Arrival Directions Of Ultrahigh-energy Cosmic Rays Research Articles

Using the “least-deflected” subsamples of ultra-high energy cosmic rays to constrain source population(s)

Context. The source population(s) of ultra-high energy cosmic rays (UHECRs) with energies of ≥57 × 1018 eV (57 EeV) are still unknown and continue to be a subject of debate. The published arrival directions and energies of 303 UHECRs from the Pierre Auger Observatory and Telescope Array enable correlations with astronomical sources. However, deflections of UHECRs in the Galactic Magnetic Field (GMF) can be considerable, especially for heavy UHECR compositions. Aims. We aim to constrain the source(s) of UHECRs by focusing on the subset of UHECRs that experience minimal deflections by the Galactic magnetic field (GMF). Methods. We used Monte Carlo simulations of UHECR trajectories in a total of eight posited GMF models (and six UHECR compositions from H to Fe) to identify two subsamples of about 40 UHECRs. The H compositions of these subsamples suffer deflections of less than a few degrees in one (or most) of the GMFs. Both the total UHECR sample and the “least-deflected” (vs. the remaining “more-deflected”) subsamples of UHECRs were cross-correlated with catalogs of astronomical sources (at D ≲ 100 Mpc) and neutrino arrival directions. Results. For H compositions, the full sample of UHECRs is most closely correlated with Cen A, nearby (< 75 Mpc) radiogalaxies, and optically selected active galactic nuclei (AGNs); the least-deflected sub sample shows a most consistent correlation with nearby (D ≲ 25 Mpc) galaxies, although some GMF models show a preference for the IceCube muon-neutrino arrival detections. For oxygen compositions, the out-of-galaxy arrival directions of least-deflected UHECRs fall on the extragalactic plane (and thus close to nearby galaxies) in many GMFs. For Fe compositions, the out-of-galaxy UHECR arrival directions typically originate in a region ∼30 deg offset from Cen A, except in the case of the JF12 model; this offset can be decreased by re-scaling (by ∼50%) the magnitudes of the dipole and disk fields of the relevant GMFs.

Observational constraints on accelerators of ultra-high energy cosmic rays

We explore two generic hypotheses for tracing the sources of ultra-high energy cosmic rays (UHECRs) in the Universe: star formation rate density or stellar mass density. For each scenario, we infer a set of constraints for the emission mechanisms in the accelerators, for their energetics and for the abundances of elements at escape from their environments. From these constraints, we generate sky maps above 40 EeV expected from a catalog that comprises 410,761 galaxies out to 350 Mpc and provides a near-infrared flux-limited sample to map both stellar mass and star formation rate over the full sky. Considering a scenario of intermittent sources hosted in every galaxy, we show that the main features observed in arrival directions of UHECRs can in turn constrain the burst rate of the sources provided that magnetic-horizon effects are at play in clusters of galaxies.

2022 report from the Auger-TA working group on UHECR arrival directions

After over 60 years, the powerful engines that accelerate ultra-high-energy cosmic rays (UHECRs) to the formidable energies at which we observe them from Earth remain mysterious. Assuming standard physics, we expect UHECR sources to lie within the local Universe (up to a few hundred Mpc). The distribution of matter in the local Universe is anisotropic, and we expect this anisotropy to be imprinted on the distribution of UHECR arrival directions. Even though intervening intergalactic and Galactic magnetic fields deflect charged UHECRs and can distort these anisotropies, some amount of information on the distribution of the sources is preserved. In this proceedings contribution, we present the results of the joint Pierre Auger Observatory and Telescope Array searches for (a) the largest-scale anisotropies (the harmonic dipole and quadrupole) and (b) correlations with a sample of nearby starburst galaxies and the 2MRS catalogue tracing stellar mass within 250 Mpc. This analysis updates our previous results with the most recent available data, notably with the addition of 3 years of new Telescope Array data. The main finding is a correlation between the arrival directions of 12.1%−3.1%+4.5% of UHECRs detected with E ≥ 38 EeV by Auger or with E ≳ 49 EeV by TA and the positions of nearby starburst galaxies on a 15.1°−3.0°+4.6° angular scale, with a 4.7σ post-trial significance, up from 4.2σ obtained in our previous study.

