1. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter Robert J. Nemiroff (Michigan Tech) Primary Collaborators: Jay P. Norris (NASA), Jerry T. Bonnell (USRA), Gabriela Marani (GMU)

2. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter Overview of: Gamma Ray Bursts Gravitational Lensing Cosmological Dark Matter Gamma Ray Burst Lensing Limits on Cosmological Dark Matter –Searches, Present Limits Future Missions –Swift, GLAST, theoretical usefulness

3. Gamma Ray Bursts Intense flashes of gamma rays –Last from milliseconds to minutes –Location unpredictable: occur all over the sky Discovered by accident in 1960s Seen now by satellites across Solar System BATSE on CGRO (1991-2000) saw most, faintest Distance “Great Debate” at Smithsonian in 1995. GRBs now known to occur at cosmological distances Optical Transients (OTs) and redshifts first recorded in 1997

4. Gamma Ray Bursts Sky Map (BATSE, final) Credit: G. Fishman, et al., BATSE, CGRO, NASA

5. Gamma Ray Bursts A GRB 000301C Symphony Telescopic instruments in Earth and space are still tracking a tremendous explosion that occurred across the universe. A nearly unprecedented symphony of international observations began abruptly on March 1 when Earth-orbiting RXTE, Sun- orbiting Ulysses, and asteroid-orbiting NEAR all detected a 10- second burst of high-frequency gamma radiation. Within 48 hours astronomers using the 2.5-meter Nordic Optical Telescope chimed in with the observation of a middle- frequency optical counterpart that was soon confirmed with the 3.5-meter Calar Alto Telescope in Spain. By the next day the explosion was picked up in low-frequency radio waves by the by the European IRAM 30-meter dish in Spain, and then by the VLA telescopes in the US. The Japanese 8-meter Subaru Telescope interrupted a maiden engineering test to trumpet in infrared observations. Major telescopes across the globe soon began playing along as GRB 000301C came into view, detailing unusual behavior. The Hubble Space Telescope captured the above image and was the first to obtain an accurate distance to the explosion, placing it near redshift 2, most of the way across the visible universe. The Keck II Telescope in Hawaii quickly confirmed and refined the redshift. Still, no one is sure what type of explosion this was. The symphony is not over - oddly no host galaxy appears near the position of this explosion. Will one appear as the din of the loud fireball fades? Credit: Andrew Fruchter (STScI) et al., STIS, HST, NASA Astronomy Picture of the Day 2000 March 14

6. Gamma Ray Bursts Aside: Sky Monitoring: CONCAM X X Y X http://concam.net Six nodes currently active, 3 more already deployed

7. Gamma Ray Bursts Aside: Sky Monitoring: CONCAM Here is the sky movie from Mauna Kea on the night of 2001 November 18. Easily visible are stars, planets, meteors, the Galactic Plane, and zodiacal light

8. Gravitational Lensing Gravity attracts even light First predicted in 1800s First detected 1919 by Eddington for Sun QSO lensing first detected 1979 Cluster of Galaxy lenses: 1986 Microlensing: 1993 GRB lensing: 20??

9. Cosmological Dark Matter Big Mystery Modern cosmology driven by observations Defining observations: –cluster motions, spiral rotation curves, nucleosynthesis, galaxy clustering, distant supernovae and the cosmic microwave background Standard Cosmological Paradigm (new!): –Omega_lambda=0.73 –Omega_CDM=0.23 –Omega_baryon=0.04 What makes up dark energy, dark matter, dark baryons?

10. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter Types of Proposed GRB Lensing: macrolensing (Galaxy-mass lens) –Nemiroff et al., ApJ, 1994 millilensing (globular cluster mass lens) –Nemiroff et al., PRL, 2001 microlensing (stellar mass lens) –Paczynski., ApJ, 1986

11. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter Femtolensing (10 -13 - 10 -16 Mo) –Gould, A. 1992, ApJ Picolensing (10 -15 - 10 -7 Mo) –Nemiroff & Gould, 1995, ApJ Nanolensing (~10 -5 Mo) –Walker & Lewis, 2003, ApJ

12. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter Search for echos of GRBs in BATSE time series Searched most BATSE GRBs No good candidates found Time from trigger, seconds

13. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter For detection, millilens must create –second image within detectable flux ratio –second image within detectable time boundaries Gravitational Lens Detection Volume: –Lens cannot be too far from axis or flux ratio drops below detectability –Lens cannot be too far from axis or time delay increases beyond detectability –Lens cannot be too close to axis or time delay decreases beyond detectability

14. Gamma Ray Burst Lensing Limits on Cosmological Dark Matter No lens echoes detected Many lens echoes expected if dark matter clumped into canonical mass aggregates.

15. Future Missions Swift Swift satellite (NASA) Scheduled launch: 12/2003 Observe >200 GRBs, many with redshifts 5 times more sensitive than BATSE

16. Future Missions GLAST GLAST satellite (NASA) Scheduled launch: 2006 >200 GRBs/yr

17. Future Missions Theoretical Potential GRBs the most variable objects visible in the distance universe –untapped potential for known objects macrolensing: galaxy formation (high z) millilensing: AGN formation (high z) microlensing: star density (high z) picolensing, nanolensing, femtolensing: –unique path to explore low mass universe