Gamma-Ray Bursts: the Most Violent Explosions in the Universe Once Upon a Time, …

Gamma-rayGamma-ray bursts:bursts: TheThe mostmost violentviolent explosionsexplosions inin thethe UniverseUniverse Olivier Godet [email protected]

Presentation available at: http://userpages.irap.omp.eu/~ogodet/

2015-01-05 Outlines  Brief history of Gamma-ray bursts & main discoveries

 Properties of Gamma-ray bursts • What does the prompt emission tells us? • What does the afterglow emission tell us?

 GRB model

 GRB progenitors & host galaxies

 Opened questions

 Interests of GRBs in astrophysics & fundamental physics • Cosmology • Quantum gravity

 The future for the GRB study • Instrumental roadmap in the next 10 years and beyond • The SVOM mission

• Non-photonic messengers & instruments Gamma-ray bursts: The most violent explosions in the Universe Once upon a time, …

• There were « nice » US militaries that launched the Vela satellites to spy on thermonuclear explosions on Earth by badass soviet soldiers.

• However, they detected nothing from Earth, but some brief and intense flashes of Gamma-ray photons from the sky.

• At first, they thought that nuclear wars might rage on other worlds …

• First GRB publication : Klebesadel et al. 1973, ApJ, 185, L85 “Observations of Gamma-Ray Bursts of Cosmic Origin” New astrophysical phenomenon

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (1) •1991-2000: deep study of the prompt Gamma-ray emission with BATSE (Burst And Transient Source Experiment) on the Compton Gamma-Ray Observatory CGRO • No multi-wavelength counterpart due to poor localization • ~ 1 GRB detected per day during 9 years • GRBs are isotropically distributed on the sky • Non thermal spectra One of the 8 • two types of GRBs: long (>2 s) & short (< 2 s) BATSE modules

BATSE, Paciesas et al. 1999; Preece et al. 2000; Band et al. 1993; Kouveliotou et al. 1993

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (2) • Revolution in 1997: detection of first multi-wavelength afterglow emission by Beppo-SAX thanks to an innovative instrumentation (combination wide-field high-E instrument & narrow field instruments) Beppo-SAX • Detection of GRB afterglows a few hours after the detection in Gamma- rays • Redshift measurement (i.e. distance of the source) • Afterglow emission from radio to X-rays for long GRBs • Afterglow emission lasts from days to weeks (sometimes months/years) • The emission drops quickly in flux. • Lightcurves display powerlaw segments & chromatic/achromatic breaks • …

(Costa et al. 1997; Djorgovski et al. 1997 ;Metzger et al. 1997) Panaitescu & Kumar 2004 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (3) •2000-2006: Study of a new class of GRBs, the X-Ray Flashes with main photon energy below 50 keV • Provide arcmin accuracy position to world community in a few tens of seconds • XRFs are long and soft GRBs showing the same properties. • Dark GRBs are not completely dark. • …

High Energy Transient Explorer

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (4)

• Since 2004: Swift era (same strategy as Beppo-SAX, but faster and more sensitive instruments) •Detection of > 800 GRBs •Characterization of the early afterglow, a time interval that was at the time not yet observed. •First detection of the afterglows of short GRBs  redshift, energetics, nature of the progenitor, etc…

Swift

Temporal gap Prompt emission

Afterglow emission

Early afterglow Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (4)

• Since 2004: Swift era •Detection of > 800 GRBs •Characterization of the early afterglow, a time interval that was at the time not yet observed. •First detection of the afterglows of short GRBs •Detection of the naked eye burst GRB 080319B ( Racusin et al. 2008) – Peak brightness in optical = 5.3 mag! •...

Prompt optical emission

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Main missions & main discoveries (5)

• Since 2008: launch of Fermi – observations of GRB prompt emission up to 200 GeV

• Constraints on the emission mechanism for prompt emission • Constraints on the dynamics of the ejecta • New spectral feature seen in the spectra of the prompt emission • Delayed/extended high-energy emission (up to GeV)

Fermi results: (e.g. Goldstein et al. 2012)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe

PropertiesProperties && naturenature ofof Gamma-rayGamma-ray burstsbursts

The game is starting now !!

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe General: distance

BATSE: Burst And Transient Source Experiment on the Compton Gamma-Ray Observatory (1991-2000)

BATSE, Paciesas et al. 1999

Question: What does the isotropy tell us about the origin of GRBs?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe General: distance

BATSE: Burst And Transient Source Experiment on the Compton Gamma-Ray Observatory (1991-2000)

BATSE, Paciesas et al. 1999

Question: What does the isotropy tell us about the origin of GRBs?