Sensitivity of the combined fit of energy spectrum, shower depth distributions, and arrival directions at the Pierre Auger Observatory

The Pierre Auger Observatory measures several characteristics of ultra-high-energy cosmic rays (UHECRs), most importantly the energy spectrum, the distribution of maximum shower depths and the arrival directions. We use all three observables for a combined fit, in which parameters of possible UHECR sources can be constrained. The astrophy sical model used in the fit consists of homogeneo usly distributed background sources as well as an adaptable contribution from a nearby source population . For this, the catalogs of starburst galaxies and active galactic nuclei are used which show an indication for a correlation with the UHECR arrival directions . The signal fraction, as well as the size of a rigidity-dependent magn etic field blurring, are part of the fit parameters, along with the parameters describing the source emission. Tn this work, we present an astro-physical simulation containing an energy-dependent contribution from starburst galaxies, which simultaneously describes the energy spectrum, shower depth distributions, and arrival directions measured by the Pierre Auger Observatory. On this simulation, the discrimination power of the method regarding the differentiation of source catalogs is demonstrated, and the expected statistical significance of the result is investigated.

Search for Spatial Correlations of Neutrinos with Ultra-high-energy Cosmic Rays

For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ∼50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses have found a significant excess, and previously reported overfluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.

Towards extracting cosmic magnetic field structures from cosmic-ray arrival directions

We present a novel method to search for structures of coherently aligned patterns in ultra-high energy cosmic-ray arrival directions simultaneously across the entire sky. This method can be used to obtain information on the Galactic magnetic field, in particular the integrated component perpendicular to the line of sight, from cosmic-ray data only. Using a likelihood-ratio approach, neighboring cosmic rays are related by rotatable, elliptically shaped density distributions and the significance of their alignment with respect to circular distributions is evaluated. In this way, a vector field tangential to the celestial sphere is fitted which approximates the local deflections in cosmic magnetic fields if significant deflection structures are detected. The sensitivity of the method is evaluated on the basis of astrophysical simulations of the ultra-high energy cosmic-ray sky, where a discriminative power between isotropic and signal-induced scenarios is found.

Cosmic Rays and Ultra High Energy Cosmic Rays (UHECR), GZK (Greisen-Zatsepin-Kuzmin) cutoff, Deflection angle of high energy cosmic rays in the propagation through the galactic and extragalactic magnetic fields, Auger Surface Detector and the Monitoring Data, Measurement of the Lifetime of Muons and Pions and The Variant Mass for a Particle in a Gravitational Field and the Binary Stars: The

