arXiv subjects

Marica Branchesi

Publications and source records attributed to Marica Branchesi.

At least 55 records · Page 3Linked to original sources

arXiv2024

The Wide-field Spectroscopic Telescope (WST) Science White Paper

The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will feature simultaneous operation of a large field-of-view (3 sq. degree), a high multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 sq. arcmin integral field spectrograph (IFS). In scientific capability these requirements place WST far ahead of existing and planned facilities. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work synergistically with future ground and space-based facilities. This white paper shows that WST can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; origin of stars and planets; time domain and multi-messenger astrophysics. WST's uniquely rich dataset will deliver unforeseen discoveries in many of these areas. The WST Science Team (already including more than 500 scientists worldwide) is open to the all astronomical community. To register in the WST Science Team please visit https://www.wstelescope.com/for-scientists/participate

astro-ph.IM↗

arXiv2023

Pre-merger alert to detect the very-high-energy prompt emission from binary neutron-star mergers: Einstein Telescope and Cherenkov Telescope Array synergy

The current generation of very-high-energy $gamma-$ray (VHE; E above 30 GeV) detectors (MAGIC and H.E.S.S.) have recently demonstrated the ability to detect the afterglow emission of GRBs. However, the GRB prompt emission, typically observed in the 10 keV-10 MeV band, has so far remained undetected at higher energies. Here, we investigate the perspectives of multi-messenger observations to detect the prompt emission of short GRBs in VHE. Considering binary neutron star mergers as progenitors of short GRBs, we evaluate the joint detection efficiency of the Cherenkov Telescope Array (CTA) observing in synergy with the third generation of gravitational wave detectors, such as the Einstein Telescope (ET) and Cosmic Explorer (CE). In particular, we evaluate the expected capabilities to detect and localize gravitational wave events in the inspiral phase and to provide an early warning alert able to drive the VHE search. We compute the amount of possible joint detections by considering several observational strategies, and demonstrate that the sensitivities of CTA make the detection of the VHE emission possible even if it is several orders fainter than the one observed at 10 keV-10 MeV. We discuss the results in terms of possible scenarios of production of VHE photons from binary neutron star mergers by considering GRB prompt and afterglow emissions.

astro-ph.HE↗

arXiv2023

Science with the Einstein Telescope: a comparison of different designs

The Einstein Telescope (ET), the European project for a third-generation gravitational-wave detector, has a reference configuration based on a triangular shape consisting of three nested detectors with 10 km arms, where in each arm there is a `xylophone' configuration made of an interferometer tuned toward high frequencies, and an interferometer tuned toward low frequencies and working at cryogenic temperature. Here, we examine the scientific perspectives under possible variations of this reference design. We perform a detailed evaluation of the science case for a single triangular geometry observatory, and we compare it with the results obtained for a network of two L-shaped detectors (either parallel or misaligned) located in Europe, considering different choices of arm-length for both the triangle and the 2L geometries. We also study how the science output changes in the absence of the low-frequency instrument, both for the triangle and the 2L configurations. We examine a broad class of simple `metrics' that quantify the science output, related to compact binary coalescences, multi-messenger astronomy and stochastic backgrounds, and we then examine the impact of different detector designs on a more specific set of scientific objectives.

gr-qc↗

arXiv2023

A bright megaelectronvolt emission line in $γ$-ray burst GRB 221009A

The highly variable and energetic pulsed emission of a long gamma-ray burst (GRB) is thought to originate from local, rapid dissipation of kinetic or magnetic energy within an ultra-relativistic jet launched by a newborn compact object, formed during the collapse of a massive star. The spectra of GRB pulses are best modelled by power-law segments, indicating the dominance of non-thermal radiation processes. Spectral lines in the X-ray and soft $γ$-ray regime for the afterglow have been searched for intensively, but never confirmed. No line features ever been identified in the high energy prompt emission. Here we report the discovery of a highly significant ($> 6 σ$) narrow emission feature at around $10$ MeV in the brightest ever GRB 221009A. By modelling its profile with a Gaussian, we find a roughly constant width $σ\sim 1$ MeV and temporal evolution both in energy ($\sim 12$ MeV to $\sim 6$ MeV) and luminosity ($\sim 10^{50}$ erg/s to $\sim 2 \times 10^{49}$ erg/s) over 80 seconds. We interpret this feature as a blue-shifted annihilation line of relatively cold ($k_\mathrm{B}T\ll m_\mathrm{e}c^2$) electron-positron pairs, which could have formed within the jet region where the brightest pulses of the GRB were produced. A detailed understanding of the conditions that can give rise to such a feature could shed light on the so far poorly understood GRB jet properties and energy dissipation mechanism.

