SS

Transient Science with CTA	

Susumu Inoue (RIKEN)	

on behalf of the�CTA Transients SWG / CTA Consortium	

A

Ca
qu
a
se

	

星風の�GRBを散らすと見る夢は�覚めても胸のさわぐなりけり	
GRBに�銀河の光をさしそへて�これや宇宙のにしきなるらん	

outline: transient�science with CTA	

1. introduction	

2. GRBs (afterglows)	

3. FRBs	

4. GW follow-up	

5. transient survey	

skip:	

neutrino follow-up	

Galactic transients	

others (TDEs, etc)	

…	

CTA Key Science Projects (KSPs)	

Dark Matter Programmedark observing time:
Galactic Centre
40% consortium KSPs
60% open observatory
Galactic Plane Survey
Large Magellanic Cloud Survey
Extragalactic Survey
Transients
Cosmic Ray PeVatrons
Star Forming Systems
Details in document“Science with CTA”
Active Galactic Nuclei
to be published on
Clusters of Galaxies
arXiv very soon
Non-Gamma-ray Science

CTA Science Working Groups (SWGs)	

overall coordinator: Stefano Vercellone; deputy: Stefan FunkGalactic SWG

coordinator: Jamie Holder; deputy: Roberta Zanin

Cosmic-ray SWG

coordinator: Stefan Ohm; deputy: Sabrina Casanova

Extragalactic SWG

coordinator: Elina Lindfors; deputy: Fabrizio Tavecchio

Transients SWG

coordinator: Susumu Inoue; deputy: Catherine Boisson

Dark Matter and Exotic Physics SWG
coordinator: Fabio Zandanel; deputy: Aldo Morselli

Intensity Interferometry SWG

coordinator: Dainis Dravins; deputy: Michael DanielMultiwavelength WG

coordinator: Sera Markoff; deputy: Emma de Oña-Wilhelmi

CTA vs current IACTs

from W. Hofmann

Real Time Analysis
Alerts in 30 sec-> transients, survey	
 Versatile Pointing
All-sky Coverage(subarrays, divergent)-> transients, surveys

CTA vs current IACTs-> transients	

adapted from W. Hofmannfor transients/variables�
CTA (IACTs) vs Fermi�
Funk & Hinton 2013	

big advantange over satellites for transients/variables:	effec. area ~104 x LAT@30GeV�for transients/variables�

modes with an enlarged FOV. The proper adaptation of such a
mode
for CTAa specific telescope array can be a non-trivial task. The
Divergent
pointing
with
Lucie Gérard
gent
pointing
with
CTA
Lucie Gérard
optimization of the pointing strategy, taking into account numerous characteristics of an array, e.g. distance between telescopes,
FOV, energy threshold etc, can significantly reduce the observation
Normalmodepointing
mode
pointing modetimetoachievea given sensitivity.
Normalneeded
pointing
Divergent Divergent
pointing mode
In this work we consider the array of15Middle15Sized Telescopes
15
15
300
300
(MST) working in various, paralleland
800 non-parallel, modes. By per800
forming high-statistics Monte Carlo (MC) simulationsof the sky10
10
10
10
700
700
250
250
survey observations, we derive for each mode the basic performance parameters at both trigger
and
600 analysis levels, which then
600
5
5
5
5
200
200
allow us to compare efficiencies of the modes. Our study is a part500
500
of an intensive work within the CTA Monte Carlo Work Package
0
0 scheme.
0
0
150
150
aimed at optimizing the CTA
Whereas we
400 observation
400
consider in detail different modes with the MST array, independent
300 for-5-5 the divergent
investigations are currently300
performed
mode of
-5
-5
100
100
Large Sized Telescopes (LST)200
sub-array
and
the
full
CTA
array
work200ing
indivergentmodes.
-10
-10
50
-10
-10
50
[degree][degree][degree][degree]divergent pointing� for MSTs/SSTs	

