Gammaray bursts Tomasz Bulik CAMK Warsaw Outline Observations
Gamma-ray bursts Tomasz Bulik CAMK, Warsaw
Outline ● Observations: prompt gamma emission, afterglows ● Theoretical modeling ● Current challenges in the field ● Future
The first GRB More than 30 years ago! Klebesadel, Strong i Olson Ap. J 182, L 85 1973
Sky distribution
Spatial distribution
Temporal properties ● Duration from 0. 01 s to 1000 s ● Irregular lightcurves ● Individual pulses: less than a ms, ● Asymmetric pulses, FRED type
Lightcurves Every burst is different! Power density spectra with a – 5/3 slope
Spectral break between 100 ke. V do 1 Me. V E (Me. V)
Spectral properties ● Nonthermal continuum ● Broken PL, ● Break energy distribution, X-ray rich bursts ● High energy tails: Ge. V, (up to 1. 5 hours) ● Even higher: Te. V (GRB 970417) ● Spectral features?
Classes of bursts Short (hard) Long (soft)
Other classes of bursts • X-ray rich bursts • Long lag-bursts – the first anisotropy found, posible connection with supergalactic plane
Afterglows X-ray Optical Radio
Afterglow lightcurve breaks
GRB host galaxies GRB 990123 GRB 990712
GRB redshifts Most observed bursts at: z<2
GRBs and supernovae 1998 bw GRB 980425 GRB 980326 Bloom et al 99
Supernovae GRB 030329 SN Ic Stanek et al 2003
Afterglow properties • Broad band phenomenon – from radio to X-rays • Power law decay, but bumps and wiggles • Achromatic brakes in the lightcurves • Underlying host galaxies • X-ray lines – probable
Characteristic GRB numbers ● Distance: z=1 -2 ● Spectrum: nonthermal, peaks around 300 ke. V ● Luminosity: ● Duration: ● Collimation: ● Rate - a few daily (observed) isotropic
Theoretical models
Compactness problem Pair creation optical depth: Relativistic motion:
Blastwave model Internal shocks – gamma ray burst prompt emission External shocks - afterglow
Afterglow lightcurve breaks Achromatic breaks – beaming estimate
Energy reservoir Collimation correction Standard energy reservoir
GRB progenitors ● ● Black hole accretion torus models – Collapsars – Binary coalescences Magnetar collapse
Collapsars ● A massive rotating star collapses ● Rotating BH is formed ● Dense matter torus ● Accretion and jets
Can a jet leave a star? Zhang Woosley 2003.
Host galaxies ● ● Typical for their redshifts Traces of active star formation GRBs inside galaxies Distribution around galaxies:
Binary coalescences: in or out of galaxies? Belczyński Bulik 2002
Magnetar model ● Quickly rotating magnetar B=10^17 Gauss ● Differential rotation ● Toroidal field ● Magnetohydrodynamic jet formed ● Delay after supernova
Caution… Not known log. N- log. S =3/2 ? ? Known
Current problems ? ?
Short bursts ● A different population? Distances? ● Other progenitors? ● Inside or outside of galaxies? ● Afterglows or not?
GRB SN connection Are all bursts accompanied by supernovae? What types of stars are connected with GRB SN? Are supernovae and bursts simultaneous?
Correlations Reichart etal 2001 Do we already see bursts at z=10 -30 ? ? ? Norris etal 2001 ● Luminosity variability ● Luminosity - lags
Polarization in gamma rays % GRB 021206 RHESSI
Polarization - possibilities ● ● ● Ordered magnetic fields in a wide jet Narrow jet, inverse Compton emission Emission from Poynting flux jet
Future…
SWIFT Arcminute accuracy 10 s After trigger XRT and UVOT observe in 50 s Launch – spring 2004
GLAST GBM – sensitive to GRBs in 5 ke. V – 25 Me. V LAT – in the range 20 Me. V – 300 Ge. V Launch – 2006
Neutrino emission ● Me. V – stellar collapse ● Ge. V – pn collision in acceleration phase ● Te. V – when jet propagates through star ● Pe. V – in internal shocks ● Ee. V – in external reverse shock
Neutrinos ● AMANDA ● Icecube ● NESTOR ● ANTARES
Gravitational waves • Binary coalescences • Supernovae • Newly formed black holes ● LIGO II ● VIRGO ● GEO 600 ● TAMA 300
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