Presentation on theme: "Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts)"— Presentation transcript:
1 Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts) Nova Físicano Espaço 2003João Braga – INPEbreve história dos GRBsBeppoSAX: afterglowsgaláxias hospedeiras e redshiftsmodelos para os progenitoresresultados recentes (HETE)SWIFT, MIRAX e o futuro
2 HistoryJuly 1967: Vela satellites detect strong gamma ray signals coming from space16 peculiar events of cosmic originshort (~s) photon flashes with E > 100 MeVpublication only in 1973 (classified before that)Phenomenology of bursts before the 90’s:almost no association with known objectsstatistically poor distributionno clue
3 History Burst of March 5th, 1979 intense -ray pulse (0.2 s), ~100 times as intense as any previous burstSNR N49 in LMC (~10,000 ys)8 s oscillations in ~200 s (softer emission)Nature of GRBs associated with Galactic neutron stars:rapid variability compact object (light-seconds)cyclotron tens of keV B ~ 1012 G : = eB/mcemission hundreds of KeV redshifted 511 keVzobs = z0 (1 – 2GM/c2 R)periodicity rotation of a NS : R3 < (GM/42) T2
4 BATSE – COMPTON GRO launched on 1991 - ~10 years 2704 bursts (~1 each day)Isotropic distribution- No concentration towards LMC, M31 or nearby clusters- No dipole and quadupole momentsNo spectral linesNo periodicityHundreds of models proposed
7 BATSE – COMPTON GRO Bimodal distribution EuclideanBimodal distribution— most are longer than 2 s— ~1/3 are shorter than 2 sSpectra: combination of two power-laws- spectrum softens with time- Ep decreases with time (in the E.f(E) x E plot)Fluence: ~ 10-6 — 10-4 erg cm-2long duration and hard spectrum bursts deviate more froma 3-D Euclidean brightness distribution
8 Soft Gamma Ray Repeaters SGR Burst of March 5th, 1979 (SGR )SNR N49 in LMC (~10,000 ys)SOFT GAMMA RAY REPEATERSbursts repeat in random timescales (normally hundreds of times) (4, maybe 5 objects known)soft spectra (E 100 keV)short duration (~100 ms)Galactic “distribution”, associated with SNRspossibly associated with magnetars and AXPs
10 BeppoSAX and Afterglows 4 narrow field instruments(.1 to 300 keV; ~arcminute res.) Wide Field Camera(2 to 28 keV; 200 x 200 ; 5’; coded-mask) Gamma Ray Burst Monitor(60 to 600 keV; side shield)WFC
11 BeppoSAX and Afterglows 97 Feb 28: GRBDiscovered by GRBM and WFCNFIs observe 1SAX JFirst clear evidence of a GRB X-ray tail Non-thermal spectra X-ray fluence is 40% of -ray fluence
12 BeppoSAX and Afterglows BeppoSAX and RXTE discovered several other afterglowsOptical transients:Observed in appr. ½ of the well localized burstsGRB is the only one observed in the optical when the gamma-ray flash was still going on
13 GRB 990123 z=1.6 Keck OT spectrum HST image: host is an irregular, possibly merging system
17 Host galaxies Optical IDs distant galaxies (low luminosity, blue) ~30 measured redshiftsAll in the z = 0.3 – 4.5 range, with the exception of GRB , possibly associated with SN z = 0.008OT is never far from center
21 Types of Bursts Long and short bursts: the normal ones. Bimodal distribution; short bursts are harderand have no counterparts; almost all longbursts have X-ray afterglows.Dark bursts: long bursts with X-ray afterglowsbut no optical or radio afterglows (½ of them).Possible explanations:Absorption in the host galaxyThey are beamed away from the observerX-ray flashes (XRF’s): little or no emissionabove ~ 25 keV. Possibly related to X-ray richGRBs.
22 Types of Bursts 25% 20 30% no 30 20% 0.3 ? Burst Class Long (normal) Percentage of allburstsTypical duration(sec)Initial gamma-ray emissionAfterglow X-ray emissionAfterglow optical emissionLong(normal)25%20(dark)30%no(X-ray rich or XRF)30Absent or weakshort20%0.3?
23 GRBs may be associated with rare types of supernovae ProgenitorsLong GRBs are probably associated with massive and short-lived progenitorsGRBs may be associated with rare types of supernovaeHypernovae: colapse of rotating massive star black hole accreting from a toroidCollapsar: coalescence with a compact companion GRBs and SN-type remnant
24 Progenitors Short GRBs - ?? associated with mergers of compact objects SGRs in external galaxiesphase transition to strange stars
25 Relativistic expanding fireball (e± , ) The fireball modelObserved fluxes require 1054 erg emitted in seconds in a small region (~km)Relativistic expanding fireball (e± , )Problem: energy would be converted into Ek of accelerated baryons, spectrum would be quasi-thermal, and events wouldn’t be much longer than ms.Solution: fireball shock model: shock waves will inevitably occur in the outflow (after fireball becomes transparent) reconvert Ek into nonthermal particle and radiation energy.
26 The fireball modelComplex light curves are due to internal shocks caused by velocity variations.Turbulent magnetic fields built up behind the shocks synchrotron power-law radiation spectrum Compton scattering to GeV range.Jetted fireball: fireball can be significantly collimated if progenitor is a massive star with rapid rotation escape route along the rotation axis jet formation alleviate energy requirements higher burst rates
28 The cannonball model Bipolar jets of highly relativistic cannon balls are launched axially in core-collapse SNeThe CB front surfaces are collisionally heatedto ~keV as they cross the SN shell and thewind ejecta from the SN progenitorA gamma-ray pulse in a GRB is the quasi-thermal radiation emitted when a CBbecomes visible, boosted and collimated byits highly relativistic motionThe afterglow is mainly synchrotron radiationfrom the electrons the CBs gather by goingthrough the ISM
29 HETE High Energy Transient Explorer space.mit.edu/HETEFirst dedicated GRB mission, X- and g-raysEquatorial orbit, antisolar pointinglaunched on Oct 9th, Pegasus3 instruments, 1.5 sr common FOVSXC ( keV) - < 30” localizationWXM (2 –25 keV) - < 10’ localizationFREGATE (6-400keV) - sr localizationRapid dissemination ( 1s) of GRB positions(Internet and GCN)
31 HETE Investigator Team RIKENMasaru Matsuoka Nobuyuki Kawai Atsumasa YoshidaMITGeorge R. Ricker (PI) Geoffrey Crew John P.Doty Al Levine Roland Vanderspek Joel VillasenorUC BerkeleyKevin Hurley J. Garrett JerniganUChicagoDonald Q. Lamb Carlo GrazianiCESRJean-Luc Atteia Gilbert Vedrenne Jean-Francois Olive Michel BoerINPEJoão BragaLANLEdward E. Fenimore Mark GalassiCNRGraziella PizzichiniCNESJean-Luc IsslerUC Santa CruzStanford WoosleySUP’AEROChristian ColongoTIRFRavi Manchanda
33 IPN annulus (radius 60o ± 0.118o) HETE results GRBBright (>80) burst detected on Sept 21, :15:50.56 UT by FREGATEFirst HETE-discovered GRB with counterpartDetected by WXM, giving good X position(10o x 20’ strip)Cross-correlation with Ulysses time historyIPN annulus (radius 60o ± 0.118o)intersection gives error region with310 arcmin2 centered at ~ 22h55m30s, ~ 40052’
35 GRB 010921 Highly symmetric at high energies Lower S/N for WXM due to offsetDurations increase by 65% at lower energiesHard-to-soft spectral evolutionPeak energy flux in the 4-25 keV band is 1/3 of keVPeak photon flux is ~4 times higher in the 4-25 keV
36 GRBLong duration GRBX-ray rich, but no XRF (high keV flux)z = isotropic energy of 7.8 x 1051 erg (M=0.3, =0.7, H0=65 km s-1 Mpc-1) - less if beamedSecond lowest z strong candidate for extended searches for possible associated supernovaFinal position available 15.2h after burst ground-based observations in the first night counterpart established well within HETE-IPN error region
38 GRB 020405 Highly significant polarization (9.9%) in the V band measured 1.3 days after the burstz = based on emission lines ofhost galaxyHigh polarization can be due to:line of sight at the very edge of the jet if themagnetic field is restricted to the plane of the shockalignment of the magnetic field over causally connectedregions in the observed portion of the afterglow