Szanecki+ 2015	

normal	
Divergent
pointing with 100
CTA100

-15
-15

-15
-10
-15

0
-52.
5 0 modes
10 5
1510-10Sky0 -5
15
survey[degree] [degree]0

Wider FoV at
expense of angular/energy resolution	

divergent	

-15
-15

-15
-10
-15

-5-10

0 -5

L

Fig. 1. Three modes of configuration of the telescope system used in the sky-survey
scans: (a) normal (parallel) mode; (b) divergent mode; (c) convergent mode.
0
0
5 0
10 5
15 10
15
[degree] [degree]

parison of the performance of the three modes and a related issue,
FoV array~20useddeg dia.	
Fig. 12015	
illustrates possible modes for a large telescope
Gérard+i.e. an optimal value of the offset angle (giving the amount of thefor sky surveys. The parallel and divergent configurations were

fast scanning of large
regions, e.g. GW follow-up

10-2
10-2

10-2
-1
10-2 10Differential Flux Sensitivity [C.U.]ttdivergent 2hnormal 8h	

Integral Flux Sensitivity (E>E ) [C.U.]

10-1

of [13], were the◦ parallelmode is referred to as convergent).
◦
0 − 7 Divergent Pointing
The performanceof a telescope system operating in the sky sur0◦ − 3.5 ◦ Normal Pointing
vey mode depends
on the FOV of the system and the time of observation needed to achieve a given significancelevel, i.e. its
11
sensitivity.
In the simplest approach, sky surveys may be performed with
10-1
telescopes pointed parallely into the same direction of the sky(Fig. 1a), however, in such a case the FOV of the telescope system
is highly limited by the FOVs of individual telescopes. The FOV of
10-1
10-1 deviating◦
a telescope array can0be
enlargedby slightly− 1 ◦significantly
◦
◦
0
−
1
1◦ − 2 ◦◦◦1 −2◦
the pointing direction
eachtelescope. In the divergent mode,2◦ − 3of2◦ − 3 ◦3◦ − 4 ◦◦3− 4 ◦ outward direction, see Fig. 1b, by◦◦telescopes are inclined
into
the
4 −5
4◦ − 5 ◦5◦ − 6 ◦◦− 6◦
an-2angle increasing withtelescopedistance from the array cen◦
◦ the 56 −7
6◦ − 7 ◦10
7◦ − 8 ◦◦◦7−
8ter. -2As explained -1below,aperformance
improvement for2 such a8◦ − 9 ◦
10
10
10
10 -2
8◦ −19 ◦10 energy-2
configuration can be expectedprimarily at highenergiesof pri[TeV]
10E
2
-2
-1
t
10
10
10-1 1 photons.
102
10-21010-1 11 10
10E [TeV]
maryenergyenergy E [TeV]tt
For the divergent configuration, images of gamma rays impingIntegral Flux Sensitivity (E>E ) [C.U.]

10-1

1

t

1

Integral Flux Sensitivity (E>E ) [C.U.]t

Integral Flux Sensitivity (E>E ) [C.U.]

eFigure4: Gamma-ray
acceptanceafter directionand energy
reconstruction
cuts. The
total
numberof events
4: Gamma-ray
acceptanceafter directionand energy
reconstruction
cuts.
The
total
of
events as defined below), appears
differenceof thenumber
pointing
directions,considered before in [13]; below we introduce also a novel, conver1 the most efficient survey strategy.
crucialmode.
for planning
1 aregthose cuts
469
051
for
thethenormal
mode
and
447
918
for918the fordivergentmode.
passing
thoseare
cuts
469
051
for
the normal
mode
and
447
gent
mode
(note
difference
betweenourterminology
andthethatdivergent
3. MC simulations

0◦ − 7 ◦ Divergent Pointing

Preliminary studies:point source survey
efficiency comparable?
-> possibly interestingfor commensal unbiased
transient survey◦◦

For all three modes, we simulate the response of the telescopearray to the Extensive Air Showers (EAS) induced by gamma rays
and proton background. To simulate the development of EAS we
10-1code [14,15], used as a standard in CTA. We simuse CORSIKA 6.99
0 − 3.5 Normal Pointing

