Transcript Fan_Yizhong - UNLV GRB Group

High energy (20MeV-TeV) photon
emission from Gamma-ray Bursts
Yi-Zhong Fan
(Niels Bohr International Academy, Denmark;
Purple Mountain Observatory, China )
Collaborators: Tsvi Piran, Ramesh Narayan, Da-Ming Wei, Bing Zhang
(Fan & Piran 2008, arXiv:0805.2221)
GRB internal-external shock model
(see Piran 1999, 2004; Meszaros 2002; Zhang & Meszaros 2004 for reviews)
UV/opt/IR/radio
gamma-ray
prompt
emission
central
engine
1E6cm
photosphere
1E9cm
internal
(shocks)
1E12-1E14cm
afterglow
gamma-ray
X-ray
UV/optical
IR
mm
radio
external shocks
(reverse)
(forward)
1E17cm for ISM
1E15cm for wind
MeV-GeV observations (EGRET)
afterglow
The first afterglow
detection, but no
redshift information
GRB 930131 (Superbowl Burst)
GRB 940217
(Hurley et al. 1994)
MeV-GeV observations (EGRET):
GRB 941017: Gonzalez et al. 2003
Much longer high
energy emission
Quick evolution
Almost constant
VHE(>50 GeV) Observations
• Milagrito observation of GRB 970417 at energies
above ∼ 0.1 TeV (3 σ? Atkins et al. 2000)
• Upper limits from Magic for several Swift bursts
(Albert et al., 06)
• Claims of detection GRAND at 2.7 σ (Poirier et al 03,
but see Fragile et al 03)
• Tibet array: 7σ coincidence ? (Amenomori et al 01)
• ARGO-YBJ array find only upper limits (Di Sciascio,
et al., 06)
Only upper limits!
The optical depth of universe to
VHE gamma-rays
(Stecker et al. 2006)
z=3
z=5
tau~6
z=1
z=0.2
z=0.5
z=0.03
z=2
Physical processes producing
high energy gamma-rays
• Synchrotron radiation (Syn-Rad) of
electrons/protons
• Inverse Compton processes
• Pion production
• Electromagnetic cascade of TeV gamma-rays
see Fan & Piran (2008 ) for a review
Inverse Compton (IC) processes
electrons
Seed photons
timescale
Synch. SelfCompton (SSC)
Shock-accelerated
Synch. radiation Simultaneous with
of the electrons
Synch. Rad
External IC
(EIC)
Shock-accelerated
Irrelevant to the
electrons and
along the
direction of
Much Longer
than that of the
seed photons
outflow material
Bulk Compton
Moving with a high
bulk Lorentz factor
(cold in their
comoving frame)
Irrelevant to
electrons and
arbitrary
Determined by
that of the ejecta
carrying the
distributed
electrons
see Fan & Piran (2008 ) for a review
One novel feature of EIC
The EIC emission lasts
much longer than the
seed photons because
the duration is affected
by (1) the spherical
curvature of the blast
wave (Beloborodov 05)
and by (2) the highly
anisotropic radiation
of the up-scattered
photons (Fan & Piran
06)
Fan, Piran, Narayan & Wei (2008 )
High energy photons from Pion production
Electromagnetic cascade of TeV photons
(Nikoshov 1962; Gould & Schreder 1967)
TeV source
Infrared background
MCB
Seed
photon
GeV photons
e  with a Lorentz
factor ~ 106 formed
High energy processes in GRBs
and afterglows
SSC in GRBs and their afterglows
Prompt
SSC
ge≈1000
Reverse
Shock
SSC
ge ≈ tens
From Piran (2003)
Forward
Shock
SSC
ge≈104-10
SSC
Synch
electron’s
Lorentz
Factor
SSC
energy
Duration
Prompt
(GRB)
100 keV
1000
100GeV
Prompt
Prompt
(XRF)
10 keV
300
1 GeV
Prompt
X-ray flares
0.2 keV
Standard internal shocks
Internal shocks (Pe’er
Energy
(Pe’er & Waxman
04)
& Waxman
04)
External
GeV-TeV
500shock model:0.2GeV
Reverse
Shock
1 eV
100
Forward
Shock
10keV-1eV
104 -10
Short
10keV
Short
Standard
forward
shock
Standard forward shock
(Fan(Fan
et al.et08)
al. 08)
TeV-keV
Long
