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X-Ray FlashesX-Ray Flashes
D. Q. Lamb (U. Chicago)
“Astrophysical Sources of High-Energy Particles and Radiation” Torun, Poland, 21 June 2005
HETE-2 Swift
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 (Sx/Sγ) > 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 SpectrumPeaks in Gamma-Rays
XRF Spectrum Peaks in X-Rays
Sakamoto et al. (2004)
Density of HETE-2 Bursts in (Density of HETE-2 Bursts in (SS, , EEpeakpeak)-Plane)-Plane
Sakamoto et al. (2005)
Dependence of Burst Spectral Peak Energy (EDependence of Burst Spectral Peak Energy (Epeakpeak) )
on Isotropic-Equivalent Energy (Eon Isotropic-Equivalent Energy (Eisoiso))
HETE
BeppoSAX
Slope = 0.5
HETE-2 results confirm & extend the Amati et al. (2002)
relation:
Epeak ~ {Eiso} 0.5
Region ofFew Bursts
Region ofNo Bursts
Implications of HETE-2 Observations Implications of HETE-2 Observations of XRFs and X-Ray-Rich GRBsof XRFs and X-Ray-Rich GRBs
HETE-2 results, when combined with earlier BeppoSax and optical follow-up results:
Provide strong evidence that properties of XRFs, X-ray-rich GRBs (“XRRs”), and GRBs form a continuum
Suggest that these three kinds of bursts are closely related phenomena
Key result: approximately equal numbers of bursts per logrithmic interval in most observed properties (SE, Eobs
peak, Eiso,Epeak, etc.)
Scientific Importance of XRFsScientific Importance of XRFs
As most extreme burst population, XRFs provide severe constraints on burst models and unique insights intoStructure of GRB jetsGRB rateNature of Type Ic supernovae
Physical Models of XRFsPhysical Models of XRFs
X-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).
“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).
At 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).
A highly collimated GRB jet viewed well off the axis of the jet will have low values of Eiso and Epeak because of the effects of relativistic beaming (Yamazaki et al. 2002, 2003, 2004).
Relation Between ERelation Between Eisoiso and E and Einfinfγγ
Uniform Jet
Einfγ = (1-cos θjet) Eiso
= Ωjet Eiso
Eiso = isotropic-equivalent radiated energy
Einfγ = inferred radiated
energy
θjet
Distributions of EDistributions of Eisoiso and E and Eγγ
Ghirlanda, Ghisselini, and Lazzati (2004); see also Frail et al. (2001), Bloom et al. (2003)
Eiso distribution is broad
Einfγ distribution is
considerably narrower
Universal vs Variable Opening Angle JetsUniversal vs Variable Opening Angle Jets
Universal Jet: Variable Opening Angle (VOA) Jet: Differences due to Differences due to different jet different viewing opening angles θjet
angles θview
20o
40oθjet = 20o 40o 60o
θview = 0o Relativistic Beaming10o
Jet ProfilesJet Profiles
Rossi, Lazzati, Salmonson, and Ghisellini (2004)
Uniform Jet Gaussian/Fisher Jet Power-Law Jet
Phenomenological Burst JetsPhenomenological 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 TheoremGraziani’s Universal Jet Theorem
Universal jet model that produces narrow distribution in one physical quantity (e.g., Einf
γ) produces narrow distributions in all other physical quantities (e.g., Epeak, Eiso, etc.)
And vice versa: Universal jet model that produces broad distribution in one physical quantity (e.g., Eiso) produces broad distributions in all other physical quantities (e.g., Epeak, Einf
γ, etc.)
But this is not what we observe – what we observe is are broad distributions in Epeak and Eiso, but a relatively narrow distribution in Einf
γ
Variable opening angle (VOA) jets can do this because they have an additional degree of freedom: the distribution of jet opening angles θjet
Determining If Bursts are Detected
HETE-2 burstsBeppoSAX bursts
DQL, Donaghy, and Graziani (2004)
Uniform Variable Opening-Angle Jet Uniform Variable Opening-Angle Jet vs. Power-Law Universal 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 Uniform Variable Opening-Angle Jet vs. Power-Law vs. Power-Law
Universal JetUniversal 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 Eiso and Eobs
peak are too narrow
DQL, Donaghy, and Graziani (2005)
Gaussian/Fisher Universal JetGaussian/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
Favor
ed
Disfavored
Special Relativistic BeamingSpecial Relativistic Beaming
Relativistic beaming produces low Eiso and Epeak values when uniform jet is viewed outside θjet (see Yamazaki et al. 2002, 2003, 2004) Relativistic beaming must occur
Therefore very faint bursts w. Epeakobs in UV
and optical must exist However, key question is whether relativistic
beaming dominates
Uniform VOA Jet + Relativistic BeamingUniform VOA Jet + Relativistic Beaming
Yamazaki, Ioka, and Nakamura (2004)
Epeak ~ Eiso1/2
Epeak ~ Eiso1/3
Uniform VOA Jet Uniform VOA Jet + Relativistic Beaming + Relativistic Beaming
Donaghy (2005)
Γ = 100 Γ = 300
Expected Behavior of Afterglow Expected Behavior of Afterglow in Relativistic Beaming Model in Relativistic Beaming Model
Observed Behavior of AfterglowObserved Behavior of Afterglow
Swift: XRF 050215b
BeppoSAX: XRF 020427
Swift/XRT observationsof XRF 050215b showthat the X-ray afterglow:
Does not show increase followed by rapid decrease Rather, it joins smoothly onto end of burst It then fades slowly Safter/Sburst ~ 1 Jet break time > 5d (> 20d) θjet > 25o (35o) 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 BeamingStrongly Disfavored
Favor
ed
Disfavored
X-Ray Flashes vs. GRBs: X-Ray Flashes vs. GRBs: HETE-2 and HETE-2 and SwiftSwift (BAT) (BAT)
GRB SpectrumPeaks in Gamma - Rays
XRF Spectrum Peaks in X-Rays
Even with the BAT’s huge
effective area (~2600 cm2), only HETE-2
can determine the spectral
properties of the most XRFs.
