2,956 research outputs found
A multiwavelength view of the transient sky: gamma-ray bursts and other fast transients from optical to gamma-rays
No full textIndividual power density spectra of
No full textContext. Timing analysis can be a powerful tool with which to shed light on the still obscure emission physics and geometry of the prompt emission of gamma-ray bursts (GRBs). Fourier power density spectra (PDS) characterise time series as stochastic processes and can be used to search for coherent pulsations and, more in general, to investigate the dominant variability timescales in astrophysical sources. Because of the limited duration and of the statistical properties involved, modelling the PDS of individual GRBs is challenging, and only average PDS of large samples have been discussed in the literature thus far.
Aims. We aim at characterising the individual PDS of GRBs to describe their variability in terms of a stochastic process, to explore their variety, and to carry out for the first time a systematic search for periodic signals and for a link between PDS properties and other GRB observables.
Methods. We present a Bayesian procedure that uses a Markov chain Monte Carlo technique and apply it to study the individual PDS of 215 bright long GRBs detected with the Swift Burst Alert Telescope in the 15−150 keV band from January 2005 to May 2015. The PDS are modelled with a power-law either with or without a break.
Results. Two classes of GRBs emerge: with or without a unique dominant timescale. A comparison with active galactic nuclei (AGNs) reveals similar distributions of PDS slopes. Unexpectedly, GRBs with subsecond-dominant timescales and duration longer than a few tens of seconds in the source frame appear to be either very rare or altogether absent. Three GRBs are found with possible evidence for a periodic signal at 3.0–3.2σ (Gaussian) significance, corresponding to a multi-trial chance probability of ~1%. Thus, we found no compelling evidence for periodic signal in GRBs.
Conclusions. The analogy between the PDS of GRBs and of AGNs could tentatively indicate similar stochastic processes that rule BH accretion across different BH mass scales and objects. In addition, we find evidence that short dominant timescales and duration are not completely independent of each other, in contrast with commonly accepted paradigms
Possible physical explanation of the intrinsic Ep,i-“intensity” correlation commonly used to “standardize” GRBs
No full textIt is recognized that very likely the correlation between peak energy Ep and bolometric intensity is intrinsic to GRBs. However, its physical origin is still debated. In this paper, we will discuss a possible interpretation of the correlation in the light of a GRB prompt emission spectral model, GRBCOMP, proposed in [L. Titarchuk, R. Farinelli, F. Frontera and L. Amati, Astrophys. J. 752 (2012) 116]. GRBCOMP is essentially a photospheric model for the prompt emission of GRBs. Its main ingredients are a thermal bath of soft seed photons and a subrelativistically expanding outflow plasma, consequence of the star explosion. The emerging spectrum is the result of two phases: first, up to the photospheric radius, Comptonization of a subrelativistic electron outflow with thermal bath of soft photons, then, convolution of the Comptonized photons in the first phase with a Green function. The result of this convolution is consistent with different physical processes, in particular Inverse Compton. GRBCOMP has been successfully tested using a significant sample of GRB time resolved spectra in the broad energy band from 2keV to 2MeV [F. Frontera, L. Amati, R. Farinelli, S. Dichiara, C. Guidorzi, R. Landi and L. Titarchuk, Astrophys. J. 779 (2013) 175]
A search for pulsations in short gamma-ray bursts to constrain their progenitors
No full textWe searched for periodic and quasi-periodic signals in the prompt emission of a sample of 44 bright short gamma-ray bursts (GRBs) detected with Fermi/GBM, Swift/BAT, andCGRO/BATSE. The aimwas to look for the observational signature of quasi-periodic jet precession, which is expected from black hole (BH)–neutron star (NS) mergers, but
not from double NS systems. Thus, this kind of search holds the key to identifying the progenitor systems of short GRBs and, in the interim before gravitational wave detectors become on-lines, represents the only direct way to constrain the progenitors. We tailored our search to the nature of the expected signal by properly stretching the observed light curves by an increasing factor with time, after calibrating the technique with synthetic curves. None of our GRBs showed evidence for periodic or quasi-periodic signals. In particular, for the seven unambiguously short GRBs with the best signal-to-noise ratios, we obtained significant upper imits to the amplitude of the possible oscillations. This result suggests that BH–NS systems do not dominate the population of short GRB progenitors,
as described by the kinematic model of Stone et al
Average power density spectrum of long GRBs detected with BeppoSAX/GRBM and with Fermi/GBM
No full textFrom past experiments the average power density spectrum (PDS) of GRBs with unknown redshift was found to be modelled from 0.01 to 1 Hz with a power-law, f^(-alpha), with alpha broadly consistent with 5/3. Recent analyses of the Swift/BAT catalogue showed analogous results in the 15-150 keV band. We carried out the same analysis on the bright GRBs detected by BeppoSAX/GRBM and Fermi/GBM. The BeppoSAX/GRBM data, in the energy range 40-700 keV and with 7.8 and 0.5-ms time resolutions, allowed us to explore for the first time the average PDS at very high frequencies (up to 1 kHz) and reveal a break around 1-2 Hz, previously found in CGRO/BATSE data. The Fermi/GBM data, in the energy band 8-1000 keV, allowed us to explore for the first time the average PDS within a broad energy range. Our results confirm and extend the energy dependence of the PDS slope, according to which harder photons have shallower PDS
Rozpor ako východisko, láska ako smer u Simone Weilovej (Contradiction as base, Love as direction in writings of Simone Weil)
No full textArticle is explaining contradiction and love, Simone Weil‘s essential terms of hermeneutics of human Being. It introduces close relation of these terms with her understanding of God as well as with her overall concept of religion. Author also mentions Simone Weil‘s inspirations with philosophical and spiritual concepts of the East
Correlation between peak energy and Fourier power density spectrum slope in gamma-ray bursts
No full textContext. The origin of the gamma–ray burst (GRB) prompt emission still defies explanation, in spite of recent progress made, for example, on the occasional presence of a thermal component in the spectrum along with the ubiquitous non-thermal component that is modelled with a Band function. The combination of finite duration and aperiodic modulations make GRBs hard to characterise temporally. Although correlations between GRB luminosity and spectral hardness on one side and time variability on the other side have long been known, the loose and often arbitrary definition of the latter makes the interpretation uncertain.
