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The standard model: Fireball ep E~1052 erg Central Engine ?? Shells are optically thick. Internal pressure (due to high energy density) drives the acceleration and internal energy is converted into kinetic energy. G r The standard model: Fireball + Internal shock Shock E~1052 erg Central Engine ?? G Shock transfers energy to the particles and magnetic field Prompt emission is synchrotron Most of the internal energy has been converted into kinetic and the shell coast with constant G r The Internal shock model explains ... … but open issues: 1) Efficiency 2) Hard spectra GRB – The Afterglow (light curve) F(E, t) ~ t – 1.5 GRB – The Afterglow (spectrum) Swift confirmed the structure in the afterglow lightcurve The standard model: Fireball + Internal + External shock GRB AFTERGLOW E~1052 erg Central Engine ?? G Merged shells are decelerated by the ISM r The standard model: synchrotron emission from external shocks N() c < m The standard modell: Fireball + Internal + External shock GRB AFTERGLOW E~1052 erg Progenitor & Central Engine ?? G Q: What is the “central engine”? Merged shells are decelerated by the ISM r At these distances gamma-ray bursts would have an energy of 1052 erg to 1054 erg if they emitted isotropically. That is up to the rest mass of the sun turned into gamma-rays in 10 seconds! The standard model: Fireball + Internal + External shock GRB AFTERGLOW E~1052 erg Central Engine ?? G Merged shells are decelerated by the ISM r Long GRB are in SF regions where most massive stars occur GRB Host Galaxies: types GRB sono in galassie tipicamente irregolari subluminous. (Fruchter et al 2005)ha mostrato che le galassie dei GRB sono molto piu’ piccole, irregolari e tipicamente la posizione dei GRB e’ strettamente correlata con le zone di piu’ alta luminosita’ all’interno delle stesse galassie GRB Host Galaxies: types GRB Host Galaxies GRB SN connection – The first SN 1998bw GRB 980425 Type Ic supernova, d = 36 Mpc Etot ~ 3 x 1052 erg GRB E ~ 8 x 1047 erg; V=3x104 Km/s T= 23 s of a massive CO star (Iwamoto et al 1998; Woosley, Eastman, & Schmidt 1999) Ia binaria con nana bianca – no H vecchie II stella massiccia Fe56 – si H giovani Types Ib and Ic supernovae are caused by the core collapse of massive stars. A Wolf-Rayet star, with a core of about 10 solar M These stars have shed (or been stripped of) their outer envelope of hydrogen, and, when compared to the spectrum of Type Ia supernovae, they lack the absorption line of silicon. Compared to Type Ib, Type Ic supernovae are believed to have lost more of their initial envelope, including most of their helium. The two types are usually referred to as stripped core-collapse supernovae GRB SN connection – The second SN 2003dh GRB 030329 GRB E ~ 10 T ~ 60 sec z=0.1685 52 erg GRB/SN Connection – a few GRB 980425 (40 Mpc) GRB 030329 (z=0.17) GRB 031203 (z=0.1) GRB 060218 (150 Mpc) (Galama et al. 1998, Matheson et al. 2003, Malesani et al. 2004, Pian et al. 2006) GRB/SN are more luminous SN1998bw SN2003dh SN2003lw SN2006aj Woosley and Bloom (2006) Long GRB central engine qjet = 0.1 rad; Ljet = 1050-1051 erg/s ms magnetar Collapsar Supranova (NS) (BH+disk) (delayed BH+disk) B~1015 G M>Mcrit Delay ~ year (clean environ) “Cold” fireball “Cold & Hot” fireball Adv: fallback Today, there are two principal models being discussed for GRBs of the “long-soft” variety: • The collapsar model MacFadyen and Zhang (2005) • The millisecond magnetar Glatzmaier The Collapsar model: BH + (fed) disk Collapsar – the jet’s fate Ejet=3x1050 erg M*=15Msun R*=9x1010 cm tjet ~ 8 s G ~ 200 The standard model: Fireball + Internal + External shock GRB AFTERGLOW E~1052 erg Central Engine ?? G Merged shells are decelerated by the ISM r Progenitors (current paradigm) Still controversial e.g. both early and late type galaxies Short (t < 2 s) Supported by: -Hosts -Position within hosts Long -Direct association with SNIbc (t > 2 s) Short Gamma-Ray burst cannot be produced in SN Their location is not only in star formation regions Figure 7. Snapshots of simulation of two neutron stars merger (each neutron star has 1.4M8 and ≈ 30 km diameter). Initially, they are less than 10 km apart, and moving at around v = 0.2c. The simulation began with a pair of magnetized neutron stars orbiting just 11 miles apart. Each star 1.5 times the mass of the sun into a sphere just 17 miles across and generated a magnetic field about a trillion times stronger than the sun's. In 15 milliseconds, the two neutron stars crashed, merged and transformed into a rapidly spinning black hole weighing 2.9 suns. The edge of the black hole, known as its event horizon, spanned less than six miles. A swirling chaos of superdense matter with temperatures exceeding 18 billion degrees Fahrenheit surrounded the newborn blackhole. The merger amplified the strength of the combined magnetic field, but it also scrambled it into disarray. Over the next 11 milliseconds, gas swirling close to the speed of light continued to amplify the magnetic field, which ultimately became a thousand times stronger than the neutron stars' original fields. At the same time, the field became more organized and gradually formed a pair of outwardly directed funnels along the black hole's rotational axis. From simulations: Merger time: Inspiral phase: 106 yrs Final 100 km less than 1 second Crash: 15 millisecond spinning black hole magnetic field amplification magnetic tower 11 millisecond: jets Ifwith G the not Formation of a GRB could begin either Fireball Model merger two compact objects the collapse The offireball expands andor with uniform, faster shells of a massive star collects ISM collide with slower 54 ergsones, As a result, an energy as high as E~10 can It starts to be decelarated and and internal 6 cm) be released in a compact volume of space (~10 an external shock forms shocks form A of e+/epairs, photons and baryons is Thefireball inital evolution is Part of formed and energy in inverted: bulkexpands kineticconverting energy is thermal the kinetic bulk kinetic baryons converted into energy internal carried energy by the energy is originally present in the explosion site (Mb) across the shock front converted in internal The When accelerated the thermalelectrons motion becomes sub prompt relativistic, the bulk Lorentz factor saturates radiate via synchrotron emission emissionto G 2 =E/M c ~ 1016 cm b afterglow emission ~ 1013 cm The fireball model How to derive clues on the nature of the progenitor? n < 1 cm-3 and uniform medium d E.g. afterglow phase: emission processes, circum-burst medium (density and structure) I will consider the link with the GW domain ~ 1013 cm ~ 1016 cm GW emission from GRB progenitors Long GRB: no in-spiral phase, only merger and ring-down Short GRB: we expect the GW signal to be emitted in 3 phases: inspiral, merger and ring-down Long GRBs: the progenitor Collapsar model (e.g. Woosley 1998): “GRB as the birth cry of a BH”: when the collapse of the iron core of a rotating massive progenitor proceeds directly to a BH formation, the stellar mantle falls into the newly formed BH and angular momentum slows the collapse along the equator, ultimately forming an accretion disk that, within a few seconds, launches particle jets along the rotation axis powering a GRB” “The jets pass through the outer shells of the star and, combined with the vigorous winds of newly forged radioactive metals blowing off the disk inside, give rise to the supernova event” Collisions among shells of the jet moving at different velocities, far from the explosion and moving close to light speed, create the GRB, which can only be seen if the jet points toward us Short GRBs: the progenitor General picture: Merger events of NS+NS or BH+NS systems widely favored: Seems unlikely that typical energies of short GRBs set free during the dynamical merging; the following accretion phase in a postmerger system consisting of a central BH and a surrounding torus is much more promising BH-torus system geometry: relatively baryon-poor regions along the rotational axis thermal energy release preferentially above the BH poles via e.g. anti- annihilation can lead to collimated, highly relativistic jets of baryonic matter if thermal energy deposition rate per unit solid angle sufficiently large. -rays produced in internal shocks when blobs of ultra-relativistic matter in the jet collide with each other. When the jet hits the ISM, the afterglow is produced GRB: progenitor models and time duration Both progenitor types result in the formation of a few solar mass BH, surrounded by a torus whose accretion can provide a sudden release of energy, sufficient to power a burst. But different natural timescales imply different burst durations: LONG: death of massive stars free-fall time of the material falling on the disk form outside, tff ≈ 30s(M/10M⊙) −1/2 (R/1010cm)3/2 SHORT: coalescing compact objects duration set by the viscous timescale of the gas accreting onto the newly-formed BH (short due to the small scale of the system) Short GRBs progenitor – Compact object merger Short GRB hosts cD Elliptical SFR<0.2 Ms/yr Gerhels et al. 2005 SF gal with offset Elliptical SFR<0.02 Ms/yr 790613 (old!) 050813 Gal-Yam et al. 2005 Gladders et al. 2005 Short vs Long HOST properties (Berger et al. 2008) Short are in more luminous and less star forming galaxies Redshift 73 Long 29 Swift 15 Sax 17 Hete N(<z) … 12 other Still few Short GRBs with measured redshifts to infer their N(z), … N(L), … 040924 050813 051221 050724 050509B 050709 Short GRB 050925 Ghirlanda et al. 2006 Swift 5/7 with redshift Short GRBs: distance scale Direct (spectroscopic) redshift measures of ~ 5(swift)+2(Hete) short bursts Z~0.11.0 Statistical analysis of BATSE GRB sample with local galaxies or clusters if Short GRBs are at z<0.1 Z<0.1 … BUT … GRB 080913 @ z=6.7 T(rest) ~1 s Belczynski et al. 2006 Eiso~10^48 erg Short bursts are spectrally and temporally similar to the first 2 sec of long bursts! long Log Epeak long short Nakar & Piran 2005 a Ghir,Ghis,Cel 2004 short …only a (mis)classification case? Short GRB with extended emission Norris et al. 2008, Gerhels et al. 2007 Log(νFν) Typical spectrum Long Single e- spectrum Short Log(ν) F N() Ghir06 4/3 -2/3 tcool ~ 10-7 ee (G/100) 2 MeV 3 s Log(νFν) -ray: synchrotron emission? Cooling Log(ν) νFν ν1/2 N(ν) ν-3/2 Ghir06 A lot of kinetic energy should remain to power the afterglow Piro astro-ph/0001436 Prompt SAX X-ray afterglow light curve Eafterglow < Eprompt Pre-Swift Afterglow Piro astro-ph/0001436 Prompt SAX X-ray afterglow light curve Typical Afterglow Prompt X-ray Afterglow Swift public archive Typical Afterglow Prompt X-ray Afterglow Swift public archive NEW: Steep-Flat-Steep Prompt X-ray Afterglow Flat Swift public archive NEW: Steep-Flat-Steep Prompt X-ray Afterglow Flat Swift public archive NEW: X-ray flares Prompt X-ray Afterglow Swift public archive NEW: X-ray flares Prompt X-ray Afterglow Swift public archive GRB – The Afterglow “Typical” afterglow (most in Opt ; some in X) Steep-flat-steep (most X ; some in Opt) Flux + flares prompt 102 103 104 105 Time