highlights of the argo-ybj experiment p. camarri university of roma tor vergata and infn on behalf...

Highlights of the ARGO-YBJ experiment

P. CamarriUniversity of Roma Tor Vergata and

INFNon behalf of the ARGO-YBJ collaboration

P. Camarri - ICATPP 2010 – Como, 7-8 October 2010

P. Camarri - ICATPP 2010 - Como, 7-8 October 2010

Longitude 90° 31’ 50” EastLatitude 30° 06’ 38” North

90 Km North from Lhasa (Tibet)

An unconventional EAS-array exploiting the full coverage approach at very high altitude to detect small air showers at an energy threshold of a few hundreds of GeV.

The ARGO-YBJ experiment

Tibet ASTibet ASγγARGOARGO

The Yangbajing Cosmic Ray Laboratory

4300 m above the sea level ~ 600 g/cm2

The ARGO-YBJ Collaboration

INFN and Dpt. di Fisica Università, LecceINFN and Dpt. di Fisica Universita’, NapoliINFN and Dpt. di Fisica Universita’, PaviaINFN and Dpt di Fisica Università “Roma Tre”, RomaINFN and Dpt. di Fisica Univesità “Tor Vergata”, RomaINAF/IFSI and INFN, TorinoINAF/IASF, Palermo and INFN, Catania

IHEP, BeijingShandong University, JinanSouth West Jiaotong University, ChengduTibet University, LhasaYunnan University, KunmingZhengZhou University, ZhengZhou Hong Kong University, Hong Kong

International Collaboration:

Chinese Academy of Science (CAS) Istituto Nazionale di Fisica Nucleare (INFN)

Experimental Hall & Detector Layout

RPC

ARGO-YBJ: aARGO-YBJ: a multi-purpose experiment multi-purpose experiment

P. Camarri - ICATPP 2010 Como, 7-8 October 2010

by 2 operational modes: scaler mode (counting rate, > 1 GeV) shower mode (full reconstruction, > 300 GeV)

Sky survey -10º δ 70º above 300 GeV (-sources, anisotropies)

High exposure for flaring activity (-sources, GRBs, solar flares)

CR physics 1 TeV 104 TeV

p/p ratio at TeV energies

Solar and heliospheric physics

p + He spectrum at low energiesKnee region p-air and p-p cross sectionsAnisotropies Multicore events


Operational Modes

Object:• flaring phenomena (high energy tail of GRBs, solar flares) • detector and environment monitor

Recording the counting rates (Nhit ≥1, ≥2, ≥3, ≥4) for each cluster at fixed time intervals (every 0.5 s) lowers the energy threshold down to ≈ 1 GeV. No information on the arrival direction and spatial distribution of the detected particles.

Scaler Mode::

Detection of Extensive Air Showers (direction, size, core …) Coincidence of different detector units (pads) within 420 ns Trigger : ≥ 20 fired pads on the central carpet (rate ~3.6 kHz)

Object:• Cosmic Ray physics (above ~1 TeV) • VHE γ-astronomy (above ~300 GeV)

Shower Mode:

IND

IPE

ND

EN

T

DA

Q

High space/time granularity + Full coverage+ High altitude

detailed study on the EAS space/time structurewith unique capabilities

3-D view of a detected shower Top view of the same shower

EAS reconstruction

Event Rate ~ 3.6 kHz for Nhit >20


• Stable data taking since Nov. 2007 with full detector• Average duty cycle ~ 90%• Trigger rate ~3.6 kHz @ 20 pad threshold • Dead time 4%• 220 GB/day transferred to IHEP/CNAF data centers


The Moon-Shadow technique

Geomagnetic Field: positively charged particles are deflected towards the West.

Ion spectrometer

The observation of the Moon shadow may provide a direct check of the relation between size and primary energy

Cosmic rays are blocked by the Moon Deficit of cosmic rays in the Deficit of cosmic rays in the direction of the Moondirection of the Moon

)(

6.1 0

TeVE

Z

Moon diameter ~0.5 deg

Size of the deficit

Position of the deficit

Angular Resolution

Pointing Error

Energy calibrationWest displacement


All data: 2006 → 2009N > 100

55 s.d.

9 standard deviations / month

PSF of the detector

3200 hours on-source

θ < 50°

The deficit surface is the convolution of the PSF of the detector and the widespread Moon disc.


Moon Shadow analysis

Measured angular resolution

Measured EW displacement

Relation multiplicity – primary energy

Δα = -12.58º · N -0.68

All-sky survey result (1 – 30 TeV)


3 sources with significance >5 σ in ~800 days (July 06 – Dec. 09)

Crab 14 σ, Mrk421 12 σ, MGRO J1908+06 6 σ

Mean = -9.3 ± 2.1 10-3

Sigma = 1.008 ± 0.002

Evidence for a signal at ≈4 s.d. from the MGRO J2031+41 region.

