physics of short gamma-ray bursts explored by cta and...

Hiroyasu Tajima Institute for Space–Earth Environmental Research

Nagoya University

17th DECIGO WorkshopNov 1, 2018

Nagoya University

Physics of Short Gamma-Ray Bursts Explored by CTA and DECIGO/B-DECIGO

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Physics of Short Gamma-Ray Bursts Explored by CTA and DECIGO/B-DECIGO H. Tajima, 17th DECIGO Workshop, Nagoya, NOV 1, 2018

Gamma-Ray Bursts Overview (1)✤ Discovered in 1967✤ Cosmological origin

❖ Large apparent energy release: 1052~1054

❖ Energetics consistent with origin of UHECR✤ Peak in ~MeV gamma rays

❖ Band function:smoothly joined two power law

❖ Synchrotron radiation of ultra-relativistic electrons in jet?

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Gamma-Ray Bursts Overview (1)✤ Discovered in 1967✤ Cosmological origin

❖ Large apparent energy release: 1052~1054

❖ Energetics consistent with origin of UHECR✤ Peak in ~MeV gamma rays

❖ Band function:smoothly joined two power law

❖ Synchrotron radiation of ultra-relativistic electrons in jet?

BATSE Trigger 907

0 50 100 150 200Seconds Since Trigger (911016 : 39694.187)

6.0•103

8.0•103

1.0•104

1.2•104

1.4•104

1.6•104

1.8•104

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(counts

s-1)

Ch: (1: 4)

Time Res: 0.500 s

BATSE Trigger 1440

0 10 20 30Seconds Since Trigger (920226 : 29728.491)

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(counts

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Time Res: 0.064 s

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BATSE Trigger 298

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Time Res: 0.064 s~0.5 s ~40 s ~180 s ~28 s10-4

10-3

10-2

10-1

100

101

102

103

Flux

(ph

oton

s · c

m–2

· s–1

· M

eV–1

)

BATSE SD0 BATSE SD1 BATSE LAD0 BATSE SD4 OSSE COMPTEL Telescope COMPTEL Burst Mode EGRET TASC

GRB 990123

Low-Energy Index = -0.6 ± 0.07

High-Energy Index = -3.11 ± 0.07

F Peak EnergyEp = 720 ± 10 keV

10-8

10-7

10-6

E2 NE

(erg

· cm

–2· s

–1)

0.01 0.1 1 10 100Photon Energy (MeV)

2

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Gamma-Ray Bursts Overview (2)✤ Bimodal Duration Distribution

❖ Short (< 2s) GRB: progenitor unknown• Merger of compact objects (NS or BH)

❖ Long (> 2s) GRB:• Association with supernovae� Core-collapse supernovae

✤ Gamma-ray emission mechanism not well understood

2 s

3

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High-Energy Emissions from GRBs

✤ EGRET observations of delayed HE gamma-ray emissions❖ It is not straightforward to explain by

conventional electron synchrotron models

❖ Proton acceleration? Origin of UHECR?

-18 – 14s

14 – 47s

47 – 80s

80 – 113s

113 – 211s

Gonzalez, Nature 2003 424, 749

EGRET/TASCBATSE

Two γ >GeV @~T0

Hurley et al. 1994

18 GeV γ @ ~T0+75 min

4

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GRB Observations by Fermi✤ Improved performance of Fermi LAT (Large Area Telescope)

❖ Larger FOV (>2.4 sr): more GRB samples❖ Larger effective area: better statistics❖ Less dead time: detailed lightcurve,

time-resolved analysis❖ Wider energy coverage:

up to > 300 GeV✤ Fermi Gamma-ray Burst Monitor

❖ Views entire unocculted sky❖ NaI: 8 keV - 1 MeV❖ BGO: 150 keV - 30 MeV

✤ Fermi GBM-LAT covers >7 decades of energy band (8 keV to > 300 GeV)

GBM NaI GBM

BGO

LAT

5

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Delayed HE Gamma-ray Emission✤ Opacity due to γγ → e+e− in the first peak✤ Late arrival of highest energy gamma rays

00108060402002

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3GBM NaI

(8 keV-260 keV)

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(> 1 GeV)

GRB 080916C

6

8 – 250 keV

0.26 – 5 MeV

> 100 MeV

> 1 GeV

All LAT events

13.2 GeV photon Science 323 1688A (2009)

GRB 090926

http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009Sci...323.1688A&db_key=AST&link_type=ABSTRACT&high=48b97d892d21271


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Delayed HE Gamma-ray Emission✤ Opacity due to γγ → e+e− in the first peak✤ Late arrival of highest energy gamma rays

