1 / 29

Radio afterglows of Gamma Ray Bursts

Radio afterglows of Gamma Ray Bursts. Poonam Chandra National Centre for Radio Astrophysics - Tata Institute of Fundamental Research Collaborators: Dale Frail and many others. Gamma Ray Bursts. Meszaros and Rees 1997. Radio Afterglows. Late time follow up.

fell
Download Presentation

Radio afterglows of Gamma Ray Bursts

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Radio afterglows of Gamma Ray Bursts Poonam Chandra National Centre for Radio Astrophysics - Tata Institute of Fundamental Research Collaborators: Dale Frail and many others

  2. Gamma Ray Bursts Meszaros and Rees 1997

  3. Radio Afterglows • Late time follow up. • Accurate energetics instead of “isotropic equivalent” energy . • Radio scintillation: Constraints on fireball size (Goodman 1997). • Density estimation

  4. Radio Afterglows: GRB 970508Frail et al. 2000, 1997, Waxman et al. 1998 • Diffractive scintillation size constraint (<1017cm). • Energetics from long lived afterglow E0=5 x 1050 ergs. • Density ~0.5 cm-2,

  5. Radio Detection Statistics • 95 out of 304 GRBs detected in radio – 31% • Pre-Swift radio detection 42/123 – 34% • Post-Swift radio detection 53/181 – 29% • X-ray detection rate 42% (pre-Swift) to 93% (post-Swift) . • Optical detection rate 48% (pre-Swift) to 75% (post-Swift) . Chandra et al. 2012, ApJ 746, 156

  6. Detectability of radio afterglows - redshift Kolmogorov-Smirnov test P=0.61 No strong redshift dependence z<2=47/88 z>2=21/43. Chandra et al. 2012, ApJ 746, 156

  7. Negative K-correction (Ciardi and Loeb 2000)(detectable at high redshifts) Chandra et al. 2012, Frail et al. 2006

  8. GRBs detected at high redshift • GRB 090423, z=8.3 (Chandra et al. 2010) • GRB 050904, z=6.3 (Gou et al. 2007) • GRB 120508C z>6 (Laskar et al. 2013)

  9. Detectability of radio afterglows - fluence P=2.6x10-7 • 176/206 (85%) non-detections fluence <1x10-6 erg cm-2 • 82/95 (86%) detections fluence>1x10-6 erg cm-2 Nysewander et al. 2009, Swirt XRT repository Chandra et al. 2012, ApJ 746, 156

  10. Detectability of radio afterglows - Energy P=9x10-7 • k-corrected bolometric in 1 keV-10 MeV range 144 grbs • 60/95 detections Energy >1x1053 erg • Only 9/206 non-detections Energy >1x1053 erg Chandra et al. 2012, ApJ 746, 156

  11. Detectability of radio afterglows - Energy Beaming corrected bolometric energy Where fb is the beaming fraction P=3.5x10-3 Chandra et al. 2012, ApJ 746, 156

  12. Detectability of radio afterglows – X-ray and optical P=3x10-6 P=1x10-9 Gehrels et al. 2008, de Pasquale et al. 2006, Sakamoto et al.2008, 2011 Chandra et al. 2012, ApJ 746, 156

  13. What determines radio flux? Isotropic Energy R-index=0.12 Fluence R-index=0.02 X-ray flux R-index=-0.05 Optical flux R-index=0.62

  14. Radio Detection Biases Chandra et al. 2012, ApJ 746, 156

  15. In meter wavebands

  16. Sample bias or different population? (Hancock et al. 2013) • Chandra et al. (2012) sensitivity limited. • Hancock et al. (2013):visibility stacking- two different populations. • No more than 70% of GRB afterglows are truly radio-bright. • Radio quiet GRBs are intrinsically weak GRBs at all wavelengths. • Gamma-ray efficiency of the prompt emission is responsible for the difference between the two populations. • One magnetar-driven, and one black-hole-driven, as gamma ray efficiency inversely proportional to magnetic field.

  17. Reverse shocks

  18. Reverse shocks in radio Kulkarni et al. 1999

  19. Radio Reverse Shocks • Possible Reverse Shock (RS) in 24 GRBs. • But 87 GRBs with no early radio data for t<3 days. • About 1:4 radio AG may be RS • In optical bands, RS is seen in 1 every 24 GRBs.

  20. Reverse shocks in Radio GRBs Chandra et al.2014

  21. Chandra et al., 2014

  22. GRB 130427A: Evidence of RS Laskar et al. 2013 • Observations with VLA, GMRT, CARMA and combined with optical/IR/UV and X-ray bands. • Most detailed modeling of RS. Wind medium with low density prefered.

  23. Conclusions (Questions?) • Are radio loud and radio quiet two different populations? • Why are reverse shocks more prominent in radio bands?

  24. Reverse Shock Emission fit For reverse shock For forward shock

  25. Statistical Methods • K-M estimator (Kaplan-Meier estimator): Survival analysis for data including the upper limits (Feigelson & Nelson 1985). • K-S test (Kolmogorov-Smirnov test): Tries to determine if 2 datasets differ significantly. P-value is its indicative probability. • Pearson R- coefficient: A measure of linear relationship between two variables. -1<R<1.

  26. K-corrected Luminosity • Luminosity L = 4 p F dL2/(1+z) • K-correction factor (1+z)a-b (where F ~ tanb) • K-corrected luminosity L = 4 p F dL2(1+z)a-b-1 • For optically thin post-jet break light curve a=0, b=1/3 (Frail et al. 2006)

  27. K-corrected Energy

  28. Bursts of different Classes Chandra et al. 2012, ApJ 746, 156

  29. Radio Detection Biases Upper limits detection Chandra et al. 2012, ApJ 746, 156

More Related