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X-Ray Flashes. D. Q. Lamb (U. Chicago). HETE-2. Swift. “Astrophysical Sources of High-Energy Particles and Radiation” Torun, Poland, 21 June 2005. X-Ray Flashes. X-Ray Flashes discovered by Heise et al. (2000) using WFC on Beppo SAX

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x ray flashes
X-Ray Flashes

D. Q. Lamb (U. Chicago)

HETE-2

Swift

“Astrophysical Sources of High-Energy Particles and Radiation”

Torun, Poland, 21 June 2005

x ray flashes1
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
HETE-2 X-Ray Flashes vs. GRBs

Sakamoto et al. (2004)

GRB Spectrum

Peaks in Gamma-Rays

XRF Spectrum

Peaks in X-Rays

dependence of burst spectral peak energy e peak on isotropic equivalent energy e iso

BeppoSAX

HETE

Region of

Few Bursts

Region of

No Bursts

Slope = 0.5

5 orders of magnitude

Dependence of Burst Spectral Peak Energy (Epeak) on Isotropic-Equivalent Energy (Eiso)

HETE-2 results confirm & extend the Amati et al. (2002) relation:

Epeak ~ {Eiso} 0.5

implications of hete 2 observations of xrfs and x ray rich grbs
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:

  • 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: approximatelyequal numbers of bursts per logrithmic interval in most observed properties (SE, Eobspeak, Eiso,Epeak, etc.)
scientific importance of xrfs
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
Physical 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 e iso and e inf
Relation Between Eiso and Einfγ

θjet

Einfγ = (1-cos θjet) Eiso

= ΩjetEiso

Eiso = isotropic-equivalent

radiated energy

Einfγ = inferred radiated

energy

Uniform Jet

distributions of e iso and e
Distributions of Eiso and Eγ
  • Eiso distribution is broad
  • Einfγ distribution is

considerably narrower

Ghirlanda, Ghisselini, and Lazzati (2004);

see also Frail et al. (2001), Bloom et al. (2003)

universal vs variable opening angle jets
Universal vs Variable Opening Angle Jets

θview = 0o

Relativistic Beaming

10o

20o

θjet = 20o

40o

60o

40o

Universal Jet: Variable Opening Angle (VOA) Jet:

Differences due to Differences due to different jet

different viewing opening anglesθjet

anglesθview

jet profiles
Jet Profiles

Uniform Jet Gaussian/Fisher Jet Power-Law Jet

Rossi, Lazzati, Salmonson, and Ghisellini (2004)

graziani s universal jet theorem
Graziani’s Universal Jet Theorem
  • Universal jet model that produces narrow distribution in one physical quantity (e.g., Einfγ) 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, Einfγ, 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 Einfγ
  • 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
Determining If Bursts are Detected

DQL, Donaghy, and Graziani (2004)

BeppoSAX bursts

HETE-2 bursts

uniform variable opening angle jet vs power law universal jet
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 jet1
Uniform Variable Opening-Angle Jet vs. Power-Law Universal Jet

DQL, Donaghy, and Graziani (2005)

  • 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 Eobspeak are too narrow

gaussian fisher universal jet
Gaussian/Fisher Universal Jet

DQL, Donaghy, and Graziani (2005)

special relativistic beaming
Special 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 beaming
Uniform VOA Jet + Relativistic Beaming

Epeak ~ Eiso1/2

Epeak ~ Eiso1/3

Yamazaki, Ioka, and Nakamura (2004)

uniform voa jet relativistic beaming1
Uniform VOA Jet + Relativistic Beaming

Donaghy (2005)

Γ = 100

Γ = 300

expected behavior of afterglow in relativistic beaming model
Expected Behavior of Afterglow in Relativistic Beaming Model
observed behavior of afterglow
Observed Behavior of Afterglow
  • Swift/XRT observations
  • of XRF 050215b 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
  • Safter/Sburst~ 1
  • Jet break time > 5d (> 20d)

θjet > 25o (35o) at z = 0.5

Swift: XRF 050215b

BeppoSAX: XRF 020427

phenomenological burst jets2
Phenomenological Burst Jets

Favored

Disfavored

Strongly Disfavored

x ray flashes vs grbs hete 2 and swift bat

HETE Passband

Swift Passband

X-Ray Flashes vs. GRBs: HETE-2 and Swift (BAT)

Even with the BAT’s huge effective area (~2600 cm2), only HETE-2 can determine the spectral properties of the most XRFs.

GRB Spectrum

Peaks in Gamma - Rays

XRF Spectrum

Peaks in X-Rays

conclusions
Conclusions
  • 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 thefirst two, whereas Swift (with Emin ~ 15 keV and 15 keV < E < 150 keV) is not; Swift is ideally suited to do thesecond two, whereas HETE-2 cannot
  • Prompt Swift XRT and UVOT observationsof HETE-2 XRFscan therefore greatlyadvance our understanding of XRFs – and therefore all bursts
scientific importance of xrfs1
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 Einfγ (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 xrfs1
Physical 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
GRBs Have “Standard” Energies

Frail et al. (2001); Kumar and Panaitescu (2001)

Bloom et al.(2003)

phenomenological jet models
Phenomenological Jet Models

(Diagram fromLloyd-Ronning and Ramirez-Ruiz 2002)

Universal

  • Power-Law Jet
  • Fisher Jet
  • Variable Opening-Angle (VOA)
  • Uniform Jet
  • Fisher Jet
  • VOA Uniform Jet + Relativistic Beaming
  • Core + Halo Jet
phenomenological jet models1
Phenomenological Jet Models

(Diagram fromLloyd-Ronning and Ramirez-Ruiz 2002)

Universal

  • Power-Law Jet
  • Fisher Jet
  • Variable Opening-Angle (VOA)
  • Uniform Jet
  • Fisher Jet
  • VOA Uniform Jet + Relativistic Beaming
  • Core + Halo Jet
slide35

Universal Jet Variable Opening

Angle (VOA) Jet

Rossi, Lazzati, Salmonson, and Ghisellini (2004)

universal versus voa fisher jets
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 jets1
Universal Versus VOA Fisher Jets

Donaghy, Graziani and DQL (2004) – see Poster P-26

Universal Fisher jet

VOA Fisher jet

  • Peak of Egammainf ~ 5 times smaller than actual value
  • Egammainf distribution has low-energy tail (of XRFs)
universal gaussian jet
Universal Gaussian Jet

Zhang et al. (2004)

  • 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
fisher jet models
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 Egammainf, 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
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
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
Uniform Jet + Relativistic Beaming

Donaghy (2004) – Poster P-27

Maximum thetajet = 2o

Maximum thetajet = 20o

uniform variable opening angle jet relativistic beaming
Uniform Variable Opening Angle Jet + Relativistic Beaming

Donaghy (2005)

uniform variable opening angle jet relativistic beaming1
Uniform Variable Opening Angle Jet + Relativistic Beaming

Donaghy (2005)

uniform universal jet relativistic beaming
Uniform Universal Jet + Relativistic Beaming

Maximum θjet = 2o

Maximum θjet = 20o

Donaghy (2005)

uniform universal jet relativistic beaming1
Uniform Universal Jet + Relativistic Beaming

Maximum θjet = 2o

Maximum θjet = 20o

Donaghy (2005)

implications of variable opening angle uniform jet
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
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