Detection of anisotropies in the arrival directions of few TeV cosmic rays with the ARGO-YBJ experiment presented by R. Iuppa University of Rome Tor Vergata INFN, sez.ne “Tor Vergata ” on behalf of the ARGO-YBJ collaboration CRISM2011 Cosmic Rays and the Interstellar Medium environment Montpellier - June 29 th , 2011
Outline What we expect: isotropy of cosmic rays Observations of CR anisotropies The ARGO-YBJ experiment The large scale anisotropy The intermediate scale anisotropy Conclusions 2011, 29th June 2 CRISM2011
What is expected: isotropy The galactic magnetic field is thought to be the superposition of a “regular” and a “ chaotic ” component (with intensities B reg ~2 μ G and B ch ~0.5 ÷ 5 μ G respectively). Alvarez Muniz J. And Stanev T. J. Giacalone and J. R. Jokipii 2006 J. Phys.: Conf. Ser. 47 126 1999 ApJ 520 204 The gyroradius of a particle of rigidity R TeraVolt is: We expect to p 4 observe their arrival r R [ TV ] 5 10 pc R [ TV ] 100 A . U . ZeB directions are Cosmic rays interact with the interstellar medium (ISM), the interactions further scattering their trajectories (minor effect w.r.t. that of B). 2011, 29th June 3 CRISM2011
What the observation of CR anisotropies might suggest there are sources nearby. the galactic magnetic field is not what we imagine: the role of the Solar wind as well as the magnetic field in the solar system may be non-negligible. there might be local (or non-local) magnetic field structures focusing CRs up to the Solar System. the chaotic component of the magnetic field may overwhelm the regular one. any combination of the two facts above. 2011, 29th June 4 CRISM2011
Observations of CR anisotropies MILAGRO - 2009 ApJ 698 2121 Super-Kamiokande – ICRC 2007 Proceedings G. Guillian et. al. 2007 PRD Tibet AS- γ - Science 20 October 2006 : ICE-CUBE - 2010 ApJ 718 L194 Vol. 314 no. 5798 pp. 439-443 2011, 29th June 5 CRISM2011
The ARGO-YBJ experiment Altitude 4300 m a.s.l. Longitude 90 ° 31’ 50” East Latitude 30 ° 06’ 38” North A strophysical R adiation with G round-based Tibet AS- γ O bservatory at Y ang B a J ing 2011, 29th June 6 CRISM2011
Operation modes Shower mode Trigger : number of fired pads (N pad ) within 420 ns on the central carpet for N pad 20, rate ~ 3.5 kHz ( ~220 GBytes/day) Detection of Extensive Air Showers (direction, size, core …) Aims : cosmic-ray physics (threshold ~ 600 GeV) VHE g -astronomy (threshold ~ 300 GeV) gamma-ray bursts Scaler mode counting rates ( 1, 2, 3, 4 coincidences) for each cluster Aims: detector and environment monitor flaring phenomena ( gamma ray bursts, solar flares) 2011, 29th June CRISM2011 7 with a threshold of few GeV
Number of Fired Strips Space pixel: single strip ( 7 × 62 cm 2 ) Time pixel: pad ( 56 × 62 cm 2 ) is the OR of 8 strips, with a resolution of ~ 1.8 ns Dynamical range for protons by means of pads, strips and big pads : ~ 600 GeV - 10 4 TeV Excellent operating performance since November 2007. Duty cycle > 85% Rate stability 0.5% (intrinsic) 2011, 29th June 8 CRISM2011
Moon shadow Angular resolution A natural tool to evaluate the performance of the detector • Pointing accuracy, • Angular resolution, • Absolute energy calibration. N pad > 100, 71 s.d. Energy calibration The energy scale uncertainty less than 13%! 26/05/2011 9 R. Iuppa - ROMA2 Physics forum
Moon shadow N pad >100: 10 s.d./month A tool to monitor the stability of the data and reconstruction Figures on the right: one point per month ! Position stable at a level of 0.1 ° Angular resolution stable at a level of 10% 26/05/2011 10 R. Iuppa - ROMA2 Physics forum
Data analysis DATA SET: 2008-2010 data N str >40 Zenith angle < 50 ° 1.4 10 11 events NO SELECTION CUT APPLIED Background estimation methods: Up to 45 ° -wide structures: Time swapping/scrambling (3 hrs, N off /N on =10) Direct integration (3 hrs) (consistent each other within 7. 10 -6 ) For larger scales: equizenith method 2011, 29th June 11 CRISM2011
The large scale anisotropy as observed by ARGO-YBJ All-data sky-map. Analysis optimized to look at large scale anisotropies (“all - distance” equizenith background estimation technique). Loss-cone Cygnus region Tail-in 2011, 29th June 12 CRISM2011
Energy spectrum of the large scale anisotropy 0.7TeV(20-60) In agreement with standard diffusion 1.5TeV(60-100) models, where the anisotropy increases with 3.9TeV(>100) the energy. 2011, 29th June 13 CRISM2011
