Training the TraP Antonia Rowlinson University of Amsterdam 

Antonia Rowlinson University of Amsterdam [email protected] Swinbank (2011) 

Antonia Rowlinson University of Amsterdam [email protected] Swinbank (2011) 

Antonia Rowlinson University of Amsterdam [email protected] Swinbank (2011) 

Antonia Rowlinson University of Amsterdam [email protected] High Bound Noise Threshold: Radio Sky Monitor dataset average RMS noise ~ 24 mJy (11 min snapshot images) 

Antonia Rowlinson University of Amsterdam [email protected] Quality Control: Script to create Quality Control plots is available to TraP commissioners here (new version in development): ! ! This script needs running on each new dataset to determine the optimum thresholds for the flux ratio high bound, ellipticity and minimum A-Team separation https://github.com/transientskp/scripts/tree/master/TraP_QC_plots 

Antonia Rowlinson University of Amsterdam [email protected] Transient search parameters After each new data point is inserted into the database we calculate: Variability Index: ! ! ! Weighted Chi-squared: ! ! ! ! 

Antonia Rowlinson University of Amsterdam [email protected] Transient Search Parameters: All newly detected sources are inserted into transient list However, the list is dominated by sources hovering at/near the source extraction detection threshold Will be resolved in Release 2 of the TraP Script providing temporary (approximate) fix available here: https://github.com/transientskp/scripts/tree/master/TraP_sort_transients 

Antonia Rowlinson University of Amsterdam [email protected] 2.7 sigma threshold 

Antonia Rowlinson University of Amsterdam [email protected] 

Antonia Rowlinson University of Amsterdam [email protected] Bright sources - statistical flux errors very small, systematic errors dominating 

Antonia Rowlinson University of Amsterdam [email protected] Faint sources - likely imaging artefacts Bright sources - statistical flux errors very small, systematic errors dominating 

Antonia Rowlinson University of Amsterdam [email protected] Dataset overview Script to create these plots is available to TraP commissioners here: ! ! Also, this script identifies transient candidates for a given sigma threshold: https://github.com/transientskp/scripts/tree/master/TraP_source_overview https://github.com/transientskp/scripts/tree/master/TraP_anomaly_detection 

Antonia Rowlinson University of Amsterdam [email protected] Antonia Rowlinson University of Amsterdam [email protected] Simulated Datasets: Simulation technique enhanced and standardised Gives a set of known stable sources and known transients Further information available on LOFAR wiki: Take existing measurement set Delete contents of data columns Use BBS to insert sources using a sky model Insert Gaussian noise Calibrate and image using standard pipeline http://www.lofar.org/operations/doku.php?id=tkp:simulateddata 

Antonia Rowlinson University of Amsterdam [email protected] Simulated datasets 

Antonia Rowlinson University of Amsterdam [email protected] 

Antonia Rowlinson University of Amsterdam [email protected] Transients which were undetected at quiescent flux but are stable after they turn on. ! N.B. if maximum flux is comparable to detection threshold, they are undistinguishable from faint stable sources (this will be rectified in release 2 of TraP) ! 

Antonia Rowlinson University of Amsterdam [email protected] 

Antonia Rowlinson University of Amsterdam [email protected] Can we do better? Logistic Regression (a linear classifier) 4 features for each source: ! ! Trained using simulated transients and ‘stable’ sources from the Radio Sky Monitor dataset 

Antonia Rowlinson University of Amsterdam [email protected] Precision ~ 99% (probability that identified transients are real) Recall ~ 80% (probability that all transients are identified) 

Antonia Rowlinson University of Amsterdam [email protected] 

Antonia Rowlinson University of Amsterdam [email protected] Conclusions: TraP works! However transient list dominated by fake “new” sources close to source detection threshold - to be resolved in TraP Release 2 (temporary fix available) Choose quality control parameters and transient thresholds very carefully to avoid spurious transients Tools to help available on GitHub (frequently improved) Transients can be identified in several ways such as: Identify anomalous transient parameters: ideally using a sigma threshold (~2.7 sigma for the Radio Sky Monitor dataset) Classify using multiple features and logistic regression (Preliminary) 

Antonia Rowlinson University of Amsterdam [email protected] Min Separation from A-Team: Significant deviation starts from ~10 degrees 

Antonia Rowlinson University of Amsterdam [email protected] Restoring Beam Ellipticity: 

Antonia Rowlinson University of Amsterdam [email protected] Current caveat: The sky is not well known at LOFAR frequencies Extrapolating fluxes to LOFAR bands using poorly constrained spectra 

Antonia Rowlinson University of Amsterdam [email protected] 

Antonia Rowlinson University of Amsterdam [email protected]