Northern sky Galactic Cosmic Ray anisotropy between 10-1000 TeV with the Tibet Air Shower Array

0.68 MB·

by  Tibet AS-gamma Collaboration

Draftversion March3,2017
PreprinttypesetusingLATEXstyleemulateapjv.12/16/11
NORTHERN SKY GALACTIC COSMIC RAY ANISOTROPY BETWEEN 10 AND 1000 TEV WITH THE
TIBET AIR SHOWER ARRAY
M. Amenomori1, X. J. Bi2, D. Chen3, T. L. Chen4, W. Y. Chen2, S. W. Cui5, Danzengluobu4, L. K. Ding2,
7 C. F. Feng6, Zhaoyang Feng2, Z. Y. Feng7, Q. B. Gou2, Y. Q. Guo2, H. H. He2, Z. T. He5, K. Hibino8, N. Hotta9,
1 Haibing Hu4, H. B. Hu2, J. Huang2, H. Y. Jia7, L. Jiang2, F. Kajino10, K. Kasahara11, Y. Katayose12, C. Kato13,
0 K. Kawata14, M. Kozai13,a, Labaciren4, G. M. Le15, A. F. Li16,6,2, H. J. Li4, W. J. Li2,7, C. Liu2, J. S. Liu2,
2 M. Y. Liu4, H. Lu2, X. R. Meng4, T. Miyazaki13, K. Mizutani11,17, K. Munakata13, T. Nakajima13, Y. Nakamura13,
H. Nanjo1, M. Nishizawa18, T. Niwa13, M. Ohnishi14, I. Ohta19, S. Ozawa11, X. L. Qian6,2, X. B. Qu2, T. Saito20,
r T. Y. Saito21, M. Sakata10, T. K. Sako14, J. Shao2,6, M. Shibata12, A. Shiomi22, T. Shirai8, H. Sugimoto23,
a
M M. Takita14, Y. H. Tan2, N. Tateyama8, S. Torii11, H. Tsuchiya24, S. Udo8, H. Wang2, H. R. Wu2, L. Xue6,
Y. Yamamoto10, K. Yamauchi12, Z. Yang2, A. F. Yuan4, T. Yuda14,b, L. M. Zhai3, H. M. Zhang2, J. L. Zhang2,
X. Y. Zhang6, Y. Zhang2, Yi Zhang2, Ying Zhang2, Zhaxisangzhu4, X. X. Zhou7
2
(The Tibet ASγ Collaboration)

1DepartmentofPhysics,HirosakiUniversity,Hirosaki036-8561, Japan
E] 2KeyLaboratoryofParticleAstrophysics,Institute ofHighEnergyPhysics,ChineseAcademyofSciences, Beijing100049, China
3NationalAstronomicalObservatories,ChineseAcademyofSciences,Beijing100012, China
H 4DepartmentofMathematics andPhysics,TibetUniversity,Lhasa850000, China
5DepartmentofPhysics,HebeiNormalUniversity,Shijiazhuang050016, China
h. 6DepartmentofPhysics,ShandongUniversity,Jinan250100, China
p 7InstituteofModernPhysics,SouthwestJiaotongUniversity,Chengdu610031, China
8FacultyofEngineering,KanagawaUniversity,Yokohama221-8686,Japan
o- 9FacultyofEducation, UtsunomiyaUniversity,Utsunomiya321-8505,Japan
10DepartmentofPhysics,KonanUniversity,Kobe658-8501, Japan
tr 11ResearchInstituteforScienceandEngineering,WasedaUniversity,Tokyo169-8555, Japan
s 12FacultyofEngineering,YokohamaNationalUniversity,Yokohama240-8501, Japan
a 13DepartmentofPhysics,ShinshuUniversity,Matsumoto390-8621, Japan
[ 14InstituteforCosmicRayResearch,UniversityofTokyo, Kashiwa277-8582, Japan
15NationalCenter forSpaceWeather, ChinaMeteorologicalAdministration,Beijing100081,China
2 16SchoolofInformationScienceandEngineering,ShandongAgricultureUniversity,Taian271018, China
v 17SaitamaUniversity,Saitama338-8570, Japan
4 18NationalInstitute ofInformatics,Tokyo101-8430, Japan
19SakushinGakuinUniversity,Utsunomiya321-3295,Japan
4 20TokyoMetropolitanCollegeofIndustrialTechnology, Tokyo116-8523, Japan
1 21Max-Planck-Institutfu¨rPhysik,Mu¨nchenD-80805,Deutschland
7 22CollegeofIndustrialTechnology, NihonUniversity,Narashino275-8576, Japan
0 23ShonanInstitute ofTechnology, Fujisawa251-8511,Japan
. 24JapanAtomicEnergyAgency, Tokai-mura319-1195, Japan
1 a nowat: ISAS/JAXASagamihara252-5210,Japan
0 b Deceased.