ulated 2:1 ! 107 gamma rays and 3:8 ! 108 proton events2 – bothwith energies between 30 GeV and 10 TeV generated from differential spectra withindex C ¼ #2:0. However, in our anal◦0◦ − 1 ◦ the 0spectral
− 1◦
◦
◦
◦
◦
1
−
2
1 −2
ysis, we use event
weights
corresponding to spectra with C ¼ #2:57
2◦ − 3 ◦2◦ − 3 ◦◦◦for gamma rays
and
C
¼
#2:73
for protons. Gamma rays are simu3 − 3.5
3◦ − 3.5 ◦◦◦3.5 ◦ − 4 ◦3.5 −test
4
lated from a4◦ −point-likesource with the direction defined by◦
4.5-2◦
104◦ − 4.5$◦
the Zenith angle=
20
andthe -1Azimuth Az = 180$ measured with◦◦
4.5 ◦ − 5Za
10-24.5 − 510110respect to the magnetic
North. The background proton showers areen
2
10
102 directions within a 10$ half-angle cone
1 10 isotropicallysimulatedwithenergy10E [TeV]
energy E [TeV]tt(larger than the FOV of all considered modes) centered on the direc-

Transients KSP	-> Tam	- GRBs	- Galactic transients	

(microquasars, PWN flares, novae, etc)	

 -> Saito	
- X-ray/optical/radio transients	

(TDEs, SN shock breakout events, FRBs, new transients)	

- HE neutrino transients	

 -> Yoshida	
 -> Aoki, Totani	- gravitational wave transients	

 -> Kisaka	
Wanted:	- serendipitous VHE transients	

- VHE transient survey via divergent pointing	 - gamblers	- fortune	

Related KSPs:	

seekers	

- thrill hounds	

- AGN (flares), LIV studies	?	

2. Gamma-Ray Bursts	

high photon statistics	

>tens of GeV 	Physics of GRBs
- Prompt: mechanism, jet properties (central engine: NS/BH?)- Early afterglow: mechanism (plateau phase),
particle acceleration, B field generation
Tools to probe the Universe- Extragalactic background light (deeper than AGN)
- Intergalactic magnetic fields
Tests of UHECR origin,fundamental physics
Search for signatures of:- Accelerated hadrons- Lorentz invariance violation

ESOGRB light curve: Fermi vs CTA	

LAT	

>100	

MeV�

GRB 080916C	

Abdo+ 09�

>1GeV�

SI+ 2013	

Astropart. Phys.	

43, 252	

oto	

e	

ki	

A)	

Clarify physics of emission
Test UHECR origin, LIV

CTA	

>30GeV, 0.1 sec bin�

GRB afterglows	

ultrarelativistic outflow+ ext. medium interaction-> relativistic blastwave+ electron acceleration-> synchrotron emission
radio - opt. - X - ~GeV	
open questions:mechanisms of- X-ray plateau (shallow) phase	- chromatic light curve breaks- B field generation- particle acceleration…

Panaitescu 06	the late-time hard x-ray afterglow also suggest thata single spectral component produces the emission from optical to multi-GeV energies. If thisemission is indeed synchrotron radiation, then thestandard afterglow shock model must be modified to account for the highest-energy photons
detected by the LAT.
These considerations suggest that other extreme high-energy-1 -1	 radiation mechanisms may be
operative,e such as external Compton processes.
The most intense source of target photons is theplasma and when they travel through intergalactic space [e.g., (36, 37)], a leptonic or hadronic
cascade component in GRBs, which is a naturalextension of colliding shell and blast wave models, might be required to explain the high-energy
emission of GRB 130427A provided that the required energies are not excessive. The observations described above demonstrate nonsynchrotron
emission in the afterglow phase of the bright
GRB 130427A, contrary to the hitherto standard
model of GRB afterglows.

afterglows at VHE: beyond the synchrotron burnoff	

maximum synchrotron photon energy for electrons	

dominated by synchrotron cooling	τaccel∝ γe B-1, τsyn∝ γ B
τaccel=τsyn -> γe,max∝ B-1/2	

4. Curves of maxiνsyn,max∝ Bγe,max2	

 Fig.
10
mum synchrotron pho2	

ton energy.
The blackcdots
Esyn,max~23/2[27/(16πα)]mAckermann+ 2013	
e timesshow the fLAT detectionof photons-1	

 with energiesx Γ(t)(1+z)
greater than 1 GeV and>90% probability of as10
-1sociation
with
GRB
130427A.
~106 Γ(t)(1+z)
MeV	
Adiabatic and radiative pre3