GRB – The Afterglow Flares Central engine restart Flux prompt 102 103 104 105 Time X-ray and optical behave differently GRBs & Cosmology GRB080916 (z=6.7) Probes of: “first light” & PopIII chemical evolution large scale structures cover the epoch of reionization Lamb 2002 SFR Figure 11. Light from a GRB and its afterglows travels on its way to the Earth through circumburst medium, host galaxy medium and intervening absorbers. All of these may imprint their signature in the spectrum. From left to right: clouds of gas in the early universe collapsed to form the first (Pop III) massive stars, which probably produced the first GRBs. GRBs may have preceded the formation of the first galaxies and active galactic nuclei/quasars, which are powered by supermassive black holes and formed even later. Thus, GRBs may probe the properties and environment of the first stars and galaxies in the Universe, as well as properties of the intervening absorbers Very high z GRBs ? Pop III Analysis of the Red Damping Wing to Constrain the Reionization ● two possibilities for the origin of the damping wing: 1) A damped Lya system (DLA) associated with the host galaxy ● ● DLAs often found in GRB afterglows GRB 030323 at z=3.372 log NHI (cm-2) ~ 21-22 (Vreeswijk et al. 2004) 2) IGM neutral hydrogen (damping wing of GP trough) ● If detected, it would give a crucial information on xHI 23 April 2009: a Gamma Ray burst at z=8.1 – 8.3 Tanvir et al.(ESO VLT) + Salvaterra et al. (TNG La Palma) Epoca della rionizzazione: z = 10.8 fino a z = 6 Bright quasars rari oltre z=7 Oggetti + lontani confermati spettroscopicamente: Galassia z = 6.96 QSS z = 6.43 z=8.26 = 625 million yrs dopo il Big Bang (4.6% eta’ universo) Duration 10.3 s (1.1 s nel sistema di rif. del burst) troppo corto? ma forse gamma + lungo 1) Stelle massicce gia’ presenti 2) Condizioni a epoca rionizzazione GRBs: distance and energetics If GRBs are isotropic sources … GRB – Spectral Properties GRB Peak Energy F() Where most of power comes out Eiso = 4 dL(z)2 1+z F(E,z,…) dE E Peak energy – Isotropic energy Correlation 9+2 BeppoSAX GRBs Amati et al. 2002 Rest Frame Eiso + 21 GRBs (Batse, Hete-II, Integral) Eiso …but is the energy really so huge? Isotropic Earth Beamed Earth If the energy were beamed to 0.1% (q~5deg) of the sky, then the total energy could be 1000 times less Jet effect Jet half opening angle G >> 1/ Log(F) G ~ 1/ Jet break Log(t) It is a property of matter moving close to the speed of light that it emits its radiation in a small angle along its direction of motion. The angle is inversely proportional to the Lorentz factor 1 G , E.g., G 100 v 0.99995 c 2 2 1 v / c q 1 / G G 10 v 0.995 c This offers a way of measuring the beaming angle. As the beam runs into interstellar matter it slows down. Measurements give an opening angle of about 5 degrees. Afterglow light curve presents a chromatic break Evidence that the GRB outflow is collimated within a jet with a certain opening angle + 21 GRBs (Batse, Hete-II, Integral) ? 1-cos(q) Energy budget with beaming Frail et al.(2001), Peak energy vs. True energy Ghirlanda, Ghisellini, Lazzati 2004 cr21.27 Similar to Supernovae Ia Perlmutter 1998 “Stretching”: the faster the brighter JGRG 17 – G.Gh. Luminosity distance Luminosity distance Luminosity distance 51 erg E=1051 erg E=10 The correlation reduces the scatter of GRBs in the Hubble Diagram Stretch-lum (SNIa) redshift Ep-Eg correlation (GRB) redshift JGRG 17 – G.Gh. Ep-E Results Ghirlanda et al. 2004, Nava et al. 2005 2005, Ghirlanda et al. 2007 17 GRBs (970828 to 041006 – Batse, SAX, Hete-II) + 16 GRBs (050318 to 061121 – Swift) 1.05 EEp EE 1.03 p cc2red dof) 2 =0.89 =1.13(23 (16 dof) red 17 GRB 25 GRB JGRG 17 – G.Gh. 15