7
1 Draft version March 3, 2017
:
v ABSTRACT
i
X Wereportontheanalysisofthe10−1000TeVlarge-scalesiderealanisotropyofGalacticcosmicrays
(GCRs) with the data collected by the Tibet Air Shower Array from 1995October to 2010 February.
r
a In this analysis, we improve the energy estimate and extend the decl. range down to −30◦. We find
that the anisotropy maps above 100 TeV are distinct from that at a multi-TeV band. The so-called
tail-in and loss-cone features identified at low energies get less significant, and a new component
appears at ∼ 100 TeV. The spatial distribution of the GCR intensity with an excess (7.2σ pre-trial,
5.2σ post-trial) and a deficit (−5.8σ pre-trial) are observed in the 300 TeV anisotropy map, in close
agreement with IceCube’s results at 400 TeV. Combining the Tibet results in the northern sky with
IceCube’s results in the southern sky, we establish a full-sky picture of the anisotropy in hundreds of
TeV band. We further find that the amplitude of the first order anisotropy increases sharply above
∼ 100 TeV, indicating a new component of the anisotropy. All these results may shed new light on
understanding the origin and propagationof GCRs.
1. INTRODUCTION to 10−3 at energies from 100 GeV to hundreds of TeV
(see Figure 5). However, the variation of the amplitude
The arrival directions of Galactic cosmic rays (GCRs)
with energy seems to be difficult to interpret in terms
are nearly isotropic due to deflections in the Galactic
of the conventional GCR diffusion model in the Galaxy
magnetic field (GMF).Only weak anisotropy is expected
(e.g. (Moskalenko et al. 2002; Ahlers & Mertsch 2016)).
from the diffusion and/or drift of GCRs in GMF. Ob-
The study ofGCR anisotropy,therefore,is importantto
servations of ground-based air shower arraysand under-
understand the origin and propagationof GCRs.
ground muon detectors do show the existence of small
anisotropieswithrelativeamplitudesoftheorderof10−4 Onlyafewresultsoftheanisotropyintheenergyrange
from hundreds of TeV up to ∼ 10 PeV have been re-
2
ported, primarily due to the low fluxes of cosmic rays upgraded to the current Tibet III, a denser array with
(CRs) in this energy range. EAS-TOP collaboration re- 7.5 m grids, in 1999 and 2003 (Amenomori et al. 2003).
ported for the first time a detection of anisotropy at The trigger rate is ∼1700 Hz for the Tibet III array.
∼200TeV(Aglietta et al.1996). Withtheaccumulation In order to maintain the uniformity of the array per-
of data, they improved their result later and reported formance, we analyze the data keeping the same config-
a sharp increase of the anisotropy amplitude at pri- urationofthe Tibet II arraythroughoutthe observation
mary energies around ∼370 TeV (Aglietta et al. 2009). period from 1995 October to 2010 February, so that the
At the PeV energy region, the Akeno experiment re- fulldatasampletakenbyTibetIIandTibetIIIarraycan
ported an increase of the CR anisotropy amplitude in be used in the present analysis. The traditional shower
1986 (Kifune et al. 1986). No hint of the anisotropy, on reconstructionprocedureisappliedtogetallthe param-
the other hand, has been found in the KASCADE data eters of one shower, such as the core position, zenith,
at higher energies between 0.7 and 6 PeV (Antoni et al. and azimuth angles (θ, φ) of the incident direction and
2004). Recently, the IceCube collaboration reported shower size Pρ (the sum of the number of particles
FT
the anisotropy observed in the southern sky, showing a per m2 counted by all the fast-timing [FT] detector).
new feature different from that obtained by EAS-TOP The following three criteria are applied to select events
(Abbasi et al.2012). Acleardeficitwithapost-trialsig- for further analyses: (1) each AS event should fire four
nificance of −6.3σ at 400 TeV was detected, which was ormoredetectors,witheachrecording1.25ormorepar-
thenconfirmedbytheresultfromIce-Top(Aartsen et al. ticles; (2) the AS core position should be located inside
2013). TheIce-Topdatafurtherrevealedtheexistenceof the array;and (3) zenith angle θ <60◦.
anisotropyatenergiesupto1PeV(Aartsen et al.2013).
2.2. Estimation of the CR Energy
The Tibet Air Shower (AS) array collaboration pre-
sented the first two-dimensional anisotropy measure- TheASsreachingthearraywithalargezenithangleθ
ments in an energy region from several TeV to several travelthroughalargerslantatmosphericdepththanthe
hundred TeV. The anisotropy features, known as the vertical ones. This leads to a zenith angle dependence
“tail-in” and “loss-cone” features, were observed with of the relation between Pρ and the primary parti-
FT
very high significances (Amenomori et al. 2006). A new cle energy. In most of the previous works of the Tibet
component anisotropy at multi-TeV energies from the ASγ Collaboration(Amenomori et al.2003,2005a,2006;
Cygnus direction was also reported (Amenomori et al. Feng et al.2009;Amenomori et al.2013),theshowersize
2006). It has been shown that the amplitude of the first Pρ is solely adopted to infer the primary energy of
FT
orderanisotropydecreasesaboveafew hundredTeV,in- an AS without considering the zenith angle dependence.
