Gamma ray burst studies with THESEUS Ghirlanda, G.; Salvaterra, R.; Toffano, M. ...
Experimental astronomy,
12/2021, Letnik:
52, Številka:
3
Journal Article
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Gamma-ray Bursts (GRBs) are the most powerful transients in the Universe, over–shining for a few seconds all other
γ
-ray sky sources. Their emission is produced within narrowly collimated ...relativistic jets launched after the core–collapse of massive stars or the merger of compact binaries. THESEUS will open a new window for the use of GRBs as cosmological tools by securing a statistically significant sample of high-
z
GRBs, as well as by providing a large number of GRBs at low–intermediate redshifts extending the current samples to low luminosities. The wide energy band and unprecedented sensitivity of the Soft X-ray Imager (SXI) and X-Gamma rays Imaging Spectrometer (XGIS) instruments provide us a new route to unveil the nature of the prompt emission. For the first time, a full characterisation of the prompt emission spectrum from 0.3 keV to 10 MeV with unprecedented large count statistics will be possible revealing the signatures of synchrotron emission. SXI spectra, extending down to 0.3 keV, will constrain the local metal absorption and, for the brightest events, the progenitors’ ejecta composition. Investigation of the nature of the internal energy dissipation mechanisms will be obtained through the systematic study with XGIS of the sub-second variability unexplored so far over such a wide energy range. THESEUS will follow the spectral evolution of the prompt emission down to the soft X–ray band during the early steep decay and through the plateau phase with the unique ability of extending above 10 keV the spectral study of these early afterglow emission phases.
The
Einstein
Telescope (ET) is going to bring a revolution for the future of multimessenger astrophysics. In order to detect the counterparts of binary neutron star (BNS) mergers at high redshift, ...the high-energy observations will play a crucial role. Here, we explore the perspectives of ET, as a single observatory and in a network of gravitational-wave (GW) detectors, operating in synergy with future
γ
-ray and X-ray satellites. We predict the high-energy emission of BNS mergers and its detectability in a theoretical framework which is able to reproduce the properties of the current sample of observed short GRBs (SGRBs). We estimate the joint GW and high-energy detection rate for both the prompt and afterglow emissions, testing several combinations of instruments and observational strategies. We find that the vast majority of SGRBs detected in
γ
-rays have a detectable GW counterpart; the joint detection efficiency approaches 100% considering a network of third-generation GW observatories. The probability of identifying the electromagnetic counterpart of BNS mergers is significantly enhanced if the sky localization provided by GW instruments is observed by wide-field X-ray monitors. We emphasize that the role of the future X-ray observatories will be very crucial for the detection of the fainter emission outside the jet core, which will allow us to explore the population of low-luminosity SGRBs in the nearby Universe, as well as to unveil the nature of the jet structure and the connections with the progenitor properties.
Context. We have investigated the dichotomy between jetted and non-jetted active galactic nuclei (AGNs), focusing on the fundamental differences of these two classes in the accretion physics onto the ...central supermassive black hole (SMBH). We tested the validity of the unification model of AGNs through the characterization of the mutual interaction between accreting and outflowing matter in radio galaxies. Aims. Our aim is to study and constrain the structure, kinematics and physical state of the nuclear environment in the broad line radio galaxy (BLRG) PKS 2251+11. The high X-ray luminosity and the relative proximity make such AGN an ideal candidate for a detailed analysis of the accretion regions in radio galaxies. The investigation will help to shed light on the analogies and differences between the BLRGs and the larger class of radio-quiet Seyfert galaxies and hence on the processes that trigger the launch of a relativistic jet. Methods. We performed a spectral and timing analysis of a ∼64 ks observation of PKS 2251+11 in the X-ray band with XMM-Newton. We modeled the spectrum considering an absorbed power law superimposed to a reflection component. We performed a time-resolved spectral analysis to search for variability of the X-ray flux and of the individual spectral components. Results. We find that the power law has a photon index Γ = 1.8 ± 0.1, absorbed by an ionized partial covering medium with a column density NH = (10.1 ± 0.8) × 1023 cm−2, a ionization parameter log ξ = 1.3 ± 0.1 erg s−1 cm and a covering factor f ≃ 90%. Considering a density of the absorber typical of the broad line region (BLR), its distance from the central SMBH is of the order of r ∼ 0.1 pc. An Fe Kα emission line is found at 6.4 keV, whose intensity shows variability on timescales of hours. We derive that the reflecting material is located at a distance r ≳ 600rs, where rs is the Schwarzschild radius. Conclusions. Concerning the X-ray properties, we found that PKS 2251+11 does not differ significantly from the non-jetted AGNs, confirming the validity of the unified model in describing the inner regions around the central SMBH, but the lack of information regarding the state of the very innermost disk and SMBH spin still leaves unconstrained the origin of the jet.
