Bursts as High Energy Transients

L. Angelo Antonelli INAF-Oss. Astronomico di Roma ASI Science Data Center INFN sez. Roma 2 “Tor Vergata”

Outline

1) Observation • The discovery • CGRO and the burst characterization • BeppoSAX and the afterglow discovery • SWIFT: deep inside the afterglow era • Fermi and the HE domain 2) Models & Physics • The central engine & emitting processes • Progenitors • The environment Gamma Ray Bursts: the discovery

• 1967-1979 4,5,6 satellites: look for X and gamma rays in order to monitor compliance with the Geneva Limited Nuclear Test Ban Treaty of 1963 (no nuclear tests in space and atmosphere) • 105 km Orbits

• Launched in pairs – launched 1963-1969

• Operated until 1979

• All satellites allowed for some localization. Gamma Ray Bursts: the discovery • Vela satellites discovered intense flashes of Gamma rays of cosmic origin.

• Due to the military nature of the satellites the discovery was maintained classified until 1973 when it was announced to the GAMMA RAY BURSTS (GRBs) (Klebesadel et al. 1973; Strong et al. 1974) astronomical community.

What Gamma Ray Bursts are?

Klebesadel et al., 1973 Gamma Ray Bursts: the discovery

• Non-imaging Cs-I detectors ≈ 150 keV – 750 keV • Coincident events in light curves • Timing studies/ triangulation ⇒ Cosmic origin

In 10 years over 73 burst were observed. Klebesadel, Strong, & Olson (1973) Not only Gamma Ray Bursts

• The so called “Vela Incident” (sometimes referred to as the South Atlantic Flash) was an unidentified “double flash" of gamma ray that was detected by a Vela satellite on September 22, 1979.

• Probably due to a real nuclear experiment performed nearby to the , it was the only terrestrial

explosion recorded by these instruments. Gamma Ray Bursts: after the discovery -Many gamma ray burst detectors equipped a large number of spacecrafts.

-Hundreds GRBs were discovered from satellite networks through the 80’s.

-No clue on source distance

Apollo 15 - Harwit in 1984 in the work “Cosmic Discovery” said: “Remarkably little is known about gamma- ray bursts.”

Venera 12 Ulysses The InterPlanetary Network

• The InterPlanetary Network (IPN) is a group of spacecrafts located in the Solar System and equipped with gamma-ray burst detectors.

• By timing the arrival of a burst at several spacecraft, its precise location can be found.

The farther apart the detectors,

the more precise the location. Theorists’ Paradise With so few constraints, all sort of models were proposed. • Solar System: comet knots, magnetic reconnection in heliopause, etc. • Galactic: SGR, quakes, Magnetic reconnections, etc. • Cosmological: hypernovae, NS-NS mergers, tidal disruption, AGN, matter-antimatter annihilation, etc. Galactic Solar System Energy Requirements may vary over more than 20 orders of magnitude! Fluence:10-7 erg cm-2

2 Energy = Fluence. x d Distance: 1 Gpc Cosmological Energy:1051 erg Distance: 100 kpc Energy: 1043 erg

By 1992, over 100 models Existed!

Exploring the GRB Phenomenon: CGRO Compton Gamma Ray Observatory (CGRO)

• The second of NASA's great observatories

• Operational in 1991-2000 • 4 instruments covering the 30 keV – 30 GeV energy range

• BATSE observed ~ 1 GRB/day with few degree accuracy and rapid

data dissemination, yielding a wealth of new results What CGRO told us about GRBs ?

A sample of GRB light curves

• Brief (1ms-100s) intense flashes of Gamma-rays

• About 1 per day

• A GRB does not repeat.

• They are isotropically distributed in the sky

• No information are available regarding the luminosity

BATSE suggestion for a cosmological origin of GRBs

• No evidence for anisotropy in GRB directions (Meegan et al. 1992) • Peak count size distribution deviates from -3/2 size distribution

GRB Peak Count Rate Distribution -3/2 N ∝ φp Gamma ray burst characteristics: Light Curves

• Wide range of morphologies • ~25% have fast rise, slow decay profile • Durations from ms up to thousands of seconds • No evidence for periodicities • No standard shape

Empirical correlations: • Hardness-Intensity • hard-to-soft evolution

Gamma ray bursts characteristcs: duration distribution.

