# The Physics of Extreme-Gravity Stars

Europe/Stockholm
122:026 (Nordita, Stockholm)

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Description

### Venue

Nordita, Stockholm, Sweden

### Scope

Massive stars, almost always found in pairs, evolve and end their lives as extreme-gravity compact objects - white dwarfs, neutron stars and black holes. Binary stellar interactions and gravitational radiation drive these two objects together resulting in their mergers. Such mergers are widely accepted to give rise to a host of the most energetic transient events known in the Universe. For instance, supernova Ia are thermonuclear explosions that map out the acceleration of the expanding Universe, short gamma-ray bursts are cosmic lighthouses powered by relativistic jets, and neutron-star binary mergers could be responsible for producing most of the rare-earth elements in our Universe. Excitingly a suite of newly upgraded instruments have detected gravitational radiation in the past year (e.g., LIGO) or are poised to detect high-energy neutrinos (e.g., Antares, Icecube) from these compact object mergers. These measurements are providing key insights into the fundamental characteristics of the compact objects, such as their masses and intrinsic spins, and the complex physics driving their mergers, jets and accretion. Furthermore, new optical and radio facilities are able to measure these transients in ways that were not possible before and provide complementary information on their environments. However to date, our uncertainties in binary stellar evolution and compact object formation result in production rates of compact object mergers that vary by several orders of magnitude. By critically assessing binary stellar interactions and evolution, this program will bring together theorists, computational astrophysicists, observers, and instrumentalists for a period of four weeks. Our aim is to systematically connect the binary progenitors through the complex merger physics to the myriad of observed and predicted cosmic transient events. This multidisciplinary program is urgent since the maximum scientific return of these new observatories and instruments will rely on the program's deliverables. The timeliness of the program is further underlined as instruments, such as LIGO and Virgo, will constrain the rates of compact object mergers within the next five years.

#### Registration deadline: 01 March 2017

Timetable

Slides from Conference Talks

### Format

The workshop will focus on the outcomes of white dwarf/neutron star/black hole binaries and the physics driving them:

 Week 1 (June 5-9th): White dwarf-white dwarf binaries Week 2 (June 12-16th): Neutron star-neutron star, neutron star-black hole and black hole-black hole systems Week 3 (June 19-22nd): CONFERENCE on compact object mergers Week 4 (June 26-30th): White dwarf-black hole and white dwarf-neutron star systems

• Monday, June 5
• 1
Meet and Greet 122:026

### 122:026

#### Nordita, Stockholm

• Tuesday, June 6
• 2
SWEDEN NATIONAL DAY 122:026

### 122:026

#### Nordita, Stockholm

• Wednesday, June 7
• 3
White dwarf mergers their diverse outcomes: observations and theory (Led by Marten Van Kerkwijk, Toronto) 122:026

### 122:026

#### Nordita, Stockholm

• 4
Astro-ph discussion (Led by Axel Widmark, Stockholm) 122:026

### 122:026

#### Nordita, Stockholm

• 5
Formation of White Dwarf Binaries (Led by Natasha Ivanova, Alberta) 122:026

### 122:026

#### Nordita, Stockholm

• Thursday, June 8
• 6
Populations and rates of double white dwarf binaries (Led by Silvia Toonen, Amsterdam) 122:026

### 122:026

#### Nordita, Stockholm

Led by Silvia Toonen (Amsterdam)
• 7
Astro-ph discussion (Led by Marten Van Kerkwijk and Epson Heringer) 122:026

### 122:026

#### Nordita, Stockholm

• 8
Gravitational wave and Electromagnetic observations with LISA, GAIA and LSST (Led by Elena Rossi, Leiden) 122:026

### 122:026

#### Nordita, Stockholm

Led by Elena Rossi (Leiden)
• Friday, June 9
• 9
Sub-types of Supernova Ia and their delay times (Led by Epson Heringer, Toronto) 122:026

### 122:026

#### Nordita, Stockholm

• 10
Astro-ph discussion (Led by Mattia Bulla, Stockholm) 122:026

### 122:026

#### Nordita, Stockholm

Led by Mattia Bulla (Stockholm)
• Monday, June 12
• 11
Meet and Greet FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• 12
Core collapse supernova, formation of neutron stars and neutron star kicks (led by Evan O'Connor and John Bray) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• Tuesday, June 13
• 13
Electromagnetic counterparts: theory and simulations (led by Kenta Hotokezaka, Koutarou Kyutoku, David Tsang) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• 14
Binary Black Hole Observations by LIGO (Led by Patricia Schmidt, Geraint Pratten, Carl-Johan Haster, Aaron Zimmerman) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• Wednesday, June 14
• 15
Fundamental Physics with Gravitational Waves and Binary Black Holes (led by Thomas Sotiriou and David Nichols) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• 16
Formation of Binary Black Holes (led by Felix Mirabel and Philipp Podsiadlowski) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• Thursday, June 15
• 17
Dynamical formation of Binary Black Holes and ULXs (led by Jay Strader) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• 18
EM follow-up of Neutron Star Binary and Binary Black Hole Mergers (led by Masaomi Tanaka and Assaf Horesh) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• Friday, June 16
• 19
Short gamma ray bursts and neutron star binary mergers: observations and theory (led by Andrew Levan, Asaf Pe'er and Gavin Lamb) FB52 of the OKC/AlbaNova

