Search for GRBs Using ARGO Data in Shower Mode

Guo Y.Q.

For ARGO-YBJ Collaboration

BeiJing 2008/09/26

Outline

1. Introduction 2. ARGO-YBJ experiment

3. Data Analysis(1) Triggered Showers

(2) Low-Hit Showers

4. Results

5. Summary

1. Introduction

GRB940217(EGRET) ~GeV Photons

no cut-off

GRBs are intense bursts of photons with short duration. They are one of the most intriguing objects in the known universe.

Energy range: keV ~ MeV

Time range: ms ~ minutes

cosmological origin

Full cover: 6500m2

High altitude: 4300mLarge field of view: 2.24 sr

ARGO-YBJ Detectors

2. ARGO-YBJ experiment

Cluster : 130(10×13) + 24 ring ClusterRPC : 12/cluster PAD : 10/RPC --the detector Unit(62cm×56cm).

TDC (ns)

Y (m) X (m)

TDC (ns)

Y (m) X (m)

Single-Front Event

3.1 Data Analysis

Trigger condition:

≥ 20 fired pads ( i.e. nHits ≥ 20 )

Low-Hit Shower （ 5 ≤ nHits ≤ 15)

Triggered Shower （ nHits ≥ 20 ）

Triggered shower

Double-front Event

Triggered Showers: ~hundreds of GeV

Low-Hit Showers: ~ tens of GeV

Can be used to search for GRB

Events Threshold Energy and Trigger Rate

N /s

time

Trigger Rate Triggered Showers: ~3700 Hz

Low-Hit Showers : ~200 Hz

e+ e- YBJ

nHits=20

nHits= 510GeV

100GeV1TeV

10TeV

100TeV

Sensitivity

Very Preliminary

Effective area for Triggered Gamma events and Low-Hit events.

The sensitivity for Triggered gamma events and Low-Hit gamma events.

From the Figs, we know at low energy, the Low-Hit event is better than Triggered events.

MC: Index= -2.0 Zenith =100

3.2 GRBs Analysis Method

Search Method : From satellite reported, we get to know the information about GRBs' trigger time and direction. The events in the R+2o angle window are looked as the GRB candidates to search for the largest significance event.

R+20

Candidate Events

Time

-300s ~ 300s

Position Precise: Triggered Shower: R= 2.0o Low-Hit Shower: R= 8.5o

Non is the number of events that followed within the solid angle (on-source window) and within the time duration (t).

Zenith

Non

Noff

t: 1s, 5s, 10s ..,100s

Estimate the background by the off-source window, with same R and same θ as on-source window.

(2)Using ±1000s data to estimate background

(1) 10 off-source windows are chosen to improve statistic.

3.2 Estimate Background for Triggered Showers

equi-zenith-angle method:()

3.2 Estimate Background forLow-Hit Shower Analysis

Because of the Azimuth asymmetryand the worse angle resolution(6.50), equi-zenith-angle method can not be used to estimate the background very well.

we use the following method to do so:

At the on-source window, using±210s ~1000s time range data to estimate the background .

Nb No

-1000 -210 0 210 1000

Time (s)

Azimuth=0 is East (clockwise)

3.3 GRBs Sample in ARGO Field of View

Time range :

2006.07 ~ 2008.03( totaled 17 )

Cut condition:

Dec: -8 ~70 degree Zen: ≤ 50 degree

GRB060714A GRB060717A GRB060801AGRB060805B GRB060807A GRB060927AGRB061028A GRB061110A GRB061122AGRB070201A GRB070219A GRB070306AGRB070531A GRB070615A GRB080207AGRB080325A GRB080328A

From http://grb.sonoma.edu/

4.1 Triggered Event Analysis Results

Cut : (1) inner events

(2) nHits<60

(3) chi2<10

Maximum Significance: S-max = 4.80

GRB061122

Angle Radius

R = 2.00

GRB061122

INTEGRAL data:

Mjd:54061.3311342691960

Ra:303.910 Dec:15.520

Zen:33.570 Azim:108.320

Maximum Significance in ARGO data:

Mjd:54061.3320497685199

Ra:302.940 Dec:13.980

Zen:33.350 Azim:111.900

det_T: after 79s

det_θ: 1.80

Considering try number (n=3294), only 2.80 Significance Level.

