Peter R. Saulson Syracuse University

1. How will theory, observation, and instrument development interact?Test case:If we find “unknown” GW bursts, how will we figure out what they are? Peter R. Saulson Syracuse University

2. Inspiration Prediction is hard, especially about the future. Niels Bohr or Yogi Berra?

3. Outline • Role of angular resolution in understanding a new astronomical phenomenon • Cautionary tale: the history of gamma ray bursts • Will we be luckier?

4. How astrophysical phenomena get understood Understanding a new astronomical phenomenon: Needed: energy scale Hence, needed: distance Could use purely geometric method, i.e. parallax But that is hard, and hasn’t worked for any of the “new astronomies” Needs very accurate position measurement Still only works very nearby Key step: identification with objects already known Whose distances are known via the distance ladder Thus linked to stellar parallax Historically, this is usually done by matching sky positions. How good do positions need to be for this to work?

5. Angular resolution GW detectors have a very broad beam pattern. “Almost” isotropic Position information from time delays between signal reception at different detectors in a global network. Precision: Historically, when has much finer angular resolution been required for identification? When is coarse angular resolution sufficient?

6. When fine resolutionwas required Famous optical identifications: • Cygnus A (Baade and Minkowski 1954) Identified with peculiar galaxy inside a radio error box of ½ arcmin diam. • 3C273 (Schmidt 1963) Identified with 13th mag star with jet, using position with errors of a few arcsec • Sco X-1 (Gursky et al. 1966) Identified with 13th mag UV-excess star inside error boxes of area 4 arcmin2 Identification requires: • Good position • Counterpart that is both visible and unusual

7. Precise position allowed the discovery of quasars Precise locations, 2 components “Star” + jet, aligned with radio sources It took arcsec precision to spot the odd starlike object (although with a jet!) coincident with 3C273. Time series from three different lunar occultations.

8. When coarse resolutionis enough When enough objects are found that sky map reveals a distinctive pattern, then, we can apply the time-tested method that dates to Harlow Shapley and H. D. Curtis. Great Debate of 1920 on the Galaxy Question. This method was recalled in the 75th Anniversary Great Debate on the nature of gamma ray bursts. esp., paper by Paczynski

9. Nearby stars

10. Planetary nebulae

11. Supernova remnants

12. Globular clusters Shapley found the shape and size of the Galaxy from this map.

13. Nearby galaxies Curtis used this map to argue that spiral nebulae are outside the Galaxy.

14. Extragalactic radio sources

15. Low mass X-ray binaries Luck smiled in this case. Distance scale was obviously of order 10 kpc; energy scale linked LMXB phenomenon to neutron stars.

16. The long sad storyof gamma ray bursts Very crude positions (tens of sq. deg., from time delays) were enough to establish from the outset (Klebesadel et al. 1973) that GRBs didn’t come from very nearby sources. • Earth (i.e., nuclear explosions) • or any other place in the Solar System There followed a long slow process of accumulating catalogs of events with only somewhat better positions, with awkwardly shaped error boxes. Ten years after discovery, confusion still reigned. It took about twenty years for the story to become clear.

17. What sky maps look like when error boxes are annuli Could one recognize with any confidence that these maps represent an isotropic distribution?

18. Gamma ray burstsfrom BATSE GRO launched 1991, first results announced September ’91.

19. Proper interpretationof log N – log S rel’n Scale-free map came along with a number vs. luminosity relation that clearly had an outer scale. Expected an outer boundary to the distribution in two cases: • If the distribution were galactic, but then expected the sky map to be anisotropic. • If the distribution were cosmological, with the outer boundary representing redshift effects. This tipped the scales in favor of cosmological distances, but many were still not convinced.

20. Breakthrough with BeppoSAX 1997 observations with multi-wavelength BeppoSAX satellite allowed observations of X-ray transients linked to GRBs. Error circles with radius of ~ 3 to 5 arcmin. GRB970508 was then identified with an optical transient. Optical spectra showed an absorption-line spectrum with redshift z = 0.83. In this case, several stages of finer angular resolution measurements used the transient character of the source to allow identification.

21. Will we be luckier? • Will we only find GW counterparts of known phenomena? That would be the most boring outcome. • Will high SNR detections yield good positions, thus identifications? • Will burst sources always have E/M counterparts?

22. Will our sourcestell their own stories? • Can the waveform of a gravitational wave burst be linked uniquely to identity of object, e.g. through the modal structure of BH or NS? • Binary systems will have distinct polarization and waveforms, and endpoints will reveal mass scale. • Collapse events have both a mass scale and a non-sphericity parameter – they will need distances to untangle.

23. Can we localize a source better than this?

24. Using theory, observation, and instrument development to make our own luck • Push noise levels down. • Learn to use a global network. Not just event timing, but detailed waveform determination will be key to getting positions, and to gaining other clues. • Operate a network with many elements, good duty cycle, and with best possible performance. Need error boxes that are boxes, not annuli. • Become confident enough to issue prompt alerts. • Run long enough to get lots of events. Spatial patterns don’t emerge unless maps are full. • Learn to sort events into classes, if necessary. • Be prepared to understand waveform information. Numerical relativity, heuristic astrophysics are valuable. (But we don’t need more theories than events. )