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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.

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search for grbs using argo data in shower mode
Search for GRBs Using ARGO Data in Shower Mode

Guo Y.Q.

For ARGO-YBJ Collaboration

BeiJing 2008/09/26

slide2

Outline

1. Introduction

2. ARGO-YBJ experiment

3. Data Analysis

(1) Triggered Showers

(2) Low-Hit Showers

4. Results

5. Summary

slide3

1. Introduction

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

cosmological origin

Time range: ms ~ minutes

Energy range: keV ~ MeV

no cut-off

GRB940217(EGRET) ~GeV Photons

slide4

2. ARGO-YBJ experiment

ARGO-YBJ

Detectors

Full cover: 6500m2

High altitude: 4300m

Large field of view: 2.24 sr

Cluster : 130(10×13) + 24 ring Cluster

RPC : 12/cluster

PAD : 10/RPC

--the detector Unit(62cm×56cm).

slide5

TDC (ns)

Y (m)

X (m)

TDC (ns)

Y (m)

X (m)

3.1 Data Analysis

Single-Front Event

Triggered shower

Trigger condition:

≥ 20 fired pads( i.e. nHits ≥ 20 )

Double-front Event

Triggered Shower(nHits ≥ 20 )

Low-Hit Shower(5 ≤ nHits ≤15)

slide6

YBJ

e+ e-

100TeV

10TeV

1TeV

100GeV

nHits=20

10GeV

nHits= 5

Events Threshold Energy and Trigger Rate

N/s

Triggered Showers:

~hundreds of GeV

Low-Hit Showers:

~tens of GeV

Canbe used to search for GRB

Trigger Rate

Triggered Showers:~3700 Hz

time

Low-Hit Showers :~200 Hz

slide7

Sensitivity

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

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

MC:Index=-2.0Zenith=100

Very Preliminary

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

slide8

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.

Candidate Events

R+20

Time

-300s ~ 300s

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

slide9

3.2 Estimate Background for Triggered Showers

Zenith

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

t: 1s, 5s, 10s ..,100s

equi-zenith-angle method:

()

Noff

Estimate the background by the off-sourcewindow, with same Rand same θ as on-sourcewindow.

Non

(1)10 off-source windows

are chosen to improve

statistic.

(2)Using ±1000s data to estimate background

slide10

No

Nb

Time (s)

-1000 -210 0 210 1000

3.2 Estimate BackgroundforLow-Hit Shower Analysis

Because of the Azimuth asymmetry

and 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:

Azimuth=0 is East (clockwise)

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

slide11

3.3GRBs SampleinARGOField of View

Timerange:

2006.07~2008.03

( totaled 17 )

Cut condition:

Dec: -8 ~70 degree

Zen: ≤ 50 degree

GRB060714 A GRB060717 A GRB060801A

GRB060805 B GRB060807A GRB060927 A

GRB061028A GRB061110A GRB061122A

GRB070201 A GRB070219A GRB070306 A

GRB070531A GRB070615A GRB080207A

GRB080325 A GRB080328A

From http://grb.sonoma.edu/

slide12

4.1 Triggered Event Analysis Results

Angle Radius

R = 2.00

Cut :

(1) inner events

(2) nHits<60

(3) chi2<10

GRB061122

Maximum Significance:

S-max = 4.80

grb061122

5s/bin

Light curve

Maximum Significance in ARGO data:

Mjd:54061.3320497685199

Ra:302.940 Dec:13.980

Zen:33.350 Azim:111.900

INTEGRAL data:

Mjd:54061.3311342691960

Ra:303.910 Dec:15.520

Zen:33.570 Azim:108.320

GRB061122

det_T: after 79s

det_θ: 1.80

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

slide14

4.2 Low-Hit Event Analysis Results

Angle Radius

R = 8.50

Cut:

(1) nHits<15

(2) chi2<10

GRB061028

Maximum Significance:

S-max = 4.58

grb061028

Maximum Significance inARGO data:

Mjd:54036.0585579861145

Ra:110.1230 Dec:42.6630

Zen:32.5440 Azim:303.2090

Swift data:

Mjd: 54036.059976861783

Ra:97.2080 Dec:46.2700

Zen:42.4880 Azim:307.1340

GRB061028

det_T: before 122.6s

det_θ: 9.880

Light curve

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

slide17

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.

slide19

Significance

for signal(Non) obey the Poisson distributions:

defined:

compare with Gauss distributions:

slide20

Effective area and sensitivity

of single-front Gamma events for different Zenith

slide21

GRBs SampleinARGOField of Vision

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

GRB060714 53930.6333 41.832 215.672 20 2.710 Swift

GRB060717 53933.3803 7.375 96.917 5 --- Swift 6.5e-08

GRB060801 53948.5112 16.823 221.300 0.5 1.131 Swift 8.1e-08

GRB060805 53952.6022 29.092 12.154 5 --- Konus-Wind 7.4e-08

GRB060807 53954.6122 12.421 280.539 15 --- Swift 7.3e-07

GRB060927 54005.5885 31.631 137.357 22.6 5.600 Swift 1.1e-06

GRB061028 54036.0599 42.488 307.134 106 --- Swift 9.7e-07

GRB061110 54049.4912 36.845 146.303 30 0.758 Swift 1.1e-06

GRB061122 54061.3311 33.572 108.318 20 --- INTEGRAL

GRB070201 54132.6410 20.609 102.419 0.15 --- Konus-Wind

GRB070219 54150.0487 39.313 1.942 15 --- Swift 3.2e-07

GRB070224 54155.8527 44.520 198.043 25 --- Swift 3.1e-07

GRB070306 54165.6954 19.850 170.830 210 1.497 Swift 5.5e-06

GRB070531 54251.0904 44.264 358.209 20 --- Swift 1.1e-06

GRB070615 54266.0977 36.918 153.310 30 --- INTEGRAL

GRB080207 54503.8960 27.668 141.323 340 --- Swift 6.1e-06

GRB080325 54550.1731 48.132 293.824 128.4 --- Swift 4.9e-06

GRB080328 54553.3354 37.188 49.753 110 --- Swift/K-W 9.4e-06

slide22

Azimuth distribution for different Zenith

(fluctuation: <6%)

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

Azimuth=0 is East (clockwise)

slide23

Azimuth distribution of

the low hit events for difference Zenith

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.

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