1. Ground-based Wide Angle Cameras
WEI Team NAOC, Beijing
Les Chouches Physics School, April 11, 2016

2. Scientific requirements on SVOM
Permit the detection of all know types of GRBs (>200), with a special care on high-z GRBs and low-z sub-luminous GRBs
Provide fast, reliable and accurate GRB positions
Measure the broadband spectral shape of the prompt emission
(from visible to MeV)
Measure the temporal properties of the prompt emission
Quickly identify the afterglows of detected GRBs, including those which are highly redshifted (z>6)
Quickly provide (sub-) arcsec positions of detected afterglows
Quickly provide redshift indicators of detected GRBs

3. Multi-wavelength capabilities of SVOM
102
103
104
105 10 1 -5
1022
1020
1016
1018
1014
1015
Time (s)
Log. scale
Time (m)
Lin. scale
Frequency (Hz)
Space
Ground
Slew
GRM
ECLAIRs
MXT VT
GWAC
F-GFT
C-GFT

4. SVOM strategy: GRB optical emission detection
T-T0=30 sec
Wang et al 2013
GWAC
GFTs VT

5. GWAC: an instrument for short time–scale optical transients
Wozniak et al. 2009
The key point: trigger by its self !

6. Scientific objectives of GWAC
Optical emission of GRBs
Optical prompt emission ；
Early optical afterglow
Prior burst optical emission (if existing)；
Other short time-scale Optical Transients(OT)
Gravitational wave burst events
Early light curve of SNs
Tidal events of supermassive black holes
Micro-lensing
Neutrino bursts
Near earth objects (NEO)
Flare stars ……

7. GWAC System: Parameters
Instruments:
GWAC: 36 wide angle cameras with diameter of 18cm
Mini-GWAC: 12 cameras with diameter of 7cm
Follow-up telescopes:
2 dedicated 60cm telescopes
Several dedicated 30cm telescopes

8. Prompt optical emission detection down to MV ~ 16.0 (10 s exposure)
Parameters of GWAC
Cameras：
Diameter： mm
Focal Length： 220mm
Wavelength： －800nm
Total FoV： ~5000Sq.deg
Limiting Mag： 16.0V（5，10sec）
Self Trigger: ~13*5sec
Prompt optical emission detection down to MV ~ 16.0 (10 s exposure)

9. Status: GFT for GWAC 2014-2015: two 60cm, from GuangXi Uni.
2015： one 30cm, from Huaibai Normal Uni.

10. Status: Mini-GWAC Mini-GWAC at Xinglong Obs.: 12 CANON EF 85/f1.2
12 U9000X CCD cameras
FoV: ~5000 Sq.Deg
Limiting Mag: ~12.5mag
Having capability to trigger OT:
Oct. 2015: in operation，
~10 flare stars detected, …
：a Flare star，Time scale~700秒
Light curve

11. -------------------------------------
Light curves of GRBs
（Wang et al. 2013）
A light curve of a flare star
（Mini-GWAC 2015） T0
T-T0=30 sec
Mini-GWAC
GWAC
700sec

12. GRB prompt detection efficiency
Sites for GFTs and GWAC
GRB prompt detection efficiency
C-GFT
GWAC
F-GFT
GWAC

13. GWAC Follow-up Observation Strategy
2M Telescops
~10Min T R I G E
Follow-up M U L T B A N D
~1min
~1day P O T M E R Y S W I F T ? +
1M NetWorks
~1hr
GWAC
60/30CM

14. 2015.12.18: early spectra from the 2.16M

15. GRB140629A ：Spectrum from 2.16M@~1hr
Z=2.275

16. The strategy for SVOM to observe GW bursts
2015
2019
2022
Error box: ~600 Sq.Deg
~>10 Sq.Deg.
GRM
Eclairs
MXT VT
GWAC

