Autoreferat - Summary of professional accomplishments

Transcription

1 Autoreferat - Summary of professional accomplishments 1. Name: Jan Pękala 2. Held diploma, scientific/academic degrees: 2007 Doctor of Philosophy degree in Physics; Institute of Nuclear Physics Polish Academy of Sciences, Kraków; supervisor: prof. dr hab. Henryk Wilczyński; PhD thesis (with distinction): Atmospheric scattering of light emitted by extensive air showers Master of Science degree in Physics, Jagiellonian University, Kraków, Faculty of Physics, Astronomy and Applied Computer Science, specialty: astrophysics; supervisor: prof. dr hab. Henryk Wilczyński; graduate dissertation (with distinction): Analiza podwójnych rozproszeń fotonów czerenkowskich w symulacjach wielkich pęków atmosferycznych ( Analysis of double scattering of Cherenkov photons in the simulations of extensive air showers ). 3. Informations concerning previous employment in scientific institutions: since 2008: research associate; Institute of Nuclear Physics Polish Academy of Sciences, Kraków; Department of Cosmic Rays 2007: physicist; Institute of Nuclear Physics Polish Academy of Sciences, Kraków; Department of Cosmic Rays : International PhD Studies; Institute of Nuclear Physics Polish Academy of Sciences, Kraków : internship; Institute of Nuclear Physics, Kraków; Laboratory of Cosmic Ray Physics 4. Indication of the scientific achievement pursuant to the art. 16 p. 2 of the act on the academic degrees and the academic title as well as on the degrees and the title within the scope of art (Dz. U. nr 65, poz. 595 ze zm.): a) title of the scientific achievement monograph titled: Efekty systematyczne w obserwacjach promieni kosmicznych najwyższych energii wielokrotne rozpraszanie światła ( Systematic effects in observations of the highest energy cosmic rays multiple scattering of light ) 1

2 b) author: Jan Pękala; published by Institute of Nuclear Physics Polish Academy of Sciences, Kraków 2016, ISBN c) discussion of the scientific aim, of the achieved results and of a possible use of the work specified above The origin of the highest energy cosmic rays is one of the greatest unsolved puzzles of astrophysics. Observations of particles reaching Earth from deep space, conducted for over a hundred years, revealed the presence of a small flux of particles with very high energies, with the spectrum reaching beyond ev. In the last few decades numerous experiments have been made, designed to determine with the best possible accuracy the properties of cosmic rays at the highest energies: the shape of the spectrum, the composition of primary particles, the directions of arrival. Observation techniques were perfected, allowing for more precise measurements of the properties of cosmic rays. At the same time also theoretical work was conducted, aimed at finding explanations how such energetic particles can be produced. Over the past several years a considerable progress in the studies of cosmic rays at the highest energies has been achieved, especially due to the data collected in the largest of the experiments to date the Pierre Auger Observatory. However, these studies can not be considered as finished to explain the origin of the most energetic particles further work is needed, which will allow to collect even more data, with even more precision. A big obstacle in the observations of cosmic rays of ultra-high energy is the very small flux of particles: above ev, it is only about one particle per km 2 per year, and it decreases even further with increasing energy. It is therefore necessary to make long observations, covering large areas. Infeasible is the detection of the primary particles that arrive at Earth using detectors placed above the atmosphere. Instead, observed are cascades of secondary particles produced in Earth s atmosphere, which are called extensive air showers. As the result of a series of interactions with the molecules of air, a cascade of energetic particles arises (the most numerous among them are the electrons/positrons, photons, muons), moving through the atmosphere close to the speed of light. Air showers induced by the primary particles with the highest energies at the maximum of their development may count many billions of secondary particles. After passing the whole depth of the atmosphere, these particles fall to the surface, where they can be registered with a network of detectors. The collected information about the density of particles on the surface of the earth, the shape of their distribution and the arrival time allow to determine the properties of the primary particles. Particles of an air shower excite air molecules on their way through the atmosphere, leading to emission of fluorescent light in the near ultraviolet. This light 2

