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

D. Q. Lamb (U. Chicago)

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. FenimoreMark 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 GrazianiTim 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. VanderspekJoel Villasenor

(Mission Scientist)

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

GRB030329: HETE “Hits a Home Run”

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)

GRB030329:Spectrum of SN 2003dh

Stanek et al. (2003)

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 laboratory for 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

HETE-2 Observations of GRB 020531

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

Lamb et al. (2002)

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

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”

HETE-2 Observations of GRB030115

Kawai et al. (2003)

APO and USNO Observations of GRB030115

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)

(Lamb et al. 2003)

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

HETE-2 Observations of GRB021211

Crew et al. (2003)

GRB021211: Afterglow Light Curve Relative to Those of Other GRBs

Fox et al. (2003)

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)

“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

““Normal”Normal”F_x/F_g < 0.32F_x/F_g < 0.32[20 GRBs][20 GRBs]

““X-Ray Rich”X-Ray Rich”F_x/F_g>0.32F_x/F_g>0.32[17 GRBs][17 GRBs]

GRB020903: SpectrumSakamoto et al. (2003)

E_peak = 3.4 kev!

GRB020903: Discovery of Optical Afterglow

Palomar 48-inch Schmidt images: 2002 Sep 6 (left image), 2002 Sep 28 (middle image; subtracted image (right image)

Soderberg et al. (2002)

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

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)

“Universal Jet” vs. Unified Jet Models

“Universal Jet” Model Unified Jet Model

(Diagram from Lloyd-Ronning and Ramirez-Ruiz 2002)

Comparison of Omega_jet (Omega_view) w. Observations

Lamb, Donaghy, and Graziani (2003)

Amati et al. (2002) Relation

BeppoSAX and HETE-2 GRBs

HETE-2 has confirmed relationand extended it by factor 300!

Comparison of Predicted and Observed BeppoSAX E_rad and E_peak Distributions

Lamb , Donaghy, and Graziani (2003)

Density of HETE-2 Bursts in (S, E_peak)-Plane Matches Prediction of Unified Jet Model

Sakamoto et al. (2003)

Comparison of Predicted and Observed HETE-2 Fluence and E_peak Distributions

Lamb, Donaghy & Graziani (2003)

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 %

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