KCDC TUTORIAL - SKYPLOT

Transcription

1 Version 4.0 / KCDC TUTORIAL - SKYPLOT HOW DOES KASCADE SEE THE SKY? This description can be downloaded from Requirements basic knowledge on cosmic radiation basic knowledge on air showers basic knowledge in astronomy knowledge in programming language C++ knowledge in using Data Analysis Framework "ROOT" Skyplot_Tutorial_v4_en.docx 1/17

2 INHALT Physical Background... 3 What can we say about the origin of cosmic radiation?... 3 What are the sources of the cosmic RADIATION?... 3 The Skymap of the Cosmic Radiation... 4 Why is the Skyplot of Cosmic Radiation interesting?... 4 Data sets and Analysis... 4 Preparing the analysis... 4 Analysing and plotting the data... 6 Interpretation of the plots... 7 Advanced tasks... 9 Glossary... 9 Sources & Links: Appendix A. Download the Data sets using the KCDC DataShop Appendix B. Used files & scripts Anhang C Data sets available Skyplot_Tutorial_v4_en.docx 2/17

3 PHYSICAL BACKGROUND High energetic cosmic rays (fully ionised atomic nuclei) collide with the molecules of air when entering the earth atmosphere initiating a particle cascade. The primary cosmic particle does then not exist anymore. Thus the KASCADE experiment is designed to measures only the part of the cosmic ray air shower reaching ground level not the primary particle. The data analysis of such a wide shower should reveal many of the properties of the primary particle. Therefore, besides the mass and the energy the origin of the particle is of interest. WHAT CAN WE SAY ABOUT THE ORIGIN OF COSMIC RADIATION? The direction from which a cosmic ray particle is penetrating in our atmosphere can be derived from the reconstructed shower direction and its arrival times. The direction of the shower, and thus the direction of the primary particle, is determined by means of the individual arrival times of the secondary particles of all detector stations participating in this event. This plot shows the distribution of the individual arrival times in the 252 detector stations of the KLASCADE Array. A plain characterising the shower front is fitted to this distribution, its surface normal point in the direction of the incoming primary particle. But even if we know the direction from which the primary particle is hitting our atmosphere we still do know nothing at all about the source of the particle in deep space. The problem is that we are talking about atomic nuclei, i.e. charged particles which are deflected in the galactic and the intergalactic magnetic fields and thus lose all information on their origin. WHAT ARE THE SOURCES OF THE COSMIC RADIATION? The cosmic radiation is classified according to their origin in solar (source is the sun) galactic (sources are within our galaxy) extragalactic (sources are outside of our galaxy) cosmic radiation. The solar wind represents the major part of the SOLAR COSMIC RADIATION. It consists mainly of charged particles like protons, electrons and helium atomic nuclei from the outer spheres of the sun. The energy of these particles is below 10 9 ev. Cosmic radiation above this energy up to about ev has a high probability of being of galactic origin and is thus called GALACTIC COSMIC RADIATION. In this energy range the gyromagnetic radius is smaller than the diameter of our galaxy. This means that the charged particles are practically caught in the magnetic field of our galaxy, no able to leave and without any information about their origin. Skyplot_Tutorial_v4_en.docx 3/17

