84 research outputs found
Prospects for future observations of off-axis short gamma-ray burst jets associated with binary neutron star mergers
No full textIn this thesis work, I assess the short- and long-term prospects for the joint detection of BNSs and SGRBs with next-generation γ-ray and GW detectors. I combine the Structured Jet (SJ) model developed by Salafia et al. (2015b; 2019) for SGRB prompt emission with the analytical model by Finn and Chernoff (1993) for the GW signal from the BNS inspiral phase and estimate future GW-SGRB joint detection rates, using the SJ profile inferred for GRB 170817A (Ghirlanda et al., 2019) and assuming that all BNS mergers can in principle produce a SGRB. I show that, despite the strong assumptions and simplifications of the adopted model, it provides realistic and consistent estimates of the detection rates of SGRBs and GWs obtained with current facilities, the Fermi/GBM and Swift/Burst Alert Telescope γ-ray detectors and the aLIGO O3a GW interferometer. I also show that, if the SJ profile of GRB 170817A is a relatively common feature of SGRBs, then there is no realistic probability of another coincident detection in the era of aLIGO at design sensitivity (i.e., when it has reached the best achievable sensitivity, the project sensitivity) and SVOM-type detectors. In the CE era, the expected rate of coincident SGRB prompt emission and GW signal detections is ≈ 21-22 yr−1 and ≈ 53-55 yr−1 for SVOM-like and THESEUS-like detectors, respectively. I discuss future prospects for this model, showing how future SGRB-GW joint detection can help to solve the tension on the Hubble parameter estimation and to provide tighter constraints on the NS EoS
Detection probability of light compact binary mergers in future observing runs of the current ground-based gravitational wave detector network
No full textWith no binary neutron star (BNS) merger detected yet during the fourth observing run (O4) of the LIGO-Virgo-KAGRA (LVK) gravitational wave (GW) detector network, despite the time volume (VT) surveyed with respect to the end of O3 having increased by more than a factor of three, a pressing question is how likely the detection of at least one BNS merger is in the remainder of the run. I present here a simple and general method of addressing such a question, which constitutes the basis for the predictions that have been presented in the LVK Public Alerts User Guide during the hiatus between the O4a and O4b parts of the run. The method, which can be applied to neutron star–black hole (NSBH) mergers as well, is based on simple Poisson statistics and on an estimate of the ratio of the VT span by the future run to that span by previous runs. An attractive advantage of this method is that its predictions are independent of the mass distribution of the merging compact binaries, which is very uncertain at the present moment. The results, not surprisingly, show that the most likely outcome of the final part of O4 is the absence of any BNS merger detection. Still, the probability of a non-zero number of detections is 34−46%. For NSBH mergers, the probability of at least one additional detection is 64−71%. The prospects for the next observing run, O5, are more promising, with predicted numbers of , and NSBH detections of (median and 90% symmetric credible range), based on the current LVK detector target sensitivities for the run. The calculations presented here also lead to an update of the LVK local BNS merger rate density estimate that accounts for the absence of BNS merger detections in O4 so far, which reads 2.8 Gpc−3 yr−1 ≤ R0 ≤ 480 Gpc−3 yr−1
Erratum: Prospects for multimessenger detection of binary neutron star mergers in the fourth LIGO-Virgo-KAGRA observing run (Monthly Notices of the Royal Astronomical Society (2022) 513 (4159) DOI: 10.1093/mnras/stac1167)
No full textThere is a typo in equation (8) of Patricelli et al. (2022). The isotropic-equi v alent luminosity observed at a viewing angle θj is (Salafia et al. 2015, 2019): (Equation Presented). where the relativistic Doppler factor δ appears to the power of three. This modification does not affect any of the results presented in Patricelli et al. (2022), that were obtained using the correct formula (equation 1) and not the one written in equation (8) of Patricelli et al. (2022). ACKNOWLEDGEMENT We thank Om Sharan Salafia for pointing out the typo in our manuscript
The Structure of Gamma Ray Burst Jets
No full textDue to relativistic bulk motion, the structure and orientation of gamma-ray burst (GRB) jets have a fundamental role in determining how they appear. The recent discovery of the GW170817 binary neutron star merger and the associated GRB boosted the interest in the modeling and search for signatures of the presence of a (possibly quasi-universal) jet structure in long and short GRBs. In this review, following a pedagogical approach, we summarize the history of GRB jet structure research over the last two decades, from the inception of the idea of a universal jet structure to the current understanding of the complex processes that shape the structure, which involves the central engine that powers the jet and the interaction of the latter with the progenitor vestige. We put some emphasis on the observable imprints of jet structure on prompt and afterglow emission and on the luminosity function, favoring intuitive reasoning over technical explanations