dicating the co-rotation of GCRs around the Galactic This approximation works well for small zenith angles
center. With more data accumulated, hints of ∼ 300 (θ <∼ 40◦), considering the natural fluctuation in the
TeV anisotropies have been revealed (Feng et al. 2009; development of the AS and the limited resolution of the
Amenomori et al. 2013). The anisotropy feature was primary energy.
found to be different from those in lower energy re- In this work,we intend to explore the anisotropywith
gionsandinagreementwithIceCube’sresultat400TeV decl. down to −30◦ by including showers with zenith
◦
(Abbasi et al. 2012). These analyses of Tibet AS array anglesupto60 . Therefore,thezenithangledependence
data cover decl. from −15◦ to 75◦, yet leaving a gap to oftheenergyreconstructionmustbetakenintoaccount.
be connected with IceCube’s result in the southern sky. We develop a two-dimensional selection criterion in the
Here we extend these analyses to include events with Pρ −secθ plane for the energy reconstruction.
FT
◦
zenith angle up to 60 , which corresponds to a cover- The uncertainty of the CR energy reconstruction has
age of decl. from −30◦ to 90◦ (Amenomori et al. 2015). beenestimatedwithafullMonteCarlo(MC)simulation
CombiningwithIceCube’sresults,wepresentforthefirst ofCRinteractionsintheatmospherebyCORSIKA(ver-
time a full-sky anisotropy observed at hundreds of TeV. sion 6.204; (Heck et al. 1998). The hadronic interaction
By improving the reconstruction of primary energy, we model QGSJET01c and the detector response modeled
willalsoextendtheanalyzedenergyrangetotwodecades by Epics (version 8.65; (Kasahara 2006) are used. In
between10TeVand1PeV,whichisalsothewidestcov- this simulation, we adoptthe compositionand spectrum
erage of such works. models of primary CRs given in (Ho¨randel 2003) as in-
puts.
2. ANALYSIS Figure 1 shows the simulated distribution in the pri-
mary CR energy as a function of Pρ and sec θ. It
2.1. Experiment and Data reconstruction FT
showsthatforagivenrangeofPρ ,smallzenithangle
FT
TheTibetASArrayislocatedatYangbajinginTibet, events (at sec θ ∼ 1) are dominated by CRs with lower
China (90.522◦E, 30.102◦N, 4300 m above sea level, 606 averageenergy, compared with large zenith angle events
g/cm2 atmospheric depth). The detector array consists (at sec θ ∼ 2). We show regions of constant primary
of plastic scintillation detectors with an area of 0.5 m2 energies(15,50,100,300,and 1000TeV) inthe plane of
each. The effective area of the Tibet AS array has been (Pρ , sec θ) as regions delimited by the dashed lines
FT
gradually enlarged, via adding the same-type detectors in Figure 1. This grouping enables us to select events in
to the array. The Tibet I arraywas constructedin 1990, five energy samples with minimal overlappings.
using 65 plastic scintillation detectors placed on grids Figure 2 shows the simulated primary energy distri-
with15mspacing. Itwasthenupgradedto221detectors butions of the five energy samples, as indicated by the
on 15 m grids, covering a total of 36,900 m2, known as dashedlines inFigure1. Theuncertaintyoftheprimary
the Tibet II array. It began operation in 1995 October, energy estimate is dominated by the fluctuation of the
with a trigger rate of ∼ 230 Hz. The Tibet II was then AS.Eventnumbersinfiveenergysamplesare2.33×1010
3
3. RESULTS
3.5
3.1. Sidereal Anisotropy map at 300 TeV
3.0
103 2.5 Figure 3 shows the significance map and the relative
ρΣFT102 12..50)(TeV)(Elogpri10 iewnnitdeertnghsyiotsyfa3mm0ap◦pleis.ofaApthpsemliesodidoteihnreintahgliaswnfiiitsghoutarreno.poyWpfteoimrcotizhmeedb3iwn0e0indTdtoehVwe
1.0 300 TeV and 1 PeV samples together in this figure to
0.5 increase the statistics. The total event number used in
110.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 0.0 this figure is 3.28×108, and the median energy is ap-
secθ proximately 300 TeV.
Fig.1.— Simulated distribution of the log-mean energy of pri- From the significance map, we find that two regions
mary CRs as a function of PρFT and zenith angle. The y-axis are significant-that is, an excess centered at (α = 263◦,
is PρFT; the x-axis is sec θ, where θ is the reconstructed zenith δ = 11◦) with a significance of 7.2σ and a deficit cen-
angle;andthecolorscalerepresentsthereconstructedlog-meanen- tered at (α = 93◦, δ = −25◦) with a significance of
ergyinunitsofTeV.Dashedlinesmarkoutthebordersofevents
withdifferentenergies(15,50,100,300,and1000TeV). −5.8σ. Note that the significance values are the pre-
trial results. We conservatively estimate a trial factor
by assuming that all scans give statistically independent
results. Sincethesearchforthisexcessisperformedover
about60×180cells,and26differentsmoothingradii,the
totaltrialfactorisestimatedtobeabout2.81×105. The
post-trialsignificanceoftheexcessis∼5.2σ. Thedeficit
is no longer significant, fail to reach the 5σ level, after
the correctionfor the trials.