• GRBs duration distribution is double peaked. It peaks around 0.2 s and 20 s. Two Populations: Short – 0.03-3s Long – 3-1000s (e.g. Briggs et al. 2002)

• Short GRBs are harder than long GRBs

(e.g. Fishman & Meegan, 1995). Gamma ray bursts characteristics: Energy spectra.

−α * E ' * E(2 +α) ' F(E) = A( % exp(− % E < Ebreak 100 ( E % ) & ) peak & GRBs spectra are well fitted by * ' (α −β ) ( % 0 E peak - ( (β −α) % the empirical “Band Function”: F(E) = A/(α − β ) , exp β E ≥ Ebreak 100(2 +α) ( E % . [ ]+ ( * ' % ( ( % % a smoothly broken power-law. ) )100 & & (α − β )E E = peak break (2 +α) (Band et al.,1993)

α Ebreak β

Epeak Band Function parameters

Preece et al. (2000) GRBs spectra properties

• The time resolved spectral analysis of GRBs shows a hard-to-soft evolution of

the spectrum and the decrease of Epeak (e.g. Frontera et al., 2000).

Spectral evolution of GRB 000214 is shown in figure (from Antonelli et al., 2002) Long and Short GRBs spectral properties.

Short bursts

• Short and Long GRBs have the same spectral shape but Long show differences in values bursts of spectral parameters. (Pecesias et al., 2002) BeppoSAX and the Afterglow Era BeppoSAX & GRBs Afterglow

• Launched on April 30, 1996 and switched-off on April 30, 2002, deorbited on April 30, 2003 • First and last observation of a GRB on July 20, 1996 and on April 30, 2002 BeppoSAX & GRBs GRB970111: the 1st fast localization & follow-up of a GRB

• Triggered by GRBM and localized by the WFC of BeppoSAX

• fast follow-up (16 hrs after the GRB) by the NFI.

• In MECS (2-10 keV) image a faint source is detected: F=(1.2±0.3)x10-13 cgs

(Feroci, Antonelli, Guainazzi, et al., 1998) GRB970228: the 1st X-ray and Optical afterglow

• Fast follow up with NFI (8hr) led to discover a bright unknown X-ray source.

• A second pointing 3 days after showed the source (Costa, et al., 1997) faded.

Thanks to the good X-ray position an optical fading source could be observed.

(Van Paradijs, et al., 1997) GRB970508: the 1st redshift • Images in the 2-10 keV range by the BSAX WFC (10-200 sec after the GRB) and by the BSAX MECS (6 hrs and 3 days). The BSAX observation led the Caltech group to the measurement of the first redshift and Frail et al. to the discovery of the 1st radio afterglow and direct measurement of relativistic expansion

Metzeger et al., 1997

GRBs are definitively sources at cosmological distances! GRB970508: direct evidence of relativistic expansion

• Discovery of the radio afterglow • Direct evidence of a relativistic expanding source. In the first 3 weeks the radio source exhibited erratic variations that then disappeared. if it is due to diffractive scintillation of radio waves on interstellar electrons, the damping of the fluctuations later on indicates that the source had expanded to a greater size 1 month => 1017 cm knowing source distance, a relativistic velocity is derived (Frail et al., 1997). GRB Redshifts (2000) GRB Redshift Isotropic GRB Redshift Isotropic Energy Energy GRB970228 0.695 5x1051 GRB990308 >1.2? NA GRB970508 0.835 8x1051 GRB990506 1.3 NA GRB970828 0.958 NA GRB990510 1.619 3x1053 GRB971214 3.418 3x1053 GRB990705 0.86 NA GRB980326 1? 3x1051 GRB990712 0.430 NA GRB980329 2 or 3-5 NA GRB991208 0.706 1.3x1053 GRB980425 0.0085 1048 GRB991216 1.02 6.7x1053 GRB980613 1.096 NA GRB000131 4.5 1054 GRB980703 0.966 1x1053 GRB000418 1.118 5x1052 GRB990123 1.600 3x1054 GRB000926 2.066 2.6x1053 GRBs are definitively sources at cosmological distances as well as the most energetic sources in the Universe! Amati Relation between Epk and Eiso

Evidence for a strong correlation between Ep and Eiso

0.52±0.06 Epk = kEiso

(Lamb et al. 2004)

(Amati et al. 2002)