Aims. We characterise the temporal variability in an objective way and search for a connection with rest-frame spectral properties for a number of well-observed GRBs.
Methods. We studied the individual power density spectra (PDS) of 123 long GRBs with measured redshift, rest-frame peak energy Ep,i of the time-averaged ν Fν spectrum, and well-constrained PDS slope α detected with Swift, Fermi and past spacecraft. The PDS were modelled with a power law either with or without a break adopting a Bayesian Markov chain Monte Carlo technique.
Results. We find a highly significant Ep,i–α anti-correlation. The null hypothesis probability is ~10-9.
Conclusions. In the framework of the internal shock synchrotron model, the Ep,i–α anti-correlation can hardly be reconciled with the predicted Ep,i ∝ Γ-2, unless either variable microphysical parameters of the shocks or continual electron acceleration are assumed. Alternatively, in the context of models based on magnetic reconnection, the PDS slope and Ep,i are linked to the ejecta magnetisation at the dissipation site, so that more magnetised outflows would produce more variable GRB light curves at short timescales (≲1 s), shallower PDS, and higher values of Ep,i
“I beg you to tell me what has become of Djamila”: The Political Mobilization of Simone de Beauvoir’s Readers During the Boupacha Affair
No full textBy Sophia Millman This is a condensed version of a Masters thesis dedicated to the political mobilization of Simone de Beauvoir’s readers. The citations from the letters were translated from French by the author. *** On June 2, 1960, the French government ordered all copies of the daily Algiers edition of Le Monde seized and destroyed to suppress the publication of Simone de Beauvoir’s article “Pour Djamila Boupacha.” Beauvoir, a self-professed “woman of letters”, not “of action[1]”, and one ..
A comparative study of form and theology in the works of Flannery O'Connor and Simone Weil
No full textIn this comparative study of the form and theology of Flannery O'Connor and Simone Weil I interrogate how Weil's philosophical writings and her theology illuminate O'Connor's use of both narrative and non-fictional forms, and her Catholicism. The Introduction analyses how Weil's concept of superposed reading provides a new method of approaching both O'Connor, her writings, and O'Connor
studies, and focuses on how such apparently different women interconnect. Chapter One explores how both Weil and O'Connor attempt to write their theologies on the
souls of their readers yet are each subject to constraints imposed by form. Weil's concept of locating equilibrium between incommensurates is discussed, and her
distinctively philosophical approach to fictions and fictionality is used to investigate O'Connor's notion of prophetic fictions and the writer's role. Chapter Two assesses how both writers revivify Christian paradoxes. Weil's monstrous concept of affiiction, and O'Connor's use of the grotesque genre to jolt secular man into an
awareness of the sacred are scrutinised. Chapter Three studies how both writers consider an encounter between God and man is possible through the action of grace. My Conclusion interrogates how Weil's work can deepen our understanding of O'Connor's writings, and examines how successful O'Connor is at realising a truly
Christian literature. I conclude that despite being a writer of powerful fictions, O'Connor can not be totally successful in her mission as writer-prophet because
ultimately fiction escapes orthodoxy
Microlinices benthovus Simone 2014
No full textbenthovus, Microlinices Simone, 2014 Microlinices benthovus Simone, 2014: 575–578 (figs 6A–J, 7A–H, 11A–C). Gastropoda, Naticidae Paratypes (22 spc): MZSP 105269. Paratypes 1 (15 spc): MZSP 105270. Paratypes 2 (16 spc): MZSP 105271. Paratypes 3 (7 spc): MZSP 105272. Localities: Brazil, Espírito Santo, off Itaúnas, Abrolhos Slope, 18°59' S, 37°50' W, MD55 sta. DC 73, 637 m depth, 27 May 1987; 1) 19°00' S, 37°48' W, MD55 sta. DC72, 950– 1050 m, 27 May 1987; 2) off Regência, 19°40' S, 37°48' W, MD55 sta. CB77, 790– 940 m depth, 27 May 1987; 3) off Itaúnas, Abrolhos Slope, 19°01' S, 37°47' W, MD55 sta. CB79, 1500–1575 m depth, 28 May 1987. Collectors: P. Bouchet, J.H. Leal and B. Métivier. Preservation: Dry. Remarks: Former MNHN, Paris. The catalogue number MZSP 105250 is mentioned twice in Simone’s (2014) paper, among the paratypes of M. ibitingus Simone, 2014 and M. benthovus. This duplicity was a mistake by the author: the latter is an erroneous designation and should be disregarded. The only valid paratype lots for M. benthovus are the ones shown above.Published as part of Cavallari, Daniel C., Dornellas, Ana Paula S. & Simone, Luiz Ricardo L., 2016, Second annotated list of type specimens of molluscs deposited in the Museu de Zoologia da Universidade de São Paulo, Brazil, pp. 1-59 in European Journal of Taxonomy 213 on page 10, DOI: 10.5852/ejt.2016.213, http://zenodo.org/record/384012
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