E [GeV]2

dictions for maximum synchrotron photon energy inuniform interstellar medium(ISM) and wind environ101
ments are plotted using
the relations described in(17). Red and blue curvesrefer to the ISM and windcases, respectively. The solid and dashed lines refer
100 -2
-1
0
1
2
3
4
5
10
10
10
10
10
10
10
10
to the adiabatic and radiative cases with G0 = 1000,
Time Since Trigger [sec]and the dot-dashed anddouble dot-dashed lines represent the adiabatic case with G0 = 500 and G0 = 2000, respectively. The
dotted lines show an extreme possibility where acceleration takes place on the inverse of the Larmor
angular frequency, in the case of an adiabatic blast wave with G0 = 1000. For cases with uniform external
medium, Eiso(1055 erg)/n0(cm–3) = 1. 	
The wind normalization was chosen to give the same value of td for

GRB afterglows	Γ<Γmax~1000 (Γ~10 at t~1d)	

-> E >100 GeV surely	

beyond synchrotron	

(SSC, EC, hadronic…)	

GRB 130427A	

Fermi LAT	

Kouveliotou+ 2013 still argue	

for synchrotron extension	

21. J. Gr
J. 67
22. P. K
400
23. G. G
R. A
24. R. B
25. T. Pi(201
26. Y.-Z(201
27. T. La
28. D. G
29. C. D
785
30. R. S
31. B. Z(200
32. R.-Y
33. C. K
779
34. C. D
35. E. B
36. S. R
107
37. K. M

Acknowle
support fr
developm
scientific
United St
INFN in It
K. A. Waland the Nfrom INAF
during th
The Fermi
GBM deve
the Unite

Supplemwww.scien
Materials
Figs. S1 a
Tables S1
Reference

24 June 2

Panaitescu arXiv:1605.09367	
GRB afterglows at HE:
emerging evidence of second hard component	

Search Region = 10 deg
-2

2

2

χ =5.7/9dof

χ =25/8dof

22

χ =6.1/9dof

10

10-0.85(.06)-710

0.10(.06)

-5

2

-4

χ =8.2/8dof-0.07(.05)

-6

-8

1

10

2

10

3

4

10

10

-1

0

10

10

1

10

Source class & t=20-500s
Transient class
10/24
well-monitored
LAT
afterglows	10
SR=5deg
SR=5degat 1-3σ CL ->	

better described by broken
power-law
SR=10deg
SR=10degsuggestiveof
hardcomponent
above
~0.5
GeV-5
GeV	

χ
=3.3/9dofχ
=8.6/8dof
102

Flux (ph/cm s)-2-0.85(.06)

22

χ =5.7/9dof

10

Energy (GeV)

MET-388741629 (s)

-3

2

10

-6

10

2
2

χ =3.1/7dof

2

10

2

-0.84(.08)-3

TRANSIENT class
SOURCE class0.46(.22)-0.88(.07)

10-4

E dN/dE (erg/cm s)

TRANSIENT class
SOURCE class(erg/cm s)

10

-6

10

2

0.1-100 GeV Flux (ph/cm s)

10

GRB 130427ASearch	
 Region = 10 deg & t=20-500s-7

10

Mrk 421	

Fν (not νFν)	

1987ApJ...313..662M

blazars before EGRET (-1991)	

prominent GeV-TeV	

components totally	

unknown and unexpected	
for GRB afterglows,	

analogous situation now:	

- missing (possibly more	than) half the picture	- possible surprises

Makino+ 1987	

3C279	

Makino+ 1989	

3. Fast Radio Bursts�

more from Aoki, Totani	

FRBs:	- new class of radio transients	

- ms duration, very frequent: ~<10000/sky/day	- likely extragalactic, extreme brightness temp.-> coherent	- multiple subclasses? 1 repeating, rest non-repeating (so far)	

- origin mysterious! no. of models >> no. of known FRBs	

- new cosmological probe	Any multi-wavelength/messenger counterpart important!	

VHE prospects:	

IF magnetar flare-like, correlated VHE bursts?	

