An overview of the AEOS Burst Camera

1. An overview of the AEOS Burst Camera Heather Swan University of Michigan June 3, 2005 1

2. Outline • Science Goals • System design • GRB Triggers/Response • Grating analysis/Simulations 2

3. AEOSBurstCameraSensitivity ROTSE-I/TAROT • Half of all GRBs have no optical counterparts • Could catch very fast faders (short bursts?) • High S/N for studying variability or spectral evolution ROTSE-III ABC w/ grating ABC w/o grating Keck 1 min. 10 min. 3

4. ABC field of view is well matched to the Swift BAT error box 90% will be localized to a 3 arc minute radius (Can see them with the ABC) 50% will be localized within 12 seconds (Can see them promptly) (From Fenimore, et al) 4

5. How many GRBs do we expect to observe in Maui? • Swift promises 90/yr • 1/3rd of the time it is dark in Maui • 1/3rd of the time the GRB will have a high enough elevation • 3/5ths of the time the weather will be good • 1/15th of the bursts can be observed, or 6 bursts/year That’s approximately the same number we’re allowed to observe per year (9) 5 5

6. The AEOS telescope is a large optical telescope used by the Air Force Advanced Electro-Optical Systems Telescope (AEOS) Largest ground based AF optical telescope (3.67m) Designed to track satellites, can quickly (~20 sec) slew to coordinates Located in Haleakala, Hawaii, at 10,000 ft ABC 6

7. The AEOS Burst Camera (ABC) is attached to the AEOS • Optics designed by Carl Akerlof • Package designed by Alan Schier • Camera built by Astronomical Research Cameras Field of view 6' x 6' F/# 4.5 Focal length of 16m 7

8. AEOS telescope image reducer design ABC 8

9. ZEMAX point spread function PSF gets bad near the edge of the FoV. 9

10. CCD camera specs • E2V 2kx2k back-illuminated CCD • Cooled to –40 F • CCD readout time ~6 seconds • Typical exposure length ~10 seconds 10

11. Improvements to the ABC image quality • The baffle • Attached to the secondary, blocks stray light • Improvements in alignment 11 11

12. The secondary baffle removes most of the stray light Image of M1 without a baffle M1 with the baffle 12

13. Other Uses of the ABC Satellite Tracking Lost Satellites Space Debris Asteroid Hunting 13

14. The ABC took images of the Genesis probe, just hours before it reached the earth! Genesis during separation 14 14

15. GRB Swift ABC Computers (Modified ROTSE Software) User Interface GCN Burst Filter Fax ::::::: ::::::: CD The ABC will try to observe GRBs within minutes after they are localized 15

16. We filter GRBs from the GCN to determine if the ABC should go after them We use the following criteria to determine if a GRB should be observed in Maui: • Less than 1 hour old • Localization should fit in our FoV • Sun should be far enough below horizon • Should be visible for at least an hour • Should be 20 degrees above horizon • Moon should not be too bright or too near • Should be 20 degrees away from galactic plane If a GRB passes all these cuts, it is automatically faxed to the AEOS control room (no humans required!) 16 16

17. Removes current images from the queue, cancels current set of exposures For GRB fax alerts ABC User Interface Camera Status Non-GRB observations Thumbnail of last image 17

18. Observation Timeline 18

19. We can also send manual GRB alerts • ROTSE-III finds an optical counterpart • Average time between GRB localization and ROTSE-III reporting afterglow, 30 minutes • If It is still bright, and should be visible when Maui can see it • We send a fax w/coordinates and finding chart • The ABC response won’t be prompt, but we know there is an afterglow! 19

20. ABC analysis pipeline Download images from Maui Correct images with flat field and dark. Use SExtractor to find objects Match stars to catalog Find limiting magnitudes Calculate magnitudes for each star Create lightcurves And many other things! Find spectra for objects 20 20

21. 030329 GRB response • 030329 – not prompt, but visible (t ~ 3 days) • 030418 –not prompt, or visible (t ~ 8 days) • 041006 – first image after 2.5 hours, bad pointing No other “real” GRBs have been requested • (2 false HETE alarms, but the weather was bad/mount was down) April 1, 2003 030418 April 25, 2003 21

22. 041006: The pointing is off, how do we fix it? Here there be Dragons! The problem was known before this GRB It’s a problem that is not easy to fix (hard to determine what is wrong) Now we send a finding chart, and the operators use wiki stars to get the correct pointing offsets We missed a GRB because of this problem! 22

23. Test Burst response times When the weather is bad, and the operators are in the room, sometimes the first images are taken seconds after the fax arrives! 23

24. Grating analysis/simulations • We installed a blazed transmission grating in Jan 2005 • 35 groves/mm, peak wavelength 640nm, blaze angle 2.2° • ~5 cm from CCD • R=/=8 • We’ve taken images of different types of objects • Red/blue stars • Quasars • We can compare images to simulations • Found limiting magnitudes for different exposure lengths 24

25. A star observed with the ABC Stars look like blackbodies Black body, sun’s temperature 25

26. Can differentiate between red and blue stars Cooler temps Hotter temps 26

27. We take a known spectrum of an object, and cram it through our simulator What we expect to see with the ABC SDSS spectrum of a quasar • Start with spectrum from SDSS • Multiply by CCD and grating efficiencies • Use grating equations to see what happens to the light • Convolve with psf simulator intensity Flux density 0 50 100 150 200 400 500 600 700 800 900 Image offset (pixels) Wavelength(nm) 0th order 1st order 27

28. Simulations look similar to actual data What we expect to see with the ABC • Quasars look “spiky” intensity 0 50 100 150 200 Image offset (pixels) 0th order 1st order What we actually see with the ABC This quasar has a z of 3.83, and an Rmag of 18.53 (10 s image, taken at twilight) 28

29. Higher orders look like what we would expect 29

30. Limiting Magnitudes Compare to SDSS images to find dimmest stars (Gives a rough estimate of limiting mag) Could be off- We have significant vignetting, and sparse fields Don’t have many fields to get limiting mags from 30

31. Conclusions • ABC is running well, operators know what to do • The pointing is off, but the operators know how to correct for that • The ABC should be able to get images a few minutes after the GRB is detected • The spectral information is crucial for understanding the GRB progenitor Questions? 31