The Transient Universe Waiting in the Sky 2021
Scientific Program
Thursday 25 November 2021
Chairs: Gerardo Urrutia and Leonardo García
Other transients:
9:00/16:00 Fink: bringing the transient sky into the Rubin Observatory era (20+5) Julien Peloton
The Legacy Survey of Space and Time (LSST), using the Vera Rubin Observatory LSST Camera at the Simonyi Survey Telescope, aims to survey the southern sky deeper and faster than any wide-field survey to date. Starting in 2024, and for its 10 years of operations, LSST will enable the discovery of an unprecedented large number of astrophysical transients, opening a new era of optical big data in astronomy. Among several challenges, the alert rate forecast for LSST will be at least one to two orders of magnitude larger than any survey to date and it will trigger on typically fainter objects, making it impossible for currently available systems to operate efficiently. In addition, the next decade will see detectors more sensitive to gravitational waves and neutrinos, and new instruments will allow a thorough search of a large part of the sky and a large part of the electromagnetic spectrum, paving the way for multi-messenger astronomy at scale. ​​Fink is an LSST community broker specifically developed to address all these challenges (https://fink-broker.org). Designed for fast and efficient analysis of big data, Fink encompasses historical developments and adds state-of-the-art machine learning techniques to generate classification scores for a variety of time-domain phenomena. I will describe the current high-level scientific platform, the current scientific results on the ZTF data stream, and the future scientific opportunities for LSST.
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The coincidental detection of the gravitational wave event GW 170817 and the gamma-ray burst GRB 170817A marked the advent of multi-messenger astronomy and represented a milestone in the study of GRBs. Significant progress in this field is expected in the coming years with the increased sensitivity of gravitational waves detectors and the launch of new facilities for the high-energy survey of the sky. In this context, the launch of SVOM in mid-2022, with its two wide-field high-energy instruments ECLAIRs and GRM, will foster the possibilities of coincidental transient detection with gravitational waves and gamma-rays events. The purpose of this talk is to assess the ability of SVOM/ECLAIRs to detect and quickly characterize high-energy transients in the local Universe (z ≤ 0.3), and to discuss the contribution of this instrument to multi-messenger astronomy and to gamma-ray burst (GRB) astrophysics in the 2020's. A list of local HE transients, along with their main characteristics, is constructed through an extensive literature survey. This list includes 41 transients: 24 long GRBs, 10 short GRBs and 7 SGR Giant Flares. The detectability of these transients with ECLAIRs is assessed with detailed simulations using tools developed for the SVOM mission, including a GEANT4 simulation of the energy response and a simulated trigger algorithm representative of the onboard trigger algorithm. SVOM/ECLAIRs would have been able to detect 88% of the short high-energy transients in our list: 22 out of 24 long GRBs, 8 out of 10 short GRBs and 6 out of 7 SGR Giant Flares. The SNR for almost all detections will be sufficiently high to allow the on-board ECLAIRs trigger algorithm to derive the localisation of the transient, transmitting it to the SVOM satellite and ground-based instruments. Coupled with the anti-solar pointing strategy of SVOM, this will enable an optimal follow-up of the events, allowing the observation of their afterglows, supernovae/kilonovae counterparts, and host galaxies. We conclude with a discussion of the unique contribution expected from SVOM and of the possibility of simultaneous GW detection for each type of transient in our sample.
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9:50/16:50 Changing Look Quasars and SVOM (10+5) Michel Dennefeld
AGN's changing state between type 1 and type 2 pose a challenge to the standard Unified Model. I will present new cases from GAIA Alerts and show how combined observations from the ground (spectroscopy first, plus possibly complementary photometry with Colibri), and space (X-rays with SVOM), together with SED modelling (specialty of UNAM) would help understand what is going on in the central regions of these active galaxies.
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10:10/17:10 GRB/HN and GW events from HMXBs that avoid CE Mergers (15+5) Enrique Moreno
I will explain a novel mechanism which explains the large BH spins observed in local HMXBs and how these binaries are likely sources of future GRB/HN events. If these binaries survive the formation of such events, they will also be candidates for BH-BH mergers in GW events similar to those detected by the LVK collaboration. A formation mechanism for BH-BH mergers in the PISN mass gap may be discussed as well.
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10:30/17:30 BREAK
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10:40/17:40 Jets in CEs: a low mass main sequence star in a red giant (15+5) Diego López Cámara
During the common envelope (CE) phase the less massive star of the binary stellar system is engulfed by the envelope of the most massive star. Also, the less massive star may accrete material hypercritically and launch a jet. In this talk, by a set of 3D hydrodynamic simulations, I will show the effects and importance that a jet launched from a main sequence (MS) star in the CE of a red giant (RG) has. Three characteristic moments (a. when the MS is grazing the RG, b. when the MS star starts plunging in the envelope of the RG, and c. when the plunge-in ends), as well as jets with different nature (self-regulated or constantly powered), are studied.
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GRBs 1:
One of the closest and least powerful bursts, GRB 190829A, was detected during the afterglow phase in very-high energies using the High Energy Stereoscopic System (H.E.S.S.). Spectral and temporal analyses during the entire observation exhibited strong similarities to the X-ray observations collected by the Swift X-ray Telescope (XRT), which challenges GRB fireball models. Based on the external forward-shock scenario in stellar-wind and constant-density medium, we present a radiative analytical model of the synchrotron and synchrotron self-Compton (SSC) processes considering an electron energy distribution with a power-law index of 1< p <2 and 2≤p. Taking into account the evolution of the spectral breaks of synchrotron and SSC fluxes and the cooling conditions, we derive the closure relations as a function of the radiative parameter and the spectral indexp. We model H.E.S.S. and Swift-XRT observations with the SSC and synchrotron afterglow model, respectively, in stellar-wind and constant-density medium. We show that although these observations satisfy the closure relations for a hard spectral index of p~2 and the radiative parameter in the range of 0.1 - 0.3, the afterglow model with a constant-density medium is favored.
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11:20/18:20 The large landscape of supernova, GRB and cocoon interactions (15+5) Fabio De Colle
Long gamma ray bursts (LGRBs) are associated to the collapse of a massive star and the formation of a relativistic jet. As the jet propagates through the star, it forms an extended, hot cocoon. The dynamical evolution of the jet/cocoon system and its interaction with
the environment has been studied extensively both analytically and numerically. On the other hand, the role played by the supernova (SN) explosion associated with LGRBs in determining the outcome of the system has been barely considered. In this talk, I will discuss the large landscape of outcomes resulting from the interaction of the SN, jet and cocoon. I will show that the outcome depends mainly on three timescales: the times for the cocoon and supernova shock wave to break through the surface of the progenitor star, and the time needed for the cocoon to engulf completely the progenitor star. The delay between the launch of the SN shock moving through the progenitor star and the jet can be related to these three timescales. Depending on the ordering of these time scales, the jet-cocoon might propagate inside the SN ejecta or the
other way around, and the outcome for the properties of the explosion would be different. I will discuss the imprint of the complex interaction between the jet-cocoon and the supernova shock on the emergent thermal and non-thermal radiation.
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11:40/18:40 The OHP MISTRAL spectro-imager for transients (15+5) Christophe Adami
We propose to present the OHP newly-operated MISTRAL spectro-imager. Designed to propose a rapid response to any kind of transients under a ToO format, it is mounted on the Observatoire de Haute Provence 2m-class telescope and is proposed to the astronomical community since September 2021. Also able to work under classical visitor mode, it will be open in ToO mode in March 2022.
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