PoS(ICRC2019)735 http://pos.sissa.it/ and M. A. Leigui de Oliveira ∗ [email protected] Speaker. We propose a model for theregion flux from of 250 very-high GeV energy (VHE) toGalaxy, gamma the 25 rays attenuation TeV. We at resulting take Earth from the in intolight photon the account, (EBL), interactions energy along and with the the the extragalactic path gamma-ray background actions oscillations from with into the extragalactic axion-like source magnetic particles to field (ALPs)gamma-ray our (EMF). due flux to We to be also their observed discuss inter- by the Imagingfirmed Air by expected Cherenkov astrophysics increases Telescopes as (IACTs), in dark if matter the ALPs particles. Key are words: con- Axion-like particles, universal transparencyTelescopes. of gamma rays, Imaging Air Cherenkov ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). 36th International Cosmic Ray Conference -ICRC2019- July 24th - August 1st, 2019 Madison, WI, U.S.A. Raquel Malta Study of axion-like particles signals atCherenkov Telescopes Imaging Air Center for Natural Sciences and HumanitiesFederal University (CCNH) of ABC (UFABC) 09210-580 Santo André, São Paulo, Brazil. E-mail: PoS(ICRC2019)735 (1.1) (1.2) is the 0 ]. Elec- E 1 Raquel Malta and s z ]: 3 , turns: , ) ) s is the photon mean free path. z E , GeV, photons interact mainly with EBL, ( ) 0 γ 1.1 E 5 E λ ( / ( γ ]. This suppression depends both on the ob- τ γ 10 D 2 − λ − e < e ]. A scenario in which a part of energetic photons 1 4 E ) = ) = s < z D , , 0 E E ( ( γγ γγ GeV the interaction with radio background (RB) becomes P P 10 1. This implies that some novel astrophysical phenomena should 10 ≥ > τ E GeV, cosmic microwave background (CMB) plays the leading role on the pair 10 10 < E is the optical depth that quantifies the dimming of the source at a redshift γ < τ 5 When an energetic cosmic ray falls upon Earth’s atmosphere it triggers a chain-reaction parti- Gamma-ray astronomy is the astronomical observation of gamma rays, the most energetic where observed energy. Evaluating the optical depth, equation cle cascade known as extensive air shower (EAS). An EAS is formed due to successive collisions is converted to an inertOne particle of the along explanations the is a way mixingson, and between the reconverts gamma so-called back rays axion-like and before particle a reaching (ALP), lightuntil which pseudoscalar reconverting the in fundamental can, observer. bo- gamma-rays, in inducing principle, a propagate hardening largely of unimpeded the observed1.2 spectrum. Gamma-ray shower tromagnetic radiation which falls upon EarthEspecially carries the information very about energetic several ones aspects provide of thein universe. understanding galactic of and physics extragalactic of objects, cosmic-ray helpingand acceleration us which to phenomena discover does new occur systems in fartheir these away sources from environments. and our can VHE galaxy directly gamma reveal raysVHE the point production photons back sites directly (100 of to energetic GeV cosmicgalactic nuclei rays. – (AGN), travel 100 through intergalactic TeV) mediumwhich and ejected undergo leads electron-positron from to creation, the sources attenuation like of the supernovae primary remnants beam or [ active form of electromagnetic radiation,gamma-ray emissions with are photon diverse, energiesergies, mostly including above identical electron-positron annihilation, 100 with the those keV. inverse Comptonthe The emitting effect, decay and X-rays mechanisms of in but radioactive some for material cases at also (gammanovae higher decay) and en- in the space behaviour reflecting of extreme events matter such under as extreme super- conditions, as in pulsars and blazars [ Study of ALPs signals at IACTs 1. Introduction 1.1 Gamma-ray astronomy served energy and the sourceto distance, pair-production which cross can section, be for measuredfor 10 by 10 GeV the source redshift. According where D is the distance travelledThe by standard the picture photon of and pair-production absorption inpected the opacity EBL of seems the to intergalactic space be limits incomplete100 the since mean of the free ex- megaparsecs, path but of TeV TeV gamma photons raysan from do increasing not slope numerous exceed of distant flux sources for haveaffect been long-distance propagation detected, of causing gamma rays [ production process, and if dominant. The photon survival probability can be measured as it follows [ PoS(ICRC2019)735 to 10 100 2 ≈ ≈ Raquel Malta 300 – 350 nm, in ≈ λ , which is the electromagnetic equiv- 2 Cherenkov