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3GBM NaI

(8 keV-260 keV)

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(> 1 GeV)

GRB 080916C

6

8 – 250 keV

0.26 – 5 MeV

> 100 MeV

> 1 GeV

All LAT events

13.2 GeV photon Science 323 1688A (2009)

GRB 090926Elena Moretti (Fermi symposium 2018)



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GRB Long-Lived HE Emission✤ HE (>100 MeV) emission shows different temporal behavior

❖ Temporal break in LE emission while no break in HE emission

7

GRB 080916CGRB 090510

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GRB Long-Lived HE Emission✤ HE (>100 MeV) emission shows different temporal behavior

❖ Temporal break in LE emission while no break in HE emission

7

GRB 080916CGRB 090510

Elena Moretti (Fermi symposium 2018)

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Extra Component✤ Extra spectral component inconsistent with Band function

❖ Both in low- and high-energy regions✤ Lack of information for short GRBs

8

3 5 6 8

/s)

2 (e

rg/c

mνFν −710

−610

−510

−410

Time−integrated photon spectrum (0.5 s − 1.0 s)

Energy (keV)10 210 310 410 510 610 710 810

/s)

2 (e

rg/cm

νFν

−710

−610

−510

−410

0.5 s − 0.6 s: Band ( fixed)0.6 s − 0.8 s: Band + PL0.8 s − 0.9 s: Band0.8 s − 0.9 s: Band ( fixed) + PL0.9 s − 1.0 s: PL (LAT only)

GRB 090510GRB 090902B

ApJ 706L 138A (2009)

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Extra Component✤ Extra spectral component inconsistent with Band function

❖ Both in low- and high-energy regions✤ Lack of information for short GRBs

8

3 5 6 8

/s)

2 (e

rg/c

mνFν −710

−610

−510

−410


Energy (keV)10 210 310 410 510 610 710 810

/s)

2 (e

rg/cm

νFν

−710

−610

−510

−410

0.5 s − 0.6 s: Band ( fixed)0.6 s − 0.8 s: Band + PL0.8 s − 0.9 s: Band0.8 s − 0.9 s: Band ( fixed) + PL0.9 s − 1.0 s: PL (LAT only)

GRB 090510GRB 090902B

ApJ 706L 138A (2009)

Soeb Razzaque (Fermi symposium 2018)

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LAT and GBM Emissions✤ LAT and GBM emissions are not strongly correlated

❖ Indicates different origins

9

Elena Moretti (Fermi symposium 2018)

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Spectral cutoff - GRB 090926A

10

Time since (275631628.987) (s)-20 0 20 40 60 80 100

Counts/Bin

0

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TE [H

z]

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aa ba b ca b c d

+ 6GBM NaI 8 + NaI7 NaI

(8 keV-14.3 keV)

(s)0Time since T5 10 15 20Co

unts

/bin

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Energy [MeV]

310

410

LAT EVENTS(> 1 GeV)

✤ Narrow spikes correlated in all energy band

✤ Significant spectral break❖ Shape is not constrained❖ if cutoff due to γ-γ absorp.

• 1st direct measurement of bulk Lorentz factor (Γ∼200-700)

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Spectral cutoff - GRB 090926A

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(8 keV-14.3 keV)


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Energy [MeV]

310

410

LAT EVENTS(> 1 GeV)

Energy (keV)10 210

310 410

510

610

/s)

2 (

erg

/cm

!F!

−710

−610

Band + CUTPL 68% CL

Band + SBPL 68% CL


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Lorentz Invariance Violation (LIV)✤ Some QG models predict a violation of Lorentz Invariance at HE:

✤ Time delay between 2 photons of energies Eh and El emitted simultaneously:

✤ GRB is a excellent light source due to long distance (high z) and short duration❖ Constraint using GRB 080916C: 13.2 GeV photon detected 16.5 sec after

trigger

11

�

c 2pγ2 = Eγ

2 1+ skk=1

∞

∑ Eγ

MQG,kc2

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

k⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

�

vγ2 =

∂Eγ

∂pγ≈ c 1− sn

1+ n2

Eγ

MQG,kc2

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

n⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

min MQG(GeV)

1016 1017 10181.8x1015

Pulsar(Kaaret 99)

0.9x1016 1.8x1017 7.2x10174x1016

GRB(Ellis 06)

GRB(Boggs 04)

AGN(Biller 98)

AGN(Aharonian 08)

