Implications for Swift of the Scientific Results of the HETE-2 Mission

1. Implications for Swift of the Scientific Results of the HETE-2 Mission D. Q. Lamb (U. Chicago)

2. Los Alamos National Laboratory Los Alamos, NM USA Center for Space Research Massachusetts Institute of Technology Cambridge, MA USA Edward E. Fenimore Mark Galassi George R. Ricker (PI) Geoffrey B. Crew John P. Doty Alan M. Levine Roland K. Vanderspek Joel Villasenor Space Science Laboratory University of California at Berkeley, CA USA Cosmic Radiation Laboratory Institute of Physical and Chemical Research (RIKEN) JAPAN Kevin Hurley J. Garrett Jernigan Masaru Matsuoka Nobuyuki Kawai Atsumasa Yoshida Astronomy and Astrophysics Department University of Chicago, IL USA Donald Q. Lamb Jr. Carlo Graziani Tim Donaghy Centre D’Etude Spatiale des Rayonnements (CESR) FRANCE Board of Astronomy and Astrophysics University of California at Santa Cruz, CA USA Jean-Luc Atteia Michel Boer Gilbert Vedrenne Stanford E. Woosley Goddard Space Flight Center Greenbelt, MD USA Brazil + India + Italy (Burst Alert Station Scientists) Joao Braga Ravi Manchanda Graziella Pizzichini Thomas L.Cline (NASA Project Scientist) HETE-2 International Science Team (Mission Scientist)

3. Outline of This Talk • HETE-2 is “going great guns:” • It is currently localizing ~ 25 - 30 GRBs yr^-1 • It has localized 41 GRBs so far • 14 of these localizations have led to the detection of X-ray, optical, or radio afterglows • 11 of these afterglows have led to redshift determinations • In this talk, I will discuss the implications of HETE-2 and follow-up observations for: • GRB-SN connection • Short, hard GRBs • “Optically dark” GRBs • X-Ray Flashes (XRFs) and X-ray-rich GRBs • Nature of GRB jets

4. GRB030329: HETE “Hits a Home Run” Vanderspek et al. (2003) z = 0.1675  probability of detecting a GRB this close by is ~1/3000 => unlikely that HETE-2 or Swift will see another such event

5. GRB030329:Spectrum of SN 2003dh Stanek et al. (2003)

6. GRB030329: Implications • HETE-2—localized burst GRB030329/SN 2003dh confirms the GRB – SN connection • Implications: • We must understand Type Ib/Ic core collapse SNe in order to understand GRBs • Conversely, we must understand GRBs in order to fully understand Type Ib/Ic core collapse SNe • Therefore GRBs are a vital laboratoryfor studying core collapse SNe • Result strengthens the expectation that GRBs occur out to z ~ 20, and are therefore a powerful probe of cosmology and the early universe

7. HETE-2 Observations of GRB 020531 Lamb et al. (2002) • BeppoSAX did not detect any short GRBs during its 6-year mission lifetime, despite extensive efforts • GRB 020531 is the first detection of a short, hard GRB that has allowed rapid optical and X-ray follow-up observations

8. GRB020531: Implications • Rapid HETE-2 and IPN localizations made possible rapid optical (t = 2 - 3 hrs) follow-up observations; no optical afterglow was detected • Chandra follow-up observation (Butler et al. 2002) => L_x (short)/L_x (long) < 0.01 - 0.03 @ t = 5 days • Suggests real time or near-real time X-ray follow-up observations of short GRBs may be crucial  Swift XRT and UVOT follow-up observations may be vital to unraveling the mystery of short GRBs

9. HETE-2 is Solving Mystery of “Optically Dark” GRBs • Two explanations of “optically dark” GRBs have been widely discussed: • Optical afterglows are extinguished by dust in the host galaxy (see, e.g., Reichart and Price 2001) • GRBs lie at very high redshifts (Lamb and Reichart 2000) • Rapid follow-up observations of HETE-2—localized burst GRB030115 show that this burst is best case to date of extinction by dust • Rapid follow-up observations of HETE-2—localized burst GRB021211 show that this burst is “optically dim” – without rapid follow-up would have been classified as “optically dark”

10. HETE-2 Observations of GRB030115 Kawai et al. (2003)

11. APO and USNO Observations of GRB030115 (Lamb et al. 2003) • APO observations on 15 Jan 2002 UT began 3.5 hours after the burst, measured i* = 22.1 +/- 0.04 (left panel) and r* = 23.40 +/- 0.11 (right panel) • USNO observations began 3.5 hours after the burst; measured J = 19.78 +/-0.20, H = 18.28 +/- 0.13 (Henden et al. 2003)