3 can be recorded using optical detectors. The amount of emitted light is locally proportional to the size of the air shower, which allows measuring the profile of its development along a substantial portion of its path through the atmosphere. The shape of the longitudinal profile of the air shower development is known (the Gaisser-Hillas profile), so it is possible to complete the measured profile with the parts not covered by the observation, which eventually enables a very precise calculation of the total energy of the air shower. The fluorescence light induced by the air shower is weak, so the observations are possible only during dark, moonless night. The observation of a light source comparable to a small light bulb, moving at the speed of light at a distance of even tens of kilometers, requires the use of highly sensitive detectors. Also, the analysis of the collected observational data must be very precise. To correctly calculate the light intensity at the source based on the measured signal, it is necessary to accurately take into account both the properties and the momentary state of the detectors, as well as the atmospheric conditions prevailing during the observation. It also requires a detailed analysis of all phenomena which may affect the propagation of light in the atmosphere neglecting any of them will result in the systematic inaccuracy of the final results of the experiment. Multiple scattering of light in the observations of air showers. The main topic of my research was the investigation of the phenomenon of multiple scattering of light in the atmosphere and its impact on the results of observations of extensive air showers. Light on its path through the atmosphere is scattered, on the molecules or aerosols. According to the distance and density of the traversed layers of the atmosphere, the light is attenuated on the way to the detector this factor was of course always taken into account in the analysis of air shower observations with the fluorescence method. But the effects associated with the multiple scattering of light, which may lead to an increase of the recorded signal, were neglected. In the observed signal the most significant part indeed comes from the light traveling in a straight line from the air shower to the detector but it is worth noting that this is only a small fraction of all the emitted photons. Fluorescence light induced by the passing of the air shower is emitted in all directions, and on its way through the atmosphere it gets scattered. As a result of these scatterings, the propagation directions of photons are randomly changed, and a small fraction of the scattered photons are deflected towards the detector. Photons may undergo multiple scatterings, which may also lead to their registration in the detector. It thus appears that the scattering in the atmosphere leads not only to the attenuation of the direct beam of light, but also to some amplification of the signal measured 3

4 in the fluorescence detectors. Neglecting this contribution in the reconstruction of the air shower properties causes an overestimation of the signal from the other contributions, which in turn causes a systematic overestimation of the calculated value of the total energy of the air shower, and also a small change of the shape of the air shower longitudinal profile. The only contribution to the recorded signal from the light scattering in the atmosphere, which until recently was considered in the analysis of air shower observation, was the contribution coming from the single scattering of Cherenkov photons. The Cherenkov emission is strongly collimated around the axis, which leads to the accumulation of a light beam, accompanying the air shower. Scattering of photons of the beam is a source of significant contribution to the observed signal. Collimated emission and similar speed of photons and air shower, lead to the fact that the scattered light is observed from the same area of the sky as direct fluorescence light, which also makes it easier to include this contribution into the analysis of observational data. In contrary, determination of the contribution from the scattered fluorescence light, as well as from multiply scattered Cherenkov light, is more difficult and requires more complex analyses. The phenomenon of multiple scattering of light and its impact on the results of observations performed with the fluorescence detectors was the subject of my PhD thesis, as well as the topic of later analyses, aimed at the most accurate examination of this phenomenon and its impact on observations of different kinds. I have investigated the multiple light scattering effect using Monte Carlo simulation. As the starting point for this work I used the Hybrid_fadc program, developed for the Fly s Eye and HiRes experiments, which was used to perform simulations of air shower observation (B. Dawson et al., Astropart. Phys., 5 (1996) 239). In the original version of the program the fluorescence and Cherenkov emission is calculated in successive moments of the air shower development. Based on this, the signal recorded in the detector is calculated, accounting for the direct light, and single scattering of Cherenkov light. in the framework of this program, I developed a new algorithm that allows to perform simulations of multiple scattering of light in the atmosphere, and to calculate the amount of the additional signal recorded in the detector. Because of the large number of photons emitted during the air shower development it is not feasible within a reasonable time to make simulations, which would separately track all the photons. Therefore fluorescence and Cherenkov light emitted at various points is divided into packets their number can be changed, so as to obtain satisfactory accuracy of the final results and an acceptable running time of the simulation. For each packet a random direction is chosen, and then along this direction a random distance to the point where the light gets scattered. When calculating the point of scattering, the density of the traversed atmosphere is taken into account. After determining the point of scattering it is 4