12

Crab Mrk421


dN/dE = (3.62 dN/dE = (3.62 0.29) ·10 0.29) ·10-11-11 · (E/1 TeV) · (E/1 TeV) –2.55 –2.55 0.100.10 cm cm –2–2 s s –1–1 TeV TeV –1–1

N PAD Events /day Emed (TeV)

40 – 100 128 24 0.85

100 – 300 17.9 6.3 1.8

> 300 9.2 2.3 5.2

Crab Nebula

~14 s.d. in ~800 days

≈ ≈ 50 % Crab/year50 % Crab/year

NO event selection

NO γ/h discrimination

NO Pb on RPCs

Absolute measurement of angular resolution capability.

MGRO J1908+06


• Pulsar Wind Nebula discovered by Milagro ( 8 s.d.) with a flux 80% Crab

• Confirmed by HESS and VERITAS. • Detected by Tibet ASγ at 4.4 s.d. (ICRC05)

LAT

HESS

MilagroMilagro

• HESS: intrinsic extension is 0.34 deg• Milagro: extension is <2.6 deg

dN/dE = 6.2·10-12 ·E-1.5 exp(-E/14.1) sec-1 cm-2 TeV-1

dN/dE = 4.14·10-12 ·E-2.1 sec-1 cm-2 TeV-1

by J.Smith arXiv:1001.3695

Discrepancy between HESS and Milagro

ARGO-YBJ preliminary analysis


Num

ber

of

even

ts

Integral angular distribution (N>100)

Intrinsic extension:

MGRO J1908+06 Energy Spectrum

ARGO preliminaryARGO preliminary

HESSHESS

MilagroMilagro

MGRO J1908: preliminary conclusions


Experiment index 1 TeV flux (10-8TeV-1m-2s-

1)

10 TeV flux(10-10 TeV-1m-2s-1)

Ecut (TeV) Source Extension

HESS -2.10 4.14 3.29 No 0.34

Milagro -1.50 5.78 9.65 14.1 < 2.6

ARGO-YBJ -2.2 0.3

18.5 12.0 No 0.48 ± 0.28

dN/dE = (3.6 ± 0.8) · 10dN/dE = (3.6 ± 0.8) · 10-13 -13 · (E/6 TeV) · (E/6 TeV) –2.2 ± 0.3 –2.2 ± 0.3 cmcm-2-2 sec sec-1 -1 TeVTeV-1-1

• The observed extension is compatible with the HESS measurement

• ARGO data are not sensitive to the cutoff

• The ARGO and HESS measured fluxes are NOT consistent !

• ARGO is consistent with MILAGRO in particular around 10 TeV

Mrk421

P. Camarri - ICATPP 2010 - Como, 7-8 October 2010

Total significance: 12 s.d. in ~800 days

Different flares observed by ARGO-YBJ in TeV range

Full DAQTEST data

Mrk421 is characterized by a strong flaring activity both in X-rays and in TeV γ–rays.

Swift (15-50 keV)

The first source observed by ARGO (2006 July)

Mrk421 cumulative light curves


RXTE/ASM 2-12 keVSwift/BAT 15-50 keV ARGO-YBJ TeV (N > 100)

Active period

The steepness of the curve stands for the flux.

Feb, June

556 days with simultaneous data averaged over 5 days.


GASP-WEBT

SWIFT RXTE

SWIFT SuperAGILE

AGILE MAGIC VERITAS

Mrk421 - June 2008 flareA set of simultaneous measurements covering 12 decades from optical to TeV energies was performed during the flaring activity in first half of June 2008

data from: GASP-WEBT (R-band; May 24 to June 23) SWIFT (UVOT & XRT; June 12-13) AGILE (E > 100 MeV; June 9-15) MAGIC and VERITAS (E> 400 GeV; May 27 - June 8)

in Donnarumma et al., ApJ 691 L13 (2009)

complemented by publicly-available data from RossiXTE/ASM (2-12 keV) and Swift/BAT (15-50 keV).

No VHE data after June 8

the moonlight hampered the Cherenkov telescopes measurements !

2 flaring episodes were reported: June 3-8 and June 9-15

Mrk421 - June 2008 flare


dN/dE = (3.2 dN/dE = (3.2 1.0) · 10 1.0) · 10-11-11 · (E/2.5) · (E/2.5) –2.1 –2.1 0.70.7 e e--(E)(E) cm cm –2–2 s s –1–1 TeV TeV –1–1

EBL from Raue, M. & Mazin, D., 2008, Int. J. Mod. Phys. D17, 1515

The spectrum slope is consistent with the one measured by Whipple in 2000/2001 observing a similar flare, suggesting that the relation spectral index – flux is a long-term property of the source.

The integral flux above 1 TeV during June 11-13 is ~6 Crab units: one of the most powerful flares from Mrk421 ever observed.