GRBs are located at cosmological distances.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe General: distance • GRBs are located at cosmological distances (from z = 0.033 to z = 8.2, maybe 9.4)

Jakobsson et al. 2006 GRB 090423, z = 8.2

 GRB 090423 with z =8.2 (Tanvir et al. 2009)  GRB 080913 with z=6.7  GRB 050904 with z=6.3 (Haislip et al. 2006)  z = 8.2 i.e. ~ 625 million years after the Big Bang & light travel ~ 13 Giga years!

 z = 0.033 i.e. light travel ~ 440 Million years Gamma-ray bursts: The most violent explosions in the Universe General: energetics 1 erg = 10-7 J • Cosmological distances 1 eV = 1.6 10-12 erg 48 55 17 Huge isotropic energy with Eiso = 10 -10 erg 10 erg ~ 2.4 tonnes TNT over a few hundreds of seconds at most! 55 2 For GRB080916C, Eiso ~ 10 erg ~ 5 MSun c !!

40W electric bulb E ~ 1.3 1016 erg over 1 year Supernovae 51 Tsar H-bomb E ~ 10 erg E = 50 Mt TNT ~ 2.1 1024 erg Milky Way L ~ 1044 erg/s

Nuclear plant P mean ~ 1 GW Sun 33 E ~ 3 1023 erg 1 km asteroid impact L ~ 4 10 erg/s 50 28 E ~ 6 10 erg over 5 Gyrs over 1 year E ~ 1.3 10 erg

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gamma-ray variability •Each GRB light-curve is unique.

•GRB light-curves are structured and highly variable.

•Timescale variability very small (down to 1 ms).

•Variability is related to the central source activity.

•Assuming δt ~ 0.1 s, then the size of the system is δd ~ c × δt ~ 3x109cm! (Sun Diameter = 1.392x1011 cm).

Question: What type of object could then be the central source in GRBs?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gamma-ray variability •Each GRB light-curve is unique.

•GRB light-curves are structured and highly variable.

•Timescale variability very small (down to 1 ms).

•Variability is related to the central source activity.

•Assuming δt ~ 0.1 s, then the size of the system is δd ~ c × δt ~ 3x109cm! (Sun Diameter = 1.392x1011 cm).

Question: What type of object could then be the central source in GRBs?

Answer : a compact object (neutron star or black hole)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe What mechanism powers GRBs?

• Cosmological distances 48 55 Huge isotropic energy with Eiso = 10 -10 erg over a few hundreds of seconds at most! • From previous slides, we know the central source is compact – probably a black hole. Question: What mechanism may be able to generate so much energy onto a BH?

Gamma-ray bursts: The most violent explosions in the Universe What mechanism powers GRBs?

Active Galactic Nuclei 39-48 Lbol ~ 10 erg/s E ~ 1053-63 erg over 107-8 yrs (e.g. Urry & Padovani 1995) X-ray binaries 39 Lmax ~ 10 erg/s 52 6 Emax ~ 10 erg over 10 yrs (e.g. Remillard & McClintock 2006) Gamma-ray bursts: The most violent explosions in the Universe What mechanism powers GRBs?

Even accretion is not able to produce so much energy over such short timescales! To avoid the energy budget crisis, the outflow be collimated as a jet. Active Galactic Nuclei must 39-48 Lbol ~ 10 erg/s E ~ 1053-63 erg over 107-8 yrs (e.g. Urry & Padovani 1995) X-ray binaries 39 Lmax ~ 10 erg/s 52 6 Emax ~ 10 erg over 10 yrs (e.g. Remillard & McClintock 2006) Gamma-ray bursts: The most violent explosions in the Universe Jets (1) • Jets are often associated with accretion phenomena.

• Mildly relativistic (Γ < 10) jets are detected in AGN & X-ray binaries.

Cen A

GRS 1915+105

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Epeak Non-thermal spectra (1)

Briggs et al. 1999 •Non thermal spectrum

•The spectrum can be described by a Band function (3 parameters) – Band et al. 1993

•Epeak = Energy for which the photon emission is maximum •From the compacity problem (Cavallo & Rees 1978): The Gamma-ray emission will produce e-/e+ pairs. The α pair opacity is then given by: β Nσ E τ ∝ T with N= iso γγ R2

53 9 Assuming =1MeV, Eiso = 10 erg and R ~ 3 10 cm, 15 τγγ ~ 4.6 x 10 >>1

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Epeak

Gamma-ray bursts: The most violent explosions in the Universe Non-thermal spectra (1)

Briggs et al. 1999 •Non thermal spectrum

•The spectrum can be described by a Band function (3 parameters) – Band et al. 1993

53 9 Assuming =1MeV, Eiso = 10 erg and R ~ 3 10 cm, 15 τγγ ~ 4.6 x 10 >>1 Question: How could we explain the non-thermal nature of the Gamma-ray spectra?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Epeak Non-thermal spectra (1)

