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Home , GW170814, GW170817, Kilonova

GW170817 – GRB 170817A – AT2017gfo: the birth of multi- messenger astronomy Carlo Ferrigno University of Geneva

07.06.2019 MM astronomy 1 Outline of this talk

Recap on and GRBs

Gravitational waves from coalescence mergers

Three electromagnetic components • The initial burst of gamma-rays • The (UV to IR) • The afterglow (X-rays to radio)

07.06.2019 MM astronomy 2 Binary track(s)

07.06.2019 MM astronomy 3 The Hulse-Taylor Evidence for radiation

• Discovered in 1974 • Nobel Prize for physics in 1993

07.06.2019 MM astronomy 4 Gamma-ray bursts (recap)

jet aperture <2s ~10

Relativistic jet n ~100-1000 o i t a r -> Strong u

D beaming of radiation

>2s -> we see a small fraction of events

07.06.2019EWASS- 4 July 2016 GW150914MM astronomy - C. Ferrigno 5 Fireball model

• Prompt gamma-rays from internal shocks • Fast decaying afterglow with non-thermal spectrum from interaction with local medium.

07.06.2019 MM astronomy 6 Gravitational waves

07.06.2019EWASS- 4 July 2016 GW150914MM astronomy - C. Ferrigno 8 Basics

• For conservation of mass and momentum, only quadrupole signals are possible

• We measure the fractional change in gravity gradient

07.06.2019 MM astronomy How “big”?

• h is the strain. The first term is roughly the size of a of mass M. The last term is sizable only in extreme systems as binary black holes or neutron or in the collapse of interior core. • h approaches unity when standing in the immediate vicinity of black holes moving about at the or neutron stars. • The strongest waves we expect to observe passing the Earth will have h ∼ 10 10-21 or less. This distorts the shape of the Earth by 10-13 m. By contrast, the tidal field of the Moon raises a tidal bulge of about 1 m on the Earth's oceans.

07.06.2019 MM astronomy Interferometers

07.06.2019 MM astronomy A global network

• Only LIGO and Virgo are powerful enough. Multiple detectors assure a high confidence for simultaneous signals, localization and measurement. 07.06.2019 MM astronomy Sensitivity

• This is the sensitivity at the time of GW170814 • Lines are resonances of external sources as electric power, seismic etc. LVC 2017a

07.06.2019 MM astronomy Sensitivity

07.06.2019 MM astronomy The three phases of a signal

• Observable for massive binary black holes

07.06.2019 MM astronomy GW170814

LVC 2017a

• Two black holes of 30 and 25 Msol at 540 Mpc

07.06.2019 MM astronomy Observing runs

• Advanced LIGO active from September 2015 to March 2016 for the first observing run (O1) • The second Advanced LIGO run (O2) began on November 30, 2016 and ended on August 25, 2017. The run was suspended for one month (May 8 - June 8) for in vacuum refurbishement activities. • The average reach of the LIGO network for binary merger

events has been around 70 Mpc for 1.4+1.4 Msun, 300 Mpc for

10+10 Msun and 700 Mpc for 30+30 Msun mergers, with relative variations in time of the order of 10%. • Virgo joined on August 1, 2017 and it was fundamental for two events: GW170814 and GW170817 • O3 started on 1 April 2019 and it detected already 1 NS-NS binary merger, one possible NS-BH and about ten BH-BH.

07.06.2019 MM astronomy Results (O1-O2)

07.06.2019 MM astronomy Localizations

• With two detectors, only poor localization. • Only tens of squared degrees with three detectors

07.06.2019 MM astronomy I segnali

07.06.2019 MM astronomy Tutte le fusion di buchi neri

07.06.2019 MM astronomy Other sources ?

• Every fast (~c) movement that is not spherically symmetric could produce GW. . Impulsive events could be generated by Hypernovae collapses • Impulsive events could be originated by starquakes

• Steady GW emission could come from spinning NS with asymmetries for instance due to accretion of matter.