39 GRB 020531 Short, hard GRB detected by FREGATE and WXM on 31 May 2002 Short, intense peak followed by a marginal peak, which is common on short, hard burstsT50 = 360 msec in the 85 – 300 keV bandPreliminary localization 88min after burst,refined IPN localization 5 days after burstRA = +15h 15m 04s, Dec = -19o 24’ 51”(22 square arcmin hexagonal region)Follow-up at radio, optical and X-raysDuration increases with decreasing energyand spectrum evolves from hard to soft► seem to indicate that short, hard bursts areclosed related to long GRBs
40 GRB 021004 detected by Fregate, WXM and SXC duration of ~100 sec (long GRB)GCN position notice (WXM) given 49 safter the beginning of the burstSXC location given 154 min after burstoptical afterglow (R) detected in 9 min (15th mag)HST and Chandra observed in the following daybest observed burst so farabsorption redshift of 2.3 (C IV, Si IV, Ly)unusual brightenings seen in the light curve
41 GRB 021211 Dark burst Duration of ~2.5 sec (“ transitional” GRB) GCN position notice (WXM) given 22 safter the beginning of the burstRaptor (LANL) observed 65 sec after burstOptical afterglow extremely faint after 2 hoursGRB may have occurred on region with nosurrouding gas or dust, so the shock wavehad little material to smash into maysupport the binary merger theory for short GRB
43 New missions SWIFT (US): 3 instruments, large area, 250-300 bursts/yr, coverage from optical to gamma-rays,arcsecond positions, will detect bursts upto z ~20. Will be launched in 2003.INTEGRAL (Europe): launched last year. Severalinstruments with high energy resolution.EXIST (US): huge area hard X-ray mission for 2010.GLAST (US): large area high energy gamma-ray mission; will study high energy afterglows. To be launched around 2007.MIRAX (Brazil, US, Holland, Germany): broadband imaging (6’) spectroscopy of a large source sample (1000 square degrees) in the central Galactic plane region. Expected to detect ~1 GRB/month. Two hard X-ray cameras and the flight model of the WFC. To be launched in ~2007.
44 What we do “know” about GRBs so far Every GRB signals the birth of a sizable stellar-mass black hole somewhere in the observable universe.Long GRBs occur in star forming galaxies at an average redshift of ~1.There are now plausible or certain host galaxies found for all but 1 or 2 GRBs with X-ray, optical or radio afterglows positioned with arcsecond precision.~30 redshifts have been measured for GRB hosts and/or afterglows, ranging from 0.25 (or maybe ) to 4.5.BATSE results and current estimates for beaming imply that GRBs occur at a rate of 1000/day in the universe.In a few cases, marginal evidence exist for transient X-ray emission lines and absorption features in the prompt and early afterglows.
45 What to expect in the coming years Early afterglows will be carefully studied the missing link between the prompt emission and the afterglow will be identified;The jet configuration will be identified universal structured jet model will be validated by future data;With accumulation of a large sampe of spectral information and redshifts for GRB/XRF with Swift, we will know a lot more about the site(s) and mechanism(s) for the prompt emission;Detection of GRB afterglows with z > 6 may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era. (Djorgovski et al. 2003);With Swift, we should get ~120 GRBs to produce Hubble diagrams free of all effects of dust extinction and out to redshifts impossible to reach by any other method (Schaefer 2003).
46 Open questions What is the exact nature of the central engine? Why does it work so intermittently, ejecting blobs with large contrast in their bulk Lorentz factors?What is the radiation mechanism of the prompt emission?What is the jet angle? If between 2o and 20o, the energy can vary by ~500 (~1050 – 1052 erg)What is the efficiency of converting bulk motion into radiation?