The Surface Detector of the Pierre Auger Observatory consists of 1600 water Cherenkov tanks sampling ground particles of air showers produced by energetic cosmic rays. Every water tank is equipped with three photomultipliers (PMTs). Every 7 minutes monitoring data are recorded from each surface detector to ensure that they are performing as intended and also to understand the detector behavior. The monitoring data set is used to study the evolution of parameters of the PMTs as a function of both time and temperature. The main objective of the monitoring data is to monitor the stability of the PMTs. In case there is abnormal behavior detected, an alarm entry is created in the database. The classification of the alarms into different categories, corresponding to the observed patterns of the PMT variables and the decision of the alarm level are subject of this work. It is also researched the photomultipliers parameters and the alarm creation with examples of it: the Free Disk and High PMT gain change Alarms using c++, root and mysql. For other hand, it is researched about the measurement of the lifetime of muons and pions theoretically, experimentally and with the application of Statistics for the uncertainties of the results. The results have high accuracy and in accordance with the values of the literature. In addition, it is to analyze theoretically the deflection angle of the high energy cosmic rays in the propagation through the galactic and extragalactic magnetic fields. It is used the magnetic force formula and the Larmor radius, trigonometry, and the tables for the values of the galactic and extragalactic magnetic field and the distances to the galactic and extragalactic sources. It is possible to observe from this analysis that the deflection angles are very small for the considered cases. Thus, UHECR arrival directions should point back to their sources in the sky. Besides, it is researched about the GZK (Greisen-Zatsepin-Kuzmin) cutoff. A sharp cutoff at approximately several times 1019 eV in the energy spectrum of the cosmic rays is expected due to the energy degradation of the cosmic rays through their interaction with photons of the microwave background radiation. It is known as the GZK (Greisen-Zatsepin-Kuzmin) cutoff. A nucleon with an initial energy above Eo=1020 eV lose about 1/5 of Eo (initial energy) in each interaction. Thus, a nucleon of initial energy above 1020 eV will reduce its energy to 6*1019 eV (GZK cutoff energy) after traveling a distance of approximately 50 Mpc. For other hand, Albert Einstein wrote in a research article: “Does the inertia of a body depend on its energy content?” (Ist die Tragheit eines Korpers von seimen Energienhalt abhangig?): “If a body emits energy E in the form of radiation, its mass decreases by E/c2”. Thus, Maxwell's theory shows that electromagnetic waves are radiated whenever charges accelerate as for example for the electron. Then, this electromagnetic radiation (photons) produces a decrease in the mass of the electron which is given by the formula of the Variant Mass for an Accelerated Charged Particle which was demonstrated by me at this research [34] and at the research of the Variant Mass of the Electron at the Atom. This is true for any type of radiation emitted: electromagnetic or gravitational energy which produce a decrease in the mass of the body. Therefore, other objective of this article is to demonstrate the discovered formula which describes exactly the variant mass for a particle which emits gravitational energy. An example of the effect of this Gravitational energy emission is the light deflection for the light passing close the Sun (gravitational redshift frequency) and the Perihelion Precession of Mercury. Thus, the results of the mass formula are of great relevance for Gravitational Interactions. The results are in accordance with the classic result for the emission of the total gravitational energy (bond total energy) for a particle orbiting a large Planet or Sun and for a Binary Star. It is in agreement with the experiment result and with the Theory of General Relativity.

Latest results and future prospects of the pierre auger observatory

The Pierre Auger Observatory is the largest observatory for the detection of ultra high energy cosmic rays (UHECRs). It allows a detailed measurement of the energy spectrum, the mass composition and the arrival directions of the primary cosmic rays with energies above 100 PeV. The data collected with the Pierre Auger Observatory show a suppression of the cosmic ray flux at energies above 40 EeV but the nature of this suppression is still unclear; according to theoretical prediction it could be caused by the interaction of cosmic rays with the CMB or by energy limitations of the cosmic rays sources. Another puzzle concerns the specific origin of UHECRs. Some indications can be obtained from studying the distribution of their arrival directions. Recently a dipole anisotropy has been observed which indicates that UHECRs have an extragalactic origin. I will present the recent results of the Pierre Auger Observatory about the energy spectrum, the mass composition and the arrival directions of UHECRs. I will also discuss the future prospects of the Observatory.

Bottom-up Acceleration of Ultra-high-energy Cosmic Rays in the Jets of Active Galactic Nuclei

Abstract It has been proposed that ultra-high-energy cosmic rays (UHECRs) up to 1020 eV could be produced in the relativistic jets of powerful active galactic nuclei (AGNs) via a one-shot reacceleration of lower-energy CRs produced in supernova remnants (the espresso mechanism). We test this theory by propagating particles in realistic 3D magnetohydrodynamic simulations of ultrarelativistic jets and find that about 10% of the CRs entering the jet are boosted by at least a factor of ∼Γ2 in energy, where Γ is the jet’s effective Lorentz factor, in agreement with the analytical expectations. Furthermore, about 0.1% of the CRs undergo two or more shots and achieve boosts well in excess of Γ2. Particles are typically accelerated up to the Hillas limit, suggesting that the espresso mechanism may promote galactic-like CRs to UHECRs even in AGN jets with moderate Lorentz factors, and not in powerful blazars only. Finally, we find that the sign of the toroidal magnetic field in the jet and in the cocoon controls the angular distribution of the reaccelerated particles, leading to a UHECR emission that may be either quasi-isotropic or beamed along the jet axis. These findings strongly support the idea that espresso acceleration in AGN jets can account for the UHECR spectra, chemical composition, and arrival directions measured by Auger and Telescope Array.

