1. Monitoring VHE Extragalactic Sources with ARGO-YBJ detector
Min ZHA
On behalf of ARGO-YBJ Collaboration
32nd International Cosmic Ray Conference, August , Beijing

2. Outline Goals Candidates Method Results and Discussion
Wide field of view & full duty circle of ARGO-YBJ
Monitor rapidly flares from known extragalactic sources;
Send an alert to the community;
Candidates
Method
Results and Discussion

3. Mrk 421 monitoring
~6 σ
July 2006
June 2008
Feb
~5 σ

4. Candidates 40 (31) extragalactic sources from R. Wagner; VHE-L3+C;
Crab  to monitor.

5. Method: Event Reconstruction
Data transferring to computer centers:
Usually < 5 min.
Time calibration
Calibration data of previous period.
Event selection for reconstruction:
nHit>100; (~ 0.9o)
In average 1.5 CPU hours for a raw file of 7 minutes.
Space angle for a same set of data with 2 different calibrations:
0.02 (2 consecutive periods);
0.08 (2 periods with 30 days’ interval).

6. Method: Background Determination
Surrounding region method:
Every sky cell has a hollow rectangular region as background;
Signal region:
In DEC  =1.8o
In RA  /cos
Background region:
In RA wa=0.75 x  to wb= + 2o
In DEC. wa x (/) to wb x (/)
Acceptance ratio R: calibrated with real data of a month.
L3+C Collaboration, APP, 33 (2010) 24

7. Shifting Sky Cells & time binning
Predefined sky cell;
66 shifts with a step of 0.3;
Only top 24 nearest shifts are adopted.
Excesses of 1, 2, 4, 8 transits of this source are calculated.

8. Chance Probability & alarm threshold
MC simulation techniques to sort out the correlated trials:
Distribution does not depends on statistics.
Alarming thresholds for two scenario:
Once per 5 years for 33 sources: 5.04 s.d.
Once per 5 years for 1 single source: 4.30 s.d.

9. Category of Sources (i) Known flaring sources: (ii) Others:
MKN421, as detected by ARGO-YBJ;
Threshold: 4.30 s.d.
(ii) Others:
Not detected by ARGO-YBJ yet;
Threshold: 5.04 s.d.
Elevation mechanism for a source:
If once detected with significance > 5.04 s.d.;
Or other analysis method once found its flares;
Elevated from (ii) to (i).

10. Alarming & Summary Emails
Some crucial plots are also attached with these s!

11. Test with MKN 421

12. Following-up Analysis
Instant analysis:
2-dimensional analysis;
Within 2 hours.
Manual analysis:
Check other observations.

13. Monitoring Status Method is firstly established in June 2010;
A test run for 2008/01-06, 2010/01-06:
3 known flares have been detected successfully.
Have been continuously monitoring all 33 sources since July 2010;
All past 3 years’ data have been analyzed by the end of 2011/07:
No flares except MKN421 have been found;
The biggest excess is s.d. from M82.

14. Most Significant Excess
Excess: s.d.;
8 days;
2009/04/08-04/16.

15. Test with MKN421 For past 3 years’ data:
4 excesses above the threshold 4.30 s.d.;
Among them, 3 are confirmed as flares already by other methods.

16. Conclusions
A real-time monitoring & alarming system to known extragalactic sources is established;
The past 3 years’ data have been analyzed;
Except Mkn421, no flare phenomenon from these sources are detected;
An occurrence analysis indicates several other sources may have ever flared, but further evidences are required.

17. BACKUPS

18. Candidate Sources?
6 sources show low chance probabilities < 0.6 (~1/5 years):
MKN 421, 1ES , 1ES , 3C 66A , M82, VHE L3+C.
cleaned-up
suspicious

19. THANKS!