The LISA Simulator ====================== Neil Cornish, Louis Rubbo, and Olivier Poujade Montana State University - Bozeman July 16, 2003 Version 2.0 Support for The LISA Simulator was provided by the NASA EPSCoR program through the Cooperative Agreement NCC5-579. _____________________________________________________________________ | | | | OVERVIEW OF THE LISA SIMULATOR The LISA Simulator is a complete computer simulation of the proposed Laser Interferometer Space Antenna (LISA). The software package is designed as an interface tool between source simulation and data analysis. The Simulator takes as its input the polarization signals from an arbitrary gravitational wave source, and returns as its output the simulated response of the LISA detector. The simulation includes a realization of the noise in the detector. We include the photon shot noise and the acceleration noise. This, combined with the response of the detector to the input polarization signals, comprises the complete output of the simulator. Version 2.0 now includes all three Michelson signals, one from each spacecraft, along with the time delay interferometer signals X, Y, and Z. The LISA Simulator is based on the analytical results found in the paper Neil J. Cornish and Louis J. Rubbo, Phys. Rev. D 67, 022001 (2003) | | |_____________________________________________________________________| _____________________________________________________________________ | | | | QUICK START TUTORIAL TLS-Runner Included in the simulator2.0 tar ball is the executable file TLS-Runner. This executable, which can be run immediately after unpacking the Simulator, will compile and run in the correct order all of the codes, both setup and signal codes, at their default settings. Additionally, TLS-Runner will run the default Simulator source AM CVn, which is a monochromatic, circular binary. The ASCII formatted output from the Simulator is located in the Data/ directory. Default Settings The default settings for The LISA Simulator are the following: NFFT = 2^20 T = 1 year Ndiv = 8 kappa = 0 lambda = 0 Here T is the observation time, NFFT is the number of data points in the observation time (with no padding included), Ndiv is the number of sections the Simulator package will divide the observation time into in order to manipulate smaller file sizes. The quantities kappa and lambda fix the orbital phase of the detector. Vertex Executables Besides the TLS-Runner, which runs every code for every vertex, the simulator2.0 tar ball includes a number of individual vertex executables called X-Setup, X-Signal, etc.. These executables will compile and run in the correct order the codes associated with a particular vertex. The Setup executables need to be run only once as long as the parameters defined in the header file LISAconstants.h have not been changed since a previous run (if they are, all of the codes included in the Setup executable must be re-run). The Signal executables compile and run the codes associated with the signal processing for a particular source. These codes must be compiled and run for each source. Note that the Signal executables do not include the gravitational wave source code. For the source we have included a final executable, Source-Runner, which compiles and runs the default Simulator source. If one were interested in only analyzing the vertex 1 response the following sequence of calls must be done (assuming the Setup codes have not already been run): ./X-Setup ./Source-Runner ./X-Signal The LISA Simulator Input The input for The LISA Simulator is a two column ASCII formatted file. Column one contains the plus polarization signal (h_plus) as measured at the origin of the helio-frame, while the second column contains h_cross measured at the same location. The length of the file must contain the full observation time for the Simulator (the value of T defined in the header file LISAconstants.h) plus padding on either end. The length of the padding on either side is twice the light travel time from the Sun to LISA's orbital position, that is, Total Observation Time For The Source = 2*AU/c + T + 2*AU/c The padding accounts for the LISA observatory being displaced from the helio-frame origin, and for the time delay interferometer variables requiring times that may extend back or forward in time from the readout time. At the beginning of the input ASCII formatted file a number of parameters need to be stated on a single line. Those parameters, listed in the correct order they should be stated, are nsource, theta, phi, the source observation time, and a character string. The variable nsource is the power of 2 that represents the number of sample data points, without padding, for the source (i.e. Ntotal = 2^nsource + Npadding). The variables theta and phi give the angular location of the gravitational wave source in the helio-frame. The character string stated at the end of the first line is used by the Simulator as a root name for all of its outputs. For example, the X signal would have an output filename of root_X_Time.dat, where