Astronomical News DOI: 10.18727/0722-6691/5079

Report on the ESO Workshop Planning ESO Observations of Future Gravitational Wave Events

held at ESO Headquarters, Garching, Germany, 31 January–1 February 2018

Bruno Leibundgut 1 gamma-ray burst (GRB170817A) two events. The programmatic aspects of Ferdinando Patat 1 ­seconds later, the search for an optical/ ESO observations were also exhaustively infrared counterpart was on. Within a explored.1 few hours, an optical counterpart was 1 ESO detected in the galaxy NGC 4993. Spec- The first session was focused on troscopic follow-up observations began GW170817 observations. The gravita- immediately, resulting in a detailed record tional wave signal was presented Understanding the nature and results of the evolution of the event over the fol- and compared to that from black hole of black hole and neutron star mergers lowing two weeks. mergers by Sarah Antier (Laboratoire de has become a hot topic in astrophysics. l’Accélérateur Linéaire Orsay), followed The combination of gravitational wave ESO and ESA telescopes and instru- by a description of the event as seen and electromagnetic observations of ments participated in this global observ- at optical and near-infrared wavelengths GW170817/GRB 170817A has triggered ing campaign. Parts of the community (Stephen Smartt, Queen’s University new and exciting science projects. The focused on the search of the optical ­Belfast), in X-rays (Maria Grazia Bernardini, timeline for observations of gravitational counterpart with ESO’s Visible and Infra- Laboratoire Univers­ et Particules de wave events lies between seconds and red Survey Telescope for Astronomy Montpellier) and in gamma rays (Roland days, and coordinated observations (VISTA) and the VLT Survey Telescope Diehl, Max Planck Institute for Extrater- of electromagnetic radiation are critical (VST), but as soon as the GRB detected restrial Physics [MPE] in Garching). when probing the nature of these events. by the ESA INTErnational Gamma-Ray The great success of the observations Astrophysics Laboratory (INTEGRAL) Marina Rejkuba (ESO) reported on the of GW170817/GRB 170817A from more ­satellite and its optical counterpart had ESO observations and the activities than 50 observatories has highlighted been identified, the event was followed up ­associated with the release of the data the importance of coordination between using several spectrographs and imagers. to the community. Optical observations different instruments and facilities. This of GW170817 could only be conducted two-day workshop focused on what has for a couple of hours before the object been learned from ESO observations of Workshop goals set each evening in Chile, with several GW170817/GRB 170817A, and discussed instruments being used simultaneously strategies for coordinating observations The goal of the workshop was to bring on the VLT. The ESA satellites INTEGRAL of future events. the community together to discuss the and X-ray Multi-Mirror satellite (XMM- best way to obtain ESO observations of Newton) also participated in the observ- future gravitational wave events. Despite ing campaign, and Peter Kretschmar­ Background the speed with which the workshop was (European Space Agency, ESA) gave organised — it was announced in the an account of the activities required at The first detection of an electromagnetic ESO Science Newsletter on 20 December the operations centres in order to obtain counterpart of a gravitational wave event 2017 — 55 participants had registered these data at short notice. had a historic dimension, as it connected by the deadline in early January. two seemingly separate “universes”. Since it is still very early days for the ­Several mergers of black holes had been The speaker list was partially defined ­electromagnetic observation of gravita- observed prior to that, indicating black through the Principal Investigators (PIs) tional wave events, Anders Jerkstrand holes of several tens of solar masses; this of exisiting proposals. Eight of the 26 (Max Planck Institute for Astrophysics, presented a puzzle, as black holes of speakers were female (corresponding to Garching) gave a theorist’s view of what these sizes had not previously been antici- 31%), which reflected the gender distribu- we should expect and how to make pated. The detection of gravitational tion amongst the registered participants sense of the observations of GW170817. waves — a technical feat requiring meas- (29% female). The first day of the pro- He gave a comprehensive overview of urements of strains of a few times 10–20 gramme was dedicated to assessing the what the signatures of the r-process ele- — in 2015 was epochal, and was recog- status of the gravitational wave detec- ments would look like in the optical and nised with the Nobel Prize in Physics in tions and their follow-up observations, near-infrared spectral sequences, and 2017. While black hole mergers are not in particular for GW170817; while the sec- outlined where we still have significant expected to carry an electromagnetic ond day focused on the planning and gaps in our interpretation of the spectra. ­signal, theoretical modelling predicted that coordination of future observations. Each There remains plenty of room for future the merger of two neutron stars would day finished with an extensive discussion observations to clarify the many questions lead to short gamma-ray bursts (GRBs), session. On 31 January, the past and and uncertainties we still have in respect and would potentially be site of the current ESO observations of (fast) tran- of these events. The session ended with ­formation of heavy elements through sients were discussed, and potential a presentation by Nial Tanvir (University the r-process. ­lessons for future observations debated. of Leicester) on his experience of ESO The afternoon of 1 February was entirely observations of fast transient phenomena, When, on 17 August 2017, an unusal devoted to a community discussion of focusing on gamma-ray bursts. Target gravitational event (GW170817) was the best strategies for future electromag- of Opportunity observations have been observed that coincided with a short netic observations of gravitational wave offered at the VLT since the beginning of