### FB52 of the OKC/AlbaNova

#### Nordita, Stockholm

• 20
Discussion on Eddington limit, thermal timescale accretion, and ULXs (led by Pavel Abolmasov) 122:026

### 122:026

#### Nordita, Stockholm

• Monday, June 19
• 21
Welcome FD5

### FD5

#### Nordita, Stockholm

• Binary Evolution (and X-ray binaries) FD5

### FD5

#### Nordita, Stockholm

• 22
Formation of Binary Black Hole mergers FD5

### FD5

#### Nordita, Stockholm

• 23
Formation of Double Neutron Stars FD5

### FD5

#### Nordita, Stockholm

In recent years, the discovery rate of double neutron star (DNS) systems has increased rapidly and the coming decade will greatly enhance the number of both radio pulsar DNS systems, with the completion of the Square-Kilometre-Array, and DNS mergers from detections of high-frequency gravitational waves using LIGO. This calls for a new investigation of the formation and evolution of DNS systems. In this talk, I will summarise the exotic journey of binary stars leading to the production of DNS systems and discuss all their key parameters. This includes correlations between spin period (of the first-formed, mildly recycled NS), orbital period and eccentricity, based on theoretical modelling. I discuss NS masses and the anticipated recorded mass spectrum from near future LIGO/VIRGO detections of DNS mergers. Finally, I will discuss NS kicks (magnitude and direction) with a surprising result and present a large set of Monte Carlo simulations of the second SN in order to extrapolate the pre-SN stellar properties and probe the explosions of these ultra-stripped SNe.
Speaker: Thomas Tauris
• 24
Black Hole X-ray Binaries in Milky Way Globular Clusters FD5

### FD5

#### Nordita, Stockholm

I will highlight results from our ongoing survey using deep radio continuum and X-ray data to search for accreting black holes in Milky Way globular clusters, presenting evidence that black holes may indeed be common in globular clusters.
• 25
Supernovae: The conservation of momentum kick' revisited FD5

### FD5

#### Nordita, Stockholm

The idea that neutron stars (and possibly black holes) could get their peculiar spacial velocities from conservation of momentum between the ejected material and the compact remnant mass has been around for many years. We investigate this concept using the BPASS v2 stellar evolution models and our own compact remnant population synthesis code. We present some of the predicted neutron star and black hole population sets using this kick' and compare them to the observational data.
Speaker: John Bray
• 10:30 AM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 26
Common envelope and compact binaries formation FD5

### FD5

#### Nordita, Stockholm

Common-envelope events are fate-defining episodes in the lives of close binary systems. During a common envelope event, two stars temporarily orbit within a shared envelope, and the episode ends with an exciting outburst, leaving behind either a significantly shrunk binary, or a single merged star. I will review what is new about what we know the common envelope physics: when does a common envelope start, how does it proceed, what marks its end, and what are the new theoretical constraints for double white dwarf and double black hole binaries formation.
Speaker: Natasha Ivanova
• 27
Shedding light on the black hole mass spectrum FD5

### FD5

#### Nordita, Stockholm

After the recent discovery of the first binary black hole mergers, the scientfic community is drawing growing attention to the study of the formation and the coalescence of compact object binary systems. Modeling the formation and the dynamical evolution of such fascinating systems is fundamental to interpret the forthcoming gravitational-wave detections and to make predictions on the nature of the merging progenitors. Still, our knowledge of the link between progenitor stars and their compact remnants is hampered by the uncertainties we have on stellar evolution processes (e.g. stars' mass-loss through stellar winds) and on the supernova explosion mechanism. In this talk, I present the mass spectrum of compact remnants I obtained using the new population synthesis code SEVN, considering up-to-date stellar evolution models and up-to-date prescriptions to model the supernova explosion. In particular, I discuss the occurrence of pulsational pair-instability supernovae and their effect on the compact remnant mass spectrum. I also discuss the implications of our predictions for the expected number of compact objects and for the merger rates of compact object binaries in several astrophysical systems, as a function of metallicity.
Speaker: Mario Spera
• 28
Formation and evolution of supergiant High Mass X-ray Binaries FD5

### FD5

#### Nordita, Stockholm

A previously unknown population of High-Mass X-ray Binaries (HMXB) hosting supergiant stars has been revealed during the last years, with multi-wavelength campaigns including high energy (INTEGRAL, Swift, XMM, Chandra) and optical/infrared (mainly ESO) observations, including interferometric VLT observations. This population is constituted of obscured supergiant HMXB, and some, so-called supergiant fast X-ray transients (SFXTs), exhibit short and intense X-ray flares. I will describe the observations of these HMXB, how they can constrain the accretion models (e.g. clumpy winds, transitory accretion disc, magneto-centrifugal barrier, etc), discuss their formation and evolution, compare the observations to results from population synthesis models, and finally attempt to propose a scenario to explain the properties of these high-energy sources. Because these HMXB are the likely progenitors of Luminous Blue Variables (LBVs), and also related to compact object mergers and emission of gravitational waves, the knowledge of their formation and evolution is of prime importance.
Speaker: Sylvain Chaty
• 29
The formation of black holes in X-ray binaries and binary stellar black holes FD5

