X-Ray Flashes D. Q. Lamb (U. Chicago) “Astrophysical Sources of High-Energy Particles and Radiation” Torun, Poland, 21 June 2005 HETE-2Swift

X-Ray Flashes  X-Ray Flashes discovered by Heise et al. (2000) using WFC on BeppoSAX  Defining X-ray flashes as bursts for which log (S x /S γ ) > 0 (i.e., > 30 times that for “normal” GRBs)  ~ 1/3 of bursts localized by HETE-2 are XRFs  ~ 1/3 are “X-ray-rich” GRBs (“XRRs”)  Nature of XRFs is still largely unknown

HETE-2 X-Ray Flashes vs. GRBs GRB Spectrum Peaks in Gamma-Rays XRF Spectrum Peaks in X-Rays Sakamoto et al. (2004)

Density of HETE-2 Bursts in (S, E peak )-Plane Sakamoto et al. (2005)

Dependence of Burst Spectral Peak Energy (E peak ) on Isotropic-Equivalent Energy (E iso ) HETE BeppoSAX Slope = 0.5 HETE-2 results confirm & extend the Amati et al. (2002) relation: E peak ~ {E iso } 0.5 Region of Few Bursts Region of No Bursts

Implications of HETE-2 Observations of XRFs and X-Ray-Rich GRBs HETE-2 results, when combined with earlier BeppoSax and optical follow-up results: q Provide strong evidence that properties of XRFs, X-ray-rich GRBs (“XRRs”), and GRBs form a continuum q Suggest that these three kinds of bursts are closely related phenomena q Key result: approximately equal numbers of bursts per logrithmic interval in most observed properties (S E, E obs peak, E iso,E peak, etc.)

Scientific Importance of XRFs As most extreme burst population, XRFs provide severe constraints on burst models and unique insights into  Structure of GRB jets  GRB rate  Nature of Type Ic supernovae

Physical Models of XRFs qX-ray photons may be produced by the hot cocoon surrounding the GRB jet as it breaks out and could produce XRF-like events if viewed well off axis of jet (Meszaros et al. 2002, Woosley et al. 2003). q“Dirty fireball” model of XRFs posits that baryonic material is entrained in the GRB jet, resulting in a bulk Lorentz factor Γ << 300 (Dermer et al. 1999, Huang et al. 2002, Dermer and Mitman 2003). qAt the opposite extreme, GRB jets in which the bulk Lorentz factor Γ >> 300 and the contrast between the bulk Lorentz factors of the colliding relativistic shells are small can also produce XRF-like events (Mochkovitch et al. 2003). qA highly collimated GRB jet viewed well off the axis of the jet will have low values of E iso and E peak because of the effects of relativistic beaming (Yamazaki et al. 2002, 2003, 2004).

Observed E iso Versus Ω jet Lamb, Donaghy, and Graziani (2005)

Relation Between E iso and E inf γ Uniform Jet E inf γ = (1-cos θ jet ) E iso = Ω jet E iso E iso = isotropic-equivalent radiated energy E inf γ = inferred radiated energy θ jet

Distributions of E iso and E γ Ghirlanda, Ghisselini, and Lazzati (2004); see also Frail et al. (2001), Bloom et al. (2003)  E iso distribution is broad  E inf γ distribution is considerably narrower

Dependence of E peak on E iso and E inf γ Ghirlanda, Ghisselini, and Lazzati (2004)

Universal vs Variable Opening Angle Jets Universal Jet: Variable Opening Angle (VOA) Jet: Differences due to Differences due to different jet different viewing opening angles θ jet angles θ view 20 o 40 o θ jet = 20 o 40 o 60 o θ view = 0 o Relativistic Beaming 10 o

Jet Profiles Rossi, Lazzati, Salmonson, and Ghisellini (2004) Uniform Jet Gaussian/Fisher Jet Power-Law Jet

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Graziani’s Universal Jet Theorem qUniversal jet model that produces narrow distribution in one physical quantity (e.g., E inf γ ) produces narrow distributions in all other physical quantities (e.g., E peak, E iso, etc.) qAnd vice versa: Universal jet model that produces broad distribution in one physical quantity (e.g., E iso ) produces broad distributions in all other physical quantities (e.g., E peak, E inf γ, etc.) qBut this is not what we observe – what we observe is are broad distributions in E peak and E iso, but a relatively narrow distribution in E inf γ qVariable opening angle (VOA) jets can do this because they have an additional degree of freedom: the distribution of jet opening angles θ jet

Determining If Bursts are Detected HETE-2 burstsBeppoSAX bursts DQL, Donaghy, and Graziani (2004)