astro-ph.HE↗

arXiv2023

Muons in the aftermath of neutron star mergers and their impact on trapped neutrinos

In the upcoming years, present and next-generation gravitational wave observatories will detect a larger number of binary neutron star (BNS) mergers with increasing accuracy. In this context, improving BNS merger numerical simulations is crucial to correctly interpret the data and constrain the equation of state (EOS) of neutron stars (NSs). State-of-the-art simulations of BNS mergers do not include muons. However, muons are known to be relevant in the microphysics of cold NSs and are expected to have a significant role in mergers, where the typical thermodynamic conditions favour their production. Our work is aimed at investigating the impact of muons on the merger remnant. We post-process the outcome of four numerical relativity simulations of BNS mergers performed with three different baryonic EOSs and two mass ratios considering the first $15$ milliseconds after merger. We compute the abundance of muons in the remnant and analyse how muons affect the trapped neutrino component and the fluid pressure. We find that depending on the baryonic EOS, the net fraction of muons is between $30 \%$ and $70 \%$ the net fraction of electrons. Muons change the flavour hierarchy of trapped (anti-)neutrinos such that deep inside the remnant, muon anti-neutrinos are the most abundant, followed by electron anti-neutrinos. Finally, muons and trapped neutrinos modify the neutron-to-proton ratio, affecting the remnant pressure by up to $7\%$ when compared with calculations neglecting them. This work demonstrates that muons have a non-negligible effect on the outcome of BNS merger simulations, and they should be included to improve the accuracy of a simulation.

astro-ph.HE↗

arXiv2023

The restframe ultraviolet of superluminous supernovae -- I. Potential as cosmological probes

Superluminous supernovae (SLSNe) have been detected to $z\sim4$ and can be detected to $z\gtrsim15$ using current and upcoming facilities. SLSNe are extremely UV luminous, and hence objects at $z\gtrsim7$ are detected exclusively via their rest-frame UV using optical and infrared facilities. SLSNe have great utility in multiple areas of stellar and galactic evolution. Here, we explore the potential use of SLSNe type-I as high-redshift cosmological distance indicators in their rest-frame UV. Using a SLSNe-I sample in the redshift range $1\lesssim z\lesssim 3$, we investigate correlations between the peak absolute magnitude in a synthetic UV filter centered at 250 nm and rise time, colour and decline rate of SLSNe-I light curves. We observe a linear correlation between $M_0(250)$ and the rise time with an intrinsic scatter of 0.29. Interestingly, this correlation is further tightened ($σ_{int} \approx 0.2$) by eliminating those SLSNe which show a pre-peak bump in their light curve. This result hints at the possibility that the "bumpy" SLSNe could belong to a different population. Weak correlations are observed between the peak luminosity and colour indices. No relationship is found between UV peak magnitude and the decline rate in contrast to what is typically found in optical band. The correlations found here are promising, and give encouraging insights for the use of SLSNe as cosmological probes at high redshifts using standardising relations in the UV. We also highlight the importance of early, and consistent, photometric data for constraining the light curve properties.

astro-ph.HE↗

arXiv2022

Constrains on the physics of the prompt emission from a distant and energetic gamma-ray burst GRB 220101A

