The Rest-Frame Afterglows of Short and Long Gamma-Ray Bursts

1. The Rest-Frame Afterglows of Short and Long Gamma-Ray Bursts (The „Eleventh Hour“ Talk) David Alexander Kann Thüringer Landessternwarte Tautenburg Brera, 080520.4583 Roma, 080521.4583 Bologna, 080522.4583

2. Astrophysical Objects Discovery: Find something very special, write a Nature paper! (e.g., Maarten Schmidt discovers Quasars) Follow-up: Find more objects of the same class, and discover that they are all slightly different Sample creation: So many of the objects that statistics can be done and subclasses can be founded (e.g., QSOs, Blazars, Radio Galaxies, Seyferts… All are AGNs) The Tool-Era: Get so ridiculously many of the objects that they can be used as tools for all kinds of things (e.g., 100,000 SDSS Quasars, use as background sources, lens studies, matter distribution, etc., etc., etc…) With GRBs and their afterglows, we have reached 3) and are moving toward 4)

3. Gamma-Ray Bursts Variable sources in the gamma-ray sky, detectable by satellites only Can be brightest sources for short times, milliseconds to ~ 1000 s Highly variable and complex light curves Short and long GRBs

4. Short and Long GRBs

5. Gamma-Ray Bursts Variable sources in the gamma-ray sky, detectable by satellites only Can be brightest sources for short times, milliseconds to ~ 1000 s Highly variable and complex light curves Short and long GRBs Rapid and precise localization in the last decade (BeppoSAX, HETE II, Swift…) allows discoversies of afterglows in X-ray, optical, radio Spectroscopy shows they lie at cosmological distances  most energetic explosions in the universe

6. The Fireball/Collapsar Model Hyperaccreting black hole: Death of massive star (long) or compact object merger (short) Ejection of ultrarelativistic jets along polar axis Collision of shells: „Internal“ shocks  prompt GRB Jet sweeps up external medium, decelerates: „external“ shocks Possible reverse shock into jet: Prompt flash Forward shock into ISM: Afterglow

7. Ye Olde Afterglow GRB 990510

8. Decays as a power-law (line in log-log • space Ye Olde Afterglow

9. Decays as a power-law (line in log-log • space • Decay is smooth and achromatic Ye Olde Afterglow

10. Decays as a power-law (line in log-log • space • Decay is smooth and achromatic • Often, a jet break is seen Ye Olde Afterglow

11. Decays as a power-law (line in log-log • space • Decay is smooth and achromatic • Often, a jet break is seen • Finally, recedes into the host galaxy Ye Olde Afterglow

12. Strong Intrinsic Variability…

13. …And Color Evolution

14. The TLS Afterglow Papers Collect the largest amount of photometry available Reanalyze the afterglows in a systematic manner Determine moderately large samples of afterglow parameters with less insecurity than single afterglow papers Determine ensemble properties and do some statistics

15. The TLS Afterglow Papers Paper I: Zeh, Klose & Hartmann 2004: Analyzed late-time afterglows to search for „bumps“ due to the contribution of SN light Found that „all GRBs at z < 0.7 have a supernova detected in the late afterglow“ Additional support for the collapsar scenario Paper II: Zeh, Klose & Kann 2006: Analyzed an almost complete set of pre-Swift afterglows in terms of light curve parameters 16 afterglows showed a clear (jet) break Some GRBs have post-break decay slopes α2 < 2

16. The TLS Afterglow Papers Paper III: Kann, Klose & Zeh 2006: Analyzed the spectral energy distributions of the pre-Swift sample to determine dust model, rest frame extinction, intrinsic spectral slope, Golden Sample: 19 Most GRBs have only small rest frame extinction, AV ~ 0.2 mag SMC-like dust is preferred (no spectral features) Intrinsic spectral slopes indicate wide distribution of electron parameter p (including p < 2)

17. Paper III: Intrinsic Afterglows Created a method to allow the direct comparison of GRB afterglows After determining the extinction and the slope, shift the afterglows to a common redshift of z = 1 This comprises a time shift (need redshift) and a magnitude shift (inluding cosmological k-correction) Intrinsically, GRB afterglows cluster in luminosity space (the distribution at late times is less wide), and there is a bimodal distribution, a faint and a bright group Result was obtained at the same time by two other groups (Nardini et al., Liang & Zhang), who used extinction values from the literature only, but did a better statistical analysis