Uniform Variable Opening-Angle Jet vs. Power-Law Universal Jet DQL, Donaghy, and Graziani (2005) Power-law universal jet Uniform variable opening-angle (VOA) jet

Uniform Variable Opening-Angle Jet vs. Power-Law Universal Jet  VOA uniform jet can account for both XRFs and GRBs  Universal power-law jet can account for GRBs, but not both XRFs and GRBs – because distributions in E iso and E obs peak are too narrow DQL, Donaghy, and Graziani (2005)

Gaussian/Fisher Universal Jet DQL, Donaghy, and Graziani (2005)

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming Favored Disfavored

Special Relativistic Beaming  Relativistic beaming produces low E iso and E peak values when uniform jet is viewed outside θ jet (see Yamazaki et al. 2002, 2003, 2004)  Relativistic beaming must occur  Therefore very faint bursts w. E peak obs in UV and optical must exist  However, key question is whether relativistic beaming dominates

Uniform VOA Jet + Relativistic Beaming Yamazaki, Ioka, and Nakamura (2004) E peak ~ E iso 1/2 E peak ~ E iso 1/3

Uniform VOA Jet + Relativistic Beaming Donaghy (2005) Γ = 100Γ = 300

Expected Behavior of Afterglow in Relativistic Beaming Model

Observed Behavior of Afterglow Swift: XRF b BeppoSAX: XRF Swift/XRT observations of XRF b show that the X-ray afterglow:  Does not show increase followed by rapid decrease  Rather, it joins smoothly onto end of burst  It then fades slowly  S after /S burst ~ 1  Jet break time > 5 d (> 20 d ) θ jet > 25 o (35 o ) at z = 0.5

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming Strongly Disfavored Favored Disfavored

X-Ray Flashes vs. GRBs: HETE-2 and Swift (BAT) GRB Spectrum Peaks in Gamma - Rays XRF Spectrum Peaks in X-Rays Even with the BAT’s huge effective area (~2600 cm 2 ), only HETE-2 can determine the spectral properties of the most XRFs.

Conclusions  As most extreme burst population, XRFs provide unique information about structure of GRB jets q Variable opening angle jet models favored; universal jet models disfavored; relativistic beaming models strongly disfavored q Absence of relativistic beaming Γ > 300 qConfirming these conclusions will require q prompt localization of many more XRFs q determination of E peak q determination of t jet from observations of X-ray afterglows q determination of redshifts z qHETE-2 is ideally suited to do the first two, whereas Swift (with E min ~ 15 keV and 15 keV < E < 150 keV) is not; Swift is ideally suited to do the second two, whereas HETE-2 cannot qPrompt Swift XRT and UVOT observations of HETE-2 XRFs can therefore greatly advance our understanding of XRFs – and therefore all bursts

Back Up Slides

Scientific Importance of XRFs  As most extreme burst population, XRFs provide severe constraints on burst models and unique insights into  Structure of GRB jets  GRB rate  Nature of Type Ic supernovae  Some key questions regarding XRFs:  Are E inf γ (XRFs) << E inf γ (GRBs)?  Is the XRF population a direct extension of the GRB and X-Ray-Rich GRB populations (e.g., θ jet )?  Are XRFs a separate component of GRBs (e.g., core/halo)?  Are XRFs due to different physics than GRBs and X-Ray Rich GRBs (e.g., relativistic beaming)?  Does burst population extend down to UV (and optical)?

Physical Models of XRFs qX-ray photons may be produced by the hot cocoon surrounding the GRB jet as it breaks out and could produce XRF-like events if viewed well off axis of jet (Meszaros et al. 2002, Woosley et al. 2003). q“Dirty fireball” model of XRFs posits that baryonic material is entrained in the GRB jet, resulting in a bulk Lorentz factor Γ << 300 (Dermer et al. 1999, Huang et al. 2002, Dermer and Mitman 2003). qAt the opposite extreme, GRB jets in which the bulk Lorentz factor Γ >> 300 and the contrast between the bulk Lorentz factors of the colliding relativistic shells are small can also produce XRF-like events (Mochkovitch et al. 2003). qA highly collimated GRB jet viewed well off the axis of the jet will have low values of E iso and E peak because of the effects of relativistic beaming (Yamazaki et al. 2002, 2003, 2004). qXRFs might be produced by a two-component jet in which GRBs and XRRs are produced by a high-Γ “core” and XRFs are produced by a low-Γ “halo” (Berger et al. 2004, Huang et al. 2004).