5 possible to calculate what fraction of the packet is directed towards the detector in the result of this scattering. According to the route traveled, the time of arrival of the pulse of scattered light at the detector is calculated, as well as its location in the sky these signals are delayed relative to the direct light, and may also be distant from the observed position of the air shower. The next step is the assumption that the remaining photons of the packet, other than the fraction directed towards the detector, get scatter and propagate together in one direction. This makes it possible to iteratively calculate successive lengths of the light path in the atmosphere and the corresponding contributions from multiple light scattering to the observed signal. As a result of the full simulation run, the information about all the pulses of scattered light reaching the detector is obtained: their size, time of arrival, the direction in the sky. To avoid generating very large files of output data, already during the execution of the program the preprocessing of results is carried out distributions of intensity of the scattered light are calculated in the subsequent moments of observation, and the full information about the registered pulses is stored only for a few selected, short periods of air shower development. This data is used for further analyses of the multiple scattering effect. My procedures for simulations of the multiple scattering of light have been developed so as to enable the study of this effect in the conditions as close as possible to the actual observations of air showers. Included was the light spectrum, angular distributions of emission and of scattering of light, atmospheric aerosols and molecular distributions. Simulations can be performed assuming the average expected conditions, it is also possible to use different models of the state of atmosphere to investigate the effect of the possible variations of conditions on the results of observations. The program also enables simulating the air showers with different inclinations and distances from the detector, which allows to determine the size of the signal from the scattered light under different conditions. The first application for this program was the analysis of the significance of the multiple scattering effect in observations of extensive air showers. In such a situation, the most important is the light from the relatively small area of the sky in the vicinity of the observed momentary position of the air shower, reaching the detector simultaneously with the direct light, which constitutes the dominating part of the recorded signal. Such was the premise for the analysis of the simulation results. The scattered light arriving at the detector has a very wide distribution, covering a large part of the sky, but the contributions recorded by pixels distant from the position of the air shower do not affect the results of observations. Difference between distributions of the direct light and the scattered light means that the contribution of the latter depends on the solid angle from which the signal is collected. To determine the size of the signal from the scattered light I made a set of 5

6 simulations covering a wide range of different observational conditions: different air shower energies, their inclinations and distances from the detector, different molecular models of the atmosphere, different concentrations and distributions of aerosols. Tested were various models of angular distribution of Cherenkov emission and detector position above sea level. For the calculation of the contribution from scattered light it is useful to calculate its size relatively to the direct signal this relative contribution does not depend on the air shower energy. The analysis of the simulation results led to the conclusion that the scattered light signal depends on a number of variables characterizing the observation conditions. Comparing the amount of light coming from a circular area of different sizes, centered on the position of the air shower, showed that the additional contribution is proportional to the radius of the area. For a fixed size of the area of the sky from which the signal is collected, the additional contribution from the scattered light increases with the distance between the air shower and the detector, and decreases with the height of the observed point. Also important is the transparency of the air if significant amounts of aerosols are present in the atmosphere, one should expect a larger contribution from the scattered light than for a purely molecular atmosphere. Expressing the distance from the observed point in dimensionless units of optical depth helps in taking into account the air transparency and its impact on the recorded signal from the scattered light. Other variables, such as the air shower age or location of the detector proved to have no significant effect on the simulation results. The main aim of this work was to determine the contribution of scattered light to the measured signal in such a way, as to allow accounting for this effect in the analyses of the air shower observations. Making time-consuming simulations is not feasible when dealing with large sets of observational data, therefore a parameterization of the simulation results is needed, which would enable fast calculation of a correction for the multiply scattered light. Therefore I made an analysis of the results obtained from a set of simulations, that covered the range of conditions characterizing real observation of air shower. The regularities found in the results allowed to construct a parameterization of the relative contribution of the scattered light as a function of the variables describing the basic conditions of observation: altitude above the ground of the air shower at the time of observation, the optical depth of the path from the air shower to the detector, size of the area of the sky from which the signal is collected. Beside my analysis of the contribution of scattered light to the observed air shower signal, available are also the results of the work of other authors (M.D. Roberts, J. Phys. G, 31 (2005) 1291; M. Giller, A. Śmiałkowski, Astropart. Phys., 6

7 36 (2012) 166). These works were done assuming some simplifications (limitations of the geometry of observation, not taking into account the multiple scattering of Cherenkov light), but they give the opportunity to verify the results. After selecting the parts of my simulation results so that they correspond best to the assumptions made in these works, it is possible to compare the results obtained independently, using different methods. These results were found to agree satisfactorily this increases the confidence that they are accurate. Parameterization obtained in my work has been incorporated into the Offline software, which is the standard tool in the analyses of the data collected in the Pierre Auger Observatory. This function is universal and can also be applied in the reconstructions of air shower properties in other experiments that use the fluorescence technique of observation. Point spread function. The analysis described above was mainly meant to determine the size of the correction that should be applied to take into account the effect of multiple scattering of light in the observations of air showers. For this purpose it was necessary to make simulations of air shower development and of the light emission along its entire path through the atmosphere. The signal from scattered light, that is recorded simultaneously with the direct light at any time of observation, consist of contributions from the light emitted in all earlier phases of the air shower development. Taking into account the contribution of multiply scattered light is necessary not only in the procedures that are used to reconstruct the properties of the observed air shower, but also in the software dedicated to simulations of air shower detection. These simulations are important for understanding the observed phenomena and improving the methods of data analysis. Performing combined chains of simulations and reconstructions, and then comparing the input data with the end results, helps to verify the accuracy of the algorithms used. Parameterization of scattered light contribution to the image of the air shower, which is a sum of contributions originating from all the previous moments of air shower development and arriving at the detector with different delays, can not be used in the simulations. Instead, a description of the scattered light distribution would be useful, when the light is emitted by a point source thus the effect of the multiple scattering could be correctly accounted for in the algorithms of air shower detection simulations. To perform the simulations of light emission from a point source and of the following atmospheric scattering of light, I have prepared a new version of the program. As the results of a simulation we get the distributions of light, as observed at the detector, as a function of time. For the air shower observation the 7