The Messenger 172 – June 2018 33 Astronomical News Leibundgut B. & Patat F., Report on the Workshop “Planning Future GW Observations”

operations, with the addition of refine- The discussion session covered past mean a serious interruption to the ments such as the rapid response mode ESO observations, and aimed to identify uploaded schedule, requiring the corre- about 10 years ago. This frank presenta- what worked and where difficulties were sponding recovery of the schedule time- tion was an excellent basis for a discus- encountered. The panel members were line afterwards. There may also be point- sion on how ESO operations could help ­Stefano Covino, Marina Rejkuba, Steven ing constraints for satellites which need to secure critical data for similar events in Smartt and Nial Tanvir. The open discus- to be evaluated before schedule interrup- the future. sion yielded some interesting comments, tions. Aitor Ibarra (ESA) and Richard and comparisons were made with the ­Saxton (ESA) set out a new tool for the The afternoon session was reserved for experience of using ESO telescopes for improved coordination of observations presentations of ongoing projects dedi- observations of gamma-ray bursts. It and information sharing. cated to the follow-up of transient events. was concluded that overall ESO provided ESO is supporting several such pro- valuable — and sometimes unique — The afternoon was devoted to a discus- grammes, either with its own telescopes resources that can be essential, providing sion centred on the optimal planning of or by hosting dedicated experiments at insights in areas where theoretical predic- future observations, including the best its sites. These include the following tions are lacking. Recommendations possible coordination of ESO telescopes ­projects: the public survey called VIsta were made to strengthen the communi- and instruments. Ferdinando Patat, Enzo Near-infraRed Observations Unveiling cations between various observatories Brocato, Peter Jonker and Erik Kuulkers Gravitational wave Events (VINROUGE), and facilities in order to avoid duplication were the panel members, and a lively which uses VISTA to obtain infrared and to increase synergies. discussion ensued between the panel light curves (Andrew Levan, University and the audience. Several important of Warwick);­ the extended Public ESO The second day of the workshop con- points were raised, among them the wish Spectroscopic Survey of Transient centrated on the planning of future that ESO accept Large Programmes Objects (ePESSTO), which uses the ESO observations. The schedule of science with Target of Opportunity observations. Faint Object Spectrograph and Camera 2 observations with the Laser Interfer­ Additionally ESO was asked to provide (EFOSC2) at the New Technology Tele- ometer Gravitational-wave Observatory rapid delivery of pre-reduced data so that scope (NTT) to ­provide optical spectros- (LIGO)-Virgo collaboration was presented quick assessments and scientific deci- copy (Maria Teresa Botticella, INAF–­ by Marica Branchesi (Gran Sasso Science sions can be made, potentially to then Osservatorio di Capodimonte); the Rapid Institute). The next science run is planned interactively modify observation blocks Eye Mount telescope­ (REM) at La Silla, to start in October 2018 and is scheduled for follow-up observations. ESO will have which is part of a larger collaboration set to last for approximately one year. The to investigate which of these requests up to follow the optical counterparts of principal investigators of the current ESO can be implemented operationally. As a gravitational wave events (Eliana Palazzi, programmes to search for and follow first step, Target of Opportunity Large INAF–IASF Bologna); and the Gamma- up electromagnetic signals from gravita- Programmes were accepted again for Ray burst Optical/Near-infrared Detector tional wave events then presented their ESO Period 102 (from October 2018 to (GROND) instrument on the Max-Planck- plans for the next semester. Elena Pian March 2019). An important discussion Gesellschaft/ESO 2.2-metre telescope (INAF–IASF Bologna) and Paolo D’Avanzo point was whether the (European) com- at La Silla, which obtains photometry in (INAF–Osservatorio Astronomico di Brera) munity could agree to submitting a single seven filters simultaneously (Janet Chen, presented their VLT proposals. A proposal ESO proposal for observations of future MPE Garching). to obtain spectropolarimetry of such gravitational wave events. As a result of events was detailed by Stefano Covino this discussion one single Period 102 A new project that is just starting opera- (INAF–Osservatorio Astronomico di proposal was submitted before the dead- tions is the Gravitational-wave Optical Brera). Aniello Grado (INAF–Osservatorio line of 28 March 2018. ESO was also Transient Observer (GOTO), which was Capodimonte) then presented two ongo- invited to attend the LIGO–Virgo town hall described by Danny Steeghs (University ing programmes with the VST. meeting in April 2018 in Amsterdam, of Warwick). In addition, the long-running where these discussions will continue. Télescopes à Action Rapide pour les A special session on the observing Objets Transitoires (TAROT) project was opportunities with ESA satellites followed. presented by Michel Boer (Centre National The capabilities of INTEGRAL, and in Acknowledgements de la Recherche Scientifique, CNRS). particular its operational constraints, We thank Svea Teupke for providing logistical sup- Future facilities to detect and characterise were introduced by Erik Kuulkers (ESA), port at very short notice. We would also like to thank the electromagnetic counterparts of followed by a presentation on XMM-­ all of the speakers for providing the slides ahead ­gravitational wave events are: BlackGEM, Newton by Norbert Schartel (ESA). Jan- of their presentations so that a seeing-impaired to be installed at La Silla (Paul Groot, Uni- Uwe Ness (ESA) described some pro- ­colleague could follow them on his own laptop. versity of Nijmegen); the Son Of X-Shooter grammatic aspects of the planning and (SOXS), to be installed on the NTT in 2020 coor­dination of space-based observa- Links (Sergio Campana, INAF–Osservatorio tions. The INTEGRAL and XMM-Newton 1 Astronomico di Brera); and the Zwicky schedules are built well in advance of Workshop programme: http://www.eso.org/sci/ meetings/2018/gw2018.html Transient Facility in California (Ulrich he observations and the rapid observa- Feindt, Oskar Klein Centre Stockholm). tion of an unexpected transient may

34 The Messenger 172 – June 2018