Accretion-to-jet energy conversion efficiency in GW170817
No full textGamma-ray bursts (GRBs) are thought to be produced by short-lived, supercritical accretion onto a newborn compact object. Some process is believed to tap energy from the compact object, or the accretion disc, powering the launch of a relativistic jet. For the first time, we can construct independent estimates of the GRB jet energy and of the mass in the accretion disc in its central engine; this is thanks to gravitational wave observations of the GW170817 binary neutron star merger by the Laser Interferometer Gravitational wave Observatory (LIGO) and Virgo interferometers, as well as a global effort to monitor the afterglow of the associated short gamma-ray burst GRB 170817A on a long-term, high-cadence, multi-wavelength basis. In this work, we estimate the accretion-to-jet energy conversion efficiency in GW170817, that is, the ratio of the jet total energy to the accretion disc rest mass energy, and we compare this quantity with theoretical expectations from the Blandford-Znajek and neutrino-antineutrino annihilation () jet-launching mechanisms in binary neutron star mergers. Based on previously published multi-wavelength modelling of the GRB 170817A jet afterglow, we construct the posterior probability density distribution of the total energy in the bipolar jets launched by the GW170817 merger remnant. By applying a new numerical-relativity-informed fitting formula for the accretion disc mass, we construct the posterior probability density distribution of the GW170817 remnant disc mass. Combining the two, we estimate the accretion-to-jet energy conversion efficiency in this system, carefully accounting for uncertainties. The accretion-to-jet energy conversion efficiency in GW170817 is η ∼ 10−3, with an uncertainty of slightly less than two orders of magnitude. This low efficiency is in agreement with expectations from the mechanism, which therefore cannot be excluded by this measurement alone. The low efficiency also agrees with that anticipated for the Blandford-Znajek mechanism, provided that the magnetic field in the disc right after the merger is predominantly toroidal (which is expected as a result of the merger dynamics). This is the first estimate of the accretion-to-jet energy conversion efficiency in a GRB that combines independent estimates of the jet energy and accretion disc mass. Future applications of this method to a larger number of systems will reduce the uncertainties in the efficiency and reveal whether or not it is universal. This, in turn, will provide new insights into the jet-launching conditions in neutron star mergers
Multi-messenger prospects for black hole - neutron star mergers in the O4 and O5 runs
No full textThe existence of merging black hole-neutron star (BHNS) binaries has been
ascertained through the observation of their gravitational wave (GW) signals.
However, to date, no definitive electromagnetic (EM) emission has been
confidently associated with these mergers. Such an association could help
unravel crucial information on these systems, for example, their BH spin
distribution, the equation of state (EoS) of NS and the rate of heavy element
production. We model the multi-messenger (MM) emission from BHNS mergers
detectable during the fourth (O4) and fifth (O5) observing runs of the
LIGO-Virgo-KAGRA GW detector network, in order to provide detailed predictions
that can help enhance the effectiveness of observational efforts and extract
the highest possible scientific information from such remarkable events. Our
methodology is based on a population synthesis-approach, which includes the
modelling of the signal-to-noise ratio of the GW signal in the detectors, the
GW-inferred sky localization of the source, the kilonova (KN) optical and
near-infrared light curves, the relativistic jet gamma-ray burst (GRB) prompt
emission peak photon flux, and the GRB afterglow light curves in the radio,
optical and X-ray bands. The resulting prospects for BHNS MM detections during
O4 are not promising, with a GW detection rate of
yr, but joint MM rates of yr for the KN and yr for the jet-related emission. In O5 we find an overall
increase in expected detection rates by around an order of magnitude, owing to
both the enhanced sensitivity of the GW detector network, and the coming online
of future EM facilities. Finally, we discuss direct searches for the GRB radio
afterglow with large-field-of-view instruments as a new possible follow-up
strategy in the context of ever-dimming prospects for KN detection.Comment: Submitted to A&A. 17 pages, 11 figures, 2 tables. Comments are
welcome
Astrophysical and relativistic modeling of the recoiling black hole candidate in quasar 3C 186
