1,721,276 research outputs found
Can we constrain the aftermath of binary neutron star mergers with short gamma-ray bursts?
No full textThe joint observation of GW170817 and GRB170817A proved that binary neutron star (BNS) mergers are progenitors of short gamma-ray bursts (SGRBs): this established a direct link between the still unsettled SGRB central engine and the outcome of BNS mergers, whose nature depends on the equation of state (EOS) and on the masses of the NSs. We propose a novel method to probe the central engine of SGRBs based on this link. We produce an extended catalogue of BNS mergers by combining recent theoretically predicted BNS merger rate as a function of redshift and the NS mass distribution inferred from measurements of Galactic BNSs. We use this catalogue to predict the number of BNS systems ending as magnetars (stable or supramassive NS) or BHs (formed promptly or after the collapse of a hypermassive NS) for different EOSs, and we compare these outcomes with the observed rate of SGRBs. Despite the uncertainties mainly related to the poor knowledge of the SGRB jet structure, we find that for most EOSs the rate of magnetars produced after BNS mergers is sufficient to power all the SGRBs, while scenarios with only BHs as possible central engine seem to be disfavoured
Three-peak GRBs and their implications for central engines
No full textGRB 110709B presented a peculiar three-peak lightcurve; this burst twice triggered the BAT detector onboard Swift. The two triggers were separated by similar to 10 min. In order to explain such an event, we unify into a single description the millisecond (ms) protomagnetar and the collapsar central-engine models. We find that such a scenario could produce GRBs with three peaks. One for the ms-protomagnetar stage, a second one for the BH-formation event and a third one for the collapsar phase. We show that the three peaks for GRB 110709B originate from different phases of the same collapsing object. We estimate the energies and timescales of the different episodes of this burst using our model and compare with previous results as well as with a reanalysis we perform on the data. We show that not only the light curve, but also the photon index evolution and the delay between the prompt emission and the afterglow of the second central-engine activity phase point toward a model like the one proposed here. We find that, with reasonable assumptions, our model correctly describes the activity in GRB 110709B. We further suggest careful study of future GRBs lightcurves which may help show the validity of our model. If our model is correct, this would be the first time that the formation of a BH from a core-collapse event is observed unimpededly. (C) 2015 Elsevier B.V. All rights reserved
Estimation of the TeV gamma-ray duty cycle of Mrk 421 with the Milagro observatory
No full textMarkarian 421 (Mrk 421) is one the brightest and closest (z=0.031) blazars known (de Vaucouleurs et al., 1991 [1]). It is also one of the fastest varying TeV γ-ray sources, with a flaring activity on time scales as short as tens of minutes. The activity of Mrk 421 at different frequencies may reflect the radiation mechanisms involved. Tluczykont et al. (2007) [2] estimated the TeV activity of Mrk 421 through calculating the fraction of time spent in flaring states at TeV energies (TeV duty cycle) by using data from several imaging atmospheric Cherenkov telescopes (IACTs). Since IACT observations are biased towards high flux states they overestimated the TeV duty cycle of Mrk 421. Here we propose an alternative approach to calculate the TeV duty cycle of Mrk 421 that takes advantage of the continuous monitoring of the source by the Milagro experiment, a water Cherenkov detector sensitive to primary γ-rays between 100 GeV and 100 TeV. We present our estimation of the TeV duty cycle and study its robustness. © 2013 Elsevier B.V
Computational challenges for multimodal astrophysics
No full textIn the coming decades, we will face major computational challenges, when the improved sensitivity of third-generation gravitational wave detectors will be such that they will be able to detect a high number (of the order of 7 x10(4) per year) of multi-messenger events from binary neutron star mergers, similar to GW170817. In this Perspective, we discuss the application of multimodal artificial intelligence techniques for multi-messenger astrophysics, fusing the information from different signal emissions
Computational challenges for multimodal astrophysics
No full textIn the coming decades, we will face major computational challenges, when the improved sensitivity of third-generation gravitational wave detectors will be such that they will be able to detect a high number (of the order of 7 × 104 per year) of multi-messenger events from binary neutron star mergers, similar to GW 170817. In this Perspective, we discuss the application of multimodal artificial intelligence techniques for multi-messenger astrophysics, fusing the information from different signal emissions
Estimation of the TeV gamma-ray duty cycle of Mrk 421 with Milagro
No full textThe blazar Markarian 421 (Mrk 421) is one of the brightest sources in the extragalactic X-ray/TeV sky. It is also one of the fastest varying TeV γ-ray sources, showing flaring activity on time scales as short as tens of minutes. To know the level of activity of this source, Tluczykont et al. (2007) [1] calculated the fraction of time spent by Mrk 421 in flaring states with fluxes above 1 Crab at TeV energies (i.e., TeV - duty cycle). Here we present an alternative approach to calculate the TeV duty cycle of Mrk 421 taking advantage of the continuous monitoring of the source by the Milagro observatory. Milagro was a water Cherenkov detector sensitive at energies between 100 GeV and 100 TeV. We present our estimation of the TeV - duty cycle and study its robustness
Detecting non-Gaussian gravitational wave backgrounds: A unified framework
No full textWe describe a novel approach to the detection and parameter estimation of a non-Gaussian stochastic background of gravitational waves. The method is based on the determination of relevant statistical parameters using importance sampling. We show that it is possible to improve the Gaussian detection statistics by simulating realizations of the expected signal for a given model. While computationally expensive, our method improves the detection performance, leveraging the prior knowledge on the expected signal, and can be used in a natural way to extract physical information about the background. We present the basic principles of our approach, characterize the detection statistic performances in a simplified context, and discuss possible applications to the detection of some astrophysical foregrounds. We argue that the proposed approach, complementarily to the ones available in literature might be used to detect suitable astrophysical foregrounds by currently operating and future gravitational wave detectors
Study of TeV variability of Mrk 421 from 3 years of monitoring with the milagro observatory
No full textThe Milagro experiment was a TeV gamma-ray observatory designed to continuously monitor the overhead sky in the 0.1-100 TeV energy range. It operated from 2000 and 2008 and was characterized by a large field of view (∼ 2 sr) and a high duty cycle (≥ 90%). Here we report on the long-term monitoring of the blazar Mrk 421 with Milagro over the period from September 21, 2005 to March 15, 2008. We present a study of the TeV variability of the source and provide upper limits for the measured flux for different time scales, ranging from one week up to one year
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