GRB080916C Planck mass

10191.5x1018 1.2x1019

QG mass: energy scale where QG effect are expected to be significant

�t =(1 + n)2H0

(Enh � En

l )(MQG,nc2)n

� z

0

(1 + z�)n

⇥⇥m(1 + z�)3 + ⇥�

dz�

geometrical distance assuming ΛCDM

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✤ 30 GeV photon from z = 0.9 (7.3B years)✤ Quantum Gravity models predicting

linear LIV are strongly disfavored

12

choice for tstart limit on Δt (ms)

lower limit on MQG,1/Mplanck

start of any observed emission

< 859 > 1.19

start of main < 1 MeV emission

< 299 > 3.42

start of > 100 MeV emission

< 199 > 5.12

start of > 1 GeV emission

< 99 > 10.0

association with < 1 MeV spike

< 10 102

LIV Test with GRB 090510

0 0.5 1 1.5 2

Coun

ts/b

in

0

50

100

150

Coun

ts/s

0

5000

10000

15000

-0.03

GBM NaIs

0 0.5 1 1.5 2

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in

050

100150200

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05000100001500020000GBM BGOs

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4000LAT(All events)

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in0

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200

400LAT(> 100 MeV)

Time since GBM trigger (May 10, 2009, 00:22:59.97 UT) (s)-0.5 0 0.5 1 1.5 2

Coun

ts/b

in

0

1

2

3

Ener

gy [G

eV]

21

51020LAT

(> 1 GeV)

0.63

0.73

Ener

gy (M

eV)

10

210

310

410

(0.26–5 MeV)

(8–260 keV)

(a)

(b)

(c)

(d)

(e)

(f)

0.53

Nature 462, 331–334 (2009)

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CTA Performance on Short Transients✤ CTA is ~104 times more sensitive than Fermi-LAT for short

transients (< 100 s)✤ However, CTA has very small field of view (~4°) and low duty

cycle (~10%)✤ CTA needs to know when

and where GRBs will occur

13

Time (s)10 210 310 410 510 610 710 810 910 1010

)-1 s-2

Diffe

rent

ial F

lux S

ensit

ivity

(erg

cm

-1310

-1210

-1110

-1010

-910

-810

-710

-610

-510

-410

-310E = 25 GeV

E = 40 GeV

E = 75 GeVFermi-LATCTA

10 years

1 hour

ArXiv: 1709.07997

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GRB Time Profile expected for CTA✤ CTA can detect ~30 times more photons above 30 GeV than

Fermi-LAT above 100 MeV (assuming E–2 spectrum)

14

z=4.3, E>30GeV, 0.1 sec time bin

0

20

40

Time from GRB [sec]40 60 80 100

Exce

ss [/

Bin]

60ArXiv: 1709.07997 Simulated CTA observation of GRB 080916C

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GRB Energy-Time Relation by CTA✤ If a event like GRB 090510 occurs 10 Mpc away from us

❖ CTA can study detailed time profile of very high energy emissions

❖ CTA can detect Lorentz Invariance Violation

15

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

210

310

410

510

610

Arrival Time [s]

Eneg

y [Ge

V]

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Summary✤ Fermi LAT revealed nature of high energy emission from

long GRBs✤ Fermi LAT observed only handful of short GRBs✤ CTA has much larger collection area than Fermi LAT and

will be able to study GRB emissions in detail✤ If DECIGO/B-DECIGO can predict the time and location of

short GRBs, CTA can observe them from the beginning at 10% probability (moonless night in La Palma or Chile)❖ CTA can place very strong constraints on violation of Lorenz

invariance

16

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backup slides

17

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GRB Afterglow

g’

r’

i’z’ J H

Ks

z = 4.35 ± 0.15

(Greiner et al. 2009)

X-ray afterglow

IR/visible light afterglow

18

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Constraints on Bulk Lorentz Factor✤ Large luminosity and short variability time imply large optical depth due

to γγ → e+e−❖ Small emission region: R ~ cΔt❖ τγγ(E) ~ (11/180)σTN>1/E/4πR2

• τγγ(1 GeV) ~ 7x1011 for fluence=106 erg/cm2, z=1, Δt=1 s✤ Relativistic motion (Γ ≫1) can reduce optical depth

❖ Lager emission region: R ~ Γ2cΔt❖ Reduced # of target photons:

N>1/E ∝ Γ2β+2 (note: β ~ -2.2)• Blue shift of energy threshold:

Eth ∝ Γ• Blue shift of spectrum:

N(E) = (ΓE)β+1

❖ Overall reduction of optical depth:Γ2β-2 ~ Γ-6.4

✤ Possible selection bias due to large EISO

✤ Assume common emission region for all gamma rays

19

physics of short gamma-ray bursts explored by cta and...

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