4 Here super nova remnants, like the crab nebula, are thought to be the sources and the location of acceleration. But also pulsars and binary star systems where both stars have very different masses and the larger stars draw matter from the smaller one could be sources. Cosmic ray particles of the highest energies are called EXTRAGALCTIC COSMIC RADIATION, accelerated by certain mechanisms to this ultra-high energies, where unfortunately the location of the acceleration is unknown. A theory of the acceleration states that a massive black hole at the center of a galaxy accretes matter from its surroundings. This matter revolves in a disk around the black hole and approaches this spirally. THE SKYMAP OF THE COSMIC RADIATION Without the presence of the different magnetic fields we could conclude from the shower direction directly on the origin of cosmic rays. If however we knew the exact structure of the magnetic fields, we could draw conclusions by means of so called transport models. Since the distribution and structure of the magnetic fields is not very well understood both in our galaxy and throughout the universe, however, only the ultra-high-energy cosmic particles may provide us with information about their origin. Because they are travelling nearly at the speed of light they are not deflected by the magnetic fields and practically come in a straight line from the source to the earth, if the source is close on an astronomical scale. WHY IS THE SKYPLOT OF COSMIC RADIATION INTERESTING? Nevertheless, it is interesting to plot a skymap of the cosmic particles in all energy ranges especially since these are also suitable to investigate the quality of the reconstruction software. Such skymaps can indicate an accumulation of events from nearby sources (point sources), or large-scale structures (anisotropy), from which we can conclude to the distributions of the source or to the magnetic field structures in our galaxy. DATA SETS AND ANALYSIS This tutorial presents the main steps for creating a skyplot in C / C ++. read and prepare the data sets transform to galactic coordinates graphical representation of data There are a numerous programming languages, which are suitable to carry out these analyses and create the plots. As an example a program in C / C ++ is discussed. Also conceivable, however, are all other programs to create histograms from a text file (ASCII) as supplied by KCDC. PREPARING THE ANALYSIS To generate a skyplot of cosmic rays measured by KASCADE the following parameters of the KCDC data sets are required: Arrival Time (Datetime, Gt, Mt): Datetime in UTC (yyyy-mm-dd hh:mm:ss) or Global Time (GT) and Micro Time (Mt) to increase the accuracy. Shower Direction (Az, Ze): Azimuth and Zenith angles Energy (E): reconstructed energy of the primary particle The ASCII data set used for this example analysis DataSkyplot.zip can be downloaded from ftp://kcdc.ikp.kit.edu/education/dataskyplot.zip or it can be generated in the KCDC Data Shop (instructions see App-A). Skyplot_Tutorial_v4_en.docx 4/17

5 The data set includes data from 2 years odf measurement (1999 and 2000). There is as well a reduced data set from just one year measurement period offered (for details see table). Data set DataSkyplot DataSkyplot-small Size Zip-File 1500 MB 677 MB Number of Events Size data files inflated 5500 MB 2500 MB The included file Info.txt contains all information about the supplied data format, like the quantities available and their ranges. For this plot we are besides in the shower direction also interested in the arrival time and for additional tasks in the energy. We see in Info.txt that the columns labeled E (energy), ZE (zenith angle), AZ (azimuth angle), Date (date) and MT (Micro time) are need. The reconstructed primary energy E can be used for interesting cuts (see advanced tasks). It is displayed logarithmically as the number varies between (10 13 ) and (10 18 ). The Global Time (GT) is a redundant information for date but much easier to handle because it counts the seconds from (often called UNIX time). R (run) and Ev (event ) numbers are always provided the user. Number of events matching Cuts: Your requested observables: Event Info (general) Datetime [DateTime] type=date unit=none Cut: to Ev [Event Number] type=numerical[int32] unit=none Gt [Global Time] type=numerical [Int32] unit=ssec Mt [Mt] type=numerical [Int32] unit=ns R [Run Number] type=numerical [Int32] unit=none KASCADE (array) Az [Azimuth Angle] type=numerical [Float64] unit= E [Energy] type=numerical [Float64] unit=ev [log10] Ze [Zenith Angle] type=numerical [Float64] unit= Number of events matching Cuts: The ranges of the parameters selected include the complete data set of KASCADE, only that the selected time is limited to 2 years, so keep the size of the data set manageable. A look into the files general.txt, array.txt and row_mapping.txt shows how the first 6 records of the data sets used in this example are stored. Skyplot_Tutorial_v4_en.docx 5/17