Because the acceptance of the detector decreases for
largerzenith angles, the relative intensity map is similar
but not completely the same as the significance map.
An excess region centered at (α = 269◦, δ = −13◦)
with a maximum excess of +1.38×10−3, and a deficit
Fig.2.—Normalizedeventnumberasafunctionofthesimulated
primary energy in each of the five energy samples, based on MC regioncenteredat(α=87◦,δ =−29◦)withamaximum
data. Thelog-meanenergiesofthefivesamplesare15TeV(red), deficit of -1.80×10−3 can be seen. Both the excess and
50TeV(black),100TeV(green),300TeV(blue),and1PeV(pink).
deficit regions are consistent with the results of IceCube
(15 TeV), 3.97×109 (50 TeV), 1.96× 109 (100 TeV), at 400 TeV in the southern hemisphere (Abbasi et al.
2012). Combining these results gives us a full-sky pic-
2.71×108 (300 TeV), and 5.72×107 (1 PeV), as listed
ture of the sidereal anisotropy of GCRs at hundreds of
in Table 1.
TeV.
ThebottompanelinFigure3alsoshowsthe1Dprojec-
2.3. Analysis of the first harmonics of the anisotropy
tion of the relative intensity before the smoothing onto
We employ the All-Distance Equi-Zenith Angle the R.A. axis. The correlation among different bins is
Method(Amenomori et al.2005a,2006),whichhasbeen carefully considered when calculating the statistical er-
showntobesensitivetoprobethelarge-scaleanisotropy, rors and fitting the data with the harmonic function in
to analyze the data. Details about this method can be equation1. If the correlationis not consideredcorrectly,
found in (Amenomori et al. 2005a). The sky of the hor- the errors of the fitting parameters would be underesti-
izontal coordinate is divided into cells with a bin size of mated. Thebluecurveshowsthebest-fittingresult,with
◦ ◦ ◦
1 in both zenith (from 0 to 60 ) and azimuth (from thefittingparametersindicatedinthefigure. Thesignif-
◦ ◦
0 to 360 ). For the equatorial coordinate, the sky is icance of non-zero amplitude is 5.6σ, which shows that
divided into cells of 2◦×2◦ between 0◦ and 360◦ in the the obtained first harmonics are indeed significant. The
R.A. (α) and between −30◦ and 90◦ in the decl. (δ). reduced χ2 value is 26.7/16, which means that the first
The two-dimensional(2D) map in the equatorialcoordi- harmonic function can describe the 1D projected profile
nateisthensmoothedinawindow,changingthewindow well.
◦
widths between 5 and 30 . One of the possible origins of the sidereal anisotropy
To quantify the magnitude of the anisotropy, we is the Compton-Getting (CG) effect, due to the or-
projectthe two-dimensional(2D) anisotropymapbefore bital motion of the solar system around the Galactic
smoothingontotheR.A.axis,throughaveragingtherel- center (Compton & Getting 1935). The relative inten-
ative intensities in all declinations from −30◦ to 90◦, to sity of this effect is carefully calculated by the MC
derivetheone-dimensional(1D)profileoftheanisotropy. method. Considering the location of the Tibet AS array
TheR.A. isbinnedinto 18bins forthis 1Danalysis,and (90.522◦E, 30.102◦N), the velocity (220 km s−1) of the
the1Dprofileoftheanisotropyisfittedbythefirstorder orbital motion of the solar system around the Galactic
harmonic function in form of center and the spectrum index (2.7) of the CRs energy
R(α)=1+A1cos(α−φ1), (1) scpelelcstroufm2,◦t×he2◦intbeentswiteyenof0◦thaensdky36t0h◦atinisthdeiviRd.eAd.in(αto)
whereR(α)denotestherelativeintensityofCRsatR.A. andbetween −30◦ and 90◦ in the decl. (δ) is calculated.
α, A is the amplitude of the first harmonics, and φ is Then the identical analyses are performed to this MC
1 1
the phase at which R(α) reaches its maximum. data sample.
4
The R(α) expected from this CG effect, shown as −30◦ to complete a full-sky coverage of the anisotropy
the black dashed line in Figure 3, has a maximum at at hundreds of TeV energies by combining with the Ice-
(α = 315◦, δ = 0◦) and a minimum at (α = 135◦, Cube’s results at the South Pole. The 2D anisotropy
δ = 0◦). Neither the amplitude nor the phase of the map at ∼ 300 TeV obtained in this work is smoothly
large-scale anisotropy observed in this work can be de- connected with IceCube’s results at 400 TeV. The en-
scribed in terms of the CG effect. ergy dependence of the large-scale sidereal anisotropy
has been derived between 10 TeV and 1 PeV. We mea-
3.2. Variation of CR sidereal anisotropy with the suredtheenergydependenceofthefirstharmonicsofthe
energy between 10 and 1000 TeV anisotropyabove100TeV,whichmaybeassociatedwith
local origins of GCRs.
