New Light on the Transient High-Energy Universe

Dark Universe | Transient Universe | Outer Solar System | Near Earth Objects | Milky Way | LSST Tour

Image Credit:X-ray - NASA/CXC/Rutgers/G.Cassam-Chenai, J.Hughes et al.; Radio - NRAO/AUI/NSF/GBT/VLA/ Dyer, Maddalena & Cornwell; Optical - Middlebury College/F.Winkler, NOAO/AURA/NSF/CTIO Schmidt & DSS


The LSST will explore a new universe of transient sources of luminosity. We already have hints of unusual and violent events at great distances. Recently, a combination of observations with the Beppo-SAX satellite and two ground-based optical telescopes has produced proof that gamma-ray burst sources are at high redshift and so must be the most luminous objects in the universe. This must be new physics or a manifestation of physics in new and extreme conditions: attempts at a theoretical explanation using known physics have encountered major difficulties. More generally, our monitoring and knowledge of transient sources in the cosmos is in its infancy. While it is unlikely that known rare and luminous objects like gamma ray bursters would be seen in quantity by LSST, their afterglows would. More significantly, it is likely that these initial intriguing data hint at much more to come. What are the "mystery transients" detected by Schmidt etal. while they were searching for distant supernovae with the Big Throughput Camera? Imagine what we might find if we could monitor the sky for 10-second optical bursts a million times fainter.

Optical burst detected by difference imaging (right hand frame) in the Deep Lens Survey.

Repeated imaging of 20,000 square degrees of the sky may uncover many bursting sources in the optical, at high redshift. The Large Synoptic Survey Telescope, in its all-sky search for near-Earth objects, will be uniquely sensitive to brief flashes of light. The LSST can reach 24th magnitude in 10 seconds, over ten square degrees of the sky, in a single snapshot. The flash of blue light resulting from redshifted prompt UV bursts in many distant supernovae might be detected. But it is the totally unexpected phenomena that will provide the payoff. Data on these sources would be released immediately to the community for correlation with satellite observations at high energy and for follow-up studies. Note that no existing telescope or camera can access this part of parameter space—rare faint transients.

STIS image and light curve of GRB990123. It peaked at brighter than 9th magnitude in the optical, despite having a cosmological redshift. That makes it the most energetic event yet detected and poses a severe challenge to theorists who model these events. The technology now exists to monitor the sky in the optical for rare faint transients of all types—a million times fainter. Top figure from Bloom et al., Astrophysical Journal (Letters), v518, p1.

The detection of transient emission provides a window on diverse astrophysical objects, from variable stars to stellar explosions to the mergers of compact stellar remnants. Perhaps even more exciting is the potential for discovering new, unanticipated phenomena. A few short lived optical bursts without precursor objects have already been seen in SN surveys and by the Deep Lens Survey. LSST will obtain deeper and better sampled multi-color data on tens of thousands of such events.