The atlas is provided as files in Mapped Vector Library (MVL) format:
the main data set O3a_2_atlas.mvl
the summary data set O3a_2_atlas_summary.mvl
the spatial index O3a_2_spatial_index.mvl
For the O3a all-sky search the Atlas contains nearly 7 billion entries. The MVL format was chosen for this data because it allows it to be memory mapped, allowing analysis on personal computers with small amounts of random access memory. We strongly recommend that the user has a solid state drive allowing random access to the data.
The MVL format specification and description of data layout is in the file data_format.txt.
The main data set O3a_2_atlas.mvl contains upper limits (for circular, linear polarization as well as new parametetric upper limits) and signal-to-noise ratios (SNR), parameterized by sky position and frequency.
The sky resolution increases with frequency. The sky coordinates are in radians, J2000.
The summary data set O3a_2_atlas_summary.mvl also has upper limits and signal-to-noise ratios, but it has been mapped onto a uniform sky grid that is the same for all frequencies. The summary data set is used by the script view_summary.R.
Once in the R environment, a script runs with the following command:
source("SCRIPT_NAME.R")
Before running any of the scripts in R the RMVL package has to be installed using the following R command:
install.packages("RMVL")
A number of example R scripts that make use of the atlas data are provided. The user is encouraged to open the scripts and modify them as needed.
view_summary.R - generates a skymap and a frequency plot from any sub-band of the atlas, plus some summary information. There are examples of how to make plots and extract data at the end of the script.
full_scan_example1.R - example of finding all points above a fixed SNR cutoff
full_scan_example2.R - example of finding all points that were analyzed by the second stage of the pipeline
full_scan_example3.R - example of finding all points that were not analyzed by the second stage of the pipeline
create_spatial_index.R - creates spatial index allowing fast queries by sky location. The size of the generated index is 56GB. Instead of running this script you can download the spatial index.
spatial_index_example1.R - example of finding points closest to points in provided file points_of_interest.csv with help of spatial index
spatial_index_example2.R - example of using spatial index to retrieve data for hardware injections and then compute upper limits for polarization parameters iota and psi provided for each injection.
spatial_index_example3.R - example of using spatial index to retrieve data for a single sky location across all frequencies
The convenience of MVL files depends on the speed of the underlying storage. At the time of writing this README file we recommend using a solid-state drive with at least 2TB capacity, attached either using USB 3.0/USB C or NVME/PCI express. SATA or USB 2.0 connections are much slower.
The 2 TB capacity is recommended because larger solid state drives usually have larger endurance and faster access speeds.
MD5 checksums of MVL files:
2a20af9669173eea3e4f552352c03e33 - O3a_2_atlas.mvl
4808891cafe43e7275276b6091302c0e - O3a_2_atlas_summary.mvl
dd36faad5cf51f4484cfdbd3896302a2 - O3a_2_spatial_index.mvl