Search for a correlation between the UHECRs measured by the Pierre Auger Observatory and the Telescope Array and the neutrino candidate events from IceCube and ANTARES

High-energy neutrinos are expected to be produced by the interaction of accelerated particles near the acceleration sites. For this reason, it is intresting to search for correlation in the arrival directions of ultra–high energy cosmic rays (UHECRs) and HE neutrinos. We present here the results of a search for correlations between UHECR events measured by the Pierre Auger Observatory and Telescope Array and high-energy neutrino candidate events from IceCube and ANTARES. We perform a cross-correlation analysis, where the angular separation between the arrival directions of UHECRs and neutrinos is scanned. When comparing the results with the expectations from a null hypothesis contemplating an isotropic distribution of neutrinos or of UHECR we obtain post-trial p-values of the order of ~ 10 2.

Prospects of testing an UHECR single source class model with the K-EUSO orbital telescope

KLYPVE-EUSO (K-EUSO) is a planned orbital detector of ultra-high energy cosmic rays (UHECRs), which is to be deployed on board the International Space Station. K-EUSO is expected to have a uniform exposure over the celestial sphere and register from 120 to 500 UHECRs at energies above 57 EeV in a 2-year mission. We employed the TransportCR and CRPropa 3 packages to estimate prospects of testing a minimal single source class model for extragalactic cosmic rays and neutrinos by Kachelrieß, Kalashev, Ostapchenko and Semikoz (2017) with K-EUSO in terms of the large-scale anisotropy. Nearby active galactic nuclei Centaurus A, M82, NGC 253, M87 and Fornax A were considered as possible sources of UHECRs. We demonstrate that an observation of more than 200 events will allow testing predictions of the model with a high confidence level providing the fraction of events arriving from any of the sources is ^10-15%, with a smaller contribution for larger samples. These numbers agree with theoretical expectations of a possible contribution of a single source in the UHECR flux. Thus, K-EUSO can provide good opportunities for verifying the minimal model basing on an analysis of the large-scale anisotropy of arrival directions of UHECRs.

Acceleration of ultrahigh-energy cosmic rays in starburst superwinds

The sources of ultrahigh-energy cosmic rays (UHECRs) have been stubbornly elusive. However, the latest report of the Pierre Auger Observatory provides a compelling indication for a possible correlation between the arrival directions of UHECRs and nearby starburst galaxies. We argue that if starbursts are sources of UHECRs, then particle acceleration in the large-scale terminal shock of the superwind that flows from the starburst engine represents the best known concept model in the market. We investigate new constraints on the model and readjust free parameters accordingly. We show that UHECR acceleration above about $1{0}^{11}\text{ }\text{ }\mathrm{GeV}$ remains consistent with observation. We also show that the model could accommodate hard source spectra as required by Auger data. We demonstrate how neutrino emission can be used as a discriminator among acceleration models.

How isotropic can the UHECR flux be?

Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 10^4 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed. On the other hand, the distribution of matter in the nearby Universe -- and, therefore, presumably also that of UHECR sources -- is not homogeneous. This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture. In this work, we investigate quantitatively this apparent inconsistency. To this end we study observables sensitive to UHECR source inhomogeneities but robust to uncertainties on magnetic fields and the UHECR mass composition. We show, in a rather model-independent way, that if the source distribution tracks the overall matter distribution, the arrival directions at energies above 30 EeV should exhibit a sizeable dipole and quadrupole anisotropy, detectable by UHECR observatories in the very near future. Were it not the case, one would have to seriously reconsider the present understanding of cosmic magnetic fields and/or the UHECR composition. Also, we show that the lack of a strong quadrupole moment above 10 EeV in the current data already disfavours a pure proton composition, and that in the very near future measurements of the dipole and quadrupole moment above 60 EeV will be able to provide evidence about the UHECR mass composition at those energies.