### FD5

#### Nordita, Stockholm

I will present the multiple strands of observational evidence for the formation of black holes in X- ray binaries and binary stellar black holes, the first sources of gravitational waves detected by LIGO. It is believed that stellar black holes (BHs) can be formed in two different ways: Either a massive star collapses directly into a BH without a supernova (SN) explosion, or an explosion occurs in a proto-neutron star, but the energy is too low to completely unbind the stellar envelope, and a large fraction of it falls back onto the short-lived neutron star (NS), leading to the delayed formation of a BH. Theoretical models set progenitor masses for BH formation by implosion, namely, by complete or almost complete collapse, but observational evidences have been elusive. Here are reviewed the observational insights on BHs formed by implosion without large natal kicks from: (1) the kinematics in three dimensions of space of five Galactic BH X-ray binaries (BH- XRBs), (2) the diversity of optical and infrared observations of massive stars that collapse in the dark, with no luminous SN explosions, possibly leading to the formation of BHs, and (3) the sources of gravitational waves produced by mergers of stellar BHs so far detected with LIGO. The multiple insights of BH formation without ejection of a significant amount of matter and with no natal kicks obtained from these different areas of observational astrophysics, and the recent observational confirmation of the expected dependence of BH formation on metallicity and redshift, are qualitatively consistent with the high merger rates of binary black holes (BBHs) inferred from the first detections with LIGO.
Speaker: Felix Mirabel
• 12:15 PM
Lunch FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 30
Mass Transfer, Binary Evolution and Gravitational Waves FD5

### FD5

#### Nordita, Stockholm

Speaker: Re'em Sari
• 31
The spin distribution of binary black hole mergers arising from field binaries FD5

### FD5

#### Nordita, Stockholm

One of the puzzles in the recent observations of gravitational waves from binary black hole mergers is their low aligned spins. This spin distribution teaches us a lot about the progenitor scenario. We discuss the implications of the low aligned spins of the BBH mergers observed by LIGO to the field binary scenario based on the tidal synchronization argument. We show Wolf-Rayet and population III progenitors can be consistent with the observed spins. We also show that a fraction of BBH mergers should have high aligned spins.
Speaker: Kenta Hotokezaka
• White dwarf — white dwarf binaries; their outcomes and merger products FD5

### FD5

#### Nordita, Stockholm

• 32
Type Ia supernovae from dynamically-driven double degenerate double detonations FD5

### FD5

#### Nordita, Stockholm

Standard Type Ia supernova (SN Ia) progenitor scenarios have encountered increasing opposition in the past decade from both theoretical and observational constraints. In this talk, I will describe a new scenario that has risen to the challenge, which invokes two white dwarfs that begin to merge unstably, triggering a helium-powered detonation that then transforms into a carbon-powered detonation and subsequent SN Ia. This "dynamically-driven double degenerate double detonation" scenario has the potential to explain the bulk of normal SNe Ia and finally solve the long-sought identity of SN Ia progenitors.
Speaker: Ken Shen
• 3:15 PM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 33
Classical Novae as Laboratories for Common Envelope Evolution FD5

### FD5

#### Nordita, Stockholm

Common envelope evolution is the largest remaining uncertainty in our understanding of close binary evolution and stellar mergers. I will present recent findings on classical novae to illustrate that novae can be powerful tests of the efficiency of common envelope evolution, and to highlight observational signatures that can be used to trace common envelope ejection.
Speaker: Laura Chomuik
• 34
Observations of WD - WD mergers [in the Type Ia supernova context] FD5

### FD5

#### Nordita, Stockholm

Among the possible outcomes predicted for double white-dwarf binaries, Type Ia supernovae are perhaps the best studied ones. Although the widely accepted picture for these events involves the thermonuclear explosion of a carbon-oxygen white dwarf in a binary system, we are still left with the embarrassing question about the nature of the companion star. In my talk, I will review recent observational evidences suggesting how some - if not all - Type Ia supernovae might stem from the merger of double white-dwarf binaries.
Speaker: Mattia Bulla
• 35
Two classes of fast declining SN1a FD5

### FD5

#### Nordita, Stockholm

Fast-declining Type Ia supernovae (SN Ia) separate into two categories based on their bolometric and near-infrared (NIR) properties. The peak bolometric luminosity (Lmax), the phase of the first maximum relative to the optical, the NIR peak luminosity and the occurrence of a second maximum in the NIR distinguish a group of very faint SN Ia. Fast-declining supernovae show a large range of peak bolometric luminosities (Lmax differing by up to a factor of ~8). All fast-declining SN Ia with Lmax<0.3⋅ 10^43 ergs^−1 are spectroscopically classified as 91bg-like and show only a single NIR peak. SNe with Lmax>0.5⋅ 10^43 ergs^−1 appear to smoothly connect to normal SN Ia. The total ejecta mass (M_ej) values for SNe with enough late time data are ≲1 M⊙, indicating a sub-Chandrasekhar mass progenitor for these SNe.
Speaker: Suhail Dhawan
• Tuesday, June 20
• White dwarf — white dwarf binaries (cont); White dwarf —neutron stars and white dwarf — black hole binaries; numerical simulations FD5