Figure 4 showsthe variationof the siderealanisotropy
The CG effect expected from the orbital motion of
with the energy between 10 TeV and 1 PeV. At 15
the solar system around the Galatic center is not ob-
TeV and 50 TeV, the tail-in and loss-cone features
served at 300 TeV, as shown in Figure 3. The basic
(Amenomori et al.2006)areobservedwithveryhighsig-
picture that GCRs are co-rotating with the local Galac-
nificances. An intensity excess in the Cygnus region can
ticneighborsstillholdsatthisenergy(Amenomori et al.
also be seen. However, these features become less sig-
2006). As pointed out earlier, the GCR rest frame may
nificant above 100 TeV, being replaced with some new
have a smaller relative velocity with a different direc-
features. At 300 TeV and 1 PeV, the anisotropy maps
tion from neighboring stars and the interstellar medium
are distinctly different from those in 15-50 TeV. We can
(Abbasi et al. 2012). This scenario is possibly respon-
clearly see the phase of the 1D projection changing with
sible for the GCR anisotropy observed at hundreds of
the primary energies, as seen in Table 1, showing the
TeV.
best-fit parameters.
The strongest excesses at hundreds of TeV are from
Figure 5 compares the amplitude and phase obtained
the direction of the Galactic center, which may im-
in this work with those reported so far from the deep
ply a Galactic center origin of GCRs at these ener-
undergroundmuonexperimentsandextensiveASexper-
gies (Guo et al. 2013). It is interesting to note that
iments. Our results are in close agreement with other
the highest-energy CR accelerators have been iden-
results in similar energy regions in both the amplitude
tified by the HESS telescope in the Galactic center
and the phase. It is interesting to note that a sharp
(HESS Collaborationet al. 2016). However, the energy
increase of the amplitude above 100 TeV can be seen in
dependencesoftheamplitudeandphasecannotbeeasily
theupperpanel. Theoriginsofthisfeaturecannotbeex-
understoodin a simple diffusion scenario with any types
plainedwiththeconventionaldiffusionscenarioofGCRs,
of GCR sources.
and may provide us with a new hint for understanding
The sharp increase of the amplitude above 100 TeV
the origin and propagationof GCRs.
mayimplyanevolutionofpropagationparameters,such
asspatialparameters(Tomassetti2015;Guo et al.2016).
3.3. Anisotropy in Solar Time and Antisidereal Time
The knowledge of the propagation of GCRs needs to be
Inordertoconfirmthattheobtainedanisotropyisnot further improved for our full understanding the proper-
affected by the seasonal variation of the AS array per- ties of the anisotropy, especially in this high-energy re-
formance, identical analyses are performed in the solar gion where the conventional diffusion/drift models may
timeandantisiderealtimeframesinfiveenergysamples. notworkanymore. Finally,weaddtonotethatthemea-
Figure6 showsthe localsolartime andantisiderealtime surementsoftheanisotropyabovePeV,whichispossibly
daily variations measured by Tibet AS Array in five en- associatedwiththekneeofGCRs,areveryimportantto
ergysamples,andthe best-fitparametersarealsoshown advance our understanding of origin and propagation of
in Table 1. The amplitude and phase in the solar time GCRs.
frame are in good agreement with the expectation from
theCGeffectduetotheterrestrialorbitalmotionaround 5. ACKNOWLEDGMENTS
the Sun (A = 0.047% and φ = 6.0 hr). In all
sol,CG sol,CG The collaborative experiment of the Tibet Air Shower
fiveenergysamples,nosignificantanisotropyisobserved
Arrays has been performed under the auspices of the
in the antisidereal time frame, ensuring that no addi-
Ministry of Science and Technology of China and the
tionalcorrectionis requiredfor the seasonaleffects. The
Ministry of Foreign Affairs of Japan. This work was
observedresultsinthesolarandantisiderealtimeframes
supported in part by a Grant-in-Aid for Scientific Re-
supportthereliabilityoftheobservedsiderealanisotropy.
searchonPriorityAreasfromtheMinistryofEducation,
Culture, Sports, Science and Technology, by Grants-in-
4. CONCLUSION AND DISCUSSION
Aid for Science Research from the Japan Society for the
FifteenyearsdatarecordedbytheTibetASarrayhave Promotion of Science in Japan, and by the Grants from
beenanalyzedtostudythesiderealanisotropyofCRs. In the National Natural Science Foundation of China and
thiswork,weimprovetheestimateoftheprimaryCRen- the Chinese Academy of Sciences. Zhaoyang Feng is
ergiesthrougha2DcutinthePρ −secθ plane,toex- supported by the Natural Sciences Foundation of China
FT
ploretheanisotropyincludinglargerzenithangleevents. (Nos.11405182,Nos.1135010). C.Liuissupportedbythe
For the first time, we extend the analyzeddecl. downto Natural Sciences Foundation of China (Nos. 11405180).