12. GRB030115: Evidence for Extinction by Dust (Lamb et al. 2003) X-ray afterglow observations are crucial: needed to fix slope of afterglow spectrum (would have determined A_v to +/- 10%) => Swift XRT will do this for most of the GRBs that Swift detects

13. HETE-2 Observations of GRB021211 Crew et al. (2003)

14. GRB021211: Afterglow Light Curve Relative to Those of Other GRBs Fox et al. (2003)

15. GRB021211: Implications for “Optically Dark” GRBs • Rapid follow-up observations of HETE-2—localized burst GRB021211 shows that there is a third explanation in the case of some bursts: their optical afterglow is much fainter (> 3 mag) at t > 1/2 hour than those observed previously (i.e., they are “optically dim” rather than “optically dark” GRBs) • Even GRBs whose optical afterglows are dim may have very bright optical afterglows at t < 10 min (suggests Swift UVOT will detect many of them)

16. “X-Ray Rich” F_x/F_g>0.32 [17 GRBs] “Normal” F_x/F_g < 0.32 [20 GRBs] “X-Ray Flashes” • Defining “X-ray flashes” (Heise et al. 2000) as bursts for which log (S_x/S_gamma) > 0 (i.e., > 30 times that for “normal” GRBs), ~20% of bursts localized by HETE-2 are XRFs • Nature of XRFs is largely unknown

17. GRB020903: Spectrum Sakamoto et al. (2003) E_peak = 3.4 kev!

18. GRB020903: Discovery of Optical Afterglow Soderberg et al. (2002) Palomar 48-inch Schmidt images: 2002 Sep 6 (left image), 2002 Sep 28 (middle image; subtracted image (right image)

19. GRB020903: Implications • HETE-2 and optical follow-up observations of GRB020903 show that this XRF: • lies on the extension of (S, E^obs_peak) distribution • lies on extension of the Amati et al. (2002) relation • host galaxy is copiously producing stars, similar to those of GRBs • host galaxy has a redshift z = 0.25, simlar to those of GRBs • These results provide strong evidence that GRBs, X-ray-rich GRBs, and XRFs form a continuum and are the same phenomenon

20. Unified Jet Model of XRFs, “X-Ray-Rich” GRBs, and GRBs D. Q. Lamb, T. Donaghy, and Carlo Graziani (U. Chicago) (Jet Simulation from Zhang and Woosley 2002)

21. “Universal Jet” vs. Unified Jet Models “Universal Jet” Model Unified Jet Model (Diagram fromLloyd-Ronning and Ramirez-Ruiz 2002)

22. Comparison of Omega_jet (Omega_view) w. Observations Lamb, Donaghy, and Graziani (2003)

23. Amati et al. (2002) Relation HETE-2 has confirmed relation and extended it by factor 300! BeppoSAX and HETE-2 GRBs

24. Comparison of Predicted and Observed BeppoSAX E_rad and E_peak Distributions Lamb , Donaghy, and Graziani (2003)

25. Density of HETE-2 Bursts in (S, E_peak)-Plane Matches Prediction of Unified Jet Model Sakamoto et al. (2003)

26. Comparison of Predicted and Observed HETE-2 Fluence and E_peak Distributions Lamb, Donaghy & Graziani (2003)

27. Implications of Unified Jet Model • Unified jet model provides a single, unified picture of XRFs, “X-ray-rich” GRBs, and GRBs • It’s predictions match the observed distributions of Omega_jet, E_rad, E_peak, L_gamma, L_x, L_R, etc. • The predictions of the “universal jet” model do not • Unified jet model makes surprising prediction that ~ all Type Ib/Ic core collapse SNe produce high energy transients • Model also implies that E_jet is ~ 100 x smaller than has been thought, and efficiency of conversion of kinetic energy in the jet into gamma rays need only be ~ 2 %

28. Conclusions • HETE-2 has confirmed the GRB – SN connection • HETE-2 and Chandra follow-up observations of short, hard GRB 020531 show that its X-ray afterglow is > 100 x fainter than is typical of long GRBs (Swift XRT observations likely crucial) • HETE-2 is solving the mystery of “optically dark” GRBs: • HETE-2 and follow-up observations of GRB030115 have provided the best example so far of a GRB which is “optically dark” because of extinction by dust (Swift XRT should detect all of these) • HETE-2 and follow-up observations of GRB021211 have shown that the afterglows of some GRBs can be much fainter than those observed previously (i.e., they are “optically dim,” rather than “optically dark”); yet these afterglows can be very bright at t < 10 minutes after the burst (Swift UVOT should detect most of these) • Other “optically dark” GRBs are expected to lie at very high redshifts (Lamb and Reichart 2000); we hope HETE-2 will soon detect some – and Swift many! • HETE-2 observations have provided strong new evidence that XRFs, “X-ray-rich” GRBs, and GRBs are the same phenomenon; and that a unified (uniform) jet model can explain them all