Estimation of KM2A@lhaaso’s Sensitivity to Gamma Ray point Sources above 30TeV Cui shuwang Hebei Normal University The 2nd workshop of air shower detection at high altitude IHEP , CAS , Beijing 2011.02.18

Introduction More and more TeV sources are identified by ground based cosmic ray experiments so far. Fine measurement of gamma ray energy spectra above 30TeV is crucial to identify sources as galactic cosmic ray accelerators or not it is one of important scientific goals of LHAASO project.

TeV sources By 2010 Oct.

Some of TeV sources have hard spectrum , A few of them，showed observational evidences of being universe accelerators with cosmic rays being accelerated. This yet to be conformed in the future experiments（for instance , LHAASO）with more concrete evidences.

KM2A KM2A is full duty cycle array of LHAASO including about 5000 Electron Detectors(EDs) and 1000 Muon Detectors (MDs). The leading aim of KM2A is to detect gamma rays above 30TeV from sources with higher particle discrimination.

Array configure ED array + MD array EDs ( 1m2)are located in an equilateral triangular grid with a side length of 15m. Covered area about 1km2. each ED has a 0.5cm lead cover, and MD has 2.8m molasses overburden.  15m  ED array + MD array  30m  MDs ( 36m2 ) are located with a side length of 30 m.

Outline Simulation data distribution Angular resolution Efficiency of the KM2A Ability for g/p discrimination Sensitivity calculation

MC Simulation Air shower simulation: Km2a detector response simulation Corsika6600 --- from data bank of Dr zhamin Primary energy of particle : 3TeV----10PeV Zenith angle: 0—45 degree Km2a detector response simulation Detector simulation and reconstructed code (detailed refer to Ma Xinhua’s talk yesterday ). Events selection: reconstructed zenith angle < 45degree. number of triggered detector > 20. Inner events: Distance from array center about 500 meter

Reconstructed Events Distribution Zenith angle distribution Azimuth angle distribution

Core of events position distribution γ p Unit: meter

Number of fired detectors  p

Energy flux response  p Log10(E0) distribution

Contribution for g/p discriminition Inner events: Denote event core reconstructed within the radius 500 m from array center. gamma E0>20TeV proton E0>20TeV muons of events as a function of Distance from array center

Moderate energy Energy(TeV) For estimation events’ energy, the events are divided into 11 parts as the number of triger Ntrig bin Moderate energy Energy(TeV) 20-30 6.4 30-45 12.6 45-65 15.8 65-90 31.6 90-120 44.7 120-180 63. 180-260 125.9 260-360 251.2 360-500 416.9 500-700 1000. 700~ 1584.9 10% of events Em Eth

Linear Correlation of Moderate Energy with the number of trigered detector log10(ntrig) log10(Em (GeV))

Angular resolution Space angle (degree) distribution dropping directions and reconstructed directions That is the km2a’s angular resolution as the function of number of hits. Opening angle as the function of Number of trigger. The plateau of the curve around 0.2 degree

Detecting efficiency Number of trigger

g/p discrimination Gamma survival log（Em GeV） Proton survival Ntrig>90 Em ~ 44.6TeV log（Em GeV）

Calculation of significance to crab source Crab flux： CR flux：

With One year’s observation , we can detect events from crab direction are listed Ntrig bin N ( >Eth ) NCR ( >Eth ) significance Icrab (5/yr) 20-30 45359 7345016 59.26 0.084 30-45 41285 5928410 111.05 0.045 45-65 24016 2770965 214.49 0.023 65-90 10732 973588 562.59 0.009 90-120 4976 390627 1042.66 0.005 120-180 2260 144195 600.11 0.008 180-260 1015 51748 924.68 0.011 260-360 351 14146 335.56 0.030 360-500 126 4123 123.23 0.081 500-700 45 1023 44.50 0.225 700~ 11 256 11.43 0.875 Background free points

The KM2A’s sensitivity curve KM2A@LHAASO

How many by LHAASO??

Summary KM2A has the high sensitivity (lower than 0.001Icrab ) to gamma ray sources at above 30TeV region, even if we have not consider in joint detection with other equipments yet. The optimization of Array’s configuration and detector design is being study now.

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