14 December, 2011 Bower, Frail and the TraP 

• VLA data analysis by Bower et al. 2007 and Frail et al. 2011 - differences and implications • Summary and comparison of Bower – Frail – Bell results • Results of testing the transients detection pipeline using the archival VLA data Bower, Frail and the TraP 14 December, 2011 2 

Bower and Frail – differences and implications • Estimated rates of two – epoch transients based on Bower et al. 2007 VLA data analysis: 0.1 sources deg−1, with flux density ~ mJy • Re–analysis of the data by Frail et al. 2011 decreased expected detection rate by an order of magnitude – 0.01 sources deg−1 • Possible implications: Expected transient detection rate for LOFAR zenith monitoring program with the 2000 deg2 survey: based on Bowers results: 200 events per day based on Frails results: 20 events per day 3 14 December, 2011 

So what is the current Log N – Log S ? LOFAR RSM Note recent Frail et al. paper suggests Bower rate overestimated by a factor 2-10 → Log N-Log S may not be well-determined Slope consistent with -3/2 

• Comparison of the results of the archival VLA data analysis obtained by Bower, Frail and Bell: summary of 7 single epoch transients reported by Bower et al. 2007, at the 5GHz frequency Summary and comparison of Bower – Frail – Bell results 5 14 December, 2011 

1. RT 19840502 Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 448 ± 74 191 ± 97 468 ± 79 SNR 6.1 2.0 5.9 Comments No optical or infrared counterparts Phase center artifact Additional observations at 15GHz: flux density (243±200 ) µJy Summary and comparison of Bower – Frail – Bell results 14 December, 2011 6 V x ? 

Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 566 ± 81 715 ± 218 253 ± 62 SNR 7.0 3.3 4.1 Comments Possible host galaxy z=0.040 side-lobe of the bright source Additional observation at 1.5GHz, flux density (133 ± 113) µJy Summary and comparison of Bower – Frail – Bell results 2. RT 19840613 14 December, 2011 7 V x ? 

Summary and comparison of Bower – Frail – Bell results 14 December, 2011 8 2. RT 19840613 Transient marked by a cross, lies at the same angle and position as a side-lobe from the bright source J150123+781806 The dirty beam for the 19840613 transients field 

Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 370 ± 67 - 352 ± 64 SNR 5.5 - 5.5 Comments No optical or infrared counterparts, 2 possible host galaxies Uncleaned side-lobe of bright source Summary and comparison of Bower – Frail – Bell results 3. RT 19860115 14 December, 2011 9 V x ? 

Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 1586 ± 248 303 ± 189 578 ± 294 SNR 6.4 1.6 2.0 Comments No optical or infrared counterparts Data in lower IF bad, when removed – no detection Summary and comparison of Bower – Frail – Bell results 4. RT 19860122 14 December, 2011 10 V x ? 

Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 642 ± 101 460 ± 80 265 ± 85 SNR 6.4 5.8 3.1 Comments Possibly associated with Galaxies or Galaxy Groups Source at this position confirmed Might be real, appears in both IF with similar flux densities Summary and comparison of Bower – Frail – Bell results 5. RT 19920826 14 December, 2011 11 V V ? 

Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 1731 ± 232 270 ± 47 242 ± 52 SNR 7.5 5.6 4.6 Comments Possibly associated with Galaxies or Galaxy Groups Antenna position correction applied Six other un-cataloged sources around with similar SNR Summary and comparison of Bower – Frail – Bell results 6. RT 19970528 14 December, 2011 12 V x ? 

Bower et al. 2007 Frail et al. 2011 Bell Flux density (µJy) 7042 ± 963 290 ± 51 260 ± 62 SNR 7.3 5.7 4.2 Comments No optical or infrared counterparts Additional observations at 8.5GHz, source not detected Summary and comparison of Bower – Frail – Bell results 7. RT 19990504 14 December, 2011 13 V x ? 

• All presented single-epoch transient candidates were run through the transient detection pipeline with transient detection threshold 4 and 5 sigma. • In both cases TraP detected few bright sources, however no transient candidates were found 14 December, 2011 14 Testing TraP with VLA data 

• If results reported by Frail are correct, LOFAR zenith monitoring program would detect 20 events per day instead of 200 • No 4-6 sigma transient sources found by TraP with detection level set to 4 and 5 • TraP needs to be as efficient as possible in order to detect possible transient source 14 December, 2011 15 Conclusion