Gamma Ray Bursts - Cosmological Perspective

1. Rick Egeland Gamma Ray Bursts - Cosmological Perspective

2. Paczynski • Supports the cosmological origin of GRBs • Stresses the importance of the isotropic distribution • Pleads that we don't use theoretical models to determine distance scale to GRBs

3. Number Density • If isotropic, N(>F) ~ F-3/2 • PVO detects ~200 "strong" bursts • N~F-1.4 • BATSE, 30 x more sensitive • N~F-0.8 • Explaination: • Burst distribution is bounded • Space is non-euclidean at large distances

4. Distance Determination • Trigonemetric parallax, ~100 pc • Dynamic parallax • Proper motions • Gravitational Lensing • Standard candles • Ly-Alpha Redshift • Distribution alone • Comparable object (Lamb)

5. Known Distributions • Billions of stars, hundreds of known types of objects, but only a few known distributions of objects • There has been no new distribution of objects for decades

6. Solar distributions • Objects of the inner solar system distributed about the ecliptic plane • Outer solar system objects, comets, Oort cloud, approximately spherically distributed about the Sun

7. Stars

8. Globular Clusters

9. Galaxies • Local group galaxies highly clustered • Faraway galaxies approximately isotropic

10. XRBs and SGRs

11. GRB DistributionBATSE 2nd Catalog

12. Distribution Conclusion • The observed isotropic distribution is automatically satisfied if we assume cosmilogical distances • Only other valid distribution is that of local stars, but why would we be so special? • Or some new distribution, a uniformly spherical and isotropic galactic distribution

13. Other Bursts • X-ray Bursts of Type I: Thermonuclear explosions on neutron stars due to acreted gasses from close binary companion star • XRBs of Type II: Unstable acreation flow onto a neutron star • Peak Luminosity: ~1038 ergs/s • Blackbody spectrum ~ 2 keV peak • Old; ~108 years • Not like GRBs

14. Other Bursts • Soft Gamma Repeaters (SGRs) • 3 known (in 1995) • Super nova remnants, neutron stars with ultra strong (1015 gauss) magnetic field • Peak luminosity 1042 erg/s • Thermal spectrum, peak at 30 keV • Young: ~ 10,000 years old • Not like GRBs

15. Other Bursts • March 5 1979 Event • SGR 0526-66: in the Large Magellanic Cloud • Peak Luminocity of 1045 erg/s • Hard spectrum (200 keV) in its ~0.2 s duration • Most similar to GRBs

16. Problems With Galactic GRBs • The observed distribution cannot be reconciled with neutron star ages of ~104 • Ad hoc assumptions • Bursting stops ~104 years, resumes at 108 • There is a broad distribution of turn on ages to hide any clustering at galactic center

17. Problems with Galactic GRBs • Mar 5 event was intense enough to be seen out to Andromeda • Must require that GRBs are on average a few orders of magnitude less intense than the Mar 5 event • GRBs must stop bursting at 3 x 108 years, otherwise those born in M31 reach us and we see a dipole in that direction

18. Problems with Galactic GRBs • Simple energy calculations using energy recieved at BATSE for SGRs requires all neutron stars to burst 3 x 106 times, at 1042 ergs/burst • This is a bit much, so another assumption is made that radio pulsars also GRB • But since low v pulsars are not found to be different than slow pulsars, we must assume that only high v pulsars, after ageing of 108 years can burst

19. Too Many Ad Hoc Assumptions! • Paczynski concludes that the coronal distribution is not a viable scientific proposition

20. Theoretical Models • In 1995, there were over 100 papers on the mechanism of GRBs • If there are 100 different theories, and only 1 can be correct, than it is probable that none of them are correct! • Success of XRB models (surface of NS) may have been the reason for so many NS models of GRBs

21. GRBs Nonthermal Broad spectrum from 1 keV - 107 keV Isotropic Do not repeat, or repeat on long time scales XRBs vs. GRBs • XRBs • Thermal • Peak at 5 keV • Galactic plane -> 8 Mpc • Repeat

22. Paczynski's Conclusion • Success of XRB model was due to knowing the distance scale • Should not use a theoretical model to determine the distance for us!

23. Hope For the Future • Notes that over the past 4 years the galactic models have moved the source halo from 100 pc to 100 kpc • Soon they may be at 1 Gpc scales and still be of galactic origin!

24. Paczynski's Suggestions • Need more sensitive detectors than BATSE to not see the proposed galactic GRBs from M31 which must exist • If GRBs are proved to be at cosmological distances they could be useful tools for cosmology • Need experiment with ~1 arcsec positions for counterparts

25. What do you think?

26. After the Debate • Transient objects observed in X-ray and optical using BeppoSAX setellite and a notification network (GRB970228)

27. Hubble Optical Transient GRB970228 Z ~ 0.7 +/- 0.1 (Lipunov et. al.)

28. Fading Away

29. May 8 1997 GRB Keck Observation -> z > 0.8

30. How Bright?

31. More Recently... • Week of Mar 23, HETE discovered four GRBs with optical transients and redshifts • A GRB was detected from the site of a supernova, supporting the supra-nova, black hole model • Some precise X-ray absorption of Si an S detected

32. The Future of GRBs • SWIFT goes up Dec 2003 • Detects GR, X-ray, UV, and Optical • GR - 5 arcmin • XR - 5 arcsec • UVO - 0.3 arcsec

33. And In Theory... • Two leading models today • Hypernova Star Death • Colliding Neutron Stars • "Chinese Lanterns"