Gamma-Ray Bursts as Cosmological Probes Robert J. Nemiroff

Gamma-Ray Bursts as Cosmological Probes Gamma ray bursts (GRBs), the most powerful explosions known in the universe, are telling us about the universe itself. These enigmatic explosions are useful probes because they are so rapidly transient and because they can be seen further out into the universe than any other transient phenomenon. The lack of a gravitational lensing signature, for example, limits the abundance of potential lenses, and hence the composition, of the universe. The high redshift of many GRBs allows a unique probe of the density of star formation rate during first few billion years of the universe. The quest to find a standard candle for GRBs, which could be used to confirm and calibrate the geometry of the universe, will be reviewed, along with the recent results. Analyses of GRB light curves allow a probe of the light path for effects of quantum gravity, limits on the energy dependence of the speed of light, and even intelligent life.

Talk Outline: GRBs and Cosmology Discovery of GRBs What and where are GRBs? How can GRBs tell us about the universe?

Gamma-Ray Burst: A Milestone Explosion Astronomy Picture of the Day: 2000 July 2 Credit: R. Klebesadel, I. Strong & R. Olson (LANL), Vela Project

The first gamma- Ray burst model Appeared before The Vela results Were published! By 1992, over 100 models Existed! