Transcript Slide 1
Gamma-Ray Bursts Brian McBreen Short and Long GRBs • Short GRBs (T90 < 2s) • Tend to be spectrally harder; i.e. have a higher proportion of high-energy -rays relative to lowenergy -rays Long Short • Long GRBs (T> 2s) •Tend to be spectrally softer; i.e. have a higher proportion of low-energy -rays relative to high-energy -rays • Originate from the collapse of massive stars Count Rate How are GRBs detected? Prompt Emission: GRB 050730 30 s Time (s) Afterglow Optical/NIR 100s to days post GRB Count Rate Optical Magnitude Afterglow X-rays 100 0.1 104 105 Time (s) 0.03h 0.01 1000 0.3h 3h 30h 1 Time (days) Pandey et al 2006 Tools of the Trade Host Galaxy Studies Galaxy lit up by GRB light for short time. Prompt emission of GRBs : High energy emission Satellites : INTEGRAL - IBIS and SPI Fermi - GBM and LAT Swift - BAT and XRT Suzaku - WAM Konus Afterglow of GRBs: X-ray to Radio observations: XRT on Swift, XMM Optical and NIR telescopes follow-up and search for the afterglow. Large telescopes take spectra of the afterglow. Radio and sub-mm follow-up. INTEGRAL GRBs • INTEGRAL has detected 62 GRBs since launch in October 2002 up to January 2009 • 3 short GRBs Posters by Meehan et al. and Topinka et al. • 2 INTEGRAL GRB catalogues published (Foley et al. A&A, 2008; Vianello et al. A&A 2009) • 4 INTEGRAL GRBs have confirmed redshifts: GRB031203 – z = 0.1055 GRB050223 – z = 0.584 GRB050502a – z = 3.79 GRB050525a – z = 0.606 Afterglow Statistics for INTEGRAL and Other Missions (up to Feb. 2009) GRBs BeppoSAX 55 HETE-2 INTEGRAL 79 62 Swift 396 X-ray 31 19 22 339 Optical 17 30 20 206 Radio 11 8 8 24 IBIS Sensitivity to Faint GRBs Band et al. 2008 GRB 041219a McBreen et al. 2006 • Extremely intense burst • Peak flux of 43 photons/cm2/s (20 keV – 8 MeV) • Emission up to a few MeV • Good candidate for polarisation analysis Background events selected from a 240s interval occurring before GRB SPI HK light curve of GRB 041219a (20 keV – 8 MeV) Compton Scatter • Photon with energy hυ scattered by free electron, results in change of photon energy and momentum • Between 300keV & a few MeV, Compton is dominant for most elements φ hυ0 θ Ge (32) hυ1 Polarisation Simulations for GRB 041219a • Compared real data to simulated polarised and unpolarised data to obtain polarisation fraction • Used spectral parameters (Band model) from real data to generate 100% polarised events Image of coded mask (yellow) + detectors (blue) taken from simulations Polarisation with SPI SPI can measure polarisation through multiple events in its 19 detectors 120° 60° 180° 0° Absence of detectors 2 & 17 removes 22% of pair possibilities 240° 300° GRB041219a Results Time % Directions Angle (deg) Polarisation 12 sec 6 96±53 60±19 12 sec 3 96±40 60±12 Weighted mean of all results 60% at 2 σ level McGlynn et al A&A 2007 and are in agreement with Kalemci et al ApJ 2007 IBIS Polarisation of GRB041219a Gotz et al. 2009 Agreement between IBIS and SPI (McGlynn et al. 2007) for brightest 12 s interval. Polarisation with GRAPE Toma et al. 2009 Simulated events that can be detected by GRAPE in the Synchrotron with ordered field (red circles), Synchrotron with random field (green filled circles) and Compton Drag (blue plus signs) models. Photoelectric Absorption - Theory 1. Photon absorbed by the material 2. Energy is transferred to an electron 3. Electron is emitted Differential cross-section for an electron emitted from the s-orbital of an atom in the non-relativistic limit (R. Bellazzini et al. 2003) φ: azimuthal angle of the emitted electron -> the emission angles are modulated by the polarisation Polarisation with LEP Toma et al. 2009 Simulated events that can be detected by LEP in the Synchrotron with ordered field (red circles), Synchrotron with random field (green filled circles) and Compton Drag (blue plus signs) models. GRB 090423 z = 8.2 Most distant object ever observed Salvaterra et al. 2009 GRB 080319B The extremely luminous afterglow of GRB 080319b imaged by the Swift X-Ray Telescope (left) and Optical/Ultraviolet Telescope (right). Peak apparent magnitude of 5.8 – farthest object observable with naked eye. Composite Light curve of GRB 080319b Racusin el at. Nature (2008) AGILE – GRB090510 Delayed gamma-ray emission from a short GRB Giuliani et al. 2009 Fermi – GRB090510 New quantum gravity limit: MQG / MPlanck ≥ several Much stronger than previous best limit of this kind from GRB080916c Abdo et al. 2009 Fermi – GRB 080916c Abdo et al. 2009 GBM and LAT lightcurves for the gamma-ray emission of GRB080916c; z = 4.35; Most energetic GRB detected – 9 x 1054 ergs isotropic energy; Γ > 1100 Fermi – GRB 080916c Fermi – GRB090902b Abdo et al. 2009 z = 1.822 Fermi - GRB090902b New power-law component at high and low energies (Abdo et al. 2009) X-Ray Afterglows Gehrels et al. 2009 Canonical X-ray Afterglow Swift X-ray & Optical Afterglows X-ray and optical lightcurves of GRB afterglows in the Swift era Gehrels et al. 2009 Types of Optical Afterglows Panaitescu et al. 2008 Formation of Long GRBs Gehrels et al. 2009 GRB-SN Connection Modjaz et al. 2006 GRB060505 GRBs without Supernovae • Lightcurves of SN 1998bw (GRB980425), SN 2002ap and SN 2006aj (GRB060218) Plotted as they would have appeared at redshift of GRB060505 (top) and GRB060614 (bottom). • Afterglow detections in each case plotted in black GRB060614 • Neither GRB associated with significant SN emission down to very faint limits Fynbo et al. 2006 GRB Host Galaxies Gehrels et al. 2009 A selection of the host galaxies of long-duration (top row) and shortduration (bottom row) gamma-ray bursts as imaged by HST. Host Galaxy Metallicities Gehrels et al. 2009 GRB Offsets from Hosts Projected physical offsets for short GRBs (black) and long GRBs (gray). The top panel shows a cumulative distribution, while the bottom panel shows the differential distribution. Fong et al. 2009 Conclusions • Swift continues to drive major advances in Gamma-Ray Bursts including X-ray, Optical and Radio afterglows • INTEGRAL has made major advances including polarisation (GRBs and Crab) and the faintest GRBs • Major advances with AGILE and Fermi – measure the GRB spectrum over 5 orders of magnitude in energy at the same time e.g. – most luminous GRB – QG limits – Band Model + new spectral features at high energies – Band Model + Power law component at high and low energies • Need to plan and deliver new missions e.g. GRI, GRIPS etc. References • Book on GRBs written by G. Vedrenne and J.L. Atteia (Springer) • Recent review by N. Gehrels, E. RamirezRuiz and D.B. Fox, “Gamma-Ray Bursts in the Swift Era”