### FD5

#### Nordita, Stockholm

• 36
Future prospect for exploiting double white dwarfs detected by GAIA, LSST and LISA FD5

### FD5

#### Nordita, Stockholm

Double white dwarf systems have a very broad range of possible outcomes, which make them physically very interesting. On the other hand, they are the most common compact object binaries in the Galaxy and they may use as tomographic probes with both electromagnetic and gravitational waves. The limiting factor to current studies is the number of objects known. Notably, the era of major unprecedented Galactic survey is beginning: I will show predictions for what Gaia and LSST will be able to do in terms of number of objects and precision of measurements. I will also show the great potential of LISA. Finally, I will show a first application of the combined optical and gravitational wave data sample.
Speaker: Elena Rossi
• 37
Type Ia supernovae with the Palomar Transient Factory FD5

### FD5

#### Nordita, Stockholm

Type Ia supernovae, at low and high-redshifts, are used as distance indicators for precision cosmology. The low-redshift SNIa sample is particularly useful for detailed studies not feasible with the distant sample. These studies are important to explore and quantify potential systematic effects in the derived distances. The Palomar Transient Factory (PTF, 2009-2012) and its successor iPTF (2013-2017) collected data from 2000 SNe Ia, starting very early after the explosion and with lightcurve coverage of several months. I will describe the properties of the PTF/iPTF data and some ongoing analysis
• 38
Probing the distribution of delay times of Type Ia SNe FD5

### FD5

#### Nordita, Stockholm

Traditional techniques used to measure the delay time distribution of SN Ia depend on physical quantities that are notoriously difficult to measure, such as the age of the progenitor system. In this talk I will introduce a novel method, in which the relevant quantites are the color and absolute magnitude of galaxies in a control sample. We find that a power-law slope of t^-1.5 is sufficient to explain the data - a result that is supportive of the double degenerate scenario. We also find that if the observed SNe Ia are separated in groups of slow and fast decliners, the delay time of the brightest events is consistent with the predictions of the single degenerate channel.
Speaker: Epson Heringer
• 39
The variety of neutron-star, white-dwarf binaries and the maximum mass of neutron stars FD5

### FD5

#### Nordita, Stockholm

Speaker: Marten Van Kerkwijk
• 10:30 AM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 40
Mass Leakage through L2 in Binaries FD5

### FD5

#### Nordita, Stockholm

Speaker: Itai Linial
• 41
Rapidly-evolving transients from white dwarf-neutron star mergers FD5

### FD5

#### Nordita, Stockholm

The merger of binaries consisting of a white dwarf (WD) and a neutron star (NS), though much less studied than their NS-NS/WD-WD brethren, are relatively common astrophysical events which may contribute to the transient sky. We describe a 1D time-dependent model of the accretion flow produced by the dynamical disruption of a WD by a NS, which accounts for the effects of nuclear burning on the disk dynamics and composition. Outflows from the disk, containing a modest quantity of Ni56, power a dim rapidly-evolving (~week-long) optical transient following the merger, broadly consistent with the class of Ca-rich gap transients’. The observed large offsets of these events from their host-galaxies results naturally from a WD-NS merger due to the large natal birth kick received by the NS. Finally, we show that a WD-NS merger provides a natural mechanism for creating planets orbiting the millisecond pulsar PSR B1257+12, providing new insight into the unusually high proper motion of the pulsar-planet system.
Speaker: Ben Margalit
• 42
White dwarf - neutron star and white dwarf - black hole binaries FD5

### FD5

#### Nordita, Stockholm

Binaries containing a white dwarf and a neutron star, and their more massive relatives containing a white dwarf and a black hole, are interesting for a number of reasons. Their existance and properties allow us to constrain the evolution of interacting binary stars, probing a number of important poorly-understood physical processes such as common-envelope evolution and neutron-star kicks. They may be observable with the LISA gravitational-wave experiment. Following gravitational-wave emission, their merger may produce luminous transients, and they are a possible candidate progenitor for calcium-rich "gap" transients. I will discuss the theory of their formation and of their ultimate destruction after gravitational-wave inspiral.
Speaker: Ross Church
• 12:00 PM
Lunch 122:026

### 122:026

#### Nordita, Stockholm

• Numerical simulations and modeling of compact object mergers FD5

### FD5

#### Nordita, Stockholm

• 43
Modeling stellar encounters with white dwarfs FD5

### FD5

#### Nordita, Stockholm

Speaker: Stephan Rosswog
• 44
Mass ejection from neutron star mergers FD5

### FD5

#### Nordita, Stockholm

I will summarize our current understanding for possible mass ejection process in the merger of binary neutron stars and in the post merger phase.
Speaker: Masaru Shibata
• 45
Free hyperboloidal evolution: results in spherical symmetry FD5