18. Paper III: Intrinsic Afterglows Afterglows corrected for Galactic extinction and host contribution, otherwise as observed GRB 030329 is brightest afterglow by far GRB 990123 has brightest prompt flash

19. Paper III: Intrinsic Afterglows Intrinsic afterglows after correcting for all extinction and shifting to a common redshift GRB 030329 is now very mediocre GRB 021004 brightest afterglow at late times

20. Paper IV: Into the Swift Era Swift has lead to the discovery of afterglows associated with short GRBs, and increased the long GRB afterglow sample by a factor of several already But data release slow, not enough „lookback time“ Original goal: Compare the afterglows of long and short GRBs Work began Autumn 2006, preliminary results presented at Ringberg Workshop on Short GRBs March 2007 Point of Critiscism: We compare Swift SGRB afterglows to pre-Swift LGRB afterglows  Add some Swift LGRBs with „Golden Sample“ quality Point of „Critiscism“: Another student working on X-ray afterglows – could I add optical for those too?  Added more LGRBs Point of Critiscism: „Golden Sample“ might be biased against fainter afterglows  Added even more LGRBs (Silver, Bronze Sample)  Paper became awfully bloated  split up into two papers

21. Paper IV: Swift LGRBs Paper IV: Kann et al. 2007, submitted to ApJ December 2007: Looks at a total of ~ 40 Swift-era afterglows (and rising, revised version not yet submitted…) Golden, Silver, Bronze samples Also collects energetics of complete sample (+19 pre-Swift LGRBs) This time, we were faster…  Very positive referee report received!!

22. Observed Sample Many more early afterglows thanks to rapid and precise Swift error boxes

23. Intrinsic Sample GRB 050904 is king! (Kann, Masetti & Klose 2007) Faint extension, but no bright extension All in all, not too different

24. Distribution of Extinction

25. Distribution over Redshift

26. Afterglows at 43 seconds

27. Paper IV: Main Results Intrinsically, Swift afterglows are very similar to pre-Swift afterglows  relative faintness (Berger et al.) mostly due to higher redshift (Jakobsson et al.) Still no good cases for high extinction found (but, e.g., 051022, 060923A, 070306, 070802) Trend of less extinction at higher z  observational bias or true effect (metallicity??) Broad distribution at early times, but three classes apparent  additional components and optical suppression? MAIN POINT: Can use complete LGRB afterglow sample to compare to SGRB sample

28. Paper V Paper V: Finally submitted to ApJ April 2008! (We were the scoopers, not the scoopeed ) (No referee report as of yet) Problem: „Beggars can‘t be choosers“ SGRB (afterglow sample) is still very small Many SGRBs have no optical afterglow (some not even X-ray) Many SGRBs have no redshift (no afterglow spectroscopy successful so far, hosts only  possible wrong identifications)  Work with several assumptions: No rest frame extinction Typical afterglow color ( composite light curves) z = 0.5 in unknown cases (or 1 for some special cases) Use even redshifts from unclear associations („better than nothing“)  Only assertions about the ensemble possible

29. What a mess!!! Observatio-nally fainter than LGRB afterglows GRB 060614 is relatively bright

30. Larger scatter than before 5 mags fainter than LGRB afterglows in the mean GRB 060121 now by far the brightest GRB 060505 very faint

31. Absolute Magnitude Distribution

32. Limits on SN contribution No SNe detected Additional evidence for a different progenitor from LGRBs

33. Energetics vs. Luminosity

34. Offset vs. Luminosity

35. Redshift vs. Luminosity

36. Paper V: Main Results SRGB afterglows are observationally much fainter than LGRB afterglows They are even more so intrinsically (5 magnitudes!), and show more, not less scatter No sign of SNe so far, also no Mini-SNe (but 080503?) Trend between prompt energy release and afterglow luminosity, similar slope to LGRBs, but offset  due to less dense medium? Trend between offset and luminosity  pretty clear effect of circumburst medium density Optical luminosity another puzzle piece for „hybrid indicator“ GRBs (060121, 060505, 060614), but still not decisive

37. Thank you for your attention!! Long Telescope Short Telescope