6 general.txt Datetime Ev Gt Mt R T00:00: T00:00: T00:00: T00:00: T00:00: T00:00: array.txt row_mapping.txt Az E Ze general array e e e e e e e e e e e e e e e e e e ANALYSING AND PLOTTING THE DATA The KASCADE experiment is at a fixed location and has thus in the local coordinate system a fixed angular range accessible for incoming cosmic ray particles (Azimuth: degrees, Zenith: 0-60 degrees). In this local coordinate system the direction of incidence of the particle is reconstructed. The rotation of the earth and its motion within the solar system within a year requires a transformation to a suitable celestial coordinate system where the exact event time, which describes the present location of the earth, is used to transform the reconstructed shower direction to a celestial coordinate system where for example the stars of our galaxy are at a fix position. For reading the data, transforming them into suitable (celestial-) coordinate system and the presentation of results in a so-called skyplot is a C ++ -program package can be downloaded. Apart from the program skymap.cpp the zip file ProgSkyplot.zip includes a definition file skymap.h and an explanation on how this program must be executed within ROOT (Skyplot_README.txt). ProgSkyplot.zip can be downloaded via the link ftp://kcdc.ikp.kit.edu/education/dataskyplot.zip. For the execution of the program a C-compiler and the Data Analysis Framework ROOT from CERN must be installed (details on ROOT see section Sources and Links). The unzipped files skymap.cpp and skymap.h need to be in the directory where ROOT is to be executed. After ROOT has been started, skymap.cpp will be translated with.l skymap.cpp + and then executed with run (). Program flow chart : definitions (coordinates of KASCADE, conversions for equatorial coordinates (J2000)) definitions for ROOT event loop o conversion zenith angle and azimuth angle to radiant Skyplot_Tutorial_v4_en.docx 6/17

7 o calculation of the sidereal time for the coordinate transformation o rotation of the coordinate system relative to KASCADE (rotation by 180 ) o transformation horizontal equatorial coordinates o transformation equatorial galactic coordinates o performing a projection after Hammer-Aitoff o filling predefined 2-dimensional histograms plot ouput o drawing the histogram o drawing the coordinate system (equatorial & galactic system) o output as pdf As a result you get 2 plots which show the sky as it is viewed by KASCADE Skymap_equ.pdf Skymap_gal.pdf skyplot in equatorial coordinates skyplot in galactic coordinates INTERPRETATION OF THE PLOTS Skymap_equ.pdf An equatorial coordinate system is a geocentric coordinate system used by the astronomers where the earth (observer) is in the centre at 0/0. The axis are called declination (angular distance from the equatorial layer, positive sign for the northern hemisphere) and right ascension. In this plot generated within the KCDC tutorial are displayed the KASCADE data as well as the galactic plane a few astronomical objects. Skyplot_Tutorial_v4_en.docx 7/17

8 Skymap_gal.pdf As it is very helpful when investigating properties of our galaxy, the galactic coordinate system is often used by the astronomers. The reference is the plane of our Milky Way called galactic plane (x-axis). The galactic longitude l is measured anti-clockwise. The galactic latitude b is measured perpendicular, pointing north is positive, pointing south is negative. remark These plots show the frequency of the measured events. This does not imply that the different colours indicate anisotropies in the distribution of the arrival directions. To investigate anisotropy one would have to correct each bin for the true measuring time of KASCADE as well as for the angular dependent efficiency of the detector. The first is necessary because KASCADE was not running uniformly for a whole year thus the sky is not uniformly exposed. The latter correction is necessary as the detector is only recording data above a certain threshold i.e. a minimum number of secondary particles in an air shower which depends on the zenith angle. As the atmospheric depth is getting larger with increasing angle the threshold energy increases as well. These corrections are called normalisation which leads to a uniform distribution of the arrival directions, i.e. KASCADE did not see any anisotropies. Skyplot_Tutorial_v4_en.docx 8/17

9 ADVANCED TASKS Finally some suggestions how this exercise can be extended by some interesting plots. draw a skyplot with a limited zenith angle range p.e. 0-5 (vertical showers) draw skyplots for different energy ranges (search for point sources) (see above remark) Both tasks can be solved with the data set DataSkyplot.zip applying appropriate cuts in skymap.cpp. As an alternative a separate data sample can be downloaded from the KCDC DataShop analog to the example displayed in Appendix A applying cuts on the quantities ZE and/or E. Another interesting task would be the normalisation of the measured distribution. This however requires some deeper knowledge in Astronomy and the principles of measuring cosmic ray showers on ground based experiments. But in principle everything is possible using the KCDC data published in the KCDC DataShop. GLOSSARY ev primary energy In physics the electronvolt is a unity of energy used in atomic physics, nuclear physics and particle physics. The symbol is ev. By definition, it is the amount of energy gained (or lost) by the charge of a single electron moved across an electric potential difference of one volt. The highest energy measured up to now (in cosmic ray physics of course!) is ev which corresponds to the energy content of a tennis ball moving at 100km/h but concentrated on the size of an atomic nucleus. The primary energy of high energetic cosmic radiation cannot be measured directly because the incoming particle collides with the molecules of the earth s atmosphere and triggers a shower cascade and is lost for the direct measurement at ground level. Huge detector systems like KASCADE can measure many of the secondary particles. From their energy deposits in the different detectors one can draw conclusions one the energy and the mass of the primary particle by means of highly sophisticated simulations including air shower properties and detector response functions. Skyplot_Tutorial_v4_en.docx 9/17