### FD5

#### Nordita, Stockholm

In the coalescence of compact objects, not only the properties of the objects and the distorted spacetime close to them are important, but the far-field behaviour is also relevant: it is at infinity that the study of global properties of spacetimes and unambiguous gravitational wave extraction are possible. A convenient way of including infinity in numerical relativity simulations is by evolving along hyperboloidal slices, which are smooth spacelike slices that reach future null infinity - the "location" in spacetime where light rays arrive and where signals can thus be unambiguously measured. The hyperboloidal initial value problem for the Einstein equations can be addressed through conformal compactification methods, which we express in terms of unconstrained evolution schemes based on the BSSN and conformal Z4 formulations, widely used in current codes that simulate binary systems. The main difficulty of the implementation is that the resulting system of PDEs includes formally diverging terms at null infinity that require a special treatment and a careful choice of gauge conditions. In this first step restricted to spherical symmetry, we present stable numerical evolutions of a massless scalar field coupled to the Einstein equations, including the collapse of a scalar field perturbation into a black hole and a scalar field perturbing a Schwarzschild black hole trumpet geometry. In the second scenario the simulations were followed long enough to measure the scalar field's power-law decay tails at future null infinity at the expected convergence order. These successful results make this approach of the hyperboloidal initial value problem a good candidate for more general numerical setups. The final goal of this work is to provide a far-field numerical framework that will effectively include null infinity in simulations of compact object mergers.
Speaker: Alex Vano-Vinuales
• 3:15 PM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 46
Compact object formation in extreme core-collapse supernovae FD5

### FD5

#### Nordita, Stockholm

Extreme core-collapse supernovae belong to the most energetic transients in the universe and are birth sites of compact objects like neutron stars and black holes. I will discuss the unique challenges in both input physics and computational modeling for these systems involving all four fundamental forces and highlight recent breakthroughs in full 3D simulations. I will pay particular attention to how these simulations can be used to reveal the engines driving the explosion and the compact object remnants left behind.
Speaker: Phillip Moesta
• 47
The physics and astrophysics of neutron-star binaries: a report from Frankfurt FD5

### FD5

#### Nordita, Stockholm

I will argue that if black holes represent one the most fascinating implications of Einstein's theory of gravity, neutron stars in binary system are arguably its richest laboratory, where gravity blends with astrophysics and particle physics. I will discuss the rapid recent progress made in modelling these systems and show how the inspiral and merger of a binary system of neutron stars is more than a strong source of gravitational waves. Indeed, while the gravitational signal can provide tight constraints on the equation of state for matter at nuclear densities, the formation of a black-hole--torus system can explain much of the phenomenology of short gamma-ray bursts, while the the ejection of matter during the merger can shed light on the chemical enrichment of the universe.
Speaker: Luciano Rezzolla
• 48
Source modeling of compact object mergers FD5

### FD5

#### Nordita, Stockholm

Speaker: Luc Blanchet
• Wednesday, June 21
• Gravitational Wave Observations and fundamental physics FD5

### FD5

#### Nordita, Stockholm

• 49
Gravitational Wave detectors: Accomplishments and Plans for the Future FD5

### FD5

#### Nordita, Stockholm

Speaker: David Shoemaker (MIT)
• 50
The dawn of gravitational-wave physics and astronomy FD5

### FD5

#### Nordita, Stockholm

Gravitational wave observations from merging black hole binaries can be used to constrain astrophysical models and test general relativity in dynamical spacetimes. In my talk I will highlight some of the astrophysical implications and bounds on deviations from GR deduced from LIGO's 3.9 detections so far.
Speaker: Bangalore Sathyaprakash
• 51
Gravitational-wave displacement and spin memory effects FD5

### FD5

#### Nordita, Stockholm

The gravitational-wave displacement and spin memory effects are predictions of general relativity that can be caused by nonlinearities in Einstein's equations. They are characterized by constant changes in the strain and in the time integral of the strain's magnetic-parity part, respectively, before and after the passage of a burst of gravitational waves. Observing these effects would not only confirm this feature of general relativity, but it would give insight into the symmetry group of asymptotically flat spacetimes. In this talk, I will introduce these effects, estimate their amplitude for binary-black hole mergers, and discuss strategies that ground-based gravitational-wave detectors can use to observe the displacement and spin memory effects.
Speaker: David Nichols
• 52
Detection of Gravitational Wave transients with minimal assumptions and signal error waveform FD5

### FD5

#### Nordita, Stockholm

Searches for transient gravitational waves are performed either by exploiting detailed knowledge of the waveform - template based searches - or by making minimal assumptions about the signal morphology - generic burst searches. The latter are sensitive to gravitational waves emitted by a wider range of sources including compact binary coalescences and isolated compact objects. This type of search was the first to identify the binary black hole merger GW150914. Dedicated low- latency pipelines produce triggers a few minutes after the arrival time at the detectors and the most significant ones are shared with the electromagnetic partners as well as neutrino observatories. I will give a general overview of the coherent WaveBurst (cWB) pipeline for generic burst searches and briefly present my Ph.D. research project using cWB to reconstruct neutron star fingerprints in binary neutron star mergers.
Speaker: Matteo Di Giovanni
• 10:40 AM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 53
Numerical modelling of binary black hole mergers FD5