root is the character string. As a model of how the input file must look, The LISA Simulator comes with a gravitational wave source code called Newtonian.c. This code calculates the polarization signals from a monochromatic, circular binary and writes them to a properly formatted file after it has written the source parameters to the initial line of the file. The output from this file should be viewed as an example of how the Simulator expects its input. The LISA Simulator Output The ASCII formatted output of The LISA Simulator is found in the sub-directory Data/. The Simulator outputs a Michelson signal from each vertex in addition to the time delay interferometer (TDI) signals X, Y, and Z. The names of the files associated with the first vertex are (the other two vertexes have similar names): root_M1pure_Time.dat root_M1_Time.dat root_Xpure_Time.dat root_X_Time.dat Here "root" is the character string found on the first line of the input ASCII file as discussed in the previous section. The filenames that contain the word "pure" after the signal type mean that noise has not been added to the signal, while those filenames without the "pure" attachment do have noise. The "Time" attachment to the filename is a reminder that the output is in the time domain. The structure of these files are a single column format with each data point separated in time from the previous by an amount dt as defined in the LISAconstants.h header file. Rather than having each file explicitly record the times, which are the same for each type of signal, the Simulator produces a separate file called root_Times.dat which contains the times that the data points are recorded. In addition to the files that contain the various detector responses, the Simulator outputs a small text file that contains a number of important simulator parameters used in the simulation. This file, called root_Response.txt is written to the Data/ directory. The model gravitational wave source code produces a file called root.txt that contains a number of parameters associated with the source. This file is also written to the Data/ directory. Fast Fourier Transforms Released with The LISA Simulator are two FFT codes. The first is explicitly designed to be used with the outputs of the noise codes, while the other is to be used with the final processed signal. The FFT codes use the free software package the Fastest Fourier Transform in the West (FFTW) Version 2.1.5, which is not the newest version of FFTW. The newest version of FFTW (3.0) is not back compatible with previous versions. Therefore, caution must be taken on which computer the Simulator is ran if one wishes to use our FFT codes. Additionally, at the end of the executable files are compile statements for the FFT codes. These compile commands are system dependent. The default commands are for the Linux operating system, while the commented out are for the Fink installed FFTW on the Mac OSX system. | | |_____________________________________________________________________| _____________________________________________________________________ | | | | USAGE POLICY The LISA Simulator codes are ``Free Software/Open Source Software'' in the technical sense defined by the Free Software Foundation (see Categories of Free and Non-Free Software). Under the same classification, the codes are not ``Public Domain Software'', which means that codes can not be used in any commercial product without buying a licenses from Montana State University. (The odds of that happening have got to be pretty low!). Using a similar model to other open source software distributions such as Linux, we encourage people to add to and improve the codes, and to send us revised versions for inclusion in subsequent releases. Other sites, such as the LISA Working Group 1 Site, may mirror the source codes, but version control rests with the Montana State Group. If you use and like the simulator, and you run into us at a conference, we encourage you to buy us a beer. Or two. (Thanks to Scott Hughes for this suggestion on usage policy). | | |_____________________________________________________________________| _____________________________________________________________________ | | | | PUBLICATION POLICY We encourage people to use The LISA Simulator in their research. If you do use the Simulator, please include the following reference: \bibitem{LISASIM} N.J. Cornish, L.J. Rubbo \& O. Poujade, {\em The LISA Simulator}, {\tt www.physics.montana.edu/LISA/}; N.J. Cornish \& L.J. Rubbo, Phys. Rev. D{\bf 67}, 022001 (2003). We would like to post a list of the papers that use the Simulator, so please e-mail us any references. | | |_____________________________________________________________________| _____________________________________________________________________ | | | | QUESTIONS OR COMMENTS If you have any further questions or comments please email either Neil Cornish at: cornish@physics.montana.edu or Louis Rubbo at: rubbo@physics.montana.edu | | |_____________________________________________________________________|