Constraints on Physical Conditions for the Acceleration on Ultra-high-energy Cosmic Rays in Nearby Active Galactic Nuclei (AGNs) Observed with the Fermi Large Area Telescope

Abstract We investigated the possibility of acceleration of ultra-high-energy cosmic rays (UHECRs) in nearby active galactic nuclei (AGNs) using archival multi-wavelength observational data, and then we constrained their physical conditions, i.e., the luminosity of the synchrotron radiation and the size of the acceleration site. First, we investigated the spatial correlation between the arrival directions of UHECRs and the positions of nearby AGNs in the Fermi third gamma-ray source catalog. We selected 27 AGNs as candidates of accelerators of UHECRs. Then, we evaluated the physical conditions in the acceleration regions of these AGNs via the Pe’er and Loeb method, which uses the peak luminosity of synchrotron radiation and the peak flux ratio of inverse Compton scattering to synchrotron radiation. From the evaluation, we found that six AGNs have the ability to accelerate ultra-high-energy (UHE) protons in the AGN cores. Furthermore, we found that the minimum acceleration size must be more than a few kpc for acceleration of UHE protons in the AGN lobes.

Roadmap for searching cosmic rays correlated with the extraterrestrial neutrinos seen at IceCube

We have built regions in a Sky map where it should be expected the arrival of 120 EeV ultrahigh energy cosmic rays (UHECR) directionally correlated with the latest astrophysical neutrino tracks observed at IceCube, which are taken as point sources. In order to calculate these arrival directions we have considered contributions to the cosmic rays deflections originated by the galactic and the extragalactic magnetic field, and a UHECR composition compatible with the current expectations. We have used the Jansson-Farrar JF12 model for the Galactic magnetic field and an extragalactic magnetic field strength of 1nG and coherence length of 1Mpc. We observe that the regions outside of the Galactic plane are more strongly correlated with the neutrino tracks than those adjacent to or in it, with the former regions being good candidates to search for excesses, or anisotropies, in the UHECR flux. Additionally, we have focused, as an example, on the region of 150 EeV UHECR arrival directions correlated with the IceCube event 37 located at $(l,b)=(-137.1^\circ,65.8^\circ)$ in the Northern Hemisphere, far away from the Galactic plane, obtaining an angular size $\sim 5^\circ$, being $\sim 3^\circ$ for 200 EeV, and $\sim 8^\circ$ for 120 EeV. The results presented in this paper represent a useful UHECR excess search Sky map guide.

Angular correlation of cosmic neutrinos with ultrahigh-energy cosmic rays and implications for their sources

Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy 0≳ 3 TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at 0>6 EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrinos are correlated with 0≥ 10 EeV UHECR arrival directions at confidence level ≈ 90%. The strength of the correlation decreases with decreasing UHECR energy and no correlation exists at energy 0∼ 6 EeV . A search in astrophysical databases within 3̂ of the arrival directions of UHECRs with energy 0≥ 10 EeV, that are correlated with the IceCube cosmic neutrinos, resulted in 18 sources from the Swift-BAT X-ray catalog with redshift z≤ 0.06. We also found 3 objects in the Kühr catalog of radio sources using the same criteria. The sources are dominantly Seyfert galaxies with Cygnus A being the most prominent member. We calculate the required neutrino and UHECR fluxes to produce the observed correlated events, and estimate the corresponding neutrino luminosity (25 TeV–2.2 PeV) and cosmic-ray luminosity (500 TeV–180 EeV), assuming the sources are the ones we found in the Swift-BAT and Kühr catalogs. We compare these luminosities with the X-ray luminosity of the corresponding sources and discuss possibilities of accelerating protons to 0≳ 10 EeV and produce neutrinos in these sources.