The emission region of $\rm γ$-ray bursts (GRBs) is poorly constrained. The uncertainty on the size of the dissipation site spans over 4 orders of magnitude ($\rm 10^{12}-10^{17}$ cm) depending on the unknown energy composition of the GRB jets. The joint multi-band analysis from soft X-rays to high energies (up to $\rm \sim$ 1 GeV) of one of the most energetic and distant GRB 220101A (z = 4.618) allows us for an accurate distinction between prompt and early afterglow emissions. The enormous amount of energy released by GRB 220101A ($\rm E_{iso} \approx 3 \times10^{54}$ erg) and the spectral cutoff at $\rm E_{cutoff} = 85_{-26}^{+16}$ MeV observed in the prompt emission spectrum constrains the parameter space of GRB dissipation site. We put stringent constraints on the prompt emission site, requiring $\rm 700<Γ_0<1160 $ and $\rm R_γ\sim 4.5 \times 10^{13}$ cm. Our findings further highlights the difficulty of finding a simple self consistent picture in the electron-synchrotron scenario, favoring instead a proton-synchrotron model, which is also consistent with the observed spectral shape. Deeper measurements of the time variability of GRBs together with accurate high-energy observations (MeV-GeV) would unveil the nature of the prompt emission.

astro-ph.HE↗

arXiv2022

Combined X-ray and optical analysis to probe the origin of the plateau emission in $γ$-ray bursts afterglows

A large fraction of gamma-ray bursts (GRBs) shows a plateau phase during the X-ray afterglow emission, whose physical origin is still debated. In this work we define 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. Combining X-ray with optical data, we find that 63% (19/30) 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 11/30 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 GRBs may not be explained with a single zone emission, indicating the necessity of invoking two cooperating processes in order to explain the broad band spectral behaviour during X-ray plateaus. We discuss our findings in the framework of different scenarios invoked to explain the plateau feature, including the energy injection from a spinning-down magnetar and the high latitude emission from a structured jet.

astro-ph.HE↗

arXiv2022

Measuring properties of primordial black hole mergers at cosmological distances: effect of higher order modes in gravitational waves

Primordial black holes (PBHs) may form from the collapse of matter overdensities shortly after the Big Bang. One may identify their existence by observing gravitational wave (GW) emissions from merging PBH binaries at high redshifts $z\gtrsim 30$, where astrophysical binary black holes (BBHs) are unlikely to merge. The next-generation ground-based GW detectors, Cosmic Explorer and Einstein Telescope, will be able to observe BBHs with total masses of $\mathcal{O}(10-100)~M_{\odot}$ at such redshifts. This paper serves as a companion paper of arXiv:2108.07276, focusing on the effect of higher-order modes (HoMs) in the waveform modeling, which may be detectable for these high redshift BBHs, on the estimation of source parameters. We perform Bayesian parameter estimation to obtain the measurement uncertainties with and without HoM modeling in the waveform for sources with different total masses, mass ratios, orbital inclinations and redshifts observed by a network of next-generation GW detectors. We show that including HoMs in the waveform model reduces the uncertainties of redshifts and masses by up to a factor of two, depending on the exact source parameters. We then discuss the implications for identifying PBHs with the improved single-event measurements, and expand the investigation of the model dependence of the relative abundance between the BBH mergers originating from the first stars and the primordial BBH mergers as shown in arXiv:2108.07276.

astro-ph.CO↗

arXiv2022

Neutrino search from γ-ray bursts during the prompt and X-ray afterglow phases using 10 years of IceCube public data

Neutrino emission from gamma-ray bursts (GRBs) has been sought for a long time, and stringent limits on the most accredited GRB emission models have been obtained from IceCube. Multi-wavelength GRB observations of the last decades improved our knowledge of the GRB emission parameters, such as the Lorentz factor and the luminosity, which can vary from one GRB to another by several orders of magnitude. Empirical correlations among such parameters have been identified during the prompt phase, with direct implications on GRB models. In this work, we use the PSLab open-access code, developed for IceCube data analyses, to search for individual neutrino emission from the prompt and afterglow phases of selected GRBs, and for stacking emission from the ensemble of such GRBs. For the afterglow phase, we focus in particular on GRBs with X-ray flares and plateaus. While past stacking searches assumed the same GRB fluence at Earth, we present a stacking scheme based on physically motivated GRB weights. Moreover, we conceive a new methodology for the prompt phase that uses the empirical correlations to infer the GRB luminosity and Lorentz factor, when redshift measurements are not available. We do not observe any significant neutrino excess. Hence, we set constraints on the GRB neutrino fluxes and on relevant GRB parameters, including the magnetic field in the jet. Notably, the baryon loading is found to be <10 for typical GRB prompts, thus disfavoring a baryonic-dominated origin of the GRB ejecta.