GRBs Have “Standard” Energies Frail et al. (2001); Kumar and Panaitescu (2001) Bloom et al.(2003)

Phenomenological Jet Models Universal ● Power-Law Jet ● Fisher Jet (Diagram from Lloyd-Ronning and Ramirez-Ruiz 2002) Variable Opening-Angle (VOA) ● Uniform Jet ● Fisher Jet ● VOA Uniform Jet + Relativistic Beaming ● Core + Halo Jet

Phenomenological Jet Models Universal ● Power-Law Jet ● Fisher Jet (Diagram from Lloyd-Ronning and Ramirez-Ruiz 2002) Variable Opening-Angle (VOA) ● Uniform Jet ● Fisher Jet ● VOA Uniform Jet + Relativistic Beaming ● Core + Halo Jet

Rossi, Lazzati, Salmonson, and Ghisellini (2004) Universal Jet Variable Opening Angle (VOA) Jet

Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming

Phenomenological Burst Jets Jet Profile Jet Opening Angle Uniform Variable Gaussian/Fisher Variable Power-Law Universal Uniform Universal Gaussian/Fisher Universal Uniform Variable + Relativistic Beaming Gaussian/Fisher Variable + Relativistic Beaming Power-Law Universal + Relativistic Beaming Uniform Universal + Relativistic Beaming Gaussian/Fisher Universal + Relativistic Beaming Favored

Universal Versus VOA Fisher Jets Donaghy, Graziani and DQL (2004) – see Poster P-26 Universal Fisher jet w. minimum theta jet = 2 o VOA Fisher jet w. minimum theta jet = 2 o

Universal Versus VOA Fisher Jets Donaghy, Graziani and DQL (2004) – see Poster P-26 VOA Fisher jetUniversal Fisher jet  Peak of E gamma inf ~ 5 times smaller than actual value  E gamma inf distribution has low-energy tail (of XRFs)

Observed Distribution of E gamma inf Berger et al. (2003)

Universal Gaussian Jet  In response to conclusion of DQL, Donaghy, and Graziani (2004), Zhang et al. (2004) proposed universal Gaussian jet  Universal Gaussian jet  can produce ~ equal numbers of bursts per logarithmic interval  requires minimum theta jet ~ 2 o as does VOA uniform jet Zhang et al. (2004)

Fisher Jet Models qWe have shown mathematically that universal jet with emissivity given by Fisher distribution (which is natural extension of Gaussian distribution to sphere) have unique property of producing equal numbers of bursts per logarithmic interval in E iso and therefore in most burst properties (Donaghy, Graziani, and DQL 2004 – Poster P-26) qWe have also shown that Fisher jet produces a broad distribution in inferred radiated gamma-ray energy E gamma inf, in contrast with VOA uniform jet qWe have simulated universal and VOA Fisher jets qWe find – as expected – that both models can reproduce most burst properties qHowever, both models require minimum theta jet ~ 2 o, similar to VOA uniform jet

Universal Versus VOA Fisher Jet Models Donaghy, Graziani and DQL (2004) – see Poster P-26 Universal Fisher jetVOA Fisher jet

VOA Uniform Jet + Relativistic Beaming  Relativistic beaming produces low E iso and E peak values when uniform jet is viewed outside theta jet (see Yamazaki et al. 2002, 2003, 2004)  Relativistic beaming must be present  Therefore very faint bursts w. E peak obs in UV and optical must exist  However, key question is whether this effect dominates  Yamazaki et al. (2004) use VOA uniform jet for XRRs and GRBs, relativistic beaming for XRFs  If Gamma ~ 100, some XRFs produced by relativistic beaming are detectable; but if Gamma ~ 300, very few are detectable => difficult to produce ~ equal numbers of XRFs, XRRs, and GRBs

Uniform Jet + Relativistic Beaming Donaghy (2004) – Poster P-27 Maximum theta jet = 2 o Maximum theta jet = 20 o

Donaghy (2005) Uniform Variable Opening Angle Jet + Relativistic Beaming

Donaghy (2005) Uniform Variable Opening Angle Jet + Relativistic Beaming

Uniform Universal Jet + Relativistic Beaming Maximum θ jet = 2 o Maximum θ jet = 20 o Donaghy (2005)

Uniform Universal Jet + Relativistic Beaming Donaghy (2005) Maximum θ jet = 2 o Maximum θ jet = 20 o

Structured (Core + Halo) Jet Models Huang et al. (2004)  It is not clear in such a model  why properties of XRFs, XRRs, and GRBs form a continuum  why there are ~ equal numbers of XRFs, XRRs, and GRBs

Implications of Variable Opening-Angle Uniform Jet qModel implies most bursts have small Ω jet (these bursts are the hardest and most luminous) but we see very few of them qRange in E iso of five decades => minimum range for Ω jet is ~ 6 x < Ω jet < 6 qModel therefore implies that there are ~ 10 5 more bursts with small Ω jet ’s for every such burst we see => if so, R GRB might be comparable to R SN qHowever, efficiency in conversion of E γ (E jet ) to E iso may be less for XRFs, in which case: q Minimum opening angle of jet could be larger q GRB rate could be smaller

