1. Swift-BAT as a Triggering Facility Amy Lien Scott Barthelmy, Hans Krimm NASA Goddard Space Flight Center The 4 th AMON workshop, Penn State University, 2015/12/04

2. Outline BAT trigger algorithm – Normal triggers – Sub-threshold triggers – Sub-sub-threshold triggers Ground processes – Transient Monitor – Ground analysis Summary

3. Burst Alert Telescope (BAT) X-Ray Telescope (XRT) UV/Optical Telescope (UVOT)

4. Burst Alert Telescope (BAT)

5. A. Rate trigger: Stage 1: Rate trigger Stage 2: Image threshold

6. 1. Rate trigger followed by image threshold: > 600 different trigger criteria Each trigger criterion has different energy bands, time periods, signal-to-noise thresholds, etc Image threshold: Additional thresholds for localization Trigger Algorithm of the BAT Time Fore- ground Elapse Time 1 Elapse Time 1 Background 1 Elapse Time 2 Elapse Time 2 Background 2 Background 2 Fore- ground Elapse Time 1 Elapse Time 1 Background 1 Elapse Time 2 Elapse Time 2 Background 2 Background 2 Fore- ground Elapse Time 1 Elapse Time 1 Background 1 Elapse Time 2 Elapse Time 2 Background 2 Background 2 Fore- ground Elapse Time 1 Elapse Time 1 Background 1 Elapse Time 2 Elapse Time 2 Background 2 Background 2 Fore- ground Elapse Time 1 Elapse Time 1 Background 1 Elapse Time 2 Elapse Time 2 Background 2 Background 2 Fore- ground Elapse Time 1 Elapse Time 1 Background 1 Elapse Time 2 Elapse Time 2 Background 2 Background 2 Create Image Check image threshold Signal-to-noise ratio using image background Localization Known souce? Check with on-board sky catalog Triggered!

7. Burst Alert Telescope (BAT) A. Rate trigger:B. Image trigger: GRB141121A Stage 2: Image threshold Stage 1: Rate trigger GRB140629A

8. Image trigger 15-50 keV Typical image exposure time: 64 s, 320 s, full observation (1-43 min). When a rate trigger is active, the image trigger is extended by increment of 8 sec – (64+8x) secs, 320 s, and full observation (1-43 min) When rate trigger happens, the image trigger is extended

9. Burst Alert Telescope (BAT) A. Rate trigger:B. Image trigger: GRB141121A Stage 2: Image threshold Stage 1: Rate trigger GRB140629A XRT image

10. Fail BAT triggers summary > 600 Rate criteria Success Image Threshold Image duration & energy from rate criterion Trigger! (1000 s event data) Failed event (10 s Event data) Image threshold on Images with 64 s, 320 s, full obs. 15-50 keV Success Fail Keep trying…. Courtesy to Scott Barthelmy Success Fail Trigger! (1000 s event data) Keep trying….

11. Fail BAT triggers summary > 600 Rate criteria Success Image Threshold Image duration & energy from rate criterion Trigger! (1000 s event data) Failed event (10 s Event data) Image threshold on Images with 64 s, 320 s, full obs. 15-50 keV Success Fail Keep trying…. Courtesy to Scott Barthelmy Success Fail Trigger! (1000 s event data) Sub-threshold Sub 2 -threshold Keep trying….

12. Courtesy to Scott Barthelmy 6.5 5.8 3.8 7.0 Successful trigger Possible trigger Sub-threshold trigger Sub-sub-threshold trigger Auto-slew, 1000 s BAT event data, XRT/UVOT observation, GCN notice BAT triggers summary: Image threshold SNR

13. Courtesy to Scott Barthelmy 6.5 5.8 3.8 7.0 Successful trigger Possible trigger Sub-threshold trigger Sub-sub-threshold trigger Auto-slew, 1000 s BAT event data, XRT/UVOT observation, GCN notice Try for another ~ 30 s to get higher SNR BAT triggers summary: Image threshold SNR

14. Courtesy to Scott Barthelmy 6.5 5.8 3.8 7.0 Successful trigger Possible trigger Sub-threshold trigger Sub-sub-threshold trigger Auto-slew, 1000 s BAT event data, XRT/UVOT observation, GCN notice Try for another ~ 30 s to get higher SNR If close to a nearby known galaxy  treated as successful trigger BAT triggers summary: Image threshold SNR

15. Courtesy to Scott Barthelmy 6.5 5.8 3.8 7.0 Successful trigger Possible trigger Sub-threshold trigger Sub-sub-threshold trigger Auto-slew, 1000 s BAT event data, XRT/UVOT observation, GCN notice Try for another ~ 30 s to get higher SNR If close to a nearby known galaxy  treated as successful trigger Info gathered on ground; Few hours delay; ～ 3000 events per day (0.4% real event); Special GCN notices BAT triggers summary: Image threshold SNR

16. Detections from Ground Process Transient Monitor – Energy range: 15-50 keV – Delay time: few hours – Image exposure: ～ 1200 s to days – Currently the public results only include known sources Ground-detected bursts – Failed-event data Auto search: Taka’s pipeline Human search: Jay Cummings/David Palmer