Simulations for a next-generation UHECR observatory

We explore the potential of a future, ultra-high energy cosmic ray (UHECR) experiment, that is able to overcome the limitation of low statistics, to detect anisotropy in the arrival directions of UHECRs. We concentrate on the lower energy range of future instruments (E≳ 50 EeV), where, if the UHECR source number density is not too low, the sources should be numerous enough to imprint a clustering pattern in the sky, and thus possibly in the UHECR arrival directions. Under these limits, the anisotropy signal should be dominated by the clustering of astrophysical sources per se in the large-scale structures, and not the clustering of events around individual sources. We study the potential for a statistical discrimination between different astrophysical models which we parametrise by the number density of UHECR sources, the possible bias of the UHECR accelerators with respect to the galaxy distribution, and the unknown fraction of UHECRs that have been deflected by large angles. We demonstrate that an order-of-magnitude increase in statistics would allow to discriminate between a variety of astrophysical models, provided that a sub-sample of light elements can be extracted, and that it represents a fraction ≳ 70% of the overall flux, sensitive to the UHECR source number density. Discrimination should be possible even without knowledge of the composition of the UHECRs, as long as the data are proton-dominated. We find that an anisotropy at the 99.7% level should be detectable when the number of detected events exceeds 2000 beyond 50 EeV, as long as the composition is proton dominated, and the number density of UHECR sources is relatively high, n̄ ⩾ 10−3 Mpc−3. If the UHECR sources are strongly biased relative to the galaxy distribution, as are for example galaxy clusters, in which the sources might be embedded, an anisotropy at the 99.7% level should be detectable once the number of detected events exceeds 1000, if the fraction of protons at the highest energies is ≳ 60%.

A Bayesian self-clustering analysis of the highest energy cosmic rays detected by the Pierre Auger Observatory

Cosmic rays (CRs) are protons and atomic nuclei that flow into our Solar system and reach the Earth with energies of up to ~10^21 eV. The sources of ultra-high energy cosmic rays (UHECRs) with E >~ 10^19 eV remain unknown, although there are theoretical reasons to think that at least some come from active galactic nuclei (AGNs). One way to assess the different hypotheses is by analysing the arrival directions of UHECRs, in particular their self-clustering. We have developed a fully Bayesian approach to analyzing the self-clustering of points on the sphere, which we apply to the UHECR arrival directions. The analysis is based on a multi-step approach that enables the application of Bayesian model comparison to cases with weak prior information. We have applied this approach to the 69 highest energy events recorded by the Pierre Auger Observatory (PAO), which is the largest current UHECR data set. We do not detect self-clustering, but simulations show that this is consistent with the AGN-sourced model for a data set of this size. Data sets of several hundred UHECRs would be sufficient to detect clustering in the AGN model. Samples of this magnitude are expected to be produced by future experiments, such as the Japanese Experiment Module Extreme Universe Space Observatory (JEM-EUSO).

Using spherical wavelets to search for magnetically-induced alignment in the arrival directions of ultra-high energy cosmic rays

Due to the action of the intervening cosmic magnetic fields, ultra-high energy cosmic rays (UHECRs) can be deflected in such a way as to create clustered energy-ordered filamentary structures in the arrival direction of these particles, the so-called multiplets. In this work we propose a new method based on the spherical wavelet transform to identify multiplets in sky maps containing arrival directions of UHECRs. The method is illustrated in simulations with a multiplet embedded in isotropic backgrounds with different numbers of events. The efficiency of the algorithm is assessed through the calculation of Type I and II errors.

CORRELATIONS OF THE ARRIVAL DIRECTIONS OF ULTRA-HIGH ENERGY COSMIC RAYS WITH EXTRAGALACTIC OBJECTS AS OBSERVED BY THE TELESCOPE ARRAY EXPERIMENT

We search for correlations between positions of extragalactic objects and arrival directions of Ultra-High Energy Cosmic Rays (UHECRs) with primary energy $E \ge 40$ EeV as observed by the surface detector array of the Telescope Array (TA) experiment during the first 40 months of operation. We examined several public astronomical object catalogs, including the Veron-Cetty and Veron catalog of active galactic nuclei. We counted the number of TA events correlated with objects in each catalog as a function of three parameters: the maximum angular separation between a TA event and an object, the minimum energy of the events, and the maximum redshift of the objects. We determine combinations of these parameters which maximize the correlations, and calculate the chance probabilities of having the same levels of correlations from an isotropic distribution of UHECR arrival directions. No statistically significant correlations are found when penalties for scanning over the above parameters and for searching in several catalogs are taken into account.