8 position on the sky of the region of interest is well defined at successive moments, therefore it is sufficient to analyze the incoming signal within a relatively small solid angle. However, when analyzing the scattered light from a point source, it is necessary to examine the distribution on much larger areas of the sky it must be remembered that the light source can move, and so the signal observed at a certain point consists of contributions from the light emitted in different places, and observed fragment of the sky may be distant from the original point of emission. The scattered light arrives at the detector delayed with respect to the direct light, so to determine the total observed signal one should include contributions from the light emitted at different times. Therefore, the distributions of scattered light must be determined for a longer period of time, corresponding to the observations carried out with different delays with respect to the time of emission. I made a set of simulations covering a wide range of positions of the light source (the distance from the detector, altitude above the ground), and assuming different air transparency, corresponding to different concentrations of aerosols in the atmosphere. Additionally, I studied the effect of different angular distributions of scattering on aerosols (aerosol phase function) on the simulation results. Monitoring of the properties of aerosols carried out in the Pierre Auger Observatory revealed that significant variation of these properties can occur. Large changes of the phase function, associated with changes in the composition of the aerosols, are relatively rare, but the simulations showed that they can have a significant impact on the contribution from multiply scattered light to the recorded signal during these periods. Analysis of the simulation results allowed me to determine the regularities occurring in the distributions of light observed in different conditions. This allowed me to develop parameterizations describing the distributions of scattered light on the sky at different time intervals. For the calculation of the additional signal of the scattered light it is sufficient to specify some basic parameters: the altitude of the point of emission above the ground, the optical depth of the path from the point of emission to the detector, angular distance between the observed area and the position of the emission point on the sky, time delay, aerosol phase function. To enable the use of this parameterization in the analyses performed in the Pierre Auger Observatory, I created an appropriate algorithm and included it into the software package Offline. Based on the information about the direct light, generated in the earlier part of the simulation, the additional contribution from the scattered light is calculated. The user is able to set the solid angle, as well as the length of the time period, from which the scattered light is accounted for in the procedure. 8

9 Investigating the halo effect. I used the program for simulation of multiple scattering of light emitted by a point source also for a separate analysis, intended for application in the studies of the calibration measurements of fluorescence detectors at the Pierre Auger Observatory. Analyses of the data collected by the detectors revealed a weak signal recorded in pixels distant from the observed position of the air shower. Attempts have been made to explain the mechanisms responsible for the formation of this large halo. Considered were possible scatterings of light on different elements of the detectors, as well as atmospheric effects. Multiple scattering is expected to distribute a small fraction of the light over large areas of the sky, therefore it must also, at least in part, contribute to the formation of such halo. One part of the studies of this halo effect were measurements performed with the use of light sources flown on remotely controlled flying devices (blimps, drones). For the most accurate determination of the signal produced by the multiple scattering of light, I made a set of simulations that imitated the conditions during these measurements as much as possible, taking into account the location and the characteristics of the light source. The measurements were performed at distances much smaller than typical observation of air showers. In agreement with the results of the previous simulations, the scattered light signal at such a short distance is very small, not sufficient to completely explain the observed halo. Using these simulations I have also performed a detailed analysis of the symmetry of the scattered light images. For the air shower observations done over large areas of the sky, comparable with the field of view of the detector, the distribution of scattered light exhibits a deviations from the central symmetry in the up-down direction. However, in smaller areas of the sky, which are considered in the analysis of observational data, the asymmetry is negligible. For very small distances from the light source, such as in the mentioned calibration measurements, the asymmetry is practically immeasurable, even for observation of large parts of the sky. Monitoring of aerosols using laser beams. For the correct interpretation of the data collected with the fluorescence detectors, a precise knowledge of the atmospheric conditions over the area of the observatory is necessary. It is particularly important to control the transparency of the air, which may be a subject to significant and rapid changes due to changes in the concentration and distribution of aerosols. Therefore, it is necessary to have the equipment that can monitor the state of the atmosphere during the operations of the detectors. One of the systems used in the Pierre Auger Observatory 9