Large scale anisotropy: possible interpretations Loss-cone Cygnus region Tail-in Xiao-bo Qu et al 2011, arXiv:1101.5273 What we see is the combination of a Uni-Directional The loss-cone is the signature of the “ poloidal ” component of the Flow and a Bi-Directional Flow (along the magnetic field galactic magnetic field (in arm). The characteristic lengths agreement with southern are so small that a emisphere data from IceCube). “ tail-in ” “ Cygnus ” local low-density The and the excess are both due to guiding by feature must be the magnetic fields along the local advocated: the Local arm (the “ tail-in ” excess is slightly Interstellar Cloud (~90 pc 3 ). deformed by the Heliosphere). Mizoguchi et al, 31 st ICRC 2009 2011, 29th June 14 CRISM2011
Large scale anisotropy: possible interpretations Loss-cone Cygnus region Tail-in Xiao-bo Qu et al 2011, arXiv:1101.5273 What we see is the combination of a Uni-Directional The loss-cone is the signature of the “ poloidal ” component of the Flow and a Bi-Directional Flow (along the magnetic field galactic magnetic field (in arm). The characteristic lengths agreement with southern are so small that a emisphere data from IceCube). “ tail-in ” “ Cygnus ” local low-density The and the excess are both due to guiding by feature must be the magnetic fields along the local advocated: the Local arm (the “ tail-in ” excess is slightly Interstellar Cloud (~90 pc 3 ). deformed by the Heliosphere). Mizoguchi et al, 31 st ICRC 2009 2011, 29th June 15 CRISM2011
The intermediate scale anisotropy MILAGRO: Discovery of Localized Regions of Excess 10-TeV Cosmic Rays Phys.Rev.Lett.101:221101,2008 DA DATA SE SET: Smoothin Sm ing rad radiu ius 10 10 ° Zenit Zen ith an angle le < < 45 45 ° Region B Region A 11 eve 2.2 2.2 10 10 11 events 12.4 s.d. 15 s.d. Med edia ian en ener ergy 1 1 TeV eV Fractional Fractional NO GAM NO GAMMA HAD ADRON excess: excess: DISCRIMINATIN AP DI APPLIED 4 10 -4 6 10 -4 Background estimation technique: Ra: a: 11 117 ° -131 131 ° | 13 131 ° -141 ° Ra: a: 66 66 ° -76 76 ° direct integration method (2 hours De: 15 De 15 ° -40 40 ° | 40 40 ° -50 50 ° De: 10 De 10 ° -20 20 ° intervals) 2011, 29th June 16 CRISM2011
The intermediate scale CR anisotropy as observed by ARGO-YBJ All-data sky-map. Analysis optimized to look at small and medium scale anisotropies (direct integration and time-swapping background estimation technique). Several extended features are already visible at 1 ° scale. Equatorial coordinates: projection of the earth longitude and latitude 2011, 29th June 17 CRISM2011
The intermediate scale anisotropy at 5° Significance SMOOTH RADIUS 5 ° GA GALACTIC AN ANTI-CENTER Ratio 2011, 29th June 18 CRISM2011
The intermediate scale anisotropy: focus on >5 s.d. significant regions SMOOTH RADIUS 5 ° Ratio (> 5 s.d.) GA GALACTIC AN ANTI-CENTER Sub-structures? Cygnus region New-structures? 2011, 29th June 19 CRISM2011
Intermediate scale anisotropy energy spectrum ARGO-YBJ MILAGRO 2008 Region A and region B defined as in slide 3 2011, 29th June 20 CRISM2011
What is behind the intermediate scale anisotropies The excesses are due to nearby sources (Geminga, Vela, Monogem … ) emitting CR. In any case it looks as particular features of the local magnetic field are needed to bring us the radiation so beamed . The spectrum and the cut-off are explained Salvati & Sacco, with the age of the Astronomy&Astrophysics 2008 source. Drury & Aharonian, Astroparticle Physics 2008 What we see is the effect of the magnetic reconnection in the heliotail . The spectrum and the cutoff are due to the efficiency of the process. Lazarian & Desiati, 2010, arxiv 1008.1981 2011, 29th June 21 CRISM2011
What is behind the intermediate scale anisotropies The excesses are due to nearby sources (Geminga, Vela, Monogem … ) emitting CR. In any case it looks as particular features of the local magnetic field are needed to bring us the radiation so beamed . The spectrum and the cut-off are explained Salvati & Sacco, with the age of the Astronomy&Astrophysics 2008 source. Drury & Aharonian, Astroparticle Physics 2008 What we see is the effect of the magnetic reconnection in the heliotail . The spectrum and the cutoff are due to the efficiency of the process. Lazarian & Desiati, 2010, arxiv 1008.1981 2011, 29th June 22 CRISM2011
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