CTA transient factory	
divergent pointingによる広視野突発天体サーベイの展望	

井上進 (理研)、D. Mazin (ICRR), P. O’Brien (Leicester),	

J. Granot (Open U. Israel), M. Szanecki (U. Lodz),	

L. Gerard (DESY), J. Hinton (MPIK) for the CTA Consortium	

34

M. Szanecki et al. / Astroparticle Physics 67 (2015) 33–46

H.E.S.S. telescope system [9–11], over a dozen new sources weredetected [12].
For CTA, an improved Galactic plane survey should be a major
objective and it will also be capable of performing an all-sky survey
in unprecedentedly short time at high sensitivity; the scientificrationale and feasibility of both survey types are thoroughly discussed in [13]. As also discussed in [13], such surveys can be performed in various modes of observation, in particular, large
number of high-performance IACTs allows for using non-parallelmodes with an enlarged FOV. The proper adaptation of such amode for a specific telescope array can be a non-trivial task. The
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
time needed to achieve a given sensitivity.
In this work we consider the array of Middle Sized Telescopes(MST) working in various, parallel and non-parallel, modes. By performing high-statistics Monte Carlo (MC) simulations of the skysurvey observations, we derive for each mode the basic performance parameters at both trigger and analysis levels, which thenallow us to compare efficiencies of the modes. Our study is a partof an intensive work within the CTA Monte Carlo Work Package

for transients/variables�
CTA (IACTs) vs Fermi�
Funk & Hinton 2013	

big advantange over satellites for transients/variables:	effec. area ~104 x LAT@30GeV�GRB light curve: Fermi vs CTA	

LAT	>100	MeV�

GRB 080916C	

Abdo+ 09�

>1GeV�

CTA	>30GeV, 0.1 sec bin�oto	e	ki	A)	

SI+ 2013	

Astropart. Phys.	

43, 252	GRB light curve: Fermi vs CTA	

LAT	>100	MeV�

GRB 080916C	

Abdo+ 09�

>1GeV�

CTA	>30GeV, 0.5 sec bin�oto	e	ki	A)	

SI+ 2013	

Astropart. Phys.	

43, 252	divergent pointing mode for MSTs	- more effective for surveys	

of persistent point sources	

M. Szanecki et al. / Astroparticle Physics 67 (2015) 33–46[9–11], over a dozen new sources wereGalactic 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. Theting strategy, taking into account numerarray, e.g. distance between telescopes,c, can significantly reduce the observation
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-- GRBs from onset	

prompt emission physics	

(crucial but poorly understood)	

- short GRBs	

Lorentz invariance violation	

(big improvement over Fermi)	

- unbiased transient survey	

e.g. fast radio bursts	

GRBs occurring in FoV (not necessarily detectable):	

GRB rate all sky ~800/yr (BAT), ~600/yr (GBM)	

duty cycle 10%	IF field of view ~1000 deg2 (0.025 sky; 25MSTs, no gap)	

-> ~0.2-0.3 /100 hr -> ~2-3 GRBs /1000 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 weNN

sensitivity for divergent mode: toy MC simulations	50 deg2~1200 deg2~700 deg2~300 deg2

by Jim Hinton, presentation at Zeuthen 2010	

simulations for divergent pointing	c.f. workby L. Gerard+	
Szanecki+
15,+Astropart.
Phys. 67,33 	
Simspipelinemode definition
Results- Skyscans+, A=1

FoV ~80 deg2 	+, A=2

FoV ~200 deg2 	-, A=1Scans are performed for area of 20ºx12º,

potential
gainlower
in surveyfor	

N, D, C havefield of efficiency
view - 2x morepoint
sources
by factor
pointings
are used
than for~2-3	

2D, 2C modes,-, A=2
Pointings
separation
for
FoV ~200
deg2 	
is optimized to give
possibly
highesthomogenity
and the best
butloss inangularand energy
mean scan sensitivity,
resolution	

Scan perf., is estimated with mean sensitivity.
->	 14/15
Slideoption for extragalactic survey	

Scans are performed for area of 20ºx12º,N, D, C have lower field of view - 2x morepointings are used than for 2D, 2C modes,
Pointings separation is optimized to give

GRB detectability estimate	collection area vs energy	a)

A [m2]