REFERENCES
Aartsen,M.G.,Abbasi,R.,Abdou,Y.,etal.2013,ApJ,765,55 —.2012, ApJ,746,33
Abbasi,R.,Abdou,Y.,Abu-Zayyad,T.,etal.2010, ApJ,718, Abdo,A.A.,Allen,B.T.,Aune,T.,etal.2009,ApJ,698,2121
L194
5
Aglietta,M.,Alessandro,B.,Antonioli,P.,etal.1995, Guillian,G.,Hosaka,J.,Ishihara,K.,etal.2007,Phys.Rev.D,
International CosmicRayConference, 2,800 75,062003
—.1996,ApJ,470,501 Guo,Y.-Q.,Feng,Z.-Y.,Yuan,Q.,Liu,C.,&Hu,H.-B.2013,
Aglietta,M.,Alekseenko, V.V.,Alessandro,B.,etal.2009, ApJ, NewJournalofPhysics,15,013053
692,L130 Guo,Y.-Q.,Tian,Z.,&Jin,C.2016,ApJ,819,54
Ahlers,M.,&Mertsch,P.2016,ArXive-prints,arXiv:1612.01873 Heck,D.,Knapp,J.,Capdevielle,J.N.,Schatz, G.,&Thouw,T.
Alekseenko,V.V.,Cherniaev,A.B.,Djappuev, D.D.,etal. 1998,CORSIKA:aMonteCarlocodetosimulateextensiveair
2009, NuclearPhysicsBProceedings Supplements, 196,179 showers.
Alexeyenko, V.V.,Chudakov, A.E.,Gulieva,E.N.,& HESSCollaboration,Abramowski,A.,Aharonian,F.,etal.2016,
Sborschikov, V.G.1981,International CosmicRayConference, Nature,531,476
2,146 H¨orandel,J.R.2003, AstroparticlePhysics,19,193
Ambrosio,M.,Antolini,R.,Baldini,A.,etal.2003,Phys.Rev.D, Kasahara,K.2006,
67,042002 http://cosmos.n.kanagawa-u.ac.jp/EPICSHome/index.html
Amenomori,M.,Ayabe,S.,Cui,S.W.,etal.2003,ApJ,598,242 Kifune,T.,Hara,T.,Hatano,Y.,etal.1986, JournalofPhysics
Amenomori,M.,Ayabe,S.,Chen,D.,etal.2005a,ApJ,633,1005 GNuclearPhysics,12,129
Amenomori,M.,Ayabe,S.,Cui,S.W.,etal.2005b,ApJ,626, Lee,Y.W.,&Ng,L.K.1987,International CosmicRay
L29 Conference,2,18
Amenomori,M.,Ayabe,S.,Bi,X.J.,etal.2006,Science,314,439 Mori,S.,Yasue,S.,Munakata, K.,etal.1995,International
Amenomori,M.,Bi,X.J.,Chen,D.,etal.2013, Proceedingsof CosmicRayConference,4,648
the33rd ICRC,RiodeJaneiro,ID256 Moskalenko,I.V.,Strong,A.W.,Ormes,J.F.,&Potgieter,
—.2015,Proceedingsofthe34th ICRC,theHaag,ID355 M.S.2002,ApJ,565,280
Munakata,K.,Yasue,S.,Mori,S.,etal.1995,International
Andreyev,Y.M.,Chudakov, A.E.,Kozyarivsky,V.A.,etal.
CosmicRayConference,4,639
1987, International CosmicRayConference, 2,22
Munakata,K.,Kiuchi,T.,Yasue,S.,etal.1997,Phys.Rev.D,
Antoni,T.,Apel,W.D.,Badea,A.F.,etal.2004,ApJ,604,687
56,23
Bartoli,B.,Bernardini,P.,Bi,X.J.,etal.2015,ApJ,809,90
Nagashima,K.,Fujimoto,K.,Sakakibara,S.,Fujii,Z.,&Ueno,
Bercovitch,M.,&Agrawal,S.P.1981,International CosmicRay
H.1989,NuovoCimentoCGeophysicsSpacePhysicsC,12,695
Conference, 10,246
Sakakibara,S.,Ueno,H.,Fujimoto,K.,Kondo,I.,&Nagashima,
Compton,A.H.,&Getting, I.A.1935, PhysicalReview,47,817
K.1973,International CosmicRayConference,2,1058
Cutler,D.J.,&Groom,D.E.1991,ApJ,376,322
Swinson,D.B.,&Nagashima,K.1985,Planet.SpaceSci.,33,
Feng,Z.,Zhang,Y.,Liu,C.,etal.2009,Proceedingsofthe31st 1069
ICRC,L ´od´z,ID0869 Thambyahpillai,T.1983,International CosmicRayConference,
Fenton,K.B.,Fenton,A.G.,&Humble,J.E.1995,International 3,383
CosmicRayConference,4,635 Tomassetti,N.2015,Phys.Rev.D,92,081301
Gombosi,T.,K´ota,J.,Somogyi,A.J.,etal.1975,International Ueno,H.,Fujii,Z.,&Yamada,T.1990,International Cosmic
CosmicRayConference,2,586 RayConference,6,361
80 6
Dec. (deg.) 2460000 -0242
-20 -4
0 50 100 150 200 250 300 350
80 1.0010
Dec. (deg.) 2460000 0011....9900990099000505
-20 0.9985
0 50 100 150 200 250 300 350
Relative Intensity 00011111........99900000999000008990011250505050 φχA 2m / n pd .f 22 767..337.e/6-1±46±101..13e-4
0.99800 50 100 150 R.A. (deg.2)00 250 300 350
Fig.3.— Large-scale sidereal anisotropy at 300 TeV by the Tibet AS Array. The 2D maps are smoothed with a 30◦ Gaussian kernel.