ConclusionsConclusions As most extreme burst population, XRFs provide unique
information about structure of GRB jets Variable opening angle jet models favored; universal jet models
disfavored; relativistic beaming models strongly disfavored Absence of relativistic beaming Γ > 300
Confirming these conclusions will require prompt localization of many more XRFs determination of Epeak
determination of tjet from observations of X-ray afterglows
determination of redshifts z
HETE-2 is ideally suited to do the first two, whereas Swift (with Emin ~ 15 keV and 15 keV < E < 150 keV) is not; Swift is ideally suited to do the second two, whereas HETE-2 cannot
Prompt 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 XRFsScientific 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 Einf
γ (XRFs) << Einfγ (GRBs)?
Is the XRF population a direct extension of the GRB and X-Ray-Rich GRB populations (e.g., θjet)?
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 XRFsPhysical Models of XRFs
X-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).
“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).
At 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).
A highly collimated GRB jet viewed well off the axis of the jet will have low values of Eiso and Epeak because of the effects of relativistic beaming (Yamazaki et al. 2002, 2003, 2004).
XRFs 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
Favor
ed
Universal Versus VOA Fisher Jets
Donaghy, Graziani and DQL (2004) – see Poster P-26
Universal Fisher jet w.minimum thetajet = 2o
VOA Fisher jet w.minimum thetajet = 2o
Universal Versus VOA Fisher Jets
Donaghy, Graziani and DQL (2004) – see Poster P-26
VOA Fisher jetUniversal Fisher jet
Peak of Egammainf ~ 5 times smaller than actual value
Egammainf distribution has low-energy tail (of XRFs)
Observed Distribution of Egammainf
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 thetajet ~ 2o as does VOA uniform jet
Zhang et al. (2004)
Fisher Jet Models
We 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 Eiso and therefore in most burst properties (Donaghy, Graziani, and DQL 2004 – Poster P-26)
We have also shown that Fisher jet produces a broad distribution in inferred radiated gamma-ray energy Egamma
inf, in contrast with VOA uniform jet We have simulated universal and VOA Fisher jets We find – as expected – that both models can
reproduce most burst properties However, both models require minimum thetajet ~ 2o,
similar to VOA uniform jet
Universal Versus VOA Fisher Jet Models
Donaghy, Graziani and DQL (2004) – see Poster P-26
Universal Fisher jet VOA Fisher jet
VOA Uniform Jet + Relativistic Beaming
Relativistic beaming produces low Eiso and Epeak values when uniform jet is viewed outside thetajet (see Yamazaki et al. 2002, 2003, 2004) Relativistic beaming must be present
Therefore very faint bursts w. Epeakobs 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 thetajet = 2o Maximum thetajet = 20o
Donaghy (2005)
Uniform Variable Opening Angle Jet Uniform Variable Opening Angle Jet + Relativistic Beaming + Relativistic Beaming
Donaghy (2005)
Uniform Variable Opening Angle Jet Uniform Variable Opening Angle Jet + Relativistic Beaming + Relativistic Beaming
Uniform Universal Jet Uniform Universal Jet + Relativistic Beaming+ Relativistic Beaming
Maximum θjet = 2o Maximum θjet = 20o
Donaghy (2005)
Uniform Universal Jet Uniform Universal Jet + Relativistic Beaming+ Relativistic Beaming
Donaghy (2005)
Maximum θjet = 2o Maximum θjet = 20o
Implications of Variable Opening-Angle Uniform Jet
Model implies most bursts have small Ωjet (these bursts are the hardest and most luminous) but we see very few of them
Range in Eiso of five decades => minimum range for Ωjet is ~ 6 x 10-5 < Ωjet < 6
Model therefore implies that there are ~ 105 more bursts with small Ωjet’s for every such burst we see => if so, RGRB might be comparable to RSN
However, efficiency in conversion of Eγ (Ejet) to Eiso
may be less for XRFs, in which case: Minimum opening angle of jet could be larger GRB rate could be smaller