10 consists of two stations that emit laser pulses that pass through the field of view of the fluorescence detectors, but not aimed directly at the telescopes. The laser light on its way gets scattered, and this scattered light is recorded by the detectors. With the distance and the intensity of the laser beam known, the analysis of the observed signals enables calculating the transparency of the air in the area between laser stations and individual detectors. Precise determinations and monitoring the changes of atmospheric conditions is critically important, because this information is the basis for determination of the energy of the air showers. In previous analyses only single scattering of laser light was included, and the additional contributions resulting from two and more scatterings were assumed to be insignificant. To determine the size of this additional contribution I made an analysis of the scattering of light emitted by a ground-based laser source. I developed a new version of the program to simulate the scattering of light, corresponding to the modified setup: the light source is on the ground and emits upwards pulses of collimated light. The distance from the detectors and wavelength of the emitted light were set in the simulations correspondingly to the real measurement setup. Then I made a set of simulations, assuming different concentrations and distributions of aerosols in the atmosphere. As a reference I take the signal observed in the detector, that comes from the single scattering of light, and its observed location in the sky. Because the laser beam is collimated, the detector records the singly scattered light only in a narrow band of the field of view. It is therefore possible to accurately determine which pixels of the detector observe the projected path of the laser pulse. Knowing this, it is easy to reject the background of scattered light that comes from distant parts of the sky. However, the simulations showed that even in a small area in the center of the image (which can not be smaller than the size of the detector pixel) the contribution from multiply scattered light can be significant. The size of this contribution depends on the altitude of the observed point and low over the horizon, especially when there are significant concentrations of aerosols in the air, it may even exceed 10% of the signal from the singly scattered light. These results of the simulations showed that the additional contribution of multiple scattering should be included in the analysis of laser measurements. Not accounting for this effect implies that the total observed signal from scattered light is assigned to the single scattering of light. Calculations carried out under this assumption lead to a systematic overestimation of the measured aerosol concentration in the air. This in turn affects the results of all analyses of air shower observations with fluorescence detectors, for example reconstructed energies are systematically overestimated. Currently, scientists are working on the implementation of the multiple scattering effect to the analysis of laser measurements. The results presented in the monograph were published in the articles A18 and A54, and in the internal reports of the Pierre Auger Observatory B34, B35, B36 10

11 and B37. I also presented these results at conferences: B2, B10, B17, B18, B23 (full references below, in the lists of publications in sections 5.1 and 5.2). 5. Discussion of other scientific achievements. Control software for the FRAM device. Among other works I have done, the most closely related to the subject of the monograph was my participation in preparation of a device for the monitoring of the air transparency called (F/ph)otometric Robotic Atmospheric Monitor (FRAM). I have done the work associated with this device after completing my doctorate. As I mentioned above, the measurement of the atmospheric state is extremely important for the proper analysis of the observational data collected with the fluorescence detectors. Therefore, a number of devices are used at the Pierre Auger Observatory, using several different measurement techniques, to precisely measure the atmospheric state during the operations of the detectors. Most of these devices emit light, which is measured directly or after scattering. Unfortunately, the beams of light passing through the field of view of the fluorescence detectors interfere with their operation. It is therefore necessary to reduce the area of the sky where the measurements are being done, or to shut down temporarily a part of the detectors. Considerations of this problem led to a question: could the measurements of air transparency be done using passive devices, that do not emit light? To check the usefulness of such an approach, the Czech members of the Pierre Auger Collaboration built a robotic telescope FRAM. With my participation the software that controls the operation of this device was prepared. With the use of a photometer precise measurements of the brightness of selected stars are performed, and also images of large areas of the sky are taken. Comparison of the observation results with the catalog brightness of stars allows us to determine the attenuation of light due to the presence of aerosols in the air. The measurement through the entire depth of the atmosphere allows to calculate the total amount of aerosols; the distribution of aerosols can not be determined based on this information alone. However, thanks to the fact that this device in no way interferes with operation of the fluorescence detector, it can support other monitoring systems and perform measurements over the entire sky. In addition to a periodical review of the sky, FRAM also performs measurements of the air transparency along the observed tracks of selected air showers, immediately after their registration in the detectors (so called shoot-the-shower procedure). I have developed an algorithm and a software module for the control 11