Briggs et al. 1999 •Non thermal spectrum

•The spectrum can be described by a Band function (3 parameters) – Band et al. 1993

53 9 Assuming =1MeV, Eiso = 10 erg and R ~ 3 10 cm, 15 τγγ ~ 4.6 x 10 >>1 Question: How could we explain the non-thermal nature of the Gamma-ray spectra? Answer: The way to make the emitting region transparent to Gamma-ray photons is that the outflow moves at relativistic velocities with large Lorentz factors. Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Non-thermal spectra (2)

• Example of GRB080916C detected with the Fermi LAT instrument (Abdo et al. 2009, Science)

• Spectra described by a Band function up to GeV range!

• Estimation of lower limits on the outflow Lorentz factor:

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Jets (2)

• Jets are often associated with accretion phenomena.

• Mildly relativistic (Γ < 10) jets are detected in AGN & X-ray binaries.

• For GRBs, jets have to be ultra-relativistic (Γ > 100) outflows.

• Microquasars & blazars are sources whose the jet is seen along the observer’s line of sight.

• Same thing for GRBs?

Gamma-ray bursts: The most violent explosions in the Universe Jets (2)

• Jets are often associated with accretion phenomena.

• Mildly relativistic (Γ < 10) jets are detected in AGN & X-ray binaries.

• For GRBs, jets have to be ultra-relativistic (Γ > 100) outflows.

• Microquasars & blazars are sources whose the jet is seen along the observer’s line of sight.

• Same thing for GRBs?

Answer: yes

Gamma-ray bursts: The most violent explosions in the Universe Jets (3) • Relativistic outflows imply relativistic Doppler boosting (i.e. enhancement of the emission flux & increase in photon energy) max. along the observer’s line of sight.

• Assuming a shell of matter expanding at a relativistic speed & spherically emitting in its rest-frame some radiation, for a distant observer the emission will no longer be spherical but elongated towards the direction of propagation of the shell.

Γ = Lorentz factor v = outflow velocity t = observer time

observer

Equal arrival light cone time surface

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Models Internal/external shock model (e.g. Meszaros & Rees 1993)

(Piran, Nature, 2003)

1 OPAQUE FIREBALL (large γ-γ opacity) Conversion of internal energy to kinematics energy acceleration phase up to coasting radius above which Γ = cst Gamma-ray bursts: The most violent explosions in the Universe Models Internal/external shock model (e.g. Meszaros & Rees 1993)

2 TRANSPARENT FIREBALL (Piran, Nature, 2003) (photospheric emission)

Gamma-ray bursts: The most violent explosions in the Universe Models Internal/external shock model (e.g. Meszaros & Rees 1993)

(Piran, Nature, 2003)

Gamma-rays

3 INTERNAL SHOCKS (Gamma-rays are emitted by accelerated electrons) Prompt emission

Gamma-ray bursts: The most violent explosions in the Universe Models Internal/external shock model (e.g. Meszaros & Rees 1993)

(Piran, Nature, 2003) From X-rays to radio

Gamma-rays 4 EXTERNAL SHOCKS (forward shock waves propagate in ISM accelerating electrons that produce synchroton multi- wavelength radiation) Afterglow emission

Gamma-ray bursts: The most violent explosions in the Universe Models Internal/external shock model (e.g. Meszaros & Rees 1993)

Reverse shock External forward (Piran, Nature, 2003) shock From X-rays to radio Density Gamma-rays

Relativistic outflow Circum GRB medium

Gamma-ray bursts: The most violent explosions in the Universe Models Standard afterglow model Panaitescu & Kumar (2001) (see also Sari, Piran & Narayan 1998) N ∝ E− p e− (non-thermal distribution)

Fermi acceleration (p ~ 2.1) • Model predictions depend on the nature of the circum-burst environment (e.g. ISM with n = cst; stellar wind with n ~ r-a, a > 2).

• Powerlaw segments & spectral breaks evolving with time.

• From the data, a constant ISM model seems to be favoured.

• From Swift data, p is sometimes less than 1.5 (e.g. Willingale et al. 2007).

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Models Standard afterglow model Panaitescu & Kumar (2001) (see also Sari, Piran & Narayan 1998)

• Model predictions depend on the nature of the circum-burst environment (e.g. ISM with n = cst; stellar wind with n ~ r-a, a > 2).

• Powerlaw segments & spectral breaks evolving with time.

• From the data, a constant ISM model seems to be favoured.

• From Swift data, p is sometimes less than 1.5 (e.g. Willingale et al. 2007).