-> simultaneous campaign with radio of repeating FRBs	

-> search for serendipitous events	

IF NS merger-like, short GRB-like prompt or afterglow, etc	-> follow-up of FRB alerts	

opti

t
n
,
;
l
s
e

t

.
h
,
5
f

FRBs: new class of transients	l (°)
UTC (dd/mm/yyyy
hh:mm:ss.sss)
DM (cm−3 pc)
DME (cm−3 pc)
Redshift, z (DMHost =100 cm−3 pc)
Co-moving distance,
D (Gpc) at z
Dispersion index, aScattering index, b
Observed width
at 1.3 GHz, W (ms)SNR
Minimum peak
flux density Sn (Jy)Fluence at 1.3 GHz,F (Jy ms)
Sn D2 (× 1012 Jy kpc2)
Energy released, E (J)−66.2

surveys close to the Galactic plane. In the absence of these conditions, our rate implies that
þ4
þ6
17þ9
−7 , 7−3 , and 12−5 FRBs should be found in
the completed high- and medium-latitude partsof the HTRU (1) and Parkes multibeam pulsar(PMPS) surveys (18).
One candidate FRB with DM > DMMW has
been detected in the PMPS [ jbj < 5○ (5, 19)].
This burst could be explained by neutron staremission, given a small scale-height error;
however, observations have not detected any
repetition. No excess-DM FRBs were detected ina burst search of the first 23% of the mediumlatitude HTRU survey [jbj < 15○ (20)].
The event rate originally suggested for
FRB 010724, R010724 ¼ 225 sky−1 day−1 (4), is
consistent with our event rate given a Euclidean universe and a population with distanceindependent intrinsic luminosities (source−3=2
count, N ºF
) yielding RFRB ðF e 3 Jy msÞ2e 10 RFRB ðF010724 e 150 Jy msÞ.
There are no known transients detected at
gamma-ray, x-ray, or optical wavelengths orgravitational wave triggers that can be temporally
associated with any FRBs. In particular there is

Thornton+ 13 Science	

 see
arX

+49.2

Parkes High Time Resolution Universe survey	

Sν~0.4-1.3 Jy @1.28-1.52 GHz	Δt~<5 ms	

20/02/2011
01:55:48.957
944.38 T 0.05
910
0.81

27/06/2011
21:33:17.474
723.0 T 0.3
677
0.61

03/07/2011
18:59:40.591
1103.6 T 0.7
1072
0.96

27/01/2012
08:11:21.723
553.3 T 0.3
521
0.45

2.8

2.2

3.2

1.7

−2.003 T 0.006−4.0 T 0.4
5.6 T 0.1

–
–
<1.4

−2.000 T 0.006
–
<4.3

–
–
<1.1

49
1.3

11
0.4

16
0.5

11
0.5

8.0

0.7

10.2
~1039

1.9
~1037

DM~550-1100 pc cm-3	

-> D~1.7-3.2 Gpc (z~<0.5-1.0)	

-> Erad~1037-1039 erg	0.6 much higher, cf. pulsars)	

(E1.8tot possibly
5.1
~1038

1.4
~1037

RFRB~104 d-1~0.1RSN,1000RGRB!�

Fig. 2. A dynamic spectrum showing the frequencydependent delay of FRB 110220. Time is measured relative
to the time of arrival in the highest frequency channel. For clarity
we have integrated 30 time samples, corresponding to the dispersion smearing in the lowest frequency channel. (Inset) The
top, middle, and bottom 25-MHz-wide dedispersed subband usedin the pulse-fitting analysis (2); the peaks of the pulses arealigned to time = 0. The data are shown as solid gray lines andthe best-fit profiles by dashed black lines.

h
s
o
e
-

,
y
n

−18° 25′

Fig. 1. The frequency-integrated flux densities for the four FRBs. The time resolutions match the

Downloaded from www.sciencemag.org on July 8, 2013

e
s
f
n
,
n
d

declination−12° 24′−44° 44′index, and−02° 52′
the telescope makes
inferring a spectral
These are symmetric W > 20 ms pulses, Beamwhich
( J2000)
hence flux densities
outside the −41.7
observing band, −59.0
imperfectly mimic a dispersive sweep (2, Galactic
8). Al- latitude,−54.7
difficult. A likely off-axis position changes the inthough perytons peak in apparent DM bnear(°)–3
trinsic spectral index
The spectral +81.0
375 cm−3 pc (range from ~200 to 420 cmGalacticpc), longitude,+50.8 substantially.
+355.8Downloaded from www.sciencemag.org on July 8,yLorSpitler+ 16, Nature; Scholz+ 1603.08880�
FRB 121102+:
first (and so far only) repeater�
6- discovered by Arecibo in 2012	

17 FRBs until June 2015,	

	

 inc. GBT, Effelsberg	

- near Galactic anti-center	

DM~559 pc cm-3 >> DMMW~200 pc cm-3		

 -> likely extragalactic, z~0.2?	