Light curve5s/bin

4.2 Low-Hit Event Analysis Results

Maximum Significance:S-max = 4.58

GRB061028

Angle Radius

R = 8.50

Cut:(1) nHits<15

(2) chi2<10

GRB061028

Swift data:

Mjd: 54036.059976861783

Ra:97.2080 Dec:46.2700

Zen:42.4880 Azim:307.1340

Maximum Significance in ARGO data:

Mjd:54036.0585579861145

Ra:110.1230 Dec:42.6630

Zen:32.5440 Azim:303.2090

det_T: before 122.6s

det_θ: 9.880

Light curve

But considering try number (n=536), only 3.03 Significance Level.

Result of ARGO Data Analysis

S_max time(s) 95%U.L.(ph/cm 2̂/s) S_max time(s) 95%U.L.(ph/cm 2̂/s)20060714 4.13 10 1.76E-003 3.78 90 1.77E-00320060717 4.67 10 2.10E-004 >< >< ><20060801 4.37 5 4.15E-004 4.24 5 1.01E-00320060805 4.53 100 2.84E-004 4.3 15 9.82E-00420060807 3.93 5 2.88E-004 4.4 1 2.13E-00320060927 3.73 5 1.16E-003 3.57 1 2.60E-00320061028 3.39 10 3.25E-003 4.58(3.03) 60 8.50E-00420061110 4.05 1 1.39E-002 4.28 100 1.39E-00320061122 4.81(2.80) 5 2.31E-003 4.05 1 3.84E-00320070201 4.47 100 9.85E-005 3.92 10 1.67E-00320070219 3.9 60 1.11E-003 3.6 5 3.04E-00320070306 4.02 90 8.84E-005 3.18 40 3.35E-00420070531 3.75 15 9.17E-004 3.54 20 3.96E-00320070615 3.52 5 5.15E-003 3.67 60 2.09E-00320080207 3.66 5 1.18E-003 3.68 1 2.78E-00320080325 3.18 40 1.50E-004 2.99 60 2.22E-00320080328 3.36 15 2.31E-003 3.62 1 1.76E-002

Triggered Events Data Low-Hit Events DataDate

5. Summary

1. Base on M.C simulation we give the ARGO detector sensitivity to search for GRB using Triggered and Low-Hit events. At low energy, the sensitivity is better using Low-Hit Events.

2. After ARGO data analysis, no GRBs' high energy emission were observed and we give the integral flux uplimit for more than 10 GRBs in ARGO view.

Significance

for signal(Non) obey the Poisson distributions:

defined:

compare with Gauss distributions:

bN

on

onNb

on e!N

N=NP )(

)(21)(

1

NonP+iP=P+Non=i

bk

dtt=Ps

bk

2exp

21 2

Effective area and sensitivity of single-front Gamma events for different Zenith

Mjd Zen Azim T90 Z Mission Flux(erg/cm2)

GRB060714 53930.6333 41.832 215.672 20 2.710 SwiftGRB060717 53933.3803 7.375 96.917 5 --- Swift 6.5e-08GRB060801 53948.5112 16.823 221.300 0.5 1.131 Swift 8.1e-08GRB060805 53952.6022 29.092 12.154 5 --- Konus-Wind 7.4e-08GRB060807 53954.6122 12.421 280.539 15 --- Swift 7.3e-07GRB060927 54005.5885 31.631 137.357 22.6 5.600 Swift 1.1e-06GRB061028 54036.0599 42.488 307.134 106 --- Swift 9.7e-07GRB061110 54049.4912 36.845 146.303 30 0.758 Swift 1.1e-06GRB061122 54061.3311 33.572 108.318 20 --- INTEGRALGRB070201 54132.6410 20.609 102.419 0.15 --- Konus-WindGRB070219 54150.0487 39.313 1.942 15 --- Swift 3.2e-07GRB070224 54155.8527 44.520 198.043 25 --- Swift 3.1e-07GRB070306 54165.6954 19.850 170.830 210 1.497 Swift 5.5e-06GRB070531 54251.0904 44.264 358.209 20 --- Swift 1.1e-06GRB070615 54266.0977 36.918 153.310 30 --- INTEGRALGRB080207 54503.8960 27.668 141.323 340 --- Swift 6.1e-06GRB080325 54550.1731 48.132 293.824 128.4 --- Swift 4.9e-06GRB080328 54553.3354 37.188 49.753 110 --- Swift/K-W 9.4e-06

GRBs Sample in ARGO Field of Vision

10o—black, 20o—blue 30o—red, 40o—purple

Azimuth=0 is East (clockwise)

Azimuth distribution for different Zenith(fluctuation: <6%)

10o—black, 20o—blue30o—red, 40o—purple Azimuth=0 is East (clockwise)

the shape is similar to the triggered events. But the difference is large than triggered events because the low energy.

Azimuth distribution of the low hit events for difference Zenith