Thetopandmiddlepanelsdisplaythesignificanceandrelativeintensitymaps,respectively,whilethebottomoneshowsthe1Dprojection
ofthe2DmapontotheR.A.axis. Thebluecurveshowsthefirstharmonicfittingtothedata,andtheblackdashedlineisthepredicted
GalacticCGeffectwithanamplitudeof∼0.19%.
TABLE 1
Fitting results of the firstharmonic(Amplitude, Phase,andReduced χ2) in the sidereal (Columns2-4),solar (Columns
5-7),andAntisidereal (Columns8-10)Times. The numberof eventsin each energysample isgivenin Column 11.
Energy Asid φsid χ2sid/ndf Asol φsol χ2sol/ndf Aasid φasid χ2asid/ndf NumberofEvent
TeV 10−4 [◦] 10−4 hr 10−4 hr
15 8.5±0.2 21.9±1.6 911./16 4.1±0.2 6.05±0.22 69.7/16. 0.53±0.24 22.2±1.7 24.4/16 2.33×1010
50 5.3±0.4 20.8±4.7 152.9/16 4.6±0.4 6.37±0.35 46.7/16 0.39±0.43 22.5±4.2 46.7/16 3.97×109
100 2.7±0.6 326.8±12.0 67.6/16 4.0±0.6 5.91±0.53 14.2/16. 0.80±0.56 22.3±2.7 9.8/16 1.96×109
300 6.0±1.4 267.1±13.5 27.0/16. 3.5±1.4 6.53±1.56 19.0/16. 1.7±1.4 5.3±3.2 11.6/16 2.71×108
1000 13.0±3.0 286.6±12.6 9.3/16 9.8±2.8 6.97±1.13 10.9/16. 1.0±2.9 14.8±11.0 6.3/16 5.72×107
6
Dec. (deg.) -246820000000 50 100 150 200 250 300 350 000111......999000999000899001505050 Relative Intensity001110......9900099900098901280642080 50 100 15φAχ0 2m / n p d . f 9 2811.15.29.e05±-0/411±.660.2e-4250 300 350
Dec. (deg.) -246820000000 50 100 150 200 250 300 350 00111.....99000990009900105050 Relative Intensity001110......9900099900098901280642080 50 100 15φAχ0 2m / n p d . f 1 2550.23.28.e0±9-0/441±.670.4e-4250 300 350
Dec. (deg.) -246820000000 50 100 150 200 250 300 350 00001111........99990000999900009999000024680246 Relative Intensity001110......9900099900099900190426080 50φAχ 2m / n p d . f 6 312720..7606e./8-1±46±120..06e1-450 200 250 300 350
Dec. (deg.) -246820000000 50 100 150 200 250 300 350 000111......999000999000899001505050 Relative Intensity00111.....9900099000890210 50φAχ 2m / n p d . f 2 216760..0700e./1-1±46±131..54e1-450 200 250 300 350
Dec. (deg.) -246820000000 50 100 15R0.A. (de2g00.) 250 300 350 0001111.......999000099900007890123 Relative Intensity011...9009008020 50 χφA12 0m / n0 p d . f 9 21.83.36/e1.6-61±35R±1002...A36e.- 3(de20g0.) 250 300 350
Fig. 4.—2Danisotropymapsinfiveenergysamples(15,50,100,300,and1000TeV,fromtoptobottom). Leftpanelsshowtherelative
intensity maps (with 30◦ smoothing), while right panels show the 1D projections. The meaning of the blue curves in the right panels is
thesameasinFigure3.