G. Aielli et al. – ApJL 714 (2010) L208

Feb. 2010: strong Mrk421 flareFeb. 2010: strong Mrk421 flare


The flux exceeded 3 Crab units for the duration of the observations. The peak flux (16 Feb.) is >10 Crab units.

For the first time an EAS-array observed a TeV flare at 5σ on a daily basis.

VERITAS reported similar observations in Atel #2443.

16-18 Feb. 16 Feb.

17 Feb. 18 Feb.

ARGO observed a strong TeV γ-ray flare from Mrk421 during 16-18 Feb. 2010 at 6σ.

~5 ~5 σσ~6 ~6 σσ


Why:

•Satellite detectors (EGRET, LAT -FERMI) confirmed emissions @ E> 1 GeV

•Ground experiments (MILAGRITO, HEGRA, AIROBICC, Tibet AS-g) reported marginal detection on VHE tail

•Many models predicts the energy cut-off

And:

•Absorbtion by Extragalatic Background Light (EBL) which modulates with redshift zThe GeV-TeV range may reveal the

spectral cutoff

Constraints on the emission modelScaler mode (E>1 GeV) & Shower Mode (E>10 GeV)

G. Aielli et al. – Search for GRBs with the ARGO-YBJ detector in scaler mode

The Astrophysical Journal 699 (2009) 1281-1287

G. Aielli et al. - ARGO-YBJ constraints on very high energy emission From GRBs

Astroparticle Physics 32 (2009) 47-52

Search for GRBs in the GeV-TeV range


• Long duration GRBs (>2s): 82• Short duration GRBs (≤2s): 11

No evidence of coincident signals over the GRB T90 duration

In stacked analysis no evidence for any integral effect

• Number of GRBs analysed: 93

• With known redshift: 16

GRB in the ARGO FOV since Dec 2004 to Apr 2010

Scaler-mode results

Looking for excess in the counting rates in coincidence with satellite detections. No

pointing capability and poor energy resolution.


Fluence U.L. for known-redshift GRBs

Only 14 over 16 analyzed are reported (up to January 2009)

Conclusions


The ARGO-YBJ detector has been taking data since The ARGO-YBJ detector has been taking data since November 2007 with excellent performanceNovember 2007 with excellent performance

First results on γ-ray astronomyFirst results on γ-ray astronomyCrab Nebula spectrum in agreement with other measurementsCrab Nebula spectrum in agreement with other measurementsAll-sky survey: observation of MGRO J1908+06All-sky survey: observation of MGRO J1908+06Long-term monitoring of Markarian 421Long-term monitoring of Markarian 421Limits on 1-100 GeV fluence from GRBsLimits on 1-100 GeV fluence from GRBs

Studies to increase the sensitivity are in progressSky survey going onMore results in cosmic-ray physics will be presented in the More results in cosmic-ray physics will be presented in the

next ARGO-YBJ talk by P. Montininext ARGO-YBJ talk by P. Montini


Detector performanceDetector performance

Angular resolutionAngular resolution Pointing accuracyPointing accuracy Energy scale calibrationEnergy scale calibration Long-term stabilityLong-term stability

Moon Shadow analysis:Moon Shadow analysis:

X-ray/TeV correlation


To quantify the correlation and the time lags between X-ray and TeV emission the Discrete Correlation Function has been used (Edelson & Krolik 1988),

0.108 ± 0.548 -0.647 ± 0.614

RXTE/ASM & ARGO Swift/BAT & ARGO

• No significant time lag is found (u.l. for the cross-band time lag 1 day).• Correlation coefficient at zero ~0.8

Positive values means TeV lag behind X-rays

TeV spectral index – flux relation


To study the Mrk421 SED in different flux levels with 2 years data, both the X-ray and TeV data are grouped into 4 bands based on the RXTE/ASM daily counting rate: 0-2, 2-3, 3-5, >5 cm-2s-1.

EBL by Franceschini et al. (2008)

The TeV flux measured by ARGO ranges from 0.9 to 7 Crab units.

The TeV spectral index hardens with increasing flux in agreement with the relation between flux and spectral index calculated by Whipple in 2002.

Krennrich et al. (2002)

X-ray/TeV flux correlation


A positive correlation is observed The relation appears quadratic

rather than linear.

Similar result has been reported by Fossati et al. (2008).

This result, based on a 2 years observation, extends similar studies carried out in much shorter periods.

We investigated the correlation between ARGO-YBJ > 1 TeV and RXTE/ASM simultaneous integral fluxes.

SSC model


The ARGO data can be described by a one-zone SSC model (Mastichiadis & Kirk, 1997, Yang et al., 2008)

Electron injection compactness

Electron max Lorentz factor

Very Very

Preliminary

Preliminary

highlights of the argo-ybj experiment p. camarri university of roma tor vergata and infn on behalf...

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