• spans 5 orders of magnitude in Eiso and 3 orders of magnitude in Epk Power laws: the hallmark of afterglows

-δ • Fx(t) ∝ t , δx≈1.1-1.4

-α • Fx(ν) ∝ ν , αx≈1.1 Prompt domain

Afterglow domain

GB000926:Piro et al, 01 Simultaneous Optical and X-ray light curves of GB990510

• Late time optical light curves of GRBs afterglow are also decaying following a typical power law behavior. • Decay behavior is not depending on wavelength (with some exception) • GRB 990510: a break in the OT at t=1 day is observed (Harrison et al 99) • BeppoSAX light curve compatible with break 1 10 T-T0(days)

(Kuulkers, Antonelli, Kuiper et al., 2000) HOST OF GRB

Bluish star-forming galaxies: dwarf irregulars or spiral host galaxies ~ 1/3 dark bursts ⇒ Dusty media? ⇒ Regions of active star formation van Paradijs et al. (2000) The GRB-SN Connection

GB980425: in the BeppoSAX error box:

SN1998bw (Pian et al99,Kulkarni et al,

Galama et al al 98).

Exploded within 1 day from the GRB. Chance P=10-4 The GRB-SN Connection

• GRB optical counterparts coincident with center or spiral arms of hosts

• Reddened supernova emission in late time optical afterglow spectra

• SN bumps in some GRB light curves behavior

GRB 980326 (Bloom et al. 99)

Bloom et al. (2002)

(Della Valle et al. 2003) GRB 030329: the smocking gun

Matheson et al. 2004

Stanek et al. 2004 • Optical afterglow spectrum resembles that of SN1998bw • Broad, shallow absorption lines imply large expansion velocities • GRB030329 was a bright (top 1%) nearby (z =

0.17) burst, discovered by HETE-II • Afterglow light curve can be decomposed into two components: • Its optical afterglow light curve and spectrum power law decay + supernova bump point clearly to an underlying supernova Ic (SN1998bw redshifted) component (SN2003dh)

⇒ Some long GRB’s can be associated with the deaths of massive (>30M¤) Exploring the Early Afterglow Triggering GRBs

HETE-2: 2 GRB/month with <10 arcmin accuracy and rapid data dissemination in 10-100 sec from burst

INTEGRAL: 1 GRB/month with <10 arcmin accuracy and rapid data dissemination in few sec from burst

SWIFT: 2 GRB/week with <3 arcmin accuracy and rapid data dissemination in few sec from burst, <6’’ in <200 sec, < 1’’ in few min Prompt Optical Emission

1 2 3 Discovery of Prompt Optical Emission of GRB 990123 (Ackerlof et al, 1999)

-1 keV -1 1 2 3 Coupss

Prompt Emission is not limited to γ-ray domain, GRB 990123 emitted in optical an isotropic equivalent energy 49 of ~ 10 ergs (mV ~ 9 in image 2 ) ROTSE-1 Prompt Optical Emission

Optical Observations of the error box of GRB 021004 m = 15,3 R detected and localized with HETE-2 and VLT follow up After 12 hrs when the OT was still R=18.2

FORS1 R~1000 UVES R=42000 CIV CIV CIV CIV z=2.296 z=2.328 z=2.296 z=2.328 NEAT/48’’ Palomar 9 min after burst

Image DPOSS Fiore et al.,, 2005 (20/8/1990) SWIFT

NASA MIDEX Mission selected in 1999

Primary science is to study gamma- ray bursts throughout the Universe

International hardware participation from UK and Italy

Launched on November 20, 2004

SWIFT BAT XRT UVOT • Burst Alert Telescope (BAT) – New CdZnTe detectors – Sensitive gamma ray imager 15-150 keV – Precision 2-3 arcmin – Field of view: 1/6 of the sky • X-Ray Telescope (XRT) – GRB positions within 3” – Imaging 0.2-10 keV – Sensitivity 2x10–14 cgs – CCD spectroscopy • (UVOT) UV/Optical Telescope – 30 cm Optical/UV telescope – Sub-arcsec imaging – Grism spectroscopy – 20th mag sensitivity (1000 sec) – Finding chart for other observers • Spacecraft – Autonomous re-pointing, 70 - 120 sec – Onboard and ground triggers – Low-orbit => Low- background

La Palma, Dec. 3, 2007 The Early Afterglow

Filling the gap between the prompt and afterglow phases

t −6 * The afterglow smoothly Flare

joins to the prompt t −0.7 emission t −1.2 * There is a steep decay 5 orders of magnitude! 5 orders after the GRB t −2.3 Jet Break Sketch of the early GRB X-ray light curve GRBs & the far Universe GRB 090423: TNG spectrum Spectrum taken with the Amici prism on the TNG/NICS camera at ~14 hrs

most distant object ever observed !