105104310N
DC2D2C

black: q = 0.0°
grey: qoff = 4.9°
off100E [GeV]

assume average prompt emission:	

luminosity L~1052 erg/s	

duration T~30 s, spectra Γ=-2.2	

simplified z-dependent EBL cutoff	

z=1: dN/dE~6x10-9 (E/TeV)-2.2	x exp(-E/100GeV) cm-2 s-1 TeV-1	

z=2: dN/dE~10-9 (E/TeV)-2.2	x exp(-E/55GeV) cm-2 s-1 TeV-1	

…	

probably detectable out to z~3	(min. 10 photons) 	
FoV ~200 deg2 -> 0.2-0.3 in 1000hr	
wider FoV desirable!	

MC simulations for wider FoV	

under way	comparison of effective area	

CTA (full, focused)
HESS
HAWC

2Aeff [cm ]ezen=20LAT
BAT
GBM

on-axislog E [GeV]NB IACTs	limited FOV	

duty cycle	

comparison of E/Aeff (“transient νfν sensitivity”)	

on-axisE/Aeff [GeV cm-2]

ezen=20LAT

HAWC

LAT GRBs:	

luminous “tip	of the iceberg”	

CTA GRBs:	

includes those	with lower L	spectra?	

z-distribution?	

GBM
HESS

BAT

NB IACTs	

limited FOV	 CTA (full, focused)
duty cycle	

log E [GeV]

fast radio bursts:	

correlated ms
TeV bursts	

Lyubarsky 15	

SKA FoV:	

200 deg2 @<1 GHz	GeGRAsMetn,;lset.
h,5f−12° 24′−44° 44′−02° 52′

fast radio bursts	−66.2

surveys close to the Galactic plane. In the absence of these conditions, our rate implies thatþ4þ617þ9−7 , 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 anyrepetition. 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), isconsistent with our event rate given a Euclidean universe and a population with distanceindependent intrinsic luminosities (source−3=2count, N ºF) yielding RFRB ðF e 3 Jy msÞ210R
ðFFRB010724
ee 150 Jy msÞ.
There are no known transients detected atgamma-ray, x-ray, or optical wavelengths orgravitational wave triggers that can be temporally
associated with any FRBs. In particular there issee also Kulkarni+	

Thornton+ Science 13	

arXiv:1402.4766	

Parkes High Time Resolution Universe survey	

Sν~0.4-1.3 Jy @1.28-1.52 GHz	Δt~<5 ms	l (°)
UTC (dd/mm/yyyyhh: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)+49.2

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––<1.1491.3

110.4

160.5

110.5

8.0

0.7

10.2~1039

1.9~1037

DM~550-1100 pc cm-3	

-> D~1.7-3.2 Gpc (z~0.45-0.96)	

-> E~1037-1039 erg	

1.8

0.6

RFRB~104 day-1~0.1RSN,10RGRB!�

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.

hsoe-,
yn−18° 25′Fig. 1. The frequency-integrated flux densities for the four FRBs. The time resolutions match the5.1~1038

1.4~1037

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

esfn,
nd

Beam declination

These are symmetric W > 20 ms pulses, which( J2000) the telescope makes inferring a spectral index, andhence flux densitiesobserving band, −59.0
imperfectly mimic a dispersive sweep (2, Galactic8). Al- latitude,−54.7 outside the −41.7(°)
difficult. A likely off-axis position changes the inthough perytons peak in apparent DM bnear–3+50.8 substantially.
+355.8trinsic spectral index
The spectral +81.0
375 cm−3 pc (range from ~200 to 420 cmGalacticpc), longitude,

Downloaded from www.sciencemag.org on July 8,ysummary	 divergent pointing observations	- 点源サーベイの効率向上の可能性	

��銀河系外サーベイのモードとして検討中	

- GRB：外部トリガーなしに発生時から捕捉可能	

long+short GRB即時放射の物理	��ローレンツ不変性破れの探査…	

- ~1000 deg2に迫る広視野が望ましい	

より詳細な検出可能性	

- 無バイアス突発天体サーベイ: 大きなdiscovery potential	

fast radio burstsのVHE対応天体	

-> SKA aperture arrayと同時観測	

未知との遭遇：fast VHE bursts？？	

transient factory (SKA+precursors, ZTF, LSST…)に	CTAも仲間入り？