Allsky search of EXPLORER data

The EXPLORER detector is opperated by Italian ROG collaboration currently led by Eugenio Coccia.

The analysis is performed by a team consisting of Pia Astone, Kazik Borkowski, Piotr Jaranowski i Andrzej Krolak and is carried out on the basis of Memorandum of Understanding between the ROG group and Institute of Mathematics of Polish Academy of Scinces.

Parameters of the data:

The Modified Julian Date of
           the first sample:   48580.79085074369
Length of observation time:    2 days
Sampling frequency:            1.5212 Hz     

Bandwidth of the search:       920.9992 -- 921.7598 Hz
No. of Fourier bins            2^19 = 512000
Spindown range:                -9.1762 10^-8  --  +9.1762 10^-8 Hz s^-1
No. of spindowns               2868 
Sky positions:                 All sky
No. of pointings               31915

There are 2¹⁹ = 512000 Fourier bins.

The details of data analysis method are given in paper "Data analysis of gravitational-wave signals from spinning neutron stars. IV. An all-sky search" by Astone, Borkowski, Jaranowski and Krolak, Phys.Rev.D (in print).

The search is performed by the following network of PCs and several SUN workstations.

--------------------------------------- Computer Procesor Location --------------------------------------- PentiumIII 2 Intel 550MHz IMPAN PentiumIII Intel 750MHz IMPAN PentiumIII 2 Intel 500MHz UwB PentiumIII Intel 800MHz UwB PentiumIV Intel 1.7GHz IMPAN PentiumIV Intel 1.7GHz IMPAN Athlon AMD 1.4GHZ IMPAN Athlon AMD 1.4GHZ IMPAN PentiumIV Intel 1.7GHz CAUMK Athlon AMD 1.333GHZ CAUMK SUN SparcII 366MHz IMPAN SUN SparcII 366MHz UwB SUN 2 SparcII 366MHz ICM --------------------------------------

IMPAN - Institute of Mathematics, Polish Academy of Sciences, Warsaw
UwB - University of Bialystok, Bialystok
CAUMK - Center for Astronomy, Nicolaus Copernicus University, Torun
ICM - International Center for Mathemtical Modeling, Warsaw University, Warsaw

The öfficial" start of the search was 1st September 2001. However some computers were crunching data before that date and some were acquired and started working after September the 1st.

3 PentiumIV and 2 Athlon computers were purchased in September from a Polish Science Committee grant. During the initial period of operation some of them broke down and they needed repair. In particular one of the Athlons had a few problems.

The computer codes to do the search were originally written in MATLAB language. On all Sun workstations and on most of the PCs they are compiled and run as executables. At the moment we are searching only the Northern Hemisphere. Each of the computers was assigned a certain part of the sky. For each position in the sky we search over 2868 values of the time derivative of the frequency (called also "frequency drift" or ßpindown"). Each loop in the code calculates, using FFT algorithm, 2¹⁹ values of the optimal statistics F (Eq.(3.9) of the paper gr-qc/0012108) corresponding to 2¹⁹ Fourier bins of the bandwidth. For Northern Hemisphere there are 31915 × 2868 = 91532220 loops. The fastest time equal to 1.4s to calculete F is achieved on PentiumIV 1.7GHz processors. To take care of possible computer crashes and to have a control over progress of the search, after each loop we save the sky position and spindown searched in a file. The threshold signal-to-noise ratio is 6.6. The parameters of the candidates are saved in MATLAB binary files that have the following name:

ss1_7_1_6_131425_79.mat

ss stands for systematic search,
1 - Northern Hemisphere,
7 , 1 - Position in the sky,
6 - Spindown,
131425 - Frequency bin number, and
79 - Means signal-to-noise ratio is approximately 7.9.
By the way this is the strongest candidate signal that we have!

__________________________________________ |__________________________________________| | SEARCH PROGRESS REPORT | |------------------------------------------| | | |Percentage of the Northern Sky searched: | | | | | | 26.5% | | | | | |Highest signal-to-noise of a candidate: | | | | | | 7.9 | | | |__________________________________________|

Keep on searching!

Ciao,

Andrzej