Amici prism: λ=0.8 – 2.4 µm R ~ 50

-0.3 λobs=1216 A (1+z) z=8.1 +0.1

Salvaterra et al., 2009, Nature, 461 GRB 090423: X-ray afterglow

canonical light curve

analysis of the XRT spectrum shows intrinsic absorption N =7x1022 cm-2 H • Come tutti i bursts e NH Lower limit to the metallicity of the • Above the critical metallicity circum-burst medium

Z> 0.04 Z€

Above critical metallicity for PopIII: -6 -4 Zcrit=10 – 10 Z€ GRB 090429B

Z= 9.4

Cucchiara et al., 2011 Redshift Distribution of Swift GRBs

Jakobsson, P., 2011 Short GRBs

GRBs duration distribution is double peaked. It peaks around 0.2 s and 20 s. Short GRBs are harder than long GRBs

BeppoSAX did not observe any Short GRB. Short GRBs: GRB050509B

Short GRBs associated with elliptical galaxies. left: GRB 050509B; z=0.226 (Gehrels et al. 2005; Bloom et al. 2006a), the red and blue circles are BAT and XRT error boxes, respectively; Right: GRB 050724; z=0.257 (Barthelmy et al. 2005b; Berger et al. 2005a) Eight years of Swift Observations

Racusin, 2012 HIGH ENERGIES PROPERTIES OBSERVED IN FERMI GRBs VHE Properties of GRBs

Hurley et al. 1994 • A 18 GeV photon observed by EGRET 90 minutes after the start of the GRB • Evidence for second component GRBs in the Fermi Era GRBs in the Fermi Era

Omodei, Fermi Symposium 2011 Delayed VHE Emission.

GRB 080916C

Delayed high energy emission

z ≈ 4.35

Eobs= Eem(1+z)

13.2 à 70.6 GeV

54 Eiso ≈ 8.8 10 ergs

Abdo et al. 2009 Delayed VHE Emission.

(long) GRB 090902B (short) GRB 090510

8 – 14.3 keV 8 - 260 keV

14.3 – 260 keV 260 keV – 5 MeV

260 keV – 5 MeV all LAT events LAT (all events) >100 MeV > 100 MeV

> 1 GeV > 1 GeV

-0.5 0 0.5 1 1.5 2 2.5 3 0 20 40 60 80 Ackermann, et al., 2010 t(s) Abdo et al. 2009 t(s) Long-lived VHE Emission

∝t-1.5 ∝t-1.38±0.07

GRB 090902B GRB 090510

Abdo et al. 2009

∝t-1.2±0.2

GRB 080916C De Pasquale, M., et al. 2010

Abdo et al. 2009 VHE Spectra of GRBs

GRB 080916C

α = -1.02 +/- 0.02 β = -2.21 +/- 0.03

Epeak = 1170 +/- 142 keV

Abdo et al. 2009 Spectra are consistent with Band functions over 7 decades A Hard Component in Long & Short GRB Spectra

GRB090510 GRB 090902B

Abdo, A., et al. 2009

Ackermann, et al., 2010 Best fit spectrum (T0+4.6 s to T0 + 9.6 s) is a band function (smoothly broken GRB090510. First bright short GRB power-law) + power-law component. Clear detection of an extra component, inconsistent with the Band function. Fermi LAT GRB detection rate ~ 6 GRB/yr with >10 photons above 100 MeV ~ 2 GRB/yr with >10 photons above above 1 GeV

Omodei, Fermi Symposium 2011 GRB properties relevant to VHE experiments

1. Very High-Energy emission is often extended in time, even for short bursts. 2. Delayed onset of high-energy emission. 3. Band spectral fits showing time evolution and different shapes: • no evidence for cut-offs or extra spectral component through 7 decades of energy, • clear detection of an extra component, inconsistent with the Band function with no measured cut-offs • (maybe cut-offs at higher energy GRB090926)