X-Ray and Optical Afterglows Lamb, Donaghy & Graziani (2004)  X-ray and optical afterglows of XRFs are also faint  Left panel: slope = /- 0.17; right panel: slope = / => tantalizing evidence that efficiency of prompt emission is less for XRFs than for GRBs (as expected from V  L estimator)

Origin of GRB Prompt Emission and X-Ray, Optical, and Radio Afterglows  In hydrodynamic picture, prompt emission arises from internal shocks  Afterglows arise from external shock

Observations of XRFs Are Stimulating New Theoretical Ideas qXRF & GRB Jet Structure and Burst Rates q A Unified Jet Model of XRFs, X-Ray-Rich GRBs, & GRBs (D. Q. Lamb, T. Q Donaghy & C. Graziani), New Astronomy Reviews, 48, 459 (2004) q Quasi-Universal Gaussian Jets: A Unified Picture for GRBs & XRFs (B. Zhang, X. Dai, N. M. Lloyd-Ronning & P. Meszaros), ApJ, 601, L119 (2004) q XRF : Evidence for a Two-Component Jet (Y. F. Huang, X. F. Wu, Z. G. Dai, H. T. Ma & T. Lu), ApJ, 605, 300 (2004) q XRF : Sub-Luminous & Evidence for A Two-Component Jet (A. Soderberg et al.), ApJ, 606, 994 (2004) q A Unified Jet Model of XRFs, X-Ray-Rich GRBs, & GRBs (D. Q. Lamb, T. Q Donaghy & C. Graziani, ApJ, in press (astro-ph/ ) (2004) q Unified Model of XRFs, X-Ray-Rich GRBs & GRBs (R. Yamazaki, K. Ioka & T. Nakamura), ApJ, 607, 103 (2004) q Gaussian Universal Jet Model of XRFs & GRBs (X. Dai & B. Zhang), ApJ, submitted (2004) qXRF—SN Connection q Possible SN in Afterglow of XRF (J. P. U. Fynbo et al.) ApJ, 609, 962 (2004) q Model of Possible SN in Afterglow of XRF (Tominaga, N., et al.), ApJ, 612,105 (2004) q XRFs & GRBs as a Laboratory for the Study of Type Ic SNe ( (D. Q. Lamb, T. Q Donaghy & C. Graziani), New Astronomy Reviews, in press (2004) q GRB-SN Connection: GRB & XRF (J. P. U. Fynbo et al.), Santa Fe GRB Workshop Proceedings, in press (2004) qRelativistic Beaming and Off-Axis Viewing Models of XRFs q Peak Energy-Isotropic Energy Relation in the Off-Axis GRB Model (R. Yamazaki, K. Ioka & T. Nakamura), ApJ, 606, L33 (2004) q Off-Axis Viewing as the Origin of XRFs (S. Ddo, A. Dr & A. De Rujula), A&A, in press (astro-ph/ ) (2004) q XRFs from Off-Axis Non-Uniform Jets (Z. P. Jin & D. M. Wei), A&A, submitted (astro-ph/ ) (2004)

Ability of HETE-2 and Swift to Measure E peak and S bol of XRFs E peak (estimated) vs. E peak : qShaded areas are 68% confidence regions qSwift (red): q well-determined for E peak > 20 keV q undetermined for E peak < 20 keV qHETE-2 (blue): q well-determined down to E peak ~ 3 keV S bol (estimated) vs. S bol :  Shaded areas are 68% confidence regions  Swift (red):  well-determined for E peak > 20 keV  undetermined for E peak < 20 keV  HETE-2 (blue):  well-determined down to E peak ~ 3 keV Lamb, Graziani, and Sakamoto (2004)

HETE-2 Synergies with Swift  HETE-2 can ~ double number of very bright GRBs at z < 0.5 that Swift XRT and UVOT can follow up – these bursts are crucial for understanding the GRB – SNe connection  HETE-2 can ~ double number of bright GRBs at z > 5 that Swift XRT and UVOT can follow up – these bursts are crucial probes of the very high-z universe  HETE-2 can increase q by factor ~ 10 the number of XRFs w. E peak < 5 keV q by factor ~ 3 the number of XRFs w. E peak < 10 keV that Swift can follow up for X-ray & optical afterglows – these bursts are crucial for determining the nature of XRFs, structure of GRB jets, GRB rate, relationship between GRBs and Type Ic SNe  HETE-2 can provide bolometric S and E peak for XRFs that Swift XRT and UVOT can follow up – these bursts are crucial for confirming that the E iso -E peak relation extends to XRFs