07.06.2019 MM astronomy Results from the Thegravitational GW results signal

07.06.2019 MM astronomy GW170817: NS+NS merger

• Identified by matched filtering • A long signal of ~100 s gives a precise • The loudest signal in GW ever detected

07.06.2019 MM astronomy GW170817

• No merging signal due to limited band width • Loose limits on equation of state 07.06.2019 MM astronomy GRB170817A The Gamma-ray burst (1.7 s after the GW)

07.06.2019 MM astronomy 26 GW170817 – GRB170817A

Binary , discovered by Fermi/ GBM and LIGO, independently observed by INTEGRAL/SPI-ACS, in good agreement with Fermi/GBM Despite an unfavorable soft GRB spectrum and moderately favorable orientation, INTEGRAL achieved a confident detection

LVC+Fermi+INTEGRAL 2017 07.06.2019 MM astronomy 27 Joint localization

• By comparing time of burst arrival to INTEGRAL, the GBM localization can be substantially improved. • LIGO/Virgo observation alone allows to measure distance to the GW source of 40 Mpc, exceptional for a short GRB, and well within LIGO BNS horizon

07.06.2019 MM astronomy 28 Fundamental consequences

At least some short GRBs are associated to BNS mergers The 2 s delay comparing to 130 Mly distance implies that can be constrained to unprecedented precision:

Such a consistency between GW speed and speed of light, implies stringent limits on Lorentz Invariance Violation

07.06.2019 MM astronomy 29 A very faint GRB

Distance of 120 Mly is much less than ever measured for any GRB (short or long). This implies low , which is much less than that measured for other sGRB with known distances (Gamma- ray to GW ratio of <10-6 ). Why? 07.06.2019 MM astronomy 30 Could have we seen it?

• There are GRBs with similar spectral properties in the GBM sample. GRB 101224A was the most probable candidate (located with doubts at 75 Mpc (?)) • The rates are expected to be low, have we been very lucky? • For INTEGRAL, predictions are more difficult at this flux level, as SPI-ACS is contaminated by short spikes. 07.06.2019 MM astronomy 31 AT2017gfo: the kilonova (observed from 11 hour to weeks after the GW)

07.06.2019 MM astronomy 32 Kilonova

• Sub-relativistic outflows emitted from tidal interaction, collision and subsequent accretion disc. • They produce heavy elements like , Platinum, Uranium, Thorium (which cannot be forged with the observed abundances in Supernovae)

07.06.2019 MM astronomy 33 Definition of kilonova

• Kilonovae are day- to week-long like thermal transients. They are powered by of heavy neutron-rich elements synthetized in the expanding ejecta. • The idea that NS-NS mergers are a source of heavy elements through r-processes dates back to 1980s and it was motivated by the abundance of heavy elements, which could not be produced only in Snae • Li and Pacynski (1998) proposed for the first time that the radioactive decay could produce an optical transient, but they overpredicted the peak luminosity to 1044 erg/s • The term “kilonova” was proposed by Metzger based on a peak luminosity 1000 times than a (the term macronova comes earlier nd refer to the same scale) • Berger et al found in 2013 a possible kilonova in the tail of a short GRB lightcurve Metzger (2018) arXiv 1610.09381v3

07.06.2019 MM astronomy Kilonova in GW170817

• Arcavi (2018) ApjL

07.06.2019 MM astronomy Time scale

• Initially the flow is optically thick and radiation cannot escape

• When the diffusion time scale

• becomes • comparable to the expansion time, radiation can emerge.

07.06.2019 MM astronomy Ejecta

• There are several sources of , including a central or residual accretion on the central black-hole • At poles, lighter material (blue) and at equator, heavier material (red) • Opacity is important to model the light curve

07.06.2019 MM astronomy 37 Kilonovae (predictions)

Fernandez & Metzger (2016)

• faster lanthanide-poor ejecta from polar regions • slower lanthanide-rich outflow from the equatorial IR belt • Evolution of spectra from UV Optical to IR over the first days.

07.06.2019 MM astronomy 38 Discovery of the optical transient

• Twelve hours after the joint GRB-GW detection, an optical/ UV counterpart has been detected in NGC 4993, at distance (40 MpC) and (0.0097) perfectly consistent with the GW: a kilonova !

07.06.2019 MM astronomy 39 Light curves

• A general agreement for mass of ejecta of 0.2 Msol • Better IR understanding than blue signal

07.06.2019 MM astronomy 40 Spectral evolution

• General continuum consistent with black body with temperature decreasing from ~7000 to ~3000 K • 0.2 Msol mass of ejecta Broad features can be interpreted as blends of heavy element lines.

