Mystery of Chromatic Jet breaks in Gamma Ray
Mystery of Chromatic Jet breaks in Gamma Ray Bursts Poonam Chandra Jansky Fellow, NRAO, Charlottesville & University of Virginia
Collaborators: Dale Frail (NRAO) Brad Cenko (Caltech) Roger Chevalier (Univ. Virginia) Shri Kulkarni (Caltech) Douglas Bock (CARMA) Jean-Pierre Macquart (ATNF). . And Caltech-Carnegie Mellon collaboration
Jet break due to beaming
Jet break: geometrical effect It should show up in all the wavebands at the same time, i. e. Achromatic jet break….
Is it really true? Observation wavebands: X-ray: not possible…only Chandra and XMM… Radio: scintillation effects, large errorbars Optical: only possibility. Acromaticity in V, B, R, I’ etc. bands
Many jet breaks were seen in optical GRB 030329 GRB 030328
Swift was launched in 2004
Swift The Burst Alert Telescope (BAT) The X-Ray Telescope (XRT) The Ultra-violet/optical Telescope (UVOT)
Well sampled curve in X-rays by Swift XRT Well sampled curve in optical by various optical telescopes Opportunity to see achromatic jet break in really different bands
Missing jet break/chromatic jet break/delayed jet break problem?
Possible Theories Chromaticity of jet breaks: Do not arise from structured outflows from jets. Missing jet breaks in XRT light curves: do not arise from the passage of a spectral break Microphysical parameters evolve with time. Optical and X-ray emissions arise from different outflows. Upscattered forward shock emission And many more………………. Panaitescu et al 2006, Panaitescu 2008, Burrows et al. 2008, Racusin et al. 2007 etc.
D N A B B F R E O G V A NG IO RA I W D E I L A T T E R F L I U OD ST W M M E S T N I H 5 G I 2 1 R B 07 0
ØX-ray band: Swift and Chandra. XO (For 40 days) ØOptical Band: Palomer 60 inch and others (For 27 days) ØSubmm Bands: IRAM in 250 GHz (For 20 days) CARMA in 95 GHz (For 24 days) ØRadio Bands: VLA in 22. 5, 15. 0, 8. 5, 4. 8 and 1. 4 GHz (For 1 year)
XRAY : JET BREAK Thanks to Swift-XRT team
Optical i’ band JET BREAK Optical R band JET BREAK
Jet breaks in optical and X-rays
Standard GRB afterglow model (Yost et al. 2003, 2004) Fits multiwaveband data Emission due to synchrotron mechanism Incorporates scintillation errors in radio data Comprehensive analysis Assumes achromatic jet break Fixed Jet break to day 3. 7, same as optical jet break time
Model (Yost et al. 2003, 2004)
Derive Inverse Compton Scattering Light curves, using synchrotron model parameters ØIC affects only X-ray bands. Not low frequency optical or radio bands. ØIC starts to become important from day 2. 8 onwards IC Light Curve: Chandra et al. 2008, accepted for publication in Ap. J, astro-ph/0802. 2748
Conclusions Inverse Compton scattering is responsible for the delay in jet break in GRB 070125. IC scattering may be responsible for chromatic jet break/ missing jet breaks. IC scattering will be depending on physical conditions. IC scattering will dominate in high density systems. Radio data is very crucial since it determines the density of the medium. Chandra et al. 2008, accepted for publication in Ap. J, astro-ph/0802. 2748
Best fit parameters • Isotropic Kinetic Energy: 2. 98 x 1052 ergs • Jet beaming angle : 0. 23 radians • Electron index: 2. 27 • Circumburst density: 16 cm-3 • Electron energy fraction: 0. 28 • Magnetic energy fraction: 0. 28 • Cooling transition time: 8 days • Jet break time: 3. 7 days
Inverse Compton (IC) scattering delayes the jet break in X-ray light curves and either push it beyond the last Swift observation or result in Chromatic jet break. IC does not affect optical or radio light curves. To deduce this crucial to have very well sampled multiwaveband data including in radio and sub-mm bands.
- Slides: 23