Monitoring VHE Extragalactic Sources with ARGO-YBJ detector Min ZHA On behalf of ARGO-YBJ Collaboration 32nd International Cosmic Ray Conference, August 11-18 2011, Beijing

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

Mrk 421 monitoring ~6 σ July 2006 June 2008 Feb. 16 2010 ~5 σ

Candidates 40 (31) extragalactic sources from R. Wagner; VHE-L3+C; Crab  to monitor. http://www.mppmu.mpg.de/~rwagner/sources/

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).

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

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.

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.

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).

Alarming & Summary Emails Some crucial plots are also attached with these emails!

Test with MKN 421

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

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 5.035 s.d. from M82.

Most Significant Excess Excess: 5.035 s.d.; 8 days; 2009/04/08-04/16.

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.

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.

BACKUPS

Candidate Sources? 6 sources show low chance probabilities < 0.6 (~1/5 years): MKN 421, 1ES 0229+200 , 1ES 1011+496 , 3C 66A , M82, VHE L3+C. cleaned-up suspicious

THANKS!