radiation at 1 TeV, arriving in a brief flash lasting between 5 and 20 ns. This Cherenkov pulse 2 MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov telescopes) is a system of two The IACT works by imaging the very short flash of Cherenkov radiation produced when a H.E.S.S. (High Energy Stereoscopic System) is a system of IACTs located in Namibia in 1800 IACTs situated at the Roque de los Muchachos Observatory (La Palma, Canary Islands) at about the detection area. In(PMTs) grouped its into concept, 16-PMT drawers the whichdigitization, also H.E.S.S. triggering contain II and the electronics camera readout. for contains The signalsystem lower storage, 2048 is threshold signal around PhotoMultiplier for 10 Tubes gamma-ray GeV and detection the in upper the threshold H.E.S.S. 102.2 TeV. MAGIC VHE gamma ray strikesof the the atmosphere. incident primary The particleoften Cherenkov and referred light illuminates to on is as the beamedshower, ground the which around an Cherenkov points the area light back direction ofsingle pool. to about telescope the providing 250 a The celestial m single diameter, object image vieworder of where obtained to a reconstruct the shower, shows it the incident is exact the difficult geometry gamma track to of ray predict the of its shower came. real multiple the2.1 structure, telescopes air With so are H.E.S.S. in used. a m above sea level, inH.E.S.S.has five an telescopes: area four well from knownof Phase for the I its array. and excellent one opticalsquare Each larger quality. with telescope telescope 120 constructed of The m in phase current side the Phase I length. center II has The a larger 12 telescope m has mirror a 28 and m they mirror, are which arranged added in 600 form m of a can be detected using large reflecting surfacesimaging to air-Cherenkov focus telescopes light (IACTs). on to sensitive photon detectors, called 2. Imaging Air Telescopes photons/m Study of ALPs signals at IACTs between nucleons and the decays of its products.nucleons in From the the upper collisions atmosphere, of the pions primary areinteract cosmic produced. with ray Neutral with nuclear pions fields decay into producing two electron-positronproduce photons more pairs. which gamma-rays Electrons by and bremsstrahlung positrons –Charged this in is pions turn the may decay electromagnetic component into of athe the muon most EAS. and penetrating and a most muonicpions, present neutrino and at kaons and the are this produced ground starts inGamma-ray level. the showers the are A central muonic mainly axis small formed component, of by portion the thetravels of electromagnetic through shower, protons, component. the forming air When the neutrons, with charged hadronic a particle component. speedelectromagnetic greater radiation than emission, the the phase velocity ofalent light of for this a medium, sonic there is boom.emission occurring when Cherenkov the light number of may particleskm be in for the primary produced cascade energies in is of the the 100 largest,the GeV air at atmosphere, – an shower, the altitude 1 with of Cherenkov TeV, for light the example.the at maximum Following ultraviolet ground absorption (UV) and level region peaks scattering of in the at electromagnetic a spectrum. wavelength The photon density is typically PoS(ICRC2019)735 ] 6 Raquel Malta ] 5 3 Overview of H.E.S.S. II telescopes array. [ made of square mirrors. The cameras of both MAGIC telescopes 2 Figure 1: The two MAGIC telescopes at the Roque de los Muchachos Observatory. [ Figure 2: VERITAS (Very Energetic Radiation Imaging Telescope Array System) is an array of four Each of the individual telescopes have a 39 feet aperture, 350 mirrors on each dish, and a 3.5 active reflective area of 236 m telescopes located at Fred Lawrencefirst light Whipple with Observatory, the at complete 1268 arraywith meters was an in above approximate 2007. separation sea of VERITAS level. telescopes 100 have m The a from 12 each m adjacent optical telescope. reflector degree field of view.cosmic VERITAS, rays, like its full the range other of sensitivity IACTs, is are from 85 most GeV sensitive to to over 30 the TeV. highest energy consist of 1039 PMTs, arrangedfield in of a circle view of in about the35 1 sky %, meter of depending diameter, 3.5 on which degrees. gives thearound each wavelength. 