### FD5

#### Nordita, Stockholm

Speaker: Harald Pfeiffer
• 54
Gravitational-wave cosmography with LISA and the Hubble tension FD5

### FD5

#### Nordita, Stockholm

We propose that stellar-mass binary black holes like GW150914 will become a tool to explore the local Universe within ~100Mpc in the era of the Laser Interferometer Space Antenna (LISA). High calibration accuracy and annual motion of LISA could enable us to localize up to ~60 binaries more accurately than the error volume of ~100Mpc^3 without electromagnetic counterparts under moderately optimistic assumptions. This accuracy will give us a fair chance to determine the host object solely by gravitational waves. By combining the luminosity distance extracted from gravitational waves with the cosmological redshift determined from the host, the local value of the Hubble parameter will be determined up to a few % without relying on the empirically constructed distance ladder. Gravitational-wave cosmography would pave the way for resolution of the disputed Hubble tension, where the local and global measurements disagree in the value of the Hubble parameter at 3.4sigma level, which amounts to ~9%.
Speaker: Koutarou Kyotoku
• 55
The Astrophysics of the Gravitational Wave Detections FD5

### FD5

#### Nordita, Stockholm

The LIGO-Virgo detections of three double black hole coalescences, plus a third likely BH-BH merger, have begun to give us a glimpse of the astrophysics of thes e events. There are currently two broad categories of models for coalescing compact binaries: evolution of an isolated massive binary and dynamical processes in dense stellar systems. I will discuss some of the specifics of both models, as well as their uncertainties, and will talk about how measurements of the rates and the effective spin parameter parallel to the orbital axis are beginning to help us elucidate the origins of these mergers.
Speaker: Cole Miller
• 12:25 PM
Lunch 122:026

### 122:026

#### Nordita, Stockholm

• GW (cont) and EM counterparts of compact object mergers FD5

### FD5

#### Nordita, Stockholm

• 56
Pulsar binaries with next generation radio telescopes FD5

### FD5

#### Nordita, Stockholm

Pulsars in binary systems provide us with excellent opportunities to understand their formation and evolution. Over the last few years there has been a staggering increase in the number of these systems as discovered in radio searches, either blind and particularly guided by Fermi. On the near horizon there are a number of facilities that provide us with even greater sensitivity to reveal more of these source types, and those that are predicted and perhaps even those that aren’t. I will review some recent discoveries and look forward to the prospects for LOFAR, MeerKAT through TRAPUM and MeerTRAP and then on to the Square Kilometer Array.
Speaker: Ben Stappers
• 57
Electromagnetic Counterparts of Neutron Star Mergers FD5

### FD5

#### Nordita, Stockholm

Hopes are high that Advanced LIGO/Virgo will detect coalescing binary neutron stars in the next few years. Maximizing the scientific return from this discovery will require identifying a coincident electromagnetic counterpart. One possible counterpart is a thermal optical/IR transient, powered by the radioactive decay of neutron-rich elements synthesized in the merger ejecta (a kilonova'). In addition to providing a beacon to the gravitational wave chirp, kilonovae provide a direct probe of an astrophysical site for rapid neutron capture (r-process) nucleosynthesis. I will present the first 3D MHD simulations of the long-term evolution of the remnant accretion disk produced in NS-NS/NS-BH mergers. Over ~400 ms of evolution, we find the ejection of ~20% of the initial torus mass in powerful neutron-rich winds, confirming this important of this site for the r-process in addition to the dynamical ejecta. I will describe how the lifetime of the hypermassive neutron star may impact the kilonova light curves and color. Free neutrons in the outermost layers of the ejecta could power a bright hours long ’precursor' to the main kilonova emission, greatly enhancing the prospects for its detection. The small fraction of short gamma-ray bursts accompanied by unexpectedly long-lived X-ray emission may suggest that a fraction of mergers result in the formation of long-lived - or even indefinitely stable - massive neutron star remnants; if confirmed, this would place stringent constraints on the high density equation of state.
Speaker: Brian Metzger
• 58
Exploring the Boundary Between Neutron Stars and Black Holes FD5

### FD5

#### Nordita, Stockholm

Even though we know that stellar mass black holes exist both from those found in our Galaxy and gravitational wave observations, the actual events that give rise to them is poorly understood. Furthermore, the transition between these black holes and neutron stars have important implications for the elusive high density equation of state. I will discuss two avenues for investigating the boundary between the formation of black holes and neutron stars: (1) the electromagnetic events that may accompany massive stars that die as black holes rather than neutron stars, and (2) the signatures when two merging neutron stars form a massive neutron star rather than a black hole. As transient surveys cover the sky with increasingly short cadences and gravitational wave observatories probe lower masses, the complementary information between these investigations will help us explore these equations.
Speaker: Tony Piro
• 3:30 PM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 59
EM signals following binary black hole mergers FD5

