kerr metric. By imposing original boundary conditions on the solutions so that they describe a collimated electromagnetic outflow, we obtain the spectra of possible {\em primary jets} of radiation, introduced here for the first time. The theoretical spectra of primary electromagnetic jets are calculated numerically. Our main result is a detailed description of the qualitative change of the behavior of primary electromagnetic jet frequencies under the transition from the KBH to the KNS, considered here as a bifurcation of the Kerr metric. We show that quite surprisingly the novel spectra describe linearly stable primary electromagnetic jets from both the KBH and the KNS. Numerical investigation of the dependence of these primary jet spectra on the rotation of the Kerr metric is presented and discussed.Comment: 18 pages, 35 figures, LaTeX file. Final version. Accepted for publication in Astrophysics and Space Science. Amendments. Typos corrected. Novel notion -"primary jet" is introduced. New references and comments adde
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