17. Detections from Ground Process Transient Monitor – Energy range: 15-50 keV – Delay time: few hours – Image exposure: ～ 1200 s to days – Currently the public results only include known sources Ground-detected bursts – Failed-event data Auto search: Taka’s pipeline Human search: Jay Cummings/David Palmer

18. Swift/BAT hard X-ray transient monitor 15-50 keV (single energy range) Built from on-board “scaled maps” from 64 to >1000 seconds duration. Rapid, near real-time pipeline processing 269 detected sources: 146 persistent and 123 in outburst Red=steady Blue=variable Green=outburst Orange=flaring Very sensitive to variable sources IGR J17391-3021 GX 9+1 GRS 1915+1051A 0535+262 Results from monitor paper: Krimm et al, ApJSS 209, 2013 Krimm, BAT Monitor & Survey Slide from Hans Krimm

19. Detections from Ground Process Transient Monitor – Energy range: 15-50 keV – Delay time: few hours – Image exposure: ～ 1200 s to days – Currently the public results only include known sources Ground-detected bursts – Failed-event data Auto search: Taka’s pipeline Human search: Jay Cummings/David Palmer

20. Detections from Ground Process Transient Monitor – Energy range: 15-50 keV – Delay time: few hours – Image exposure: ～ 1200 s to days – Currently the public results only include known sources Ground-detected bursts – Failed-event data Auto search: Taka’s pipeline Human search: Jay Cummings/David Palmer

21. Detections from Ground Process Transient Monitor – Energy range: 15-50 keV – Delay time: few hours – Image exposure: ～ 1200 s to days – Currently the public results only include known sources Ground-detected bursts – Failed-event data Auto search: Taka’s pipeline Human search: Jay Cummings/David Palmer

22. Detections from Ground Process Transient Monitor – Energy range: 15-50 keV – Delay time: few hours – Image exposure: ～ 1200 s to days – Currently the public results only include known sources Ground-detected bursts – Failed-event data ( ～ 10 s; pass rate failed image) Auto search: ground scripts from Takanori Sakamoto Human search: Jay Cummings/David Palmer

23. GRBs missed by on-board triggers Off-axis On-axis

24. GRBs missed by on-board triggers Off-axis On-axis ～ 50 o Off-axis ～ 30 o Off-axis

25. Sub-threshold short GRBs (from the BAT trigger simulation) Rate SNR: ～ 52 Image SNR: ～ 34 Rate SNR: ～ 9 Image SNR: ～ 5 Troja, Lien et al.

26. Sub-threshold short GRBs (from trigger simulation) Rate SNR: XXX Image SNR: XXX Rate SNR: XXX Image SNR: XXX Burns et al. (2015) Search Fermi/GBM sGRBs in BAT Expect 30 sGRBs in BAT FOV + observe time 22 triggered BAT 5 found on ground-analysis (not during slew) A few more GBM sGRBs are likely found in BAT failed event data. BAT see most of GBM sGRBs.

27. Fail BAT triggers summary > 600 Rate criteria Success Image Threshold Image duration & energy from rate criterion Trigger! (1000 s event data) Failed event (10 s Event data) Image threshold on Images with 64 s, 320 s, full obs. 15-50 keV Success Fail Keep trying…. Courtesy to Scott Barthelmy Success Fail Trigger! (1000 s event data) Sub-threshold Sub 2 -threshold Keep trying….

28. Fail BAT triggers summary > 600 Rate criteria Success Image Threshold Image duration & energy from rate criterion Trigger! (1000 s event data) Failed event (10 s Event data) Image threshold on Images with 64 s, 320 s, full obs. 15-50 keV Success Fail Keep trying…. Courtesy to Scott Barthelmy Success Fail Trigger! (1000 s event data) Sub-threshold Sub 2 -threshold Keep trying…. Transient Monitor Human analysis of failed evt data

29. Thank you!

30. Back-up slides

31. Sub-threshold Normal image-domain threshold=6.5 sigma Subthreshold Notices (image sigma is in the 5.7-6.5 range) Location uncertainty: 2-4 arcmin (90% CL) False-positive rate: ~ 96% (3 real astrophysical sources in 75 subthreshold triggers) – ~6.3

32. Sub-sub threshold Scaled-map images (from the shortest duration of the rate foreground period up to full observation of 43 min) SNR: 3.8-6.5 Rate: 3000 per day (1000 known source) False-detection rate: very high (3-4 real event in 1000 notice) Time delay: 1-8 hours Location error: 1-4 arcmin

33. BAT transient monitor Based on scaled map (15-50 keV) Search known and unknown sources in images for each pointing (~ 1200 s), 1, 2,, 4, 8, 16 days

34. Trigger statistics for the successful triggers Image trigger (16.6%) Rate trigger (83.4%) Rate trigger (100%) Short GRBsAll GRBs

35. Trigger statistics for the successful triggers Image trigger (16.6%) Rate trigger (83.4%) Rate trigger (100%) Short GRBsAll GRBs Foreground timeNumber of sGRB triggers 0.51212 1.0248 0.0329 0.25612 0.06423 0.1288 0.3842