Combined Analysis of Cosmic-Ray Anisotropy with IceCube and HAWC - PowerPoint PPT Presentation

Gamma-Ray Observatory Gamma-Ray Observatory Combined Analysis of Cosmic-Ray Anisotropy with IceCube and HAWC Juan Carlos Díaz Vélez a,b , M. Ahlers c , D. Fiorino d , P. Desiati b July 19, 2017 ICRC 2017 Busan, South Korea a Centro Universitario de los Valles, Universidad de Guadalajara, Guadalajara, Jalisco, México b Wisconsin IceCube Particle Astrophysics Center (WIPAC) and Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA c Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark d Department of Physics, University of Maryland, College Park, MD, USA Universidad de Guadalajara Centro Universitario de los Valles

Over the last few decades, several studies have measured a large scale anisotropy at 10 ‐ 3 level and a small-scale structure with an amplitude of 10 − 4 and angular size from 10° to 30°. Super-K Milagro HAWC Guillian et al., Phys Rev D, Vol 75, 063002 (2007) A. U. Abeysekara et al. Astrophys. J. (2014) Abdo et al., ApJ, Vol 698-2, pag 2121 (2009) Tibet Array ARGO-YBJ North Zhang et al. Proc. 32nd ICRC (2009) Amenomori et al., Science Vol. 314, pp. 439 (2006) South IceCube M. G. Aartsen et al. Astrophys.J. 826 (2016) Large-scale features in South appear to be a continuation of those observed in the Northern Hemisphere. Universidad de Guadalajara 2 Centro Universitario de los Valles

Origin of anisotropy Distribution of CR sources A number of theories have proposed scenarios where the large-scale anisotropy results from the distribution of cosmic ray sources in the Galaxy and of their diffusive propagation Diffusive propagation from distribution of cosmic ray sources L. G. Sveshnikova, et al. Astropart. Phys. 50 (2013) 33–46. A. D. Erlykin and A. W. Wolfendale, Astropart. Phys. 25 (2006) 183–194. R. Kumar and D. Eichler, Astrophys. J. 785 (2014) 129. P. Blasi and E. Amato, JCAP 1 (2012) 11. P. Mertsch and S. Funk, Phys. Rev. Lett. 114 (2015) 021101. 
 V. Ptuskin, Astropart. Phys. 39 (2012) 44–51. M. Pohl and D. Eichler, Astrophys. J. 766 (2013) 4. (a) A.D. Erlykin and A.W.Wolfendale P. Blasi and E. Amato arxiv/1105.4529 Astropart. Phys. 25 (2006) 183–194 Universidad de Guadalajara 3 Centro Universitario de los Valles

Origin of small-scale anisotropy It is expected that cosmic rays should lose any correlation with their original direction due to diffusion as they traverse through interstellar magnetic fields. Propagation effects in ISMF Giancinti & Sigl, Phys. Rev. Lett. 109, 071101 (2012) López-Barquero, et al, ApJ 830 19 (2016) 154 CR propagation Turbulent GMF 156 Small-scale structure 163 164 0.1 0 +360 0 X (kpc) 0 -0.1 0.94 0.96 0.98 1 1.02 1.04 1.06 1.08 -0.2 8.7 8.6 8.5 8.4 8.3 Y (kpc) Giacinti & Sigl arxiv/1111.2536 Giacinti & Sigl arxiv/1111.2536 Heliospheric effects Desiati and Lazarian, ApJ, 762, 1 (2013) Ripples in heliospheric Pogorelov et al., ApJ772 (2013) 2 
 boundary M. Zhang, et al, Astrophys. J. 790 (2014) 5 López-Barquero, et al ApJ, 842, 54 (2017) Desiati & Lazarian arxiv/1111.3075 CR scattering on ripples in the heliosphere boundary CRs streaming along LIMF induce small-scale anisotropy. Universidad de Guadalajara 4 Centro Universitario de los Valles

Data Sets Individual experiments have provided partial sky coverage that limits the interpretation of the results. This first full-sky combined observation at the same energy is done with two observatories covering most of the celestial sphere. IceCube HAWC Hemisphere Southern Northern -90 ◦ 19 ◦ Latitude air showers produced by CR and γ muons produced by CR Detection method -90 ◦ /-20 ◦ , ∼ 4 sr (same sky over 24h) -30 ◦ /64 ◦ , ∼ 2 sr (8 sr observed)/24 h Field of view Livetime 5 years 269 days over a period of 336.36 days Detector trigger rate 2.5 kHz 25 kHz quality cuts energy cuts quality cuts energy cuts Median primary energy 20 TeV 10 TeV 2 TeV 10 TeV Energy resolution ( logE/GeV ) 0.5 0.5 0.2 0.2 2-3 ◦ 2-6 ◦ 0.3-1.5 ◦ 0.3-1.5 ◦ Approx. angular resolution Number of events 2.8 × 10 11 1.7 × 10 11 2.6 × 10 10 4.4 × 10 9 Data selected for analysis come from 5 years of the complete IceCube array, as well as 1 year of HAWC in its final configuration of 300 tanks. Only continuous sidereal days* of data were chosen for these analyses in order to reduce the bias of uneven exposure along right ascension. * Gaps of 20 min. allowed within each 24 h period Universidad de Guadalajara 5 Centro Universitario de los Valles