No full textThe compact object in quasar 3C 186 is one of the most promising recoiling black hole candidates, exhibiting both an astrometric displacement between the quasar and the host galaxy as well as a spectroscopic shift between broad and narrow lines. 3C 186 also presents a radio jet that, when projected onto the plane of the sky, appears to be perpendicular to the quasar-galaxy displacement. Assuming a gravitational-wave kick is indeed responsible for the properties of 3C 186 and using state-of-the-art relativistic modeling, we show that current observations allow for exquisite modeling of the recoiling black hole. Most notably, we find that the kick velocity and the black hole spin are almost collinear with the line of sight and the two former vectors appear perpendicular to each other only because of a strong projection effect. The targeted configuration requires substantial fine-tuning: while there is a region in the black hole binary parameter space that is compatible with 3C 186, the observed system appears to be a rare occurrence. Using archival radio observations, we explored different strategies that could potentially confirm or rule out our interpretation. In particular, we developed two observational tests that rely on the brightness ratio between the approaching and receding jet as well as the asymmetry of the jet lobes. While the available radio data provide loose constraints, deeper observations have the unique potential of unveiling the nature of 3C 186
Jet-driven and jet-less fireballs from compact binary mergers
No full textDuring a compact binary merger involving at least one neutron star (NS), a small fraction of the gravitational energy could be liberated in such a way to accelerate a small fraction (∼10-6) of the NS mass in an isotropic or quasi-isotropic way. In presence of certain conditions, a pair-loaded fireball can form, which undergoes accelerated expansion reaching relativistic velocities. As in the standard fireball scenario, internal energy is partly transformed into kinetic energy. At the photospheric radius, the internal radiation can escape, giving rise to a pulse that lasts for a time equal to the delay time since the merger. The subsequent interaction with the interstellar medium can then convert part of the remaining kinetic energy back into radiation in a weak isotropic afterglow at all wavelengths. This scenario does not require the presence of a jet: the associated isotropic prompt and afterglow emission should be visible for all NS-NS and BH-NS mergers within 90 Mpc, independent of their inclination. The prompt emission is similar to that expected from an off-axis jet, either structured or much slower than usually assumed (Γ ∼ 10), or from the jet cocoon. The predicted afterglow emission properties can discriminate among these scenarios
Proton–synchrotron as the radiation mechanism of the prompt emission of gamma-ray bursts?
No full textWe discuss the new surprising observational results that indicate quite convincingly that the prompt emission of gamma-ray bursts (GRBs) is due to synchrotron radiation produced by a particle distribution that has a low-energy cut-off. The evidence of this is provided by the low-energy part of the spectrum of the prompt emission, which shows the characteristic Fν ∝ ν1/3 shape followed by Fν ∝ ν−1/2 up to the peak frequency. This implies that although the emitting particles are in fast cooling, they do not cool completely. This poses a severe challenge to the basic ideas about how and where the emission is produced, because the incomplete cooling requires a small value of the magnetic field to limit synchrotron cooling, and a large emitting region to limit the self-Compton cooling, even considering Klein–Nishina scattering effects. Some new and fundamental ingredient is required for understanding the GRBs prompt emission. We propose proton–synchrotron as a promising mechanism to solve the incomplete cooling puzzle
Gamma-ray burst jet propagation, development of angular structure, and the luminosity function
No full textThe fate and observable properties of gamma-ray burst jets crucially depend on their interaction with the progenitor material that surrounds the central engine. We present a semi-analytical model of this interaction (which builds upon several previous analytical and numerical works) aimed at predicting the angular distribution of jet and cocoon energy and Lorentz factor after breakout given the properties of the ambient material and of the jet at launch. Using this model, we constructed synthetic populations of structured jets, assuming either a collapsar (for long gamma-ray bursts – LGRBs) or a binary neutron star merger (for short gamma-ray bursts – SGRBs) as progenitor. We assumed all progenitors to be identical, and we allowed little variability in the jet properties at launch: our populations therefore feature a quasi-universal structure. These populations are able to reproduce the main features of the observed LGRB and SGRB luminosity functions, although several uncertainties and caveats have yet to be addressed. We make our simulated populations publicly available
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