12 of the device during these measurements. Upon receiving the information about passing of an air shower, which also includes the information about its direction, calculated is the projection of this direction on the celestial sphere, as it is observed from the point of view of FRAM. At the angular distances determined by the size of the field of view of the device, images of the sky are taken, covering the air shower track between the elevations of 30 and 0 over the horizon, which correspond to the limits of the field of view of the fluorescence detectors. In addition, an image is taken in the direction from which the primary particle came. These observations enable to determine (as a function of the elevation above the horizon) the concentration of aerosols in the area, which the air shower traversed. If there are clouds in this area, it is easy to detect them using these images of the sky. Developing the models of the molecular atmosphere. Beside the monitoring of the air transparency, whose variation is mainly caused by the changes in the aerosol concentration, it is also important to know the state of the molecular part of the atmosphere. A group of scientists from the Institute of Nuclear Physics, with my participation, performed an analysis of the changes of the air density distribution, and their impact on the air shower observations. The air showers develops as a result of interactions of energetic particles with air matter, and so the rate at which air showers develop depends rather on the density of the traversed layers of atmosphere than on the traveled distance. Observations provide information about the air showers at different positions the atmospheric depth corresponding to these positions must be determined. For the correct interpretation of the observations it is therefore necessary to know the vertical profile of the air density. This has the greatest impact on the measurements of the depth of maximum, X max, where the air shower reaches the maximum of its development. Our analysis has shown that the variability of the atmosphere introduces significant differences in the observed properties of air showers, therefore using average atmospheric model is insufficient. On the basis of available measurements we have developed monthly atmospheric models for the area of the Pierre Auger Observatory, that allowed us to reduce the systematic uncertainty of the X max determination, which in turn strongly affects the results of the cosmic ray composition studies. I worked on this topic before the PhD, and the results were presented in the paper A7. Analysis of the air shower image. Also before my PhD I took part in the work of the Pierre Auger collaboration members from Kraków and Karlsruhe, that was done in order to describe the 12

13 image of air showers observed in the fluorescence detectors. The intensity of light induced by passing of an air shower depends on the concentration of charged particles, which is largest at the air shower axis, and decreases with the distance. Inevitable are the limitations associated with the detector sensitivity and with the background light, which means that the signal coming only from the central part of the air shower image will be registered; the signal from the remote parts is insufficient to trigger pixels. In order not to underestimate the size of the observed air shower, it is necessary to determine what fraction of the total signal falls into the pixels that do not trigger, and therefore is not recorded. To determine this, an analysis was made which provided a description of the distribution of light intensity over the air shower image. A parameterization of the light distribution was developed it is universal and can also be applied in other analyses. This parameterization is used in the standard analysis of the data from the fluorescence detectors of the Pierre Auger Observatory. These results were published in the papers A3 and A6. Identification of photons among the primary particles of cosmic rays. Also as a part of the collaboration of scientists from Kraków and Karlsruhe, I took part in the studies of the properties of air showers induced by photons. The study of the composition of the cosmic rays is an important and complex problem; it helps to verify the models of the origin of ultra-high energy cosmic rays. Some of the models, so called top-down models, postulate the existence of exotic particles, with masses or energies sufficiently high, so that when decaying they would produce the ultra-high energy cosmic rays. These models predict production of significant contribution of photons, therefore identification of photons among the ultra-high energy cosmic rays could provide evidence for the existence of particles beyond the Standard Model. Distinguishing the air showers induced by photons from those induced by protons and other atomic nuclei is only possible with the precise knowledge about the properties of air showers initiated by each of these types of particles. These properties can be determined with the help of computer simulation. All the phenomena that may influence the air shower development must be taken into account, as precisely as possible. One of the effects investigated in detail by our group, is the so called preshowering. Ultra-high energy photon arriving at Earth can be converted in the Earth s magnetic field into the electron-positron pair, and these particles on their further way to the atmosphere emit photons of synchrotron radiation. As a result, at the top of the atmosphere there is not one, but many particles. Each of them initiates cascades of secondary particles, which overlap. The preshowering significantly changes the properties of the observed air showers. The results of this work were published before the completion of my doctorate in A2, A4, A5 and A9. 13

