Gamma-ray bursts Tomasz Bulik CAM K, 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 ApJ 182, L

Sky distribution

Spatial distribution

Temporal properties ● Duration from 0.01 s to 1000s ● 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

Spectra Spectral break between 100keV do 1MeV E (MeV)

Spectral properties ● Nonthermal continuum ● Broken PL, ● Break energy distribution, X-ray rich bursts ● High energy tails: GeV, (up to 1.5 hours) ● Even higher: TeV (GRB970417) ● 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 Opt ical Radio

Afterglow lightcurve breaks

GRB host galaxies GRB GRB

GRB redshifts Most observed bursts at: z<2

GRBs and supernovae 1998bw GRB GRB Bloom et al 99

Superno vae Stanek et al 2003 GRB SN Ic

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 300keV ● Luminosity : isotropic ● D uration : ● Collimation : ● Rate - a few daily (obs erved )

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 e nergy 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

Zhang Woosley Can a jet leave a star?

Host galaxies ● Typical for their redshifts ● Traces of active star formation ● GRBs inside galaxies ● Distribution around galaxies:

Binary coalescences : in or out of galaxies? Belczy ń ski Bulik 2002

Magnetar model ● Quickly rotating magnetar B=10^17 Gauss ● Differential rotation ● Toroidal field ● Magnetohydrodynamic jet formed ● Delay after supernova

Caution… Not known logN- logS = 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 ● Luminosity variability ● Luminosity - lags Reichart etal 2001 Norris etal 2001 Do we already see bursts at z=10-30 ???

Polarization in gamma rays GRB RHESSI %

Polarization - possibilities ● Ordered magnetic fields in a wide jet ● Narrow jet, inverse Compton emission ● Emission from Poynting flux jet

Future…

SWIFT Arcminute accuracy 10s After trigger XRT and UVOT observe in 50 s Launch – spring 2004

GLAST GBM – sensitive to GRBs in 5keV – 25MeV LAT – in the range 20MeV – 300GeV Launch – 2006

Neutrino emission ● MeV – stellar collapse ● GeV – pn collision in acceleration phase ● TeV – when jet propagates through star ● PeV – in internal shocks ● EeV – in external reverse shock

Neutrin os ● AMANDA ● Icecube ● NESTOR ● ANTARES

Gravitational waves ● LIGO I ● LIGO II ● VIRGO ● GEO 600 ● TAMA 300 Binary coalescences Supernovae Newly formed black holes