- average 3 FRBs/hr, but strongly		 time-clustered, no periodicity	- large variations in profile, spectra	similar to Crab GRPs		

 -> extragalactic pulsar super-GRPs?	

- comparison with other FRBs:	

Arecibo sensitivity >10x Parkes	

-> fainter repetition in other FRBs?	

duration ~3-9ms, significantly longer	-> separate class?	

Figure 2. Dynamic spectra for each of the bursts detected in 2015 November and December using GUPPI (bursts 12 16) and PUPPI(burst 17) dedispersed at DM=559 pc cm 3 . For each burst, total intensity is shown in grayscale, the top panels show the burst time seriest MPI Physics on May 12, 2014

1
γtotalTherefore,
γgiven1 > γisotropicEcurase etdistance1&rbyequation
(7).
the
al.
# γ1
dn
1
HE shock, these particles rotate in the magDownstream of the2forward
'
(
1
(17)
me c γradio emissiondγ = is estimatedξ = of the maser
2−α assenergyγ
1mξ=
netic 3p
field.
the downstream
frame,
factor is the particle γLorentz
VHE
prospectsfor1�dγFRBs1Inthem,<γ.
ncestherein).
Among
extragalactic
1
E
γE
3p 1
n
"(NSs) including
2
2
2
46
2
2
−1
ron stars
stronglymagne= 2γ ! cd andparticlemomentumis btransferredtoerg.
the downγpulsar/magnetar-like
methe
c n!
&r =
2 × 10 η−3B∗15 l6 ξ nprogenitor	

radio = η4πrscd
eso-called- Emagnetars)
have been considered as
Substituting
equation(16), one atgets
anaequation
fortheξ . Larmor
At α = 1, Substituting e
streammedium,if it Lyubarsky
completes
least
quarter of)andidateshyper-flare
driven(Popov & Postnov
2010;pulse/outflow	

(11)frotation
beforeloses the2016;energy to the synchrotron emission. The
thisyields& Rezzolla
2014;
Cordes&itWasserman+
nebulainteraction	

this yields
evers & PenThe402016).
NSs
areexpectedtoform
as) ofcondition
correspondingis * radio bursts, ∼10 erg, could beenergies
the observed)
12/7
mnantsofcorecollapsesupernova(SN)
explos0.9# densities
e
−6
−3
e.g.
model
of
Lyubarsky
14�
cm. Note (18)achievedattheparticleinthenebulan∼
10
a significant
fractionofthemagnetic
energyξ4 =" min
1;.
"2
2 6/7 2/7
ξ = min 1;
8/7.tion energy
extracted
from
the
young
ωcan
γ be
<
me cγ3 E5
/e
(14)
FRB:
synchrotronb,maser	

p−8
that
is
comparable
withthe particle density in the Crab nebula.
Bthis
9fields have not decayed yet. ComnmagneticTaking
intoaccount
the√transittime effects, the observed duration
VHE:
shock
synchrotron	

models For
are also
often
discussed,
where
ei"
α=
1.5,
one
gets
)
For α = 1.5, o
where
ωor
eB
/( duration)	

2m
c!cd ) is Murase+
the Larmor
frequency in thepulsems
white
dwarf
(WD)
black
hole
(BH)
are einof
the
burst
is
B =
16�
(correlated) 2013; Zhang 2014; *)he mergerdownstream
system (Totani
frame.
This
4/5 condition means that the maximal energy
2# NS-BH,
Ioka & Mészáros 2013).
For NS-NS,−4
Figure1. Schematic
pictureof theburst-in-bubble
model. cor)
wD mergers,
&r
=
1.3
×
10
(12)
δt
=
−5l6 s. bysynchrotron
photons
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at
rest
is
.
(19)
ξof=
min
1;
ξ
=
min 1;
baryonic
10 2/15−
2 ejecta with
8/15 ∼
2/5
c!
cf.
b
p
cd with γaE5
t expected to moverefastvelocityof−8!me c3b1/2
c.
-> simultaneous radio+ VHE	