14 Software for monitoring of the status of the Observatory. After my PhD I participated in the development of software used to monitor the status of the Pierre Auger Observatory. On the large area of the Observatory (3000 km 2 ) are distributed numerous and various devices: more than 1600 autonomous stations of the surface detector, 27 fluorescence telescopes in four locations, networks of underground muon detectors and of antennas recording the radio signal from air showers, a number of instruments dedicated to measurements of the atmospheric conditions over the Observatory. To assure proper operation of all these instruments, separate systems are required to provide reliable communication, collection and storage of data, and power supply to all the elements of the Observatory. Inevitably, random failures or changes of weather conditions will lead to situations, which require the intervention of experts or local technical staff. To maintain maximum efficiency of the Observatory, quick detection of irregularities in the operations of hardware and software is necessary. To this end, the software to monitor the status of the Observatory was developed. Using a web browser the members of the collaboration have access to the data collected on-line, presenting the status of the individual systems of the Observatory. It is possible to review the current status, as well as changes occurring in a selected period. Available is the information about the status of all key elements of the Observatory, as well as about the processes of the collection and transmission of data. I worked on the part of the system, that controls the quality of the collected data besides some irregularities that are easy to identify, like a shutdown of a device, there are also those that can be seen only in a review of the data collected by detectors and transmitted to the central database. The monitoring system includes a set of alarms, that helps to quickly identify the problems requiring attention. All these tools help keep the detectors in the best operating condition, necessary for efficient observations and for collecting high quality data. Microwave detection of air showers in the CROME experiment. Basic methods of air shower observation are the use of a network of surface detectors and the recording the fluorescence light using optical telescopes. In addition to perfecting these techniques, that have been proven in numerous experiments over the past decades, the scientist continue to seek for new methods of air shower observations. Recently, promising results have been obtained using antennas recording radio emission of air showers in the range of tens of MHz. A few years ago, laboratory measurements, performed on electron beams, gave reason to believe that the air showers should induce microwave emission, that would come from the bremsstrahlung radiation of electrons/positrons on molecules of air. The interest aroused by these results led to the several experiments, 14

15 dedicated to testing the feasibility of detection of this potential signal in the microwave range (MIDAS, AMBER, EASIER, CROME, TARA). The background, both cosmic and atmospheric, is very low in the spectral range of about a few gigahertz, and also good transparency of atmosphere would enable continuous observations. In addition, the technology developed for satellite communication in this frequency range causes that the construction of the detectors would be easy and inexpensive. One of the experiments, which investigated the potential capabilities of this technique was CROME. I was a member of the group that performed this experiment, and I took part in the analysis of the collected data. Detectors of this experiment were placed at the Karlsruhe Institute of Technology, which made it possible to use the data from the KASCADE-Grande air shower array. The array performed air shower observations in that area, and provided precise information about the air showers passing through the field of view of the detectors of CROME experiment. This independent timing information greatly facilitated the identification of the microwave signal among the noise. The observational data from the selected time intervals has been carefully examined. The analysis of the data revealed that the microwave signals were detected for about 30 air showers passing through the field of view of the antennas. Characteristic of these measurements is that the signals were registered only for the air showers landing close to the detectors, which means that the microwave emission is concentrated close to the air shower axis. Analysis of the observation geometry, and of the characteristics of the recorded signals (polarization, duration), suggests that this emission is most likely the result of the geomagnetic radiation and of the Askaryan effect. Air shower emission from these mechanisms is observed by the radio detectors in the range of tens of MHz this emission is suppressed at higher frequencies, but can be amplified in the directions close to the Cherenkov angle. The results of this analysis were published in paper A62. In all the other experiments dedicated to observation of the microwave emission only one signal from the air shower has been registered. These results, and especially the results of the CROME experiment, are a strong evidence against the existence of an intense, isotropic microwave emission from air showers. This means that the molecular bremsstrahlung radiation is not as significant as expected. Focused microwave emission, close to the air shower axis, makes observations difficult to achieve a high efficiency of air shower detection, a dense array of detectors would be needed, each covering with its field of view a large area of the sky. Also, the time compression, which occurs near the Cherenkov angle, would make the determination of the air shower properties much more difficult than for observations with the fluorescence detectors. This technique, however, has also advantages: low background and very good air transparency make very good conditions for microwave observation, which could be performed continuously. The 15

16 detectors operating at these wavelengths would be much easier and cheaper to build than optical telescopes used in the fluorescence observations. The future will show whether this technique will be pursued. Analysis of the dynamics of spiral galaxies. Also, after completing my PhD I took part in the work of a Kraków group of astrophysicists, that aimed to determine the dynamics and the mass distribution in spiral galaxies. For decades, scientists worked on a solution to the problem of rotation curves the measured orbital velocities of objects in the spiral galaxies are significantly higher than the values predicted based on the distribution of luminous matter. One approach to solving this puzzle is the disk model of spiral galaxies, without assumptions about the value of the ratio between the mass and the luminosity of a galaxy (so called mass-to-light ratio). For some galaxies, whose rotation curves are measured precisely in a wide range of distances from the center, one can perform a fit of the model to the observational data. The mass distribution resulting from this fit can be compared with the observed luminosity it turns out that the mass-to-light ratios calculated this way are small, in the range expected for galaxies composed of stars and clouds of gas and dust. Measurements of rotation curves are largely based on the observations of gas clouds. If the gas is at least partially ionized, its movement will depend not only on the mass distribution in the galaxy, but also on the magnetic field. It is therefore necessary to estimate what effect this may have on the results of observation. My work in these analyses was focused on the possible effects of the galactic magnetic fields. The results of this work have been published in A38 and A List of publications included in the Journal Citation Reports (JCR) Before doctorate: A1 J. Abraham, M. Aglietta, C. Aguirre et al. (Pierre Auger Collaboration), Properties and performance of the prototype instrument for the Pierre Auger Observatory, Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment 523 (2004) [I contributed to the papers A1, A8, A10-A17, A19-A37, A39-A45, A47-A53, A55-A58, A60, A61 and A63-A78 published by the Pierre Auger Collaboration by participation in the construction of the detector, development of algorithms of data analysis, data acquisition of the fluorescence detector and in discussions on the results. I estimate my contribution at approx. 1%.] 16

