Letters of Intent received in 2016

LoI 2018-1923
GA Symposium: Transients across and beyond the electromagnetic spectrum

Topics

- Transient surveys and facilities
- Gamma-ray bursts across the physical scale
- Supernovae: are the old classes still valid?
- Tidal disruption events
- Non-electromagnetic observations: Gravitational wave and neutrino sources
- Fast radio bursts: what are they?
- Cross-disciplinary efforts in transient naming, observations and data storage
- Models and theories of transient sources
- Hosts and environments of transients
- Computational efforts and challenges

Rationale

Transient astronomical sources have been a hot topic for decades, and now enter a golden era of discovery. In recent years all-sky surveys in different wavelengths have detected new types of transients and new facilities have expanded our knowledge even beyond the electromagnetic spectrum. The immediate future will see a range of new surveys such as ZTF, Gaia transients, BlackGEM and LSST in the optical, MeerKAT, SKA and LOFAR at low frequencies and eROSITA in the X-rays. Cross-matches and follow-up of transients detected in one survey by facilities in other wavelengths and non-electromagnetic detectors is being coordinated to some extent but have to be improved in order to study these sources in the best possible way. Likewise, naming conventions are very different across fields and storage of reduced data is still pursued on an individual basis. It is therefore timely to bring together the different transient communities to shed light on the physical nature of those events including all possible information and at the same time coordinate naming, alerts, follow-up campaigns and data accessibility across the entire community.

The longest known transients apart from novae and variable stars are supernovae (SNe). For some types we have detected their progenitors but other types are still a mystery. New surveys and observations have revealed a lot of new classes and the picture of SN classes is becoming ever more complex. This should let us start to reflect whether the "old" classes are still valid or whether we should find new definitions. Gamma-ray bursts (GRBs) have been detected in the 60ies but their afterglows have only been found 20 years ago. Long GRBs are connected to massive stars and hence supernovae while short GRBs, being the merger of two compact objects should actually be sources of gravitational waves (GWs). Tidal disruption events (TDEs) are a recent addition to the transient class but the distinction between GRB, SN or TDE is sometimes difficult to make. And most recently, fast-radio bursts (FRBs), brief radio pulses that so far do not have any counterpart in other wavelengths, are still a mystery in the field. Any of these events can or could be sources of non-electromagnetic signals such as GWs and neutrinos.

Despite ample observations, we will not decipher many of the physical properties of transient sources without the help of theoretical modelling. Recent 3D models of various explosive transients are starting to unravel the processes going on during the event. Particularly important is the production of observable outputs from these models that we can directly verify (or falsify) with observations. Another important aspect is the study of the environments and/or hosts of these transients, as they can give us additional information on the nature of these transients. This is a two-sided coin: as our understanding of transients improves we can use them as probes of their environments, analytically or with theoretical models. For example, GRB can be used to study galaxies out to the very early times of the Universe, the rate of core collapse SNe can be a proxy for star formation, and SNeIa are effective as tracers of old, low surface brightness stellar populations such as intra-cluster stars.

A central part of the proposed symposium will be a common discussion on the most urgent issues in today's transient community: How do we name the different transients in a consistent way? How do we make sure detections in different physical regimes are properly connected? What can we do to improve follow-up to report transients more rapidly and widely in order not to miss observing opportunities? Which follow-up facilities are most needed and how could we get or get access to those? Where do we store the final data so that everyone has access? The community has only just taken it's first steps to resolve some of these issues, with new public data servers coming online such as the IAU Transient Name Server. By the time of the 2018 GA we will have ~2 years of preliminary metadata on community usage to assess which initiatives are working and why, and plan for the future data explosion.

Our idea with this symposium is to bring together observers and theorists from all areas of the transient community focusing on non-repetitive transient sources: GRBs, SNe, FRBs, TDEs, GWs and whatever new transient class might have been discovered until the start of the next GA. The program will be centered on the common discussion on transient naming, follow-up and data storage. We are aware that a symposium dedicated only to Gamma-ray bursts is being proposed and another one on GWs. In the following months we will discuss how to best accommodate the different communities and topics and how to coordinate the different meeting proposals. The crucial focus of our proposal is to bring these communities in the 2018 GA, as reflected in our SOC, composed of observers and theorists from the various communities, as well as being a geographical and gender balanced group.

The following people have agreed to serve as SOC members of the proposed symposium: Rubina Kotak (Queens Univ. Belfast, UK), Joseph Anderson (ESO, Chile), Vicky Kaspi (McGill Univ., Canada), Keiichi Maeda (Kyoto Univ., Japan), Ariel Goobar (Oskar Klein Centre, Sweden), Samaya Nissanke (Radboud University Nijmegen, NL), Leo Singer (NASA; US), Melissa Graham (Univ. of Washington, US)