1. The HETE-2 Mission and GRBs

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

4. Why work on GRBs? The first GRBs detected by an Italian instrument, the second error box not fron IPN

6. Why Optical Observations of GRB Afterglows? See Pedersen et al., Nature, 1984 (It was an SGR in N49, but no one knew that)

7. HETE-2 RESULTS on GRBs  HETE-2 :  Instruments: Fregate 6-400 keV, 3 sr; WXM 2 – 25 keV, 1.6 sr; SXC 0.5 keV, o.91 sr.  is currently localizing ~ 25 GRBs yr^-1, many more are detected, but not localized  has localized 41 GRBs so far, delays ranging from < 1 minute for onboard error boxes to 2 – 3 hours for refined ground locations  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  HETE is a small mission : height 89 cm, width < 47 cm, weight <124 Kg: no pointing instruments for afterglow observations  Implications of HETE-2 and follow-up observations for: q GRB-SN connection q Short, hard GRBs q “Optically dark” GRBs q X-Ray Flashes (XRFs) and X-ray-rich GRBs q Nature of GRB jets

8. Which hardware did we contribute to HETE? qIn order to disseminate fast on-board burst alerts and locations, HETE needs to be constantly in contact with a chain of “Secondary Ground Stations” along its equatorial orbit. Our double SGS, funded by ASI and hosted by CRPSM, is located in the San Marco base in Malindi, Kenia. It was set up by Ennio Morelli and Fulvio Gianotti. We constantly monitor it. qFunding: only ASI, residual from 2002, ~ 20000 euro q“mesi-uomo” 24 (11 + 9 + 2 + 2)

9. HETE’s future qHETE’s operations are approved by NASA until July 2004. qNew “senior review” in 3 months shall decide on further extension qHETE is complementary to Swift and INTEGRAL: it observes a different part of the sky than both of them and it detects and localizes very well also XRFs, while Swift shall detect mostly “classical”, i.e. > 30 keV GRBs. HETE points in the “anti-sun” direction, its GRB locations are well suited for optical observations. Note: HETE was built for GRBs, but it detects also many x-ray flashes and SGR events. It has probably discovered a new SGR source.

10. GRB030329: HETE “Hits a Home Run” (Don Lamb’s quotation) 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 Vanderspek et al. (2003)

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

12. GRB030329: Implications qHETE-2—localized burst GRB030329/SN 2003dh confirms the GRB – SN connection qScience Magazine lists this one and other HETE result as one of the top ten in 2003, actually the only one in Astrophysics, and explicitly mentions HETE’ results and HETE’s key “Team work” qImplications: q We must understand Type Ib/Ic core collapse SNe in order to understand GRBs and GRBs in order to fully understand Type Ib/Ic core collapse SNe q GRBs are a vital laboratory for studying core collapse SNe q GRBs occur out to high z, and are therefore a powerful probe of cosmology and the early universe q Quotation from Palumbo, Pizzichini & Vespignani, 1974: “If one assumes that the burst is of extragalactic origin, the energy output would call for a supernova explosion……”

13. HETE-2 Observations of GRB 020531  GRB 020531 is the first detection of a short, hard GRB that has allowed rapid (t = 2-3 hours) optical and X-ray follow-up observations: none from BeppoSax in 6 years.  X-Ray afterglow detected (Butler et al. 2002), no optical detection  Probably need even faster localizations Lamb et al. (2002)

14. HETE-2 is Solving Mystery of “Optically Dark” GRBs  Two explanations of “optically dark” GRBs have been widely discussed: q Optical afterglows are extinguished by dust in the host galaxy (see, e.g., Reichart and Price 2001) q GRBs lie at very high redshifts (Lamb and Reichart 2000) qRapid follow-up observations of HETE-2—localized burst GRB030115 show that this burst is best case to date of extinction by dust qRapid 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”

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

16. GRB021211: Afterglow Light Curve Relative to Those of Other GRBs The optical afterglow of some bursts is much fainter (~ 3 mag) than those previously observed: without HETE’s prompt localization, this GRB would very likely have been listed as “dark”, instead of “dim”. But it proves that at t < 10 min even “dim” afterglows may be bright (m ~ 13). This is very promising for Swift. Fox et al. (2003)

17. HETE-2 extends “Amati’s relationship” to XRFs and X-ray Rich GRBs: same phenomenon? Sakamoto et al. (2003)

18. Conclusions qHETE-2 has confirmed the GRB – SN connection qHETE-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) qHETE-2 is solving the mystery of “optically dark” GRBs: q 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) q 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) q 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! qHETE-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

19. Observations of GRB afterglows from Loiano: GRB021004 TOO Observations of GRB optical afterglows made at the 152 cm telescope of the Bologna Observatory in Loiano, in collaboration with C. Bartolini, A, Guarnieri and A. Piccioni of the Department of Astronomy of the University of Bologna, for a short time also with N. Masetti (IASF/CNR, Bologna). We try as much as possible to make multifilter observations, in order to further confirm the findings of Simon, Hudec, Pizzichini & Masetti, 2001 on the colors of afterglows. THE FUTURE: we expect many more TOO observations also from INTEGRAL and Swift GRBs.

20. Observations of optical afterglows from Loiano: GRB030226

21. Observations of optical afterglows from Loiano: GRB030328

22. Observations of Optical Afterglows from Loiano: GRB030418