4. LAT GRBs show evidence of ultrarelativistic outflows with Γ>1000 5. LAT GRBs are constraining EBL models 6. LAT GRBs are constraining QG models Models & Physics The compactness problem

Briggs et al. (1999) Light curve variability ~ 1 ms

Non thermal spectra

• Fluence (γ): (0.1-100) x 10-6 erg/cm2 (Ω/4π) • Total Energy: E ~ 1051 ÷ 1054 erg The compactness problem

Very High Optical Depth to pair production

Size Pair fraction

Piran (1999) Relativistic motion of the emitting region The fireball model

• The solution: a relativistic expanding fireball (Cavallo & Rees, 1978) The internal energy is converted in kinetic energy of baryons through 2 γ-γ=>e+e- and Coulomb coupling of electron with protons: Eγ->Eb=Γmbc – The shell expands freely (coasting phase) with Lorentz factor Γ ≈ 100-1000 sweeping up the mass in the environment m(R) like a snow-plough until the 2 mass-energy collected is equal to the initial baryon mass: Γm(R)=mbc For 3 16 17 typical values of density of ISM (n=1 cm ), R ≈ 10 -10 cm (=> τγγ <1) – The relativistic shell is braked, Γ ≈ t-b and the kinetic energy is converted back to electromagnetic radiation by synchrotron radiation of shock- accelerated electrons (Power law spectrum) – The spectrum emitted in the reference frame of the shell is Doppler boosted by Γ. Since Γ is decreasing as a power law, the flux at a fixed frequency will decrease following a power law. – Another possible dissipation mechanism is the Internal shocks: collisions between different parts of the plasma (Rees & Meszaros, 1992, 1994) The Fireball model

• Relativistic motion of the emitting region • Shock mechanism converts the kinetic energy of the shells into radiation. • Baryon Loading problem

External Shock § Synchrotron & SSC § High conversion efficiency § Not easy to justify the rapid variability

Internal Shocks § Source activity § Synchrotron Emission § Rapid time Variability § Low conversion efficiency Internal Shock Scenario • Prompt emission • Solve variability problem • Spectral evolution

Internal Shock variability The radiation mechanisms GRBs: the largest explosions since the Big Bang

GRB990123 is one the brightest event ever observed by BATSE, it was at z=1.6 implying an energy release of

E= 4x1054 erg => M=E/c2 = 2 Masses

1 Etot = Eγ,iso εγ

Etot: the total energy Eγ,iso: observer γ-ray isotropic energy GRBs energetics

θ 2 E = ε −1E = ε −1 E tot γ γ γ 2 γ iso

Eγ: actual γ-ray energy Jet and Energy Requirements

Frail et al. (2001) Jet vs spherical expansion

F -1 Spher. Γ (t4)=θ

Jet t 4 t

θ The break is t t t t t θ = few deg achromatic 1 2 3 4 5 The Afterglow model

• External Shock scenario

• Forward + Reverse Shock

• Jet structure confirmation

• External density

Radiation: synchrotron + IC (?) (Sari, Piran & Narayan 98) Clean, well defined problem. Few (?) parameters:

E, n, p, εe, εB Blast wave deceleration Afterglow Theory

- FIREBALL MODEL -

§ Relativistic Shocks § Power Law distribution of e- § Synchrotron Emission § IC Emission § Early fast variability

Sari, Piran & Narayan (1998) Comparison with Observations (Sari, Piran & Narayan 98; Wijers & Galama 98; Granot, Piran & Sari 98; Panaitescu & Kumar 02)

GRB 970508

Radio observations

Radio to X-ray The progenitor of GRB

• NS-NS (BH-NS & BH-WD) travel far from their formation sites before producing GRB’s (Fryer et al 2000) => “clean environment”

• Hypernovae/collapsar evolve much faster, going off in their formation site =>“mass-rich environment”

NS/BH Binary Mergers

• Merging of compact objects (NS-NS, NS-BH, etc.) • These objects are observed in our Galaxy. • The merging time is about 108 yr, via GW emission. • Well describes behavior of Short GRBs Eichler et. al. (1989) Collapsar model

Woosley (1993)

• V ery massive star that collapses in a rapidly spinning BH. • Identification with SN explosion. • Well describes the behavior of Long GRBs All Collapsar models will produce JETS! GRBs must be beamed! Thank you!