### FD5

#### Nordita, Stockholm

Speaker: Andrew King
• 60
Resonant Shattering Flares as EM Counterparts FD5

### FD5

#### Nordita, Stockholm

Resonant Shattering Flares (RSFs) are expected to occur during the inspiral phase for some NS-NS and NS-BH mergers. They result from the resonant tidal excitation of the NS crust-core interface mode fracturing the crust and sparking a relativistic pair-photon fireball, emitted seconds before the merger. RSFs are prompt, bright, and isotropic, allowing detection and triggering from well beyond the LIGO-horizon and may be an important source for detectable electromagnetic counterparts to GW mergers. When a GRB is present, they appear as pre-cursors to the main flare, while for off-axis systems they should appear as isolated under-luminous GRBs with extremely short duration. I will discuss the parameter space and detectable emissions for RSFs compared to other counterparts, as well as afterglow, detection, and triggering strategies.
Speaker: David Tsang
• 61
The Cocoon Emission - a bright electromagnetic counterpart to neutron star mergers FD5

### FD5

#### Nordita, Stockholm

It is widely accepted that short GRBs are associated from neutron star mergers. As these mergers involve a significant mass ejection, the GRB jet must penetrate this mass before producing the observed radiation. As the jet propagates within the ejecta is create a hot cocoon containing a significant amount of energy. Eventually the cocoon breakout from the ejecta and produces a bright optical/uv signal lasting a few hours. A rapid followup of a gravitational radiation signal might enable us to detect this signal and identify the location of the merger.
Speaker: Tsvi Piran
• Thursday, June 22
• EM counterparts of compact object mergers (cont) and Binary Black Hole Astrophysics FD5

### FD5

#### Nordita, Stockholm

• 62
In Search for an Optical or Infrared Counterpart to Neutron Star Mergers FD5

### FD5

#### Nordita, Stockholm

We are all enjoying the dawn of a new era with multiple direct detections of gravitational waves from merging black holes and eagerly a waiting a merger with at least one neutron star. Here, I will present my ongoing efforts and my view on prospects to identify and characterize an electromagnetic counterpart. Among the various models for electromagnetic emission from binary neutron star mergers, free neutron decay and disk wind emission give the most luminous and fast-evolving optical counterpart. I will describe co-ordinated global effort, the GROWTH (Global Relay of Observatories Watching Transients Happen) network working in tandem with the Zwicky Transient Facility to search for this optical effort. I will also describe my phased efforts to build a wide-field infrared camera to look for longer wavelength kilonova emission hidden by high opacity.
Speaker: Mansi Kasliwal
• 63
A new hope - the search for gravitational wave — radio counterparts FD5

### FD5

#### Nordita, Stockholm

Speaker: Assaf Horesh
• 64
Searches for radio counterparts to GW sources with LOFAR, AMI and MeerKAT FD5

### FD5

#### Nordita, Stockholm

Speaker: Rob Fender
• 65
ULTRASAT and GW Target of opportunity FD5

### FD5

#### Nordita, Stockholm

Speaker: Eran Ofek
• 10:30 AM
Coffe break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 66
EM counterparts from NS-NS, BH-BH and WD-WD mergers FD5

### FD5

#### Nordita, Stockholm

We discuss electromagnetic signals expected from mergers of various compact stars, stressing the ''Faraday wheel'' mechanism of converting mechanical energy into electromagnetic.
Speaker: Maxim Lyutikov
• 67
Machine learning for gravitational wave electromagnetic counterparts FD5

### FD5

#### Nordita, Stockholm

Since the first direct detection of gravitational waves in 2015, a new window of discovery in Physics has opened up. However, in order to use gravitational waves as probes of cosmology and fundamental Physics, an electromagnetic counterpart must be detected. As the sky localisation for a gravitational wave detection is large, detected transient sources from follow-up and synoptic astronomy surveys need to be rapidly classified to locate potential counterparts in real time. Machine learning has emerged as a powerful tool to potentially solve this problem. In this talk, I will introduce the concepts of machine learning and use our work in supernova light curve classification to illustrate how it can be used for transient classification for searches of gravitational wave electromagnetic counterparts.
Speaker: Michelle Lochner
• 68
High energy radiation from jets and accretion disks near rotating black holes FD5

### FD5

#### Nordita, Stockholm

Speaker: Asaf Pe'er
• 12:00 PM
Lunch FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 69
Transients from magnetically active compact objects FD5

### FD5

#### Nordita, Stockholm

Magnetized compact objects are capable of generating strong intermittent outflows resembling coronal mass ejections from the sun. Internal shocks in these outflows can produce bright transients with a broad spectrum. This activity should be especially strong for differentially rotating objects formed in mergers. For instance, white dwarf mergers should produce bright transients, even if there is no nuclear explosion. Magnetically active neutron stars (magnetars) are plausible sources of fast radio bursts. Models for these and related transients will be discussed.
Speaker: Andrei Belbodorov
• 70
What GW detections can tell us about jet structure of short GRBs FD5