y
TeV.
(15)
!
=
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εIn1 ∼
cd total available
any case,theenergyanyiscase,er case, one naturally
the formation
show that theobservation
escape of gamma-rays
andrepeater(s)�
radioIn
waves
pos- the2 expects
ξ 1/4 #of FRBus wind bubble embedded
baryonic
for NSs with ages of T ! 10 − 100 yr. In Section 3, we
2 HIG
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2 G2Y Esible
2
4
V
E
RY
E
N
M
I
S the
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N F RO
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r by
lestimates=the10b(4)B∗15l6 (6)
Edhe relativistic
Substituting
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and
into
totalwindis pulse
drivenspin-down
discuss
impact of (14),a highlyrelativistic
outflow->ansearchforserendipitous
events�
O
RWA
R
D
S
H
O
C
K
the NSs F
or
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It
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nates
from
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magnetic
dissipation
event.
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withtheLorentz
factors
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FRB/4
4.5 thedegFOV	s that are isinitially
Poynting-dominatedbecome 2	 celerating
emittedultrahigh-energyband~1(15)
as flow
adays
pulse
with
the
relativistic
mayinboost
pre-existing
non-influence~10in-8 the(DGpc)-2 erg/cm
3/2
time
they
reach thethe energy
light cylinder,
and and thethermalparticlesis indetermined
the nebula, andgammaInPWNe,
densitypressureby high-energy
-21/8
9 cm
2	

observed
yby
duration(12).
ξ
#duration
(12).
Such
a
pulse
could
be
from
the
distance~10
photons
(D
)
for
A
~10
)bethe4via magnetic
Gpc
eff
accelerated
in
the
wind
zone
ray
flashes(HEGFs)areexpectedinthe
GeV-TeVrange.
4
6γ < γ1 = 9.2
× 10 with 1/4
(16)
∼
10
–10
.
At
high-energy
particles
theLorentz
factorsγ
E
tprocesses (e.g.,
3/4∼100
Mpc. EBL;
Komissarov
2013, andWe also argue that possible dissipation at the∼100
reverseMpc.
shock(neglectingsets
in>~0.4 TeV	b referencesp−8−α, the particle
spectrum∝γ , gamma-ray
with a rather
γ < γ E pulsar
wind nebulae(oftenis a power
leads tolaw,
lower-energy
emission in the MeV-GeV
rudies of Galactic
for
D=1
Gpc
or
z=0.25)	

as plerions)suggestslope,that amomenta
fraction
In medium.
Section4, wediscuss findthe possibility of a subsetransfer
theirtothe downstream
shallow
αsignificant= 1–1.5.
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a slope,most ofparticles
ddown
energy is dissipated at the termination
quent afterglow emission, and show that interactions
with
)
5 MAS
ER
Downloaded from http://mn4. Gravitational Wave Follow-up	

VHE prospects:	

- short GRB on-beam (prompt or) afterglow cf. GRB 090510	

- short GRB off-beam “orphan” afterglow?	

- merger ejecta + CBM interaction?	

trophysical Journal, 746:48 (15pp), 2012 February 10
Metzger & Berger
potential “prompt” component from fastest part of ejecta	

pecific stellar populations). Because merger counterparts
Kyutoku+
edicted to c.f.
be faint,
obtaining a 14	

spectroscopic redshift
allenging (cf. Rowlinson et al. 2010), in which caseoscopy of the host galaxy is the most promising meansaining the event redshift.
s important to distinguish two general strategies for cong EM and GW events. One approach is to search for a
Bartos+ignal following
an EM13	
trigger, either in real time or at-processing stage (e.g., Finn et al. 1999; Mohanty et al.
. This is particularly promising for counterparts predicted
ur in temporal coincidence with the GW chirp, such as
duration gamma-ray bursts (SGRBs). Unfortunately, mostpromising counterparts (none of which have yet been
endently identified) occur hours to months after coales6
Thus, the predicted arrival time of the GW signal willn uncertain, in which case the additional sensitivity gained
this information is significantly reduced. For instance, if
me of merger is known only to within an uncertainty ofrs (weeks), as we will show is the case for optical (radio)
erparts, then the number of trial GW templates that mustarched is larger by a factor ∼104 –106 than if the merger