30 All camera GeV The a PMTs and lower the have threshold upper aninternational threshold for effective is collaboration gamma-ray 100 quantum of detection TeV. The about efficiency in MAGIC 165 of telescopes MAGIC astrophysicistscountries. are 25 is from currently to 24 run institutions by an and consortia from 11 2.3 VERITAS Study of ALPs signals at IACTs 2200 m above sea level.built The at first a telescope distance started of routine 85 operation in m 2004 from and the the first second one, one, started taking data in 2010. Each telescope has an PoS(ICRC2019)735 ). Raquel Malta 2.4 ] 8 ] 7 4 VERITAS array of four telescopes. [ A comparative illustration of the three telescopes sizes [ Figure 3: ] through significant improvements in sensitivity and angular and temporal 8 Figure 4: Cherenkov Telescope Array will be the next generation ground-based gamma-ray telescopes resolution, covering a wider energyany range. existing instrument. CTA will As be astudy about consequence of a it large factor samples will, of of for known the 10 source first more types, time, sensitive it allow than will detection explore and a in-depth wide range of classes of suspected The CTA Observatory should consist inin two the sites, Atacama one Desert at in 2365 the meterslos southern above Muchachos hemisphere, sea Observatory, level, more Canary and Islands. precisely one The inplane northern southern and hemisphere, site at see will Roque many cover de nearby the center galacticthe of sources, southern the some hemisphere galactic of array which will willarray span produce will the PeV be gamma entire more rays. energy limited range in While the size of northern and CTA, will hemisphere the focus site northern on will hemisphere the notThe low- host and aim any mid-energy SSTs. ranges, of for CTA thisSuperNova is reason Remnants to (SNRs) make and progress cosmicdark in matter ray, and over star-forming more existing history [ experiments of in the several universe, science black areas holes, like for very high energy (GeV-TeV) astronomy,be currently operative in a its pre-construction few phase yearsdifferent and from sizes: forseen now. the to Large-Size The Telescope (LST), array whichof comprise will CTA cover different between the 20 numbers unique and low of energy 150 telescopesenergy sensitivity GeV, range of the of Medium-Size three CTA Telescope – (MST), from withsensitive about to sensitivity 150 the in GeV highest the to energy core 10 gamma rays, TeV and between Small-Size a Telescope few (SST), TeV and which 300 is TeV. (Fig. 2.4 Cherenkov Telescope Array (CTA) Study of ALPs signals at IACTs PoS(ICRC2019)735 (3.1) ]. The 11 symmetries, Raquel Malta X symmetry, pro- ) 1 ( PQ ) U 1 ( U ]. 13 [ 12 ) in the presence of an external − E −→ ]: , and it is equivalent to the total distance  z 12 [ B γ 2 a g 3.1 domain  5 2 sin ] to solve the strong CP problem. Spontaneous break- 9 ' are unrelated for ALPs. is called a γ a z P m and ]. ALPs arise from spontaneous breaking of γ a 10 g , in general . There are strong theoretical, astrophysical and cosmological motivations for a B m −→ ) is that they can couple to photons (represented by to search effects of this anomalous transparency is 10 a γ is the coupling constant and a g γ a g We developed a computer simulation written in C++ language which describes the processes The axion a very light pseudo-Nambu-Goldstone boson of the broken that occur with photons alongprocess its and path photon from x Centaurus Apower ALP law to mixing. spectrum our galaxy of First regarding AGN, ofto pair considering 25 all production 1 TeV, we and million three used photons different ais with slopes divided Monte energy – according ranging Carlo 2.00, to from 2.35, algorithm the 250 2.73. toWay, region since GeV of These simulate the propagation: files a regions were source have read galaxy, differentof intergalactic by magnetic the medium the problem fields. and code, and Milky Figure which some possible 5For events. each shows region, a we schematic calculated the representation number ofsions. electron-positron It production is and photon-ALP important conver- to emphasizeregion. that the At output the data end of one of region each is step, the input we of produced the the subsequent spectra of each type of particle to observe the 4. Methodology ALP-photon propagation over cosmologicalstructure, distance being is a strongly possiblefrom affected explanation by AGNs for travels the the in magnetic anomalousing the field transparency pairs) form and problem of converts since ALPs backconstant radiation to for photons a before significant their fraction detections. of The distance lower (without threshold of produc- coupling posed by Roberto Peccei and Helen Quinn [ magnetic field models postulating the existence of additionalAxion-Like particles Particles which (ALPs) behave [ just as axions, the so-called oscillation probability is described by the equation where traveled by the particle. While forthe axions axion there mass exists a relation between the coupling constant and ing symmetry should leave athis Nambu-Goldstone boson boson, is but not since massless. thisinteraction Axions is cross-sections would an for have no anomalous strong electric symmetry, and charge,by weak a the forces. very field An small important mass aspect and very of low axions (represented Study of ALPs signals at IACTs gamma-ray emitters and be sensitive tocurrent possible instruments. new phenomena that lie beyond the sensitivity of 3. Axions and Axion-like particles and their production is relatedlike to the Primakoff Sun. effect In inside this the paper, wecoupling, nucleus will a of consider photon astrophysical this can more objects, oscillate general just into group. an As ALP a and result vice-versa of in the an photon-ALP external magnetic field [ PoS(ICRC2019)735 (right) 12 − 10 Raquel Malta = γ a g (left) and 11 − 10 = γ a g 6 ] 14 Primary spectrum with 1 million photons simulated with three different slopes. AGN output for a 2.73 slope and coupling constant Some photon/ALP conversions that can occur since the emission of photons from a cosmological Figure 6: Since for the three slopes the results are similar, we choose only one to illustrate the gen- Here we present the particles output flux in each region of propagation as a result of the simu- with non-attenuated photons and ALPs created along the path. Figure 7: eral scenario. We can infer that the coupling constant makes all the difference in photon x ALP 5.1 AGN lated phenomena. First, the primary spectrum can be observed in figure 6. conversions that occurred in that specificin region. the The top final of spectrum containsradiation. the the atmosphere primary which photons will trigger gamma-ray air showers and produce5. Cherenkov Results Figure 5: Study of ALPs signals at IACTs source until its arrival on Earth. Adapted from [ PoS(ICRC2019)735 12 12 − − 10 10 = = γ γ a a g g Raquel Malta (left) and (left) and 11 11 − − we have a low conversion 10 10 = 12 = γ − γ a a g 10 g , we are close to a maximum, and = 11 γ − a g the composition is 97,8% photons and 10 lower then the AGN magnetic field, the 4 12 = − γ a 10 g = times higher than in intergalactic medium so for 7 γ 4 a g m) for 20 10 · 83 . 2 = z G and 5 − 10 = we can see a great conversion of ALP into photons, which increases the total photon B 11 Intergalactic output for a 2.73 slope and coupling constant Flux arriving in Earth for a 2.73 slope and coupling constant − 10 In this last region the magnetic field is 10 Since the intergalactic magnetic field is a factor 10 = γ a Figure 9: (right) with photons that could be detected and ALPs 5.3 Milky Way flux in comparison with the input(in flux. comparison The with flux arriving the on primary Earth is flux). 13,9% photons For and 86% ALP Figure 8: (right) showing the amount of photons and ALPs in comparison of photons arriving from AGN. g 2,12% with no significant changes in relation to the previous region. Study of ALPs signals at IACTs oscillation. Since the oscillationparameters probability ( is described by aso almost sine-squared all function, of using the AGN and photons the are output converted number into of ALPs. photons is For almost equal to the primary spectrum. 5.2 Intergalactic Medium oscillation is severely suppressed and therewe is can almost no notice conversion or pair reconversion.photons production is In decreased. process this region due to interaction with EBL and so the total number of PoS(ICRC2019)735 Raquel Malta oscillation is , no. 06, 006 2015/15897-1, 11 ◦ − 1606 10 = γ a g , 037 (2014 1406 8 , 69 (2015). (2013) 189. 2015 43 (2013) 3245. 432 [Cherenkov Telescope Array Consortium], “Science with the Cherenkov oscillation process is severely suppressed, and the number of photons arriving 12 [CTA Consortium], “Dark Matter and Fundamental Physics with the Cherenkov et al. − 10 et al. = γ a g (1977) 1440. 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Vaudrevange, Doro “The Quest for an a dominant effect and we have awould like boost to in acknowledge photon the flux São duefor Paulo to Research the a Foundation support. high (FAPESP), reconversion grant in n Milky Way. We References on Earth is almost the number produced in AGN. For coupling constant from Centaurus A, pair production is not aconstant dominant process and occurs in a low scale. For coupling Study of ALPs signals at IACTs 6. Conclusion