10 SOURCES & LINKS: Cosmic radiation in general (german videos): Astronomy: Jean Meeus, Astronomical Algorithms, Atlantic Books; 1998 Programming: Skyplot_Tutorial_v4_en.docx 10/17

11 APPENDIX A. DOWNLOAD THE DATA SETS USING THE KCDC DATASHOP As a registered KCDC user you have access to the DataShop on the KCDC Homepage ( If you are not registered you will be asked to register by generating a user account Fig. A.1.. KCDC DataShop Skyplot_Tutorial_v4_en.docx 11/17

12 Fig. A.2.. Select detector components and quantities This window enables you to select the quantities required for your analysis and to apply cuts to reduce the amount of data transferred via ftp. For our example we need the following quantities: Ze Az E DateTime Gt Mt Zenith angle Azimuth angle Reconstructed Energy Date & Time Global time Mikro time The parameters Run Number and Event Number are always shipped with the data for a unique identification of an event. These two quantities cannot be deselected. Skyplot_Tutorial_v4_en.docx 12/17

13 Fig. A.3. Applying Cuts If alle parameters are selected some cuts have to be applied by pressing the add cut button of the respective quantity. As in our case the amount of data should be reduced we will cut on the Date parameter. All other quantities are requested within their full range. The information boxes at the right hand side provide helpful information on how to supply the quantitie s cuts. Check and submit your request Tis page holds an overview on the parameters chosen as well as the cuts applied. If everything is fine submit your request using the submit retrieval request button. Skyplot_Tutorial_v4_en.docx 13/17

14 Fig. A.4.. Overview on data selected and cuts On the KCDC User Review Page you can follow the status of your job. After a few seconds the status information will switch from PENDING to PROCESSING, indicating that the data selection is in progress. After successfully terminating your request the status will switch to SUCCESS and you will get an with a link to download your data selection via the DOWNLOAD button on this page. Skyplot_Tutorial_v4_en.docx 14/17

15 Fig. A.5.. Your request Skyplot_Tutorial_v4_en.docx 15/17

16 APPENDIX B. USED FILES & SCRIPTS The packed file Skyplot.zip contains 5 files array.txt Data file for the quantities E, Ze, Az general.txt Data file for the quantities Datetime, Gt, Mt and R, Ev (always provided) row_mapping.txt Mapping table holding the correlations between array.txt and general.txt info.txt Information concerning the selected parameters, cuts and the number of events EULA.pdf License agreement to use the KCDC data The packed file ProgSkyplot.zip holds program codes and helps skymap.cpp C++ programm code skymap.h Include file skymap_readme.txt Help file Skyplot_Tutorial_v4_en.docx 16/17

17 ANHANG C DATA SETS AVAILABLE For this tutorial two data sets are available. The 'normal' data set DataSkyplot.zip contains data as described above, the file DataSkyplot-small.zip contains data from to Details are given in the following tables Data set DataSkyplot DataSkyplot-small Size Zip-File 1468 MB 677 MB Number Events Size data files inflated 5613 MB 2577 MB Cuts at Data set DataSkyplot DataSkyplot-small Datetime Gt [sec] 8.946e e e e+9 Mt [ns] e e8 E (log10) [ev] Ze [ ] Az [ ] Download: ftp://kcdc.ikp.kit.edu/education/dataskyplot.zip ftp://kcdc.ikp.kit.edu/education/dataskyplot-small.zip Skyplot_Tutorial_v4_en.docx 17/17