Pian et al. 2017 07.06.2019 MM astronomy 41 Prediction = Observations

?

Fernandez & Metzger (2016) • Not observed a normal GRB • Not seen the early afterglow • Radio signal from interactions of kilonova with ISM ? 07.06.2019 MM astronomy 43 The X-ray and radio afterglow

07.06.2019 MM astronomy 44 Late radio off-axis afterglow

Troja et al 2017

• X-ray and Radio observations detected a source after 9 and 16 days and they can be joined in a synchrotron emission model. • Late appearance can be due to slowing down of jet (reduced Doppler beaming), but also to a structured emission pattern. 07.06.2019 MM astronomy 45 Break simulations

• The light curves of an inhomogeneous jet observed from different angles (From Rossi et al. ). From the top theta0 = 0.5, 1, 2, 4, 8, 16°. https://ned.ipac.caltech.edu/level5/March04/Piran/Piran7_9.html • Acromatic break in afterglows let us estimate an opening angle between 5 an 10 degrees for most GRBs. But see GRB170817A next lecture.

2407.06.2019 May 2017 GRBsMM astronomy- C. Ferrigno Off-axis event

?

Mooley et al. (2018)

• As revealed by LIGO/Virgo data, the merger was observed at 20-60 deg off-axis, proving that a considerable amount of EM energy is emitted far from the axis of the system • Has the jet broken through or has it formed a hot cocoon?

07.06.2019 MM astronomy 47 A panchromatic light curve

From X-rays to radio, the same light curve up to 300 days after the event: synchrotron emission.

Ghirlanda et al. (2018) Two models consistent with the data

07.06.2019 MM astronomy 48 Very Long Baseline Interferometry (radio)

Able to reach milliarcsecond resolution.

07.06.2019 MM astronomy 49 Superluminal motion detection: a jet !

Mooley et al. (2018)

A displacement of 2.4+/-0.4 marcsec confirms jet model and rules out cocoon. Combining image and light curve allows parameter estimation 07.06.2019 MM astronomy 50 Inconsistent with a chocked jet Comparison of image with simulations favors strongly a successful jet rather than a choked jet in a cocoon.

Ghirlanda et al. (2018)

07.06.2019 MM astronomy 51 A sharp break in radio

It must be a very narrow jet (<5 deg) viewed at about 20 degrees off-axis. Transition happens in less than 25 days.

Mooley et al. (2018)

07.06.2019 MM astronomy 52 Rate of observable binary neutron star mergers • At least 10% of events have a successful jet • Depending on how the jet fades and is opened, we might observe more or less events in the future.

Ghirlanda et al. (2018)

07.06.2019 MM astronomy 53 An incredible initial campaign (summary paper: 3500 authors, 574

7 citations in 14 1 0 2

r e

b months) o t c O + observations up to ~300 days after the event

07.06.2019 MM astronomy 54 LISA

• We can go to space to enlarge baseline and reduce frequency

07.06.2019 MM astronomy Design sensitivity

07.06.2019 MM astronomy 56 LISA pathfinder • Two free-falling gold-platinum masses in a spacecraft • The goal was to isolate the system from any external perturbation to be a perfect test mass. Requirements exceeded.

07.06.2019 MM astronomy LISA

• Timescale of supermassive black-hole mergers • Study structure formation across the history • Predict years in advance the merging of neutron star systems or stellar black holes • Extreme mass ratio inspirals

07.06.2019 MM astronomy 58 Take away

– Gravitational waves and EM follow-up observations gave the definitive confirmation that binary neutron star mergers produce short gamma-ray bursts, kilonovae, and GRB afterglows. – The GW170817 event was see off-axis and is possibly even more energetic than the average. – It produced a very narrow jet, which came completely into sight only 175 days after the merging. Structured coccon was dominating beforehand. – This event allows us to measure for the first time properties of the short GRB with high precision. – Predictions on event rate are still very uncertain, but at least one other good candidate has been identified among the population of faint GRBs in 2015 at z=0.131 (Troja et al., 2018), beyond the reach of LIGO. – More events are likely to be observed with the new runs of LIGO and Virgo starting in March 2019 ! 07.06.2019 MM astronomy 59 GW + Gamma-rays

07.06.2019 MM astronomy 60