�� � �� �� �� �� � ��� �� �� �� �� �� �� � ����� ������������� � �� �� �� �� �� �� �� �� �� �� � �� �� �� �� ����� ��� ���� ��� ������� ��� ��� ����� �� �� �� � ��� ��� ��������������������� � �� �� ���� ��� �� �� � 0.040 PRELIMINARY HAWC PRELIMINARY � IceCube 0.035 �� �� �� �� � �� �� �� �� �� �� 0.030 0.025 �� � �� �� 0.020 0.015 �� �� �� � �� � �� �� �� �� �� �� �� 0.010 � � 0.005 0.000 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 log(E/GeV) Distribution of events as as a function of declination for IceCube and HAWC. Restricting datasets to overlapping energy bins significantly reduces statistics for HAWC. After cuts, both CR data sets have a median energy of approximately 10 TeV with little dependence on zenith angle. Universidad de Guadalajara 6 Centro Universitario de los Valles

Iterative maximum likelihood method Ahlers, BenZvi, Desiati, Díaz-Vélez, Fiorino, Westerhoff (arXiv:1601.07877) • Traditional time-integration methods can strongly attenuate large-scale structures exceeding the size of the instantaneous field of view for detectors located at middle latitudes. • A fixed position on the celestial sphere is only observable over a relatively short j q j q � � � period every day. The total number of cosmic ray events from a fixed position W j q = ò � can only be compared against reference data observed during the same period. • This can lead to an under- or overestimation of the isotropic reference level. M. Ahlers et al (arXiv:1601.07877) Figure 1. Simulated cosmic-ray anisotropy in equatorial coordinates using the f a d = f a d d = - Universidad de Guadalajara � 7 Centro Universitario de los Valles = a d a d d ¢ = j q - j q q - w F - w F F = w - w w F w F F DW t m t � � � t t º D f � t t t º DW � q j � � ¢ W º � t t

Iterative maximum likelihood method Ahlers, BenZvi, Desiati, Díaz-Vélez, Fiorino, Westerhoff (arXiv:1601.07877) The likelihood of observing n cosmic rays is given by the product of Poisson probabilities relative intensity relative acceptance When to stop the iteration? expected number of events from isotropic background Maximize the likelihood ratio via null hypothesis in N, A y I ent distributions maximum values ( I ⋆ ,N ⋆ ,A ⋆ ) must follow ges, . which can be solved iteratively. M. Ahlers et al (arXiv:1601.07877) 12 Universidad de Guadalajara 8 Centro Universitario de los Valles

����������� One-dimensional RA projection of the relative intensity of cosmic rays for adjacent δ bins at -20 ◦ for HAWC-300 and IC86 data. There is general agreement for large scale structures. The two curves correspond to different δ bands but some differences in the small scale structure might also be attributed to mis-reconstructed events that migrate from nearby δ bins with larger statistics. Universidad de Guadalajara 9 Centro Universitario de los Valles

Relative Intensity Significance Map PRELIMINARY PRELIMINARY • Relative intensity and significance maps after 20 iterations smoothed over 5deg radius. • First full-sky combined observation at same energy with two observatories covering most of the celestial sphere. • Significance of features in the northern sky is lower than previously published HAWC results due to decreased statistics from energy cuts. Universidad de Guadalajara 10 Centro Universitario de los Valles

Angular Power Spectrum PRELIMINARY The angular pseudo-power spectrum of the cosmic ray anisotropy for the combined IceCube and HAWC dataset. The gray band represent the power spectra for isotropic sky maps at the 90% confidence level. The structure appears to have a very steep spectrum at low l and a flatter spectrum at l > 3. Universidad de Guadalajara 11 Centro Universitario de los Valles

Iterative method recovers most of the power of large • scale structure in mid-latitude observatories like HAWC. PRELIMINARY No appreciable gain for IceCube. • The highest angular power for l = 1 is obtained by • iteration 1 combining data from both observatories and using the iterative method. Angular Power Spectrum PRELIMINARY PRELIMINARY iteration 2 PRELIMINARY iteration 10 Universidad de Guadalajara 12 Centro Universitario de los Valles

Multipole fit Small-scale Anisotropy PRELIMINARY PRELIMINARY Universidad de Guadalajara 13 Centro Universitario de los Valles