(M’esz’aros & Rees 94; Pilla & Leob 98; Pe’er & Waxman 04; Gupta & Zhang 07, 08
Guetta & Granot 03; Wei et al. 06; Wang et al. 06; Fan et al. 08; Galli & Perna 08
Wang et al. 01a,b; Granot & Guetta 03; Pe’er & Waxman 04b; Kobayashi et al. 07
Dermer et al. 00; Sari & Esin 01; Zhang & M´esz´aros 01; Wei & Fan 07; Galli & Piro 07;
Gou & Meszaros 07; Yu et al. 07)
IC of very early afterglow
(Both reverse shock (RS) and forward shock (FS) exist)
SSC of RS
IC: RS emission
+ FS electrons
IC: FS emission
+ RS electrons
SSC of FS
(Wang et al. 2001a,b; Granot & Guetta 2003; Piran et al. 2004)
IC of very early afterglow
Weak RS
Relativistic RS
The energy of RS
electrons to total energy
of RS+Fs electrons
Importance of RS
IC emission
timescale
~0.1
Unimportant
Longer than the
prompt emission
Important but
dominated by EIC
Longer than the
prompt emission
(Nakar & Piran 04)
~0.5
Prompt photon flow
The prompt photon flow overlaps RS/FS
shock regions and the cooling of
RS/FS electrons may be dominated by
EIC, and GeV-TeV EIC plateaus are
produced
(Beloborodov 05: EIC in RS;
Fan, Zhang & Wei 05, ApJ629: EIC in RS + FS)
(in GRB 080319B: prompt optical
photons cool the FS electrons+prompt
gamma-rays cool the RS electrons)
Is strong reverse shock popular?
• Bright optical flashes, predicted in RS model, are
detected only in a few bursts (Akerlof et al. 1999; Fox et al. 2003;
Li, W. et al. 2003; Boer et al. 2006; Klotz et al. 2006; Roming et al. 2006)
• Even for these limited detections, the afterglow
modeling usually suggests a weakly magnetized RS
region (Fan et al. 2002; Zhang et al. 2003; Kumar & Panaitescu 2003;
Wei et al. 2006; Klotz et al. 2006). A stronger magnetization may
account for the non-detection in other events (Fan, Wei &
Wang 2004; Zhang & Kobayashi 2005; Giannios et al. 2008).
• The IC emission of reverse shock is expected to be
weak in most cases (cf. Kobayashi et al. 2007)
EIC in early afterglow
(Wang et al. 06; Fan & Piran 06; Fan et al. 2008)
Any central engine
afterglow photons
Fan & Piran (2006 )
EIC in early afterglow
(Fan, Piran, Narayan & Wei 2008)
Bulk Compton in GRBs and their
afterglows
• Shemi (94) and Shaviv & Dar (95a,b) suggested that the
ultra-relativistic GRB ejecta was moving into a dense soft
photon background and the electrons in the ejecta
Compton scattered on the photons and boosted them to
MeV-GeV (producing GRB prompt emission)
• Bulk Compton in GRB internal shocks (Takagi & Kobayashi
05), producing GeV-TeV emission (efficiency ~1E-3)
• Bulk Compton in GRB afterglows (Panaitescu 08a, b),
producing flares, plateaus followed by a sharp drop, some
X-ray flattening and GeV emission
The late outflow launched by the re-activity of the central engine has
to have a Gamma~104 and is electron/positron dominated
Electromagnetic cascade of TeV photons
• In the presence of intergalactic magnetic field (B_IGM), the magnetic
deflection
angle of the electron/positron at a radius R_IC they lose
z~0.1 and BIGM~10-20 Gauss (Murase et
most ofal.
their
07) energy through IC scattering the CMB
 B  RIC /(g e me c 2 / eBIGM )
• The time-delay caused by the magnetic deflection is
t B  (1  z ) RIC B2 /( 2c)  6 1011 sec(
ge
BIGM 2
5
11
)
(
)
(
1

z
)
106
10 16 G
• BIGM<10-18 G is needed to get detectable GeV emission signatures. It
is not clear that whether such a small value is realistic within a radius
~10 Mpc to the GRB host galaxy.