Jet ISM Shock (Afterglow)
Optical (hours days)
Radio (weeks years)

efficient scan of large error region
via tiling or divergent pointing

Ejecta ISM ShockRadio (years)

GRB

obs

(t ~ 0.1 1 s)

detection of- any emission: ID of host galaxy,distance (less confusion
than other freq.)- on-beam: test of short GRB origin- off-beam: insight into merger physics

Kilonova

Optical (t ~ 1 day)j

Merger Ejecta
Tidal Tail & Disk Windv ~ 0.1 0.3 c

BH

Metzger & Berger 11	

Figure 1. Summary of potential electromagnetic counterparts of NS–NS/

5. transient survey via divergent pointing	M. Szanecki et al. / Astroparticle Physics 67 (2015) 33–46[9–11], over a dozen new sources were

Galactic plane survey should be a major
be capable of performing an all-sky survey
t time at high sensitivity; the scientificof both survey types are thoroughly disscussed in [13], such surveys can be perdes of observation, in particular, large
ance IACTs allows for using non-paralleld FOV. The proper adaptation of such acope array can be a non-trivial task. The
ting strategy, taking into account numerarray, e.g. distance between telescopes,c, can significantly reduce the observationa given sensitivity.
der the array of Middle Sized Telescopes, parallel and non-parallel, modes. By perMonte Carlo (MC) simulations of the skyderive for each mode the basic perforth trigger and analysis levels, which thenciencies of the modes. Our study is a partthin the CTA Monte Carlo Work Package
e CTA observation scheme. Whereas we
nt modes with the MST array, independent
tly performed for the divergent mode ofST) sub-array and the full CTA array work-- possibly effective for surveys	

of persistent point sources	

N- GRBs from onset	

N
prompt emission physics	

(crucial but poorly understood)	

- Lorentz invariance violation	

(big improvement over Fermi)	

- unbiased transient survey	

e.g. FRBs	

transients occurring in FoV (not necessarily detectable) 	

GRBs: all sky ~1000/yr (BAT+GBM)	

FRBs: all sky ~6000/dy	

IF FoV~300 deg2 ->	

~8 GRBs/yr -> ~1 GRBs /1000 hr	

~45 FRBs/dy -> ~2 FRBs / 1 hr	

ble modes for a large telescope array usedrallel and divergent configurations were; below we introduce also a novel, convererence between our terminology and thatmode is referred to as convergent).
telescope system operating in the sky sure FOV of the system and the time of obsereve a given significance level, i.e. its

ach, sky surveys may be performed with

Fig. 1. Three modes of configuration of the telescope system used in the sky-survey
scans: (a) normal (parallel) mode; (b) divergent mode; (c) convergent mode.

parison of the performance of the three modes and a related issue,
i.e. an optimal value of the offset angle (giving the amount of thedifference of the pointing directions, as defined below), appears
crucial for planning the most efficient survey strategy.
3. MC simulations

For all three modes, we simulate the response of the telescopearray to the Extensive Air Showers (EAS) induced by gamma rays
and proton background. To simulate the development of EAS wesummary	

 Transients with CTA	

crucial advantages over Fermi, current IACTs	

- large effective area	

- all sky coverage, versatile pointing, real-time analysis…	

Exciting new prospects for:	

- GRBs: prompt - detailed spectra, light curves…	

afterglow - new components beyond sync.	

- FRBs: test of origin(s)	

- GW: localization, SGRB/FRB connection, merger physics…	

- unbiased transient search via divergent pointing 	- others: neutrinos, Galactic transients, etc…	

Transients are most valuable for CTA Japan! 	
GRBの絶ゆ光�諸行無常の兆しあり…	

VHE prospects for FRBs 2�
- NS merger progenitor -> similar to prospects for GWs	FRB: quasi-isotropic coherent emission from NS magnetosphere, etc	e.g. Totani 13, Falcke & Rezzolla 13	

VHE: short GRB on-beam prompt+afterglow cf. GRB 090510	

short GRB off-beam “orphan” afterglow?	

merger ejecta + ext. medium interaction?	

-> follow-up of FRB alerts (currently Parkes, future CHIME, FAST…)	

VHE�
VHE?�
FRB?�

from	

Fernandez &	

Metzger 16