astro-ph.HE↗

arXiv2022

Perspectives for multi-messenger astronomy with the next generation of gravitational-wave detectors and high-energy satellites

The Einstein Telescope (ET) is going to bring a revolution for the future of multi-messenger 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 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 (SGRB). 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 will 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 localisation 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 probe the yet unexplored 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.

astro-ph.HE↗

arXiv2022

A study of globular clusters in a lenticular galaxy in Hydra I from deep HST/ACS photometry

We take advantage of exquisitely deep optical imaging data from HST/ACS in the F475W ($g_{F475W}$) and F606W ($V_{F606W}$) bands, to study the properties of the globular cluster (GC) population in the intermediate mass lenticular galaxy PGC 087327, in the Hydra I galaxy cluster. We inspect the photometric (magnitudes and color) and morphometric (compactness, elongation, etc.) properties of sources lying in an area of $\sim19\times19$ kpc centered on PGC 087327, and compare them with four neighbouring fields over the same HST/ACS mosaic. This allowed us to identify a list of GC candidates and to inspect their properties using a background decontamination method. Relative to the four comparison fields, PGC 087327 shows a robust overdensity of GCs, $N_{GC}=82\pm9$. At the estimated magnitude of the galaxy, this number implies a specific frequency of $S_N=1.8\pm0.7$. In spite of the short wavelength interval available with the $g_{F475W}$ and $V_{F606W}$ passbands, the color distribution shows a clear bimodality with a blue peak at $\langle g_{F475W}{-}V_{F606W} \rangle =0.47\pm0.05$ mag and a red peak at $\langle g_{F475W}{-}V_{F606W}\rangle =0.62\pm0.03$ mag. We also observe the typical steeper slope of the radial distribution of red GCs relative to blue ones. Thanks to the unique depth of the available data, we characterize the GC luminosity function (GCLF) well beyond the expected GCLF turn-over. We find $g^{TOM}_{F475W} = 26.54\pm0.10$ mag and $V^{TOM}_{F606W} = 26.08 \pm 0.09$ mag, which after calibration yields a distance of $D_{GCLF} = 56.7 \pm 4.3(statistical) \pm 5.2(systematic)$ Mpc.

astro-ph.GA↗

arXiv2022

Multi Order Coverage data structure to plan multi-messenger observations

We describe the use of Multi Order Coverage (MOC) maps as a practical way to manage complex regions of the sky for the planning of multi-messenger observations. MOC maps are a data structure that provides a multi-resolution representation of irregularly shaped and fragmentary regions over the sky based on the HEALPix (Hierarchical Equal Area isoLatitude Pixelization) tessellation. We present a new application of MOC, in combination with the \texttt{astroplan} observation planning package, to enable the efficient computation of sky regions and the visibility of these regions from a specific location on the Earth at a particular time. Using the example of the low-latency gravitational-wave alerts, and a simulated observational campaign with three observatories, we show that the use of MOC maps allows a high level of interoperability to support observing schedule plans. Gravitational-wave detections have an associated credible region localization on the sky. We demonstrate that these localizations can be encoded as MOC maps, and how they can be used in visualisation tools, and processed (filtered, combined) and also their utility for access to Virtual Observatory services which can be queried 'by MOC' for data within the region of interest. The ease of generating the MOC maps and the fast access to data means that the whole system can be very efficient, so that any updates on the gravitational-wave sky localization can be quickly taken into account and the corresponding adjustments to observing schedule plans can be rapidly implemented. We provide example python code as a practical example of these methods. In addition, a video demonstration of the entire workflow is available.