### FD5

#### Nordita, Stockholm

The peak magnitude for orphan afterglows from the jets of gravitational wave (GW) detected BH/NS-NS mergers highly depends on the jet half-opening angle. For a short GRB with a homogeneous jet structure, the jet half opening angle that gives an orphan afterglow viewed at the typical inclination for a GW detected event, 38 degrees, that is brighter at optical frequencies than the comparable macronova emission can be found. Structured jets, where the energetics and Lorentz factor vary with angle from the central axis, may have low-Lorentz factor components where the prompt emission is suppressed; GW electromagnetic (EM) counterparts may reveal a population of failed-GRB orphan afterglows. Features in the light- curves from orphan afterglows can be used to indicate the presence of extended structure within the jets from compact binary mergers.
Speaker: Gavin Lamb
• 71
Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution FD5

### FD5

#### Nordita, Stockholm

I'll be present our recent paper on black hole mergers that occur due to secular evolution in stellar triples. I'll show the expected rates and characteristics and what sets them apart from other formation channels.
Speaker: Silvia Toonen
• R process nucleosynthesis FD5

### FD5

#### Nordita, Stockholm

• 72
brief review is made of the r-process and the historical development of ideas about its astrophysical origins FD5

### FD5

#### Nordita, Stockholm

Speaker: Jim Lattimer
• 3:30 PM
Coffee break FD5 (Nordita, Stockholm)

### FD5

#### Nordita, Stockholm

• 73
R process nucleosynthesis of compact object merger FD5

### FD5

#### Nordita, Stockholm

Speaker: Jennifer Barnes
• 74
Kilonova/Macronova Emission from Dynamical and Wind Ejecta of Compact Binary Mergers FD5

### FD5

#### Nordita, Stockholm

Kilonova/macronova is optical and near-infrared emission powered by radioactive decays of r-process nuclei. Properties of the emission are mainly determined by the opacity in the ejecta as well as the mass and velocities of the ejecta. The opacities of r-process elements are one of the most uncertain factors to predict the properties of the emission. We have recently performed new atomic structure calculations for Se (Z=34), Ru (Z=44), Te (Z=52), Nd (Z=60) and Er (Z=68). Using these results, we have performed wavelength-dependent radiative transfer simulations in the ejecta from compact binary mergers. We found that the opacity of Lanthanide-rich ejecta is as high as ~10 cm^2 g^-1 (as previously studied) while the opacity of Lanthanide- free ejecta is approximated as ~0.5 cm^2 g^-1. We show expected brightness of kilonova/macronova emission based on these results, and discuss observing strategies of EM follow-up observations.
Speaker: Masomi Tanaka
• 75
Predicting the spectra and lightcurves of macronovae: electromagnetic signatures or the r-process nucleosynthesis FD5

### FD5

#### Nordita, Stockholm

Neutron star mergers are some of the most energetic events in the Universe, powerful emitters of gravitational waves, mysterious engines behind short GRBs, possibly the main sites of the strong r-process nucleosynthesis. A new type of transients, -- called macronova or kilonova -- has been recently suggested and possibly discovered in the afterglow of GRB 130603B. These isotropic, infrared transients might be the only possible way to pinpoint the source of gravitational waves coming from the merging neutron stars. Here we present a study of their light curves and spectra, computed with the new multidimensional radiative transfer code SuperNu and accurate state-of-theart LTE opacities for a few representative elements (lighter elements: Cr, Pd, Se, Te, Br, Zr, lanthanides: Sm, Ce, Nd, and an actinide U) for a range of ejecta morphologies. We assess the importance of various physics ingredience in the brightness and duration of the signal.
Speaker: Oleg Korobkin
• 76
Learning from EM observations of compact binary mergers FD5

### FD5

#### Nordita, Stockholm

Speaker: Nial Tanvir
• Monday, June 26
• 77
A New Empirical Model for Type Ia Supernovae Using Data from the Nearby Supernova Factory (Claire Saunders) 122:026

### 122:026

#### Nordita, Stockholm

• 78
Meet and greet/organisation meeting 122:026

### 122:026

#### Nordita, Stockholm

• 79
Core-collapse discussion (Led by Philipp Moesta, Tony Piro and Phillip Podsiadlowski) 122:026

### 122:026

#### Nordita, Stockholm

• Tuesday, June 27
• 80
White-dwarf neutron star and white dwarf-black hole binaries and outcomes (led by Brian Metzger) 122:026

### 122:026

#### Nordita, Stockholm

• 81
White-dwarf neutron star binaries and their outcomes (led by Ben Margalit and Ken Shen) 122:026

### 122:026

#### Nordita, Stockholm

• Wednesday, June 28
• 82
Dynamics in the Galactic Center (led by Re'em Sari) 122:026

### 122:026

#### Nordita, Stockholm

• 83
Gravitational wave measurements and tests of GR (led by Lionel London) 122:026

### 122:026

#### Nordita, Stockholm

• Thursday, June 29
• 84
Rates and formation of WD-NS/WD-BH systems (led by Ross Church and Silvia Toonen) 122:026