17 A2 M. Risse, P. Homola, D. Góra, J. Pękala, B. Wilczyńska, H. Wilczyński, Primary particle type of the most energetic Fly s Eye air shower, Astroparticle Physics 21 (2004) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A3 D. Góra, D. Heck, P. Homola, H. Klages, J. Pękala, M. Risse, B. Wilczyńska, H. Wilczyński, Simulation of air shower image in fluorescence light based on energy deposits derived from CORSIKA, Astroparticle Physics 22 (2004) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A4 M. Risse, P. Homola, R. Engel, D. Góra, D. Heck, J. Pękala, B. Wilczyńska, H. Wilczyński, Upper limit on the photon fraction in highest-energy cosmic rays from AGASA data, Physical Review Letters 95 (2005) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A5 P. Homola, D, Góra, D. Heck, H. Klages, J. Pękala, M. Risse, B. Wilczyńska, H. Wilczyński, Simulation of ultra-high energy photon propagation in the geomagnetic field, Computer Physics Communications, 173 (2005) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A6 D. Góra, R. Engel, D. Heck, P. Homola, H. Klages, J. Pękala, M. Risse, B. Wilczyńska, H. Wilczyński, Universal lateral distribution of energy deposit in air showers and its application to shower reconstruction, Astroparticle Physics 24 (2006) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A7 B. Wilczyńska, D. Góra, P. Homola, J. Pękala, M. Risse, H. Wilczyński, Variation of atmospheric depth profile on different time scales, Astroparticle Physics 25 (2006) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A8 J. Abraham, M. Aglietta, C. Aguirre et al. (Pierre Auger Collaboration), An upper limit to the photon fraction in cosmic rays above ev from the Pierre Auger Observatory, Astroparticle Physics 27 (2007) [I estimate my contribution at approx. 1%; see A1.] A9 P. Homola, M. Risse, R. Engel, D. Góra, J. Pękala, B. Wilczyńska, H. Wilczyński, Characteristics of geomagnetic cascading of ultra-high energy photons at the southern and northern sites of the Pierre Auger Observatory, 17

18 Astroparticle Physics 27 (2007) [I contributed by participation in planning of analysis, discussion of the results and in the preparation of the manuscript; I estimate my contribution at approx. 3%.] A10 J. Abraham, M. Aglietta, C. Aguirre et al. (Pierre Auger Collaboration), Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory, Astroparticle Physics 27 (2007) [I estimate my contribution at approx. 1%; see A1.] After doctorate: A11 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Correlation of the highest-energy cosmic rays with nearby extragalactic objects, Science 318 (2007) [I estimate my contribution at approx. 1%; see A1.] A12 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei, Astroparticle Physics 29 (2008) [I estimate my contribution at approx. 1%; see A1.] A13 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Upper limit on the cosmic-ray photon flux above ev using the surface detector of the Pierre Auger Observatory, Astroparticle Physics 29 (2008) [I estimate my contribution at approx. 1%; see A1.] A14 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Upper limit on the diffuse flux of ultrahigh energy tau neutrinos from the Pierre Auger Observatory, Physical Review Letters 100 (2008) [I estimate my contribution at approx. 1%; see A1.] A15 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Observation of the suppression of the flux of cosmic rays above 4x10 19 ev, Physical Review Letters 101 (2008) [I estimate my contribution at approx. 1%; see A1.] A16 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Limit on the diffuse flux of ultrahigh energy tau neutrinos with the surface detector of the Pierre Auger Observatory, Physical Review D 79 (2009) [I estimate my contribution at approx. 1%; see A1.] A17 J. Abraham, P. Abreu, M. Aglietta et al. (Pierre Auger Collaboration), Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory, Astroparticle Physics 31 (2009) [I estimate my contribution at approx. 1%; see A1.] A18 J. Pękala, P. Homola, B. Wilczyńska, H. Wilczyński, Atmospheric multiple scattering of fluorescence and Cherenkov light emitted by extensive air showers, Nuclear Instruments & Methods in Physics Research Sec- 18