A large fraction of
γ
-ray bursts (GRBs) show a plateau phase during the X-ray afterglow emission, which has a physical origin that is still debated. In this work, we select a sample of 30 GRBs with ...simultaneous X-ray and optical data during and after the plateau phase. Through a time-resolved spectral analysis of the X-ray plateaus, we test the consistency of the unabsorbed optical fluxes with those obtained via X-ray-to-optical spectral extrapolation by assuming a synchrotron spectrum. By combining X-ray with optical data, we find that 63% (19/30) of GRBs are compatible with a single synchrotron spectrum, thus suggesting that both the optical and X-ray radiations are produced from a single emitting region. For these GRBs, we derive the temporal evolution of the break frequency, and we compare it with the expectations predicted by several models. For 11 of the 30 GRBs, the optical emission is above the predicted range of values extrapolated from the X-rays in at least one temporal bin of the light curve. These 11 GRBs may not be explained with a single-zone emission, indicating the necessity of invoking two co-operating processes in order to explain the broad-band spectral behaviour. We discuss our findings in the framework of different scenarios that are invoked to explain the plateau feature, including the energy injection from a spinning-down magnetar and the high latitude emission from a structured jet.
An important step in the planning of future gravitational-wave (GW) detectors and of the networks they will form is the estimation of their detection and parameter-estimation capabilities, which is ...the basis of science-case studies. Several future GW detectors have been proposed or are under development, which might also operate and observe in parallel. These detectors include terrestrial, lunar, and space-borne detectors. In this paper, we present gwfish,11github.com/janosch314/GWFish. a new software to simulate GW detector networks and to calculate measurement uncertainties based on the Fisher-matrix approximation. gwfish models the impact of detector motion on PE and makes it possible to analyze multiband scenarios, i.e., observation of a GW signal by different detectors in different frequency bands. We showcase a few examples for the Einstein Telescope (ET) including the sky-localization of binary neutron stars, and ET’s capability to measure the polarization of GWs.
We present the results from multi-wavelength observations of a transient discovered during the follow-up of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a ...possible binary neutron star merger in a low latency search. This search yielded SN2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance ($\sim$150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude ($M_i \sim -16.7$ mag) and the $r-$band decline rate of $\sim 1$ mag per 5 days appeared suggestive of a compact binary merger. However, SN2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of $\sim 0.1\,M_\odot$, with $^{56}$Ni comprising $\sim 20\%$ of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitors that could give rise to the observed properties of SN2019wxt, and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling electromagnetic counterparts to GW events from transients such as SN2019wxt is challenging: in a bid to characterise the level of contamination, we estimated the rate of events with properties comparable to those of SN2019wxt and found that $\sim 1$ such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.
Gamma-ray Bursts (GRBs) are the most powerful transients in the Universe, over-shining for a few seconds all other \(\gamma\)-ray sky sources. Their emission is produced within narrowly collimated ...relativistic jets launched after the core-collapse of massive stars or the merger of compact binaries. THESEUS will open a new window for the use of GRBs as cosmological tools by securing a statistically significant sample of high-\(z\) GRBs, as well as by providing a large number of GRBs at low-intermediate redshifts extending the current samples to low luminosities. The wide energy band and unprecedented sensitivity of the Soft X-ray Imager (SXI) and X-Gamma rays Imaging Spectrometer (XGIS) instruments provide us a new route to unveil the nature of the prompt emission. For the first time, a full characterisation of the prompt emission spectrum from 0.3 keV to 10 MeV with unprecedented large count statistics will be possible revealing the signatures of synchrotron emission. SXI spectra, extending down to 0.3 keV, will constrain the local metal absorption and, for the brightest events, the progenitors' ejecta composition. Investigation of the nature of the internal energy dissipation mechanisms will be obtained through the systematic study with XGIS of the sub-second variability unexplored so far over such a wide energy range. THESEUS will follow the spectral evolution of the prompt emission down to the soft X-ray band during the early steep decay and through the plateau phase with the unique ability of extending above 10 keV the spectral study of these early afterglow emission phases.
Purpose. This paper aims to illustrate how organisations, especially cultural heritage organisations, can respond to a crisis and plan for recovery when dealing with multiple future uncertainties by ...applying Futures Thinking techniques. It does this by describing the approach that Historic Environment Scotland (HES) has been taking to plan for recovery and renewal during the COVID-19 pandemic.
Approach/methodology/design. The paper uses the case study methodology to explore how different Futures Thinking techniques have been used to build flexibility in HES’s work when facing an uncertain future. The paper will also examine how the methodology used in this process will aid the development of a Futures Thinking toolkit and a Virtual Intelligence Hub in support of all HES’s operations.
Findings. This paper demonstrates how Futures Thinking techniques, such as scenario planning, can be effectively used to map critical uncertainties and identify business priorities across different possible scenarios for cultural organisations. It does so by illustrating the journey taken so far by HES to embed Futures Thinking techniques in the organisation, how it engaged with these and used them to begin the process of creating resilience and sustainability in its operations during this crisis.
Originality/value. Because cultural organisations do not traditionally engage in Futures Thinking, this paper makes the case that such tools are a valuable approach to foreseeing and surviving crises.
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