astro-ph.IM↗

arXiv2021

Exceptionally bright optical emission from a rare and distant $γ-$ray burst

Long $\rm γ$-ray bursts (GRBs) are produced by the dissipation of ultra-relativistic jets launched by newly-born black holes after the collapse of massive stars. Right after the luminous and highly variable $γ$-ray emission, the multi-wavelength afterglow is released by the external dissipation of the jet in circumburst medium. We report the discovery of a very bright ($\rm \sim 10$ mag) optical emission $\rm \sim 28$ s after the explosion of the extremely luminous and energetic GRB 210619B located at redshift 1.937. Early multi-filter observations allowed us to witness the end of the shock wave propagation into the GRB ejecta. We observed the spectral transition from a bright reverse to the forward shock emission, demonstrating that the early and late GRB multi-wavelength emission is originated from a very narrow jet propagating into an unusually rarefied interstellar medium. We also find evidence of an additional component of radiation, coming from the jet wings which is able explain the uncorrelated optical/X-ray emission.

astro-ph.HE↗

arXiv2021

On the single-event-based identification of primordial black hole mergers at cosmological distances

The existence of primordial black holes (PBHs), which may form from the collapse of matter overdensities shortly after the Big Bang, is still under debate. Among the potential signatures of PBHs are gravitational waves (GWs) emitted from binary black hole (BBH) mergers at redshifts $z\gtrsim 30$, where the formation of astrophysical black holes is unlikely. Future ground-based GW detectors, Cosmic Explorer and Einstein Telescope, will be able to observe equal-mass BBH mergers with total mass of $\mathcal{O}(10-100)~M_{\odot}$ at such distances. In this work, we investigate whether the redshift measurement of a single BBH source can be precise enough to establish its primordial origin. We simulate BBHs of different masses, mass ratios and orbital orientations. We show that for BBHs with total masses between $20~M_{\odot}$ and $40~M_{\odot}$ merging at $z \geq 40$ one can infer $z>30$ at up to 97\% credibility, with a network of one Einstein Telescope, one 40-km Cosmic Explorer in the US and one 20-km Cosmic Explorer in Australia. A smaller network made of one Einstein Telescope and one 40-km Cosmic Explorer in the US measures $z>30$ at larger than 90\% credibility for roughly half of the sources than the larger network. We then assess the dependence of this result on the Bayesian redshift priors used for the analysis, specifically on the relative abundance of the BBH mergers originated from the first stars, and the primordial BBH mergers.

astro-ph.CO↗

arXiv2021

Spectral index-flux relation for investigating the origins of steep decay in $γ$-ray bursts

$γ$-ray bursts (GRBs) are short-lived transients releasing a large amount of energy ($10^{51}-10^{53} $ erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star's death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.

astro-ph.HE↗

arXiv2021

Electromagnetic Counterparts of Compact Binary Mergers

The first detection of a binary neutron star merger through gravitational waves and photons marked the dawn of multi-messenger astronomy with gravitational waves, and it greatly increased our insight in different fields of astrophysics and fundamental physics. However, many open questions on the physical process involved in a compact binary merger still remain and many of these processes concern plasma physics. With the second generation of gravitational wave interferometers approaching their design sensitivity, the new generation under design study, and new X-ray detectors under development, the high energy Universe will become more and more a unique laboratory for our understanding of plasma in extreme conditions. In this review, we discuss the main electromagnetic signals expected to follow the merger of two compact objects highlighting the main physical processes involved and some of the most important open problems in the field.

astro-ph.HE↗

arXiv2021

Multi-Messenger Astrophysics with THESEUS in the 2030s

Multi-messenger astrophysics is becoming a major avenue to explore the Universe, with the potential to span a vast range of redshifts. The growing synergies between different probes is opening new frontiers, which promise profound insights into several aspects of fundamental physics and cosmology. In this context, THESEUS will play a central role during the 2030s in detecting and localizing the electromagnetic counterparts of gravitational wave and neutrino sources that the unprecedented sensitivity of next generation detectors will discover at much higher rates than the present. Here, we review the most important target signals from multi-messenger sources that THESEUS will be able to detect and characterize, discussing detection rate expectations and scientific impact.

astro-ph.IM↗