ABSTRACT
Gamma-ray bursts (GRBs) are known to be highly collimated events, and are mostly detectable when they are seen on-axis or very nearly on-axis. However, GRBs can be seen from off-axis angles, ...and the recent detection of a short GRB associated with a gravitational wave event has conclusively shown such a scenario. The observer viewing angle plays an important role in the observable spectral shape and the energetic of such events. We present a numerical model that is based on the single-pulse approximation with emission from a top-hat jet and has been developed to investigate the effects of the observer viewing angle. We assume a conical jet parametrized by a radius Rjet, half-opening angle θjet, a comoving-frame emissivity law and an observer viewing angle θobs, and then study the effects for the conditions θobs < θjet and θobs > θjet. We present results considering a smoothly broken power-law emissivity law in jet comoving frame, albeit the model implementation easily allows to consider other emissivity laws. We find that the relation $E^{\rm i}_{\rm p}\propto E_{\rm iso}^{0.5}$ (Amati relation) is naturally obtained from pure relativistic kinematic when $\Gamma \gtrsim 10$ and θobs < θjet; on the contrary, when θobs > θjet it results $E^{\rm i}_{\rm p}\propto E_{\rm iso}^{0.25}$. Using data from literature for a class of well-know sub-energetic GRBs, we show that their position in the $E^{\rm i}_{\rm p}\!-\!E_{\rm iso}$ plane is consistent with event observed off-axis. The presented model is developed as a module to be integrated in spectral fitting software package xspec and can be used by the scientific community.
Abstract
The double neutron star (DNS) merger event GW170817 signifies the first multimessenger (MM) event with electromagnetic-gravitational (EM-GW) observations. LIGO-Virgo-KAGRA observational runs ...O4-5 promise to detect similar events and as yet unknown GW signals, which require confirmation in two or more detectors with comparable performance. To this end, we quantify duty cycles of comparable science quality of data in coincident H1L1-observations, further to seek consistent event rates of astrophysical transients in upcoming EM-GW surveys. Quite generally, discovery power scales with exposure time, sensitivity, and critically depends on the percentage of time when detectors operate at high quality. We quantify coincident duty cycles over a time-frequency domain
W
×
B
, defined by segments of duration
W
= 8 s, motivated by a long-duration descending GW-chirp during GRB170817A, and the minimum detector noise over about
B
= 100–250 Hz. This
detector yield factor
satisfies 1%–25% in S5-6 and O1-O3ab, significantly different from duty cycles of H1 and L1 individually with commensurable impact on consistency in event rates in EM-GW surveys. Significant gain in discovery power for signals whose frequency varies slowly in time may be derived from improving detector yield factors by deploying
time-symmetric
data analysis methods. For O4-5, these can yield improvements by factors up to
(
10
5
)
relative to existing data and methods. Furthermore, the diversity of MM afterglows to DNS mergers may be greatest for systems similar to GW170817 but possibly less so for systems of substantially different mass such as GW190425. We summarize our findings with an outlook on EM-GW surveys during O4-5 and perspectives for next-generation GRB missions like
THESEUS
.
ABSTRACT
The correlation between the cosmological rest‐frame νFν spectrum peak energy, Ep,i, and the isotropic‐equivalent radiated energy, Eiso, discovered by Amati et al. in 2002 and ...confirmed/extended by subsequent osbervations, is one of the most intriguing and debated observational evidences in gamma‐ray burst (GRB) astrophysics. In this paper, I provide an update and a re‐analysis of the Ep,i–Eiso correlation basing on an updated sample consisting of 41 long GRBs/X‐ray flashes (XRFs) with firm estimates of z and observed peak energy, Ep,obs, 12 GRBs with uncertain values of z and/or Ep,obs, two short GRBs with firm estimates of z and Ep,obs and the peculiar subenergetic events GRB 980425/SN1998bw and GRB 031203/SN2003lw. In addition to standard correlation analysis and power‐law fitting, the data analysis here reported includes modelling that accounts for sample variance. All 53 classical long GRBs and XRFs, including 11 Swift events with published spectral parameters and fluences, have Ep,i and Eiso values, or upper/lower limits, consistent with the correlation, which shows a chance probability as low as ∼7 × 10−15, a slope of ∼0.57 (∼0.5 when fitting by accounting for sample variance) and an extra‐Poissonian logarithmic dispersion of ∼0.15, it extends over ∼5 orders of magnitude in Eiso and ∼3 orders of magnitude in Ep,i and holds from the closer to the higher z GRBs. Subenergetic GRBs (980425 and possibly 031203) and short GRBs are found to be inconsistent with the Ep,i–Eiso correlation, showing that it can be a powerful tool for discriminating different classes of GRBs and understanding their nature and differences. I also discuss the main implications of the updated Ep,i–Eiso correlation for the models of the physics and geometry of GRB emission, its use as a pseudo‐redshift estimator and the tests of possible selection effects with GRBs of unknown redshift.