(Plaga 95; Cheng & Cheng 96; Dai & Lu 02; Guetta & Granot 03;
Wang et al. 04; Razzaque et al. 04; Murase et al. 07; Ichiki et al. 07)
pion production
• The collision of relativistic nucleons (Gamma~300)
with a dense cloud to produce \pi^0 (Katz 94; to account for
the 18 GeV photon detected in afterglow of GRB 940217 )
• Pions produced in standard GRB internal shocks
(Waxman & Bahcall 97; Gupta & Zhang 07)
• Neutron rich GRB outflow: inelastic n, p collision
produces \pi^0 (Bahcall & Meszaros 01; Meszaros & Rees 01)
• The neutral beam model (Dermer & Atoyan 04; >1018 eV
neutrons created in p+\gamma process escaped from internal shocks and
were subjected to further photopion processes with photons……; see also
Ioka et al. 04)
Interpretation of the EGRET data
High energy afterglow of GRB 940217: the SSC
component of a slowly decaying X-ray light curve?
(Wei & Fan 2007)
Afterglow emission
Ek  t 0.5 ,  e  t 0.4 , p ~ 4
We
need
The SSC of an X-ray plateau
to reproduce
thedecline?
followed
by a sharp
spectrum and the
nearly constant count
rate.
30MeV- 30GeV
GRB 940217 (Hurley et al. 1994)
The ~0.2 GeV hard component of GRB 941017:
the EIC of the RS+FS shocks in wind medium?
(Fan & Piran 08 based on Beloborodov 05 + Fan, Zhang & Wei 05)
Fan et al. 08
1. The MeV-GeV plateau
has a duration about 3
times that of the sub-MeV
emission
2.The MeV-GeV emission
energy is at least
~3 times that of the
sub-MeV emission
3. The MeV-GeV emission
has a very hard spectrum
Fv ~v0
The timescale favors a process
relevant to the very early
afterglow (Granot & Guetta 04)
Prompt emission overlaps
FS+RS (Sari & Piran 99; Fan
et al. 05): EIC works
Suppose that a significant part
of MeV-GeV emission is
powered by the RS, the reverse
shock has to be relativistic
Fan et al. 08
What can GLAST tell us?
Do something with GLAST detections
• Constrain the physical composition of the GRB
outflow (If magnetized, no GeV-TeV excess: Giannios 08), the
particle acceleration models and the radiation
mechanisms
• Probe the initial Lorentz factor of the GRB ejecta
(Lithwick & Sari 01; Dai & Lu 02; Fan & Wei 04) and the radius of
the prompt energy dissipation (Gupta & Zhang 08)
• Test current various modifications of forward shock
model that introduced to account for the peculiar
Swift X-ray data (Fan et al. 08)
Is there a canonical high energy
afterglow light curve?
(Fan, Piran, Narayan & Wei 08)
?
Given the small number
of high energy photons,
these novel features
are not expected to be
identified as frequently
as in X-ray band. But
in some extremely
? bright bursts, like
GRBs 940217, 941017
and 030329, more than
1000 sub-GeV photons
may be collected.
?
MAGIC-II, HESS-II: ~30 GeV
photons from GRBs?
z=1
Thank you!
EIC in early afterglow
(something to be clarify)
• The total energy to be emitted into GeV energies is that of the
blast wave and does not strongly depend on the brightness of
the central engine afterglow (e.g., X-ray flares).
• The SSC of the early forward shock also peaks at GeV
energies. In the absence of EIC, the SSC will convert a
significant of blast wave energy into high energy emission. So
the EIC can not enhance the GeV detection significantly.
• After taking into account the SSC of the forward shock before
and after the X-ray flare, the detected high energy lightcurve
should be a plateau rather than a GeV flare.
The SSC of the X-ray flares can be distinguished as sub-GeV (Wei et al. 2006; Wang et al.
2006; Fan et al. 2008)or even GeV-TeV flashes (Galli & Piro 2007; Fan et al. 2008)
SSC and 2nd IC in GRBs?
2nd IC
SSC
Syn
Stern & Poutanen (2004)
Naked-eye GRB 080319B: energetic GeV source (Zou et al. 08)?