1,721,091 research outputs found
THESEUS XGIS INSTRUMENT RISK ASSESMENT AND MITIGATION
No full textThe aim of risk management is to identify any items that may prevent the successful completion of the
programme (schedule, technical, financial, etc.) and to address these areas early on to reduce the risk
associated with them. The risk management process continues to evolve throughout the course of the
project, identifying any new risks as they arise and managing them appropriately.
This section details the process of risk management, concluding with the risk reduction plan and proposed
mitigation
XGIS Instrument Requirements
No full textThe purpose of this XGIS instrument requirements specification is to derive the
instrument requirements based on the scientific objectives and the technical and
programmatic requirements as defined in the Mission Requirement Document [AD1],
the Science Requirement Document [AD2] and the Environment Specification
Document [AD3].
For the purpose of this first version the requirement specifications are derived for:
- The top level (level 0) Instrument Requirements Specification
- Elements that are not procured by the payload consortium (TBD)
In addition, a preliminary functional and performance specification shall be described
for:
Level 1 Requirements Specifications
Elements that are subjected to technology developments in Phase B1
Note: All interface requirements to the S/C shall be summarized and presented in the
EID-B and are therefore not included in this document
An Upscattering Spectral Formation Model for the Prompt Emission of Gamma-Ray Bursts
No full textWe propose a model for the spectral formation of gamma-ray burst (GRB) prompt emission, where the phenomenological Band function is usually applied to describe this emission. We suggest that the GRB prompt emission is mainly a result of two upscattering processes. The first process is the Comptonization of relatively cold soft photons of the star off electrons of a hot shell of plasma of temperature T e of the order of 109K (or kT e 100keV) that moves subrelativistically with the bulk velocity V b substantially less than the speed of light c. In this phase, the Comptonization parameter Y is high and the interaction between a blackbody-like soft seed photon population and hot electrons leads to formation of a saturated Comptonization spectrum modified by the subrelativistic bulk outflow. The second process is an upscattering of the previously Comptonized spectrum by the plasma outflow once it becomes relativistic. This process gives rise to the high-energy power-law (PL) component above the peak in the EF(E) diagram where F(E) is the energy flux. The latter process can be described by a convolution of the Comptonized spectrum with a broken-PL Green function. Possible physical scenarios for this second upscattering process are discussed. In the framework of our model, we give an interpretation of the Amati relation between the intrinsic spectral peak photon energy and radiated energy or luminosity, and we propose a possible explanation of the GRB temporal variability. © 2012. The American Astronomical Society. All rights reserved.
An analytical late–Universe approach to the weaving of modern cosmology
Full text linkCombining cosmological probes has consolidated the standard cosmological model with per cent precision, but some tensions have recently emerged when certain parameters are estimated from the local or primordial Universe. The origin of this behaviour is still under debate; however, it is crucial to study as many probes as possible to cross-check the results with independent methods and provide additional pieces of information to the cosmological puzzle. In this work, by combining several late-Universe probes (0 < z < 10), namely, Type Ia supernovae, baryon acoustic oscillations, cosmic chronometers, and gamma-ray bursts, we aim to derive cosmological constraints independently of local or early-Universe anchors. To test the standard cosmological model and its various extensions, considering an evolving dark energy equation of state and the curvature as a free parameter, we analyse each probe individually and all their possible permutations. Assuming a flat Lambda cold dark matter (Lambda CDM) model, the full combination of probes provides H-0=67.2(-3.2)(+3.4) km s(-1) Mpc(-1) and Omega(m) = 0.325 +/- 0.015 [68 per cent confidence level (C.L.)]. Considering a flat wCDM model, we measure omega(0)=-0.91(-0.08)(+0.07) (68 per cent C.L.), while by relaxing the flatness assumption (Lambda CDM model, 95 per cent C.L.) we obtain Omega(k )= 0.125(-0.165)(+0.167). Finally, we analytically characterize the degeneracy directions and the relative orientation of the probes' contours. By calculating the figure-of-merit, we quantify the synergies among independent methods, estimate the constraining power of each probe, and identify which provides the best contribution to the inference process. Pending the new cosmological surveys, this study confirms the exigency for new emerging probes in the landscape of modern cosmology
Individual power density spectra of
Full text linkContext. 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
General relativistic electromagnetic and massive vector field effects with gamma-ray burst production
Full text linkWe propose a new energy extraction mechanism from the rotational energy of a Kerr-Newman black hole by a gravitating massive photon field generated by electromagnetic and gravitational field coupling effects. Numerical studies show that this mechanism that depends on the black hole rotation parameter, a, shows a clear dependence on the black hole mass, M, and charge, Q, and can extract energies up to 1054 erg for a black hole of the solar mass size. With this mechanism we can set a lower bound on the coupling ξ∼10−38 between electromagnetic and gravitational fields that might be used to explain the hypothetical extremely high energy release, >1053 erg, suggested by the observations of some gamma-ray bursts in the controversial “energy crisis” problem if and when gamma-ray bursts seem not to show evidence for collimated emission
Theseus Payload Consortium Product Assurance and Quality Assurance Plan
No full textThe scope of this plan is to define a PA Programme to support the PA activities at THESEUS Payload Consortium Level, covering activities performed by each Instrument Team and by potential supplier/contractor.
The ECSS standards are considered reference documents and as guidelines, tailored to the needs of the Payload. The QA plan is integrated in this PA plan
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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