10-3
e
d
u
plit 10-4
m
A Norikura1973 Misato1985 Liapootah1995 Baksan1981 ARGO2011
Ottawa1981 Socomo1985 Matsushiro1995 Norikura1989 IceCube2010
10-5 London1983 Yakutsk1985 Poatina1995 EASTOP1995 IceCube2012
Bolivia1985 Baksan1987 Kamiokande1997 EASTOP1996 IceTop2013
Budapest1985 HongKong1987 Macro2003 EASTOP2009 Tibet2005
Hobart1985 Sakashita1990 SuperKamiokande2007 Baksan2009 Tibet2013
London1985 Utah1991 PeakMusala1975 Milagro2009 This work
1011 1012 10E13nergy (eV) 1014 1015 1016
10
5
s) 0
r
h
( -5
e
s
a -10
h
P Norikura1973 Misato1985 Liapootah1995 Baksan1981 ARGO2011
-15 Ottawa1981 Socomo1985 Matsushiro1995 Norikura1989 IceCube2010
London1983 Yakutsk1985 Poatina1995 EASTOP1995 IceCube2012
Bolivia1985 Baksan1987 Kamiokande1997 EASTOP1996 IceTop2013
-20 Budapest1985 HongKong1987 Macro2003 EASTOP2009 Tibet2005
Hobart1985 Sakashita1990 SuperKamiokande2007 Baksan2009 Tibet2013
London1985 Utah1991 PeakMusala1975 Milagro2009 This work
-25
1011 1012 10E13nergy (eV) 1014 1015 1016
Fig.5.— The energy dependences of amplitude (top) and phase (bottom) of the first harmonics of the CRs anisotropy obtained in
this work, and reported from previous measurements. They are underground muon observations: Norikura(1973) (Sakakibara etal.
1973), Ottawa(1983) (Bercovitch&Agrawal 1981), London(1983) (Thambyahpillai 1983), Bolivia(1985) (Swinson&Nagashima 1985),
Budapest(1985) (Swinson&Nagashima 1985), Hobart(1985) (Swinson&Nagashima 1985), London(1985) (Swinson&Nagashima
1985), Misato(1985) (Swinson&Nagashima 1985), Socorro(1985) (Swinson&Nagashima 1985), Yakutsk(1985) (Swinson&Nagashima
1985), Banksan(1987) (Andreyevetal. 1987), HongKong(1987) (Lee&Ng 1987), Sakashita(1990) (Uenoetal. 1990), Utah(1991)
(Cutler&Groom 1991), Liapootah(1995) (Munakata etal. 1995), Matsushiro(1995) (Morietal. 1995), Poatina(1995) (Fenton etal.
1995), Kamiokande(1997) (Munakata etal. 1997), Marco(2003) (Ambrosioetal. 2003), SuperKamiokande(2007) (Guillianetal. 2007),
and air shower array experiments: PeakMusala(1975) (Gombosi etal. 1975), Baksan(1981) (Alexeyenko etal. 1981), Norikura(1989)
(Nagashimaetal. 1989), EASTOP(1995,1996,2009) (Agliettaetal. 1995, 1996, 2009), Baksan(2009) (Alekseenko etal. 2009), Mila-
gro(2009) (Abdoetal. 2009), IceCube(2010,2012) (Abbasietal. 2010, 2012), IceTop(2013) (Aartsenetal. 2013), ARGO-YBJ(2015)
(Bartolietal.2015),Tibet(2005,2013) (Amenomorietal.2005b;Amenomorietal.2013).
7
Relative Intensity00111.....990009900099001050500 5 10 Aχφ 2m 1/ n 5p d . f 6 649..0.175e±/-1406±.202.22e0-4 25 00111.....990009900099001050500 5 10 χφA 2m 1/ n 5p d . f 2 2542..3.42e/±-1516±.72.42e0-5 25
Relative Intensity00111.....990009900099001050500 5 10 φAχ 2m 1/ n 5p d . f 4 646..3.677e/±-1406±.305.42e0-4 25 00111.....990009900099001050500 5 10 φχA 2m 1/ n 5p d . f 4 2362..9.75e±/-1546±.24.32e0-5 25
Relative Intensity00111.....990009900099001050500 5 10 φAχ 2m 1/ n 5p d . f 1 544..9.021e±/-1046.±503.62e0-4 25 00111.....990009900099001050500 5 10 φχA 2m 1/ n 5p d . f 9 28.28.0./3e1±-652±.75.62e0-6 25
Relative Intensity00111.....990009900099001050500 5 10 Aχφ 2m 1/ n 5p d . f 1 639..5.503e±/-1416±.516.42e0-4 25 00111.....990009900099001050500 5 10 φAχ 2m 1/ n 5p d . f 1 511..3.76±e/31-4.62±1.42e0-4 25
Relative Intensity 110...0090090280 5 Lo10cal solar tφAχi 2mm 1/ n 5p de . f ( 1 6h90..r9.89)7e/±-1416±.123.82e0-4 25 110...0090090280 5 Loca1l 0anti-siderφAχa 2m 1/l n 5p td .i f m 6 11.e43.0. /8(e1±h-641r1±).20.92e0-4 25
Fig.6.— Local solar timeand antisidereal timedailyvariations measured byTibet ASArrayinfive energy samples, 15, 50, 100, 300,
and1000TeV,fromtoptobottom. Leftpanelsshowthesolartimedailyvariations,withbluecurvesshowingthefirstharmonicfittothe
dataandtheblackdashedcurves indicatingtheexpected CGeffectduetotheEarth’sorbitalmotionaroundthesun,withanamplitude
of0.047%andanphaseof6hr. Rightpanelsshowtheantisiderealtimedailyvariationsandthefirstharmonicfittingresults.