17. March 2015: MoU between SVOM and LIGO/VIRGO

18. 2015.12.26：Mini-GWAC first pointed to G211117
The report to LIGO
Mini-GWAC covered the north sky
LIGO/Virgo G211117: List of near-term future observation regions by Project Mini-GWAC of SVOM
J.Y. Wei (NAOC), C. WU(NAOC), N.Leroy (LAL), L.P. Xin (NAOC), X.H. Han (NAOC), X.M. Meng(NAOC), L. Huang(NAOC), Y. Xu(NAOC), H.B. Cai(NAOC),J. Wang(NAOC), X.M. Lu(NAOC), Y.L. Qiu (NAOC), J.S. Deng(NAOC), L. Cao(NAOC),S. Wang(NAOC), E.W.Liang (GXU), Y.G. Yang (HBNU), B. Cordier(CEA),S.N. Zhang (NAOC),S. Basa (LAM), B.B. Wu(IHEP), Jean-Luc Atteia (IRAP), D. Götz (CEA), Cyril Lachaud (APC) on behalf of the SVOM Gravitational Astronomy group report:
We observed about 3200 square degree (8 sky regions) of the skymap of the advanced LIGO and Virgo trigger G211117, with Mini-GWAC(Mini Ground Wide Angle Camera), at Xinglong Observatory of NAOC equipped with U9000 camera(FOV~400 square degree/camera). Mini-GWAC comprises of 12 wide field angle cameras(aperture=7cm), working with unfiltered band. The observations are operated in time-series mode, taking one exposure in 15 seconds (10s exposure + 5s readout). The limit magnitude is ~12 mag in R band. The coordinates of the 8 regions and observation time are list following:

19. Current Status and Schedule
Mini-GWAC
: ready for observation
GWAC
：dome at Xinglong Obs.
：40 CCD chips
：engineering models
: Pipelines ( V1.0)
： 1/2 of GWAC
2017： /2 of GWAC
Follow-up telescopes
2015: two 60cm.
2015： one 30cm
: more 20cm
Re-set up at Chile
2018/20： TBD
Budget
~33 + ~30M ￥(10M USD)
(~6000Sq.deg)
20M ￥ more?
(~9000Sq.deg)

20. Summary
GWAC is an dedicated instrument for short time scale optical transcients:
10~20 GRBs per year will be monitored;
Several bursting SNs per year will be detected;
A promising instrument to detect GW counterparts.
Several years before SVOM launch:
excellent chances to train BAs and Science Centers.

21. Engineering models of GWAC ----Camera(FoV + high image quality) + Mount

22. Camera design and manufacture
Optical design
装配图

23. GWAC：大面阵e2v CCD Oct. 2010：signed contract with e2v
July 2012: k4k back-illu. CCDs

24. Dowar with cooling system
-50C ！
Vacuum is stable
Dowar with cooling system

25. Sept. 24,2014, New Dowar, -70C! 目标温度：-71C 冷端：-71C 热端：+32.7C V：8.37V
I：5.38A
平稳态
Sept. 24,2014, New Dowar, -70C!
目标温度：-50C
冷端：-49.9C
热端：+25.8C
V：5.75V
I：3.52A
目标温度：-70C
冷端：-66.1C
热端：+47.3C
V：13V
I：9.6A
全力上升中
目标温度：-71C
冷端：-71C
热端：+30.0C
V：7.64V
I：4.91A
当若真空度很好

26. 10-6 ？？ ？
Visible
Detection prompt emission in visible will extend 3-4 orders to low energy band, to provide new chances to understand GRBs.

27. Comparing with the Existing Instruments
FoV(Sq.Dec.）
Lim. Mag.
Reference
WIDGET (Japan)
4000 12
Urata et al 2010
Pi of the Sky (Poland)
1600*n
Sokolowski et al 2009
TORTORA (Russia)
720 11
Greco et al.2009
RAPTOR-Q (USA)
～15000
9.5
Woznizk et al. 2009
Mini-GWAC (China)
~5000
12.5
Wei at al. 2015
GWAC (China)
～5000
16.0
Wei et al. 2015
GWAC is 2~3 orders more powerful !