The correlation between the photon energy at which the redshift-corrected νFν spectrum peaks (hereafter called “peak energy”, Ep,i) and the isotropic equivalent radiated energy (Eiso) is one of the ...most intriguing and debated peaces of observational evidence in Gamma-Ray Burst (GRB)astrophysics. I present the updated Ep,i – Eiso correlation and discuss its main implications for the physics and the geometry of the GRB emission, with particular emphasis on the properties of Swift GRBs and the location in the Ep,i – Eiso plane of sub-energetic long GRBs, GRB/SN events, short GRBs and the recently discovered sub-class of long GRBs without association with a hypernova. KCI Citation Count: 3
The mission concept THESEUS (Transient High Energy Sky and Early Universe Surveyor) aims at exploiting Gamma-Ray Bursts (GRB) to explore the early Universe, as well as becoming a cornerstone of ...multi-messenger and time-domain astrophysics. To achieve these goals, a key feature is the capability to survey the soft X-ray transient sky and to detect the faint and soft GRB population so far poorly explored. Among the expected transients there will be high-redshift GRBs, nearby low-luminosity, X-ray Flashes and short GRBs. Our understanding of the physics governing the GRB prompt emission will benefit from the 0.3 keV–10 MeV simultaneous observations for an unprecedented large number of hundreds of events per year. In particular the mission will provide the identification, accurate sky localisation and characterization of electromagnetic counterparts to sources of gravitational wave and neutrino sources, which will be routinely detected during the 2030s by the upgraded second generation and third generation Gravitational Wave (GW) interferometers and next generation neutrino detectors.
We report on an accurate measurement of the CXB in the 15-50 keV range performed with the Phoswich Detection System (PDS) instrument aboard the BeppoSAX satellite. We establish that the most likely ...CXB intensity level at its emission peak (26-28 keV) is approximately 40 keV cm super(-2) s super(-1) sr super(-1), a value consistent with that derived from the best available CXB measurement obtained over 25 years ago with the first High Energy Astronomical Observatory (HEAO-1) satellite mission (Gruber et al.), whose intensity, lying well below the extrapolation of some lower energy measurements performed with focusing telescopes, was questioned in recent years. We find that 90% of the acceptable solutions of our best-fit model to the PDS data give a 20-50 keV CXB flux lower than 6.5 x 10 super(-8) ergs cm super(-2) s super(-1) sr super(-1), which is 12% higher than that quoted by Gruber et al. when we use our best calibration scale. In combination with the CXB synthesis models we infer that about 25% of the intensity at similar to 30 keV arises from extremely obscured, Compton-thick AGNs (absorbing column density N sub(H) > 10 super(24) cm super(-2)), while a much larger population would be implied by the highest intensity estimates. We also infer a mass density of supermassive black holes of similar to 3 x 10 super(5) M unk Mpc super(-3). The summed contribution of resolved sources (Moretti et al.) in the 2-10 keV band exceeds our best-fit CXB intensity extrapolated to lower energies, but it is within our upper limit, so that any significant contribution to the CXB from sources other than AGNs, such as star-forming galaxies and diffuse warm-hot intergalactic medium (WHIM), is expected to be mainly confined below a few keV.
Cosmology with gamma-ray bursts Demianski, Marek; Piedipalumbo, Ester; Sawant, Disha ...
Astronomy and astrophysics (Berlin),
02/2017, Letnik:
598
Journal Article
Recenzirano
Context. Explaining the accelerated expansion of the Universe is one of the fundamental challenges in physics today. Cosmography provides information about the evolution of the universe derived from ...measured distances, assuming only that the space time geometry is described by the Friedman-Lemaitre-Robertson-Walker metric, and adopting an approach that effectively uses only Taylor expansions of basic observables.Aims. We perform a high-redshift analysis to constrain the cosmographic expansion up to the fifth order. It is based on the Union2 type Ia supernovae data set, the gamma-ray burst Hubble diagram, a data set of 28 independent measurements of the Hubble parameter, baryon acoustic oscillations measurements from galaxy clustering and the Lyman-α forest in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and some Gaussian priors on h and ΩM.Methods. We performed a statistical analysis and explored the probability distributions of the cosmographic parameters. By building up their regions of confidence, we maximized our likelihood function using the Markov chain Monte Carlo method.Results. Our high-redshift analysis confirms that the expansion of the Universe currently accelerates; the estimation of the jerk parameter indicates a possible deviation from the standard ΛCDM cosmological model. Moreover, we investigate implications of our results for the reconstruction of the dark energy equation of state (EOS) by comparing the standard technique of cosmography with an alternative approach based on generalized Padé approximations of the same observables. Because these expansions converge better, is possible to improve the constraints on the cosmographic parameters and also on the dark matter EOS.Conclusions. The estimation of the jerk and the DE parameters indicates at 1σ a possible deviation from the ΛCDM cosmological model.Key words: dark energy / cosmological parameters / cosmology: theory
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