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Models Jet break (1) (e.g. Rhoads 1999) Break

Time

Early times

Γ ~cst >> 1/θ0 Deceleration

Γ > 1/θ0 Γ < 1/θ0

Question: What will happen when the blastwave will start decelerating?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Models Jet break (1) (e.g. Rhoads 1999) Break

Time

Early times

Γ ~cst >> 1/θ0 Deceleration

Γ > 1/θ0 Γ < 1/θ0

Question: What will happen when the blastwave will start decelerating? • The jet break being a hydrodynamical effect, it should be an achromatic break. • The observation of jet breaks enables us to derive the jet opening angle. Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Models Jet break (2)

• In the pre-Swift era, some jet breaks were observed, but mostly in optical.

• Only a few were observed in several energy bands.

• From the observed jet breaks, the jet opening angle was estimated.

Frail et al. 2001

50 = 5 x 10 erg

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe

GRBGRB progenitorsprogenitors && HostHost GalaxiesGalaxies

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Comparison short & longs GRBs

Watson et al. 2006 • Lower Redshifts ✔ < z > = 0.4 short ✔ < z > = 2.8 long

• Weaker Afterglows -10 -2 -1 ✔ < FX short > = 7x10 erg cm s -9 -2 -1 ✔ < FX long> = 3x10 erg cm s

• Less Jet Collimation? Burrows et al. 2006 ✔ θ ~ 15˚ (wide spread) short ✔ θ ~ 5˚ (wide spread) long

• Less Total Energy long ✔ E ~ 1049 ergs short GRBs rad ✔ 51 Erad ~ 10 ergs long

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe GRB host galaxies Comparison short & longs GRBs Short GRB Long GRB

GRB 050724 - Swift GRB 990123 - SAX elliptical host SF dwarf host Cnts/s Cnts/s

Chandra

XRT GRB

• Hosts: non star-forming (e.g. • Hosts: dwarf, spiral & irregular star- elliptical) & star-forming galaxies forming galaxies

• GRBs located in the outskirts of SF • GRB positions associated with galaxies brightest parts of the host galaxy (assumed to be star-forming regions) • SF galaxies with SF rate less than for long GRB hosts Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe GRB host galaxies Comparison short & longs GRBs Short GRB Long GRB Cnts/s Cnts/s

Grosabel et al. (2006) GRB

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe GRB progenitors Longs GRBs & supernovae Ib/c (1) • GRB980425 & SN1998bw: first association between an underluminous 48 GRB (Eiso ~ 10 erg) and a SN Ib/c (Galama et al. 1998, Nature)

ESO184-G82

Credits: ESO

ESO184-G82

Credits: ESO

Question: What does power a supernova?

ESO184-G82

Credits: ESO

Question: What does power a supernova? Answer: decay of radioactive elements produced during the explosion of the star

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe GRB progenitors Longs GRBs & supernovae Ib/c (2)

• GRB980425 & SN1998bw: first association between an underluminous 48 GRB (Eiso ~ 10 erg) and a SN Ib/c (Galama et al. 1998, Nature)

• GRB 030329: First connections between long classical GRBs & SNe Ib/c (HETE-2; Stanek et al. 2003)

SN2003dh

Matheson, GCN 2120

• Detection of associations XRFs/SNe Ib/c (HETE-2)

Q: What could we learn from the SNe spectra?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe GRB progenitors Longs GRBs & supernovae Ib/c (3) • SNe Ib/c linked with GRBs are more powerful than normal SNe Ib/c. • Their spectra in general show that the ejected matter moves ten times faster than that observed in normal SNe Ib/c Q: what does that imply? GRB SN 2003lw

SN 2006aj

SNe Ic

Link between long GRBs and the death of massive stars (SNe Ib/c)

SN 2006aj

SNe Ic

Link between long GRBs and the death of massive stars (SNe Ib/c)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Long GRB progenitors Collapsar model • What type of stars do we need to produce a GRB? • a massive star with Minitial > 20 Msun • a star compact enough to let the relativistic jets escape from the star envelop Red supergiants (R ~ a few 1013 cm)

Blue supergiant (R ~ a few 1012 cm)

Red & blue supergiants = Progenitors of Type II SNe

Blue supergiant (R ~ a few 1012 cm)

Red & blue supergiants = Progenitors of Type II SNe

• Wolf-Rayet stars = evolved massive stars

with Minitial > 20 MSun

-4 -1 • important mass loss (up to 10 MSun yr ) – lost of the H envelop

• Radius ~ a few to a few tens of RSun Credit: HST image – WR 124

• Formation of SNe Ib/c

• Location in star forming regions

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Long GRB progenitors Collapsar model http://cosmo.nyu.edu/~wqzhang/movies/ (e.g. MacFadyen & Woosley 1999)

• Compact massive star (Wolf-Rayet C,N,O star)

• Stars with high angular momentum and low metallicity  Catastrophic formation of a BH coupled with an accretion disk

 Energy emitted through polar regions – jets (funnel and lateral collimation from ram pressure in the envelop)

 Jet breakout from the stellar envelop after a tens of seconds.

 Conversion of internal energy after breakout to kinetic energy (large Lorentz factors)

 strong winds from accretion disk energizes the material from the star envelop (hypernovae)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Example • Case of GRB 060218 Campana et al., Pian et al., Soderberg et al. (2006)

• Super-long GRB T90 ~35 minutes

• BAT, XRT, UVOT during GRB

• z = 0.033 (145 Mpc)

49 • Eiso = few x 10 erg - underluminous

3 GRB SNe • Associated SN 2006aj SN Ib/c •Thermal emission Shock break-out SN 2006aj seen for the first time (from X-ray to UV/opt.) • R ~ 4 x 1011 cm (Wolf Rayet star) SNe Ic

Chevalier 2008 Gamma-ray bursts: The most violent explosions in the Universe Example • Case of GRB 060218 Campana et al., Pian et al., Soderberg et al. (2006)

• Super-long GRB T90 ~35 minutes

• BAT, XRT, UVOT during GRB

• z = 0.033 (145 Mpc)

49 • Eiso = few x 10 erg - underluminous

3 GRB SNe • Associated SN 2006aj SN Ib/c •Thermal emission Shock break-out SN 2006aj seen for the first time (from X-ray to UV/opt.) • R ~ 4 x 1011 cm (Wolf Rayet star) SNe Ic

Chevalier 2008 Gamma-ray bursts: The most violent explosions in the Universe Short GRBs progenitors NS-NS merger (e.g. Eichler et al. 1989; Narayan et al. 1992) • Hosts: elliptical galaxies or galaxies with weak SFR (older stellar population) • Merger of compact objects (NS-NS ou NS-BH)  Timescale of the merger ~ ms

 Dynamical kick What could be the consequences? •Consequence: ejection of the NS in a region of lower density weaker afterglow emission

 No or very weak SNe is expected (kilonovae).

 Less collimation is also expected.

 Energy reservoir is smaller.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Example: kilonovae • First detection of a kilonova associated with a short GRB in 2013 (GRB130603B - Tanvir et al. 2013)

Metzger & Berger 2012 • Following the merger of 2 NS, neutron rich gas can be ejected.

• This material undergoes rapid neutron capture (r-process), creating heavy elements from merger of original nuclei with the available neutrons.

• When those elements undergo radioactive decay, they emit light in the optical and near-IR bands. The energy emitted can reach 103 times the energy emitted in a nova (kilo-nova). Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Short GRBs progenitors magnetars • Other possibility: (e.g. Usov 1992) • Magnetars (a NS with an intense magnetic field of 1014-15G; see Rea & Esposito 2011) may produce giant flares due to magnetic reconnection following a crust quake (e.g. SGR1806-20 – December 2004; Palmer et al. 2005)

• Only detectable in the local Universe (~50 Mpc)

Swift-BAT lightcurve

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Misleading example GRB 060614 (1) Gal-Yam et al. 2006, Nature, • Long GRB (T90 ~ 102 s)

• z = 0.125

• No SN detected

• SN emission > 102 weaker than normal SNe Ib -4 i.e. MNi < 8 x 10 MSun << MNiSN

• Fall-back accretion from the Ni core on the BH? (the collapsar model does not predict the formation of a SN Ib/c for each long GRB.)

(e.g. Gehrels et al. 2006; Host galaxy with a low SFR ~ 0.004 M yr-1 << Gal-Yam et al. 2006) • Sun SFR (host galaxies for long GRBs)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Misleading example GRB 060614 (2) • GRB 060614 may be not a long GRB, but instead a short GRB with a soft extended tail? - No SN expected in this case (or at least a very faint one) - Consistent with the properties of the host galaxy

Zhang et al. 2007 GRB 060614 would have been detected as a short GRB by BATSE

The classification of GRBs only on their T90 values may ! induce some misinterpretation of their nature in some

cases.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe

OldOld && newnew openedopened questionsquestions

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Swift era Early afterglow

• Since 2004, Swift enables to observe an unknown time interval (i.e. the early afterglow)

• Opportunity to test model predictions with more data

• Bring somehow more questions than answers ☺

Mangano et al. 2007 Nousek et al. 2006

10-100 s 103 -104 s

(e.g. Nousek et al. 2006; Zhang et al. 2006)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Early afterglow Steep decay

I Segment I – Fast decline: ~60% of the afterglows −α Flux F ∝t α ~ 3 – 6 (e.g. Tagliaferri et al. 2005, Nature) Possible interpretation: high latitude emission (Kumar & Panaitescu 2000) Model predicts no spectral variation T (s)

At t = t0 , emission from the core (θ < 1/Γ) stops

Observer Photons emitted at the same time in the source rest frame for θ > 1/Γ will reach the observer with a certain delay.

Opened question: steep decays observed with spectral variation

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Early afterglow Plateau phase

Segment II – Plateau phase : t -0.2 – t -0.5 Flux II • Incompatible with the standard afterglow model

T (s)

Possible interpretations:

• Energy injection in the external forward shock (Zhang et al. 2006) Extended activity or restart of the central engine for both short & long GRBs

Not expected from GRB progenitor models

• Hydrodynamical effect related to the deceleration of the blastwave ( Kobayashi & Zhang 2007)

Not able to explain every GRB plateaus

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Jet break problem

• In the Swift era, it appears that the situation is more complex (e.g. chromatic breaks).

• Absence of jet breaks for most GRBs/XRFs

Willingale et al. 2007

GRB 060729 Grupe et al. 2007 • Large jet opening angle in some cases θ > 28o

• Do the X-ray & optical afterglow track the same emitting regions?

• What values for the GRB jet opening angle? Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Origin of X-ray flaresLes X-ray flares • X-ray flares present in > 50% of the GRBs (long & short) detected by Swift

• Similar spectral properties to those of the Gamma-ray peaks

δt/tpeak << 1 Burrows et al. 2005

δt/tpeak << 1

(e.g. Falcone et al. 2007; Chincarini et al. 2010) ● All the elements point towards an origin internal • External origin? to the jet (internal shocks, magnetic Energetics issue argues against reconnection) an origin due to external • Problem: this implies an extended activity of the shocks central engine or a restart of the central engine up to several days in some cases (e.g. King et al. 2005; Proga & Zhang 2006). Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Prompt emission: questions

• Where is the photospheric emission? What is the magnetization of the outflow?

• Prompt emission mechanism: internal shocks? magnetic dissipation ? relativistic turbulence? photospheric emission?

• Radiative processes : synchrotron vs IC vs something else

• Origin of the prompt optical emission

• Origin of the high-energy Gamma-ray emission? (prompt / extended emission)

• Some questions are connected to:

- the poorly known physics of the central engine (acceleration mechanism / nature of the outflow);

- the poorly known physics of shock acceleration (magnetic field amplification / particle acceleration).

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Prompt emission: questions

• GRB 021206 (RHESSI) : Π = 80 ± 20 %? ( Coburn & Boggs 2003) See however : Rutledge & Fox 2004.

• GRB 930131 & GRB 960924 : Π > 35 % & Π > 50 % ? (Willis et al. 2005)

• GRB 041219A (INTEGRAL) : variable degree of polarization <4% to 43±25 % Götz et al. 2009

• Polarization information is important to constrain the nature of the dominant emission process in GRBs (Synchrotron, IC, SSC)?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Afterglow: questions

• Afterglow emission region: forward shock vs reverse shock vs internal shocks (early afterglow – late afterglow - flares)

• Plateau / X-ray flares : physical origin, consequences for the central engine (energetics, lifetime)

• Origin of the variability (bumps, rebrightening, …)

• Missing jet break problem / origin of the achromatic breaks

• What is the outflow particle or poynting driven?

• What are the manifestations of off-axis viewings?

• What properties of the central source / environment can we deduce from the afterglow observations?

• Why do the observations favour a constant density medium for long GRBs?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe

GRBsGRBs asas toolstools forfor cosmology,cosmology, fundamentalfundamental physics,physics, etc.etc.

What could we do with such bright objects?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Cosmology (1) • GRBs are a class of objects observable on cosmological distances.

• GRBs with their intense brightness illuminate their environment and all the matter along the GRB line of sight.

• The main applications are as follows: - Host galaxy properties (information on the stellar formation rate, the metallicity, the kinematics of gas as a function of redshift)

- Evolution of foreground structures

• Study of the absorption systems along the GRB line of sight to trace the spatial distribution & dynamics of baryons and their evolution since the Big-Bang through the intergalactic medium & complex structures (e.g. galaxies, clusters of galaxies);

• Quasars already used, but GRBs thanks to their transient nature do not disturb their environment.

• GRBs are expected to be able to be detected further away than quasars.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Cosmology (2) • GRBs are a class of objects observable on cosmological distances.

• GRBs with their intense brightness illuminate their environment and all the matter along the GRB line of sight.

• The main applications are as follows: - Host galaxy properties (information on the stellar formation rate, the metallicity, the kinematics of gas as a function of redshift)

- Evolution of foreground structures

• Quasars already used, but GRBs thanks to their transient nature do not disturb their environment.

• GRBs are expected to be able to be detected further away than quasars.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Cosmology (3) - Reionization phase Robertson et al. (2010)

• After the decoupling of matter & radiation, the matter cooled down and became neutral. • This is the time of the dark ages up to z = 10.8 +/-1.4 (from WMAP CMB anisotropy measurements).

• From z ~10.8 to z~6, it is the time of the reionization of the Universe thanks to the UV/X-rays photons from pop. III stars & quasars.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Cosmology (4)

• The GRB lights may enable us to explore this not yet explored time.

• High redshift GRBs may give us some clues on the population III stars.

• They may tell us something on the SFR at this epoch.

• They may give us some clues on the environment of these stars and the neutral material along the GRB line of sight.

• The furthest GRB ever detected comes from a time when the Universe was only ~625 Myr -old!! (GRB 090423 with z = 8.2 , Tanvir et al. 2009).

• This GRB tells us that stars exist at that time in the early Universe.

• This GRB happened at a time when the reionisation was still not complete.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Cosmology (4) • The GRB lights may enable us to explore this not yet explored time.

• High redshift GRBs may give us some clues on the population III stars.

• They may tell us something on the SFR at this epoch.

• They may give us some clues on the environment of these stars and the neutral material along the GRB line of sight.

• The furthest GRB ever detected comes from a time when the Universe was only ~625 Myr -old!! (GRB 090423 with z = 8.2 , Tanvir et al. 2009).

• This GRB tells us that stars exist at that time in the early Universe.

• This GRB happened at a time when the reionisation was still not complete.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Cosmology (5) - Standard candles? • If GRBs could be made standard candles, then they could be used to derive cosmological parameters (H0, ΩM, ΩΛ) in a similar way to what is done with SNe Ia in the local Universe (z < 2).

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Quantum gravity (1) • Quantum gravity is a theoretical framework describing both gravity effects and QM effects when they have similar intensity. ? • Unification of the 4 known forces back in time and at different temperatures.

• One of these theories is the string theory.

• A way to test this theory would be to 2 19 EPlanck = MPlanck c ~ 1.22 x 10 GeV prove the violation of the Lorentz -33 lPlanck ~ 1.62 x 10 cm symmetry i.e. there is a linear energy dispersion in the photon speed.

Q: why are GRBs interesting for testing the Lorentz symmetry? • they are distant i.e. delays more important and easier to measure; • their light spans several decades on energy i.e. large ΔE.

• One of these theories is the string theory.

Q: why are GRBs interesting for testing the Lorentz symmetry?

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Quantum gravity (2) • To test QG effects, it is important to distinguish between a propagation effect and a source effect that may induce a temporal delay. QG effect Source effect

ΔE • As a first approx., we have: Δt∝ M QG

18 2 For GRB 080916C, MQG > 1.3 x 10 GeV/c (Abdo et al. 2009, Science)

For GRB 090510, MQG > 1.2 EPlanck l < lPlanck / 2!! (Adbo et al. 2009)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Other domains

• Biology: impact of the explosion of a GRB in our own Galaxy – Could such a GRB event be at the origin of one of the past mass extinctions on Earth?

• Stellar physics & shock physics

• Origin of cosmic rays of ultra high energy & particle acceleration mechanisms

• Generation of gravitational waves

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe

TheThe futurefuture ……

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Instrumental roadmap in the next 10 years and beyond VLT/X-SHOOTER VLT/MUSE ATCA Fermi? eVLA ALMA E-ELT HESS-2 LOFAR JWST PanStarrs CTA SKA

LSST SVOM

ATHENA

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Future GRB missions SVOM • SVOM = Space Variable Object Monitor • Chinese-French collaboration (0.3-10 keV) (4-150 keV) ● Launch date : 2021 ● Nominal lifetime = 3 years (V & R bands) ● Low Earth orbit (h ~ 630 km) and inclination ~ 30o

(~50 keV-5 MeV) • Multi-wavelength science payload from Gamma- rays (2 wide-field cameras) to X-rays/optical (2 narrow field instruments) & dedicated ground robotic telescopes (one Visible/nIR camera developped at IRAP).

• SVOM will be operated à la Swift (automatic and rapid re-pointing of the plateform following the detection of a GRB with ECLAIRs in order to follow-up the GRB emission with the narrow field instruments VT and MXT)

• Anti-Sun pointing to favor the follow-up of SVOM GRBs with large telescopes (e.g. VLT, E-ELT, Keck, ...)

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe SVOM ECLAIRs: the GRB triggering camera • ECLAIRs ECLAIRs = GRB triggering camera • IRAP = PI of ECLAIRs

• Consortium of French labs under CNES supervision

• ECLAIRs = wide-field coded mask

camera (FoV~2sr; ΔE=4-150 keV; Sgeo~1000 cm2) + Data Process Unit (automatic trigger software)

• IRAP provides the detection plane (DPIX = 80x80 CdTe detectors = 200 XRDPIX) & the readout electronic chain (ELS) performing the coding of detected events (time, position, energy) in real time.

• Elementary module (XRDPIX) = 8x4 detectors associated with a low-noise & low-power-consumption ASIC

(e.g., Godet et al. 2012, 2014;

Nasser et al. 2014) UGTS Gamma-ray bursts: The most violent explosions in the Universe SVOM Ph-D position

• The CNES (French Space Agency) has pre-selected a proposed ph-D subject on the characterization of the performance of the ECLAIRs detection plane.

• The description of the Ph-D subject can be found at http://userpages.irap.omp.eu/~ogodet/ in the sub-directory « Ph-D position».

• Search for an applicant (M2 or engineer) before March 2015 → Final selection by the CNES HQ in June 2015.

• The 3yr Ph-D will start in October 2015.

• Supervisor : Dr. Olivier Godet & Dr. Jean-Luc Atteia

• CNES Ph-D funding grants offer a larger salary than State Ph-D funding grants.

• To those of you that may be interested in, please contact me ( [email protected]) as soon as possible.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Other messengers Introduction

• GRBs may be also a source of non electromagnetic radiation.

• GRBs may be priviledged sites for the acceleration of UHE cosmic rays, high-energy neutrinos and gravitational waves.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe High-E cosmic rays (1)

• Cosmic rays are ionised particles (p+, nuclei, electrons).

• On Earth, we can study particles accelerated up to 14 TeV in Sun accelerators at most. SNe in our Galaxy Extragalactic

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe High-E cosmic rays (2) Containment of the UHE Cosmic Rays • Above 1018-19 eV, the Galactic magnetic field intensity is too low E Larmor radius : R= EeV to confine the protons. ZB kpc μG • So, the origin of the UHE cosmic rays must be extragalactic. Assuming a 3 μG magnetic field

proton • GRBs may be able to accelerate 100 EeV 21 particles up to 10 eV (e.g. O Waxman 2000). Fe • The sources must be located Earth close to Earth (< 200 Mpc) due to 10 kpc the GZK cutoff (Greisen-Zetspin- Kusmin, 1966).

• The GZK cutoff is the result of the interaction between UHECR and CMB photons (~2.7 K).

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Particle detectors ANTARES JEM-EUSO (particle detector) (strong involvement of IRAP)

Observatoire Auger

• HESS 1-2 & CTA (Cherenkov telescope with a strong IRAP involvement)

• ICE CUBE & KM3 (large neutrino telescopes)

SeminarSeminar M2 M2 ASEP ASEP Olivier Olivier Godet Godet 2015 2012 – 01 – –10 05 – 08 Gamma-ray bursts: The most violent explosions in the Universe Gravitational waves (1)

• The gravitational waves are a prediction of the general relativity theory.

• No direct detection was performed so far. However there are indirect evidence of their existence. Binary pulsars PSR B1913 + 16 (Hulse & Taylor 1975; Weisberg et al. 2010)

The decrease in the orbital period of binary pulsars is a consequence of orbital energy loss through gravitational waves.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gravitational waves (2)

• The gravitational waves are a prediction of the general relativity theory.

• No direct detection was performed so far. However there are indirect evidence of their existence.

• Their direct detection would open a new science window and would enable to detect the catastrophic formation of BHs.

• The formation of a BH can generate gravitational waves provided the event is asymmetrical (Kobayashi & Mészáros 2003).

• GRB events being related to the catastrophic formation of BHs via the collapse of a massive star or the merger of two compact objects, they are of great interest to detect GWs.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gravitational waves (3)

• Several ground and space facilities planned to detect GWs.

aLIGO = Advanced Laser Interferometer Gravitational Wave Observatory (10 Hz – 10 kHz) Operational after 2018

aVirgo = Advanced Virgo (French-Italian Interferometer; 10 Hz – 10 kHz)

eLisa = Laser Interferometer Space Antenna or NGO = New Gravitational wave Observatory (0.1 mHz – 0.1 Hz) Operational after 2030

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe Gravitational waves (4)

• The detection of GWs is done by measuring the distance change between two test masses.

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05 Gamma-ray bursts: The most violent explosions in the Universe References

• References accessible via the NASA/ADS web interface http://adsabs.harvard.edu/abstract_service.html

• Gehrels & Meszaros (2012) • Zhang, B. 2007 • Godet, O & Mochkowitz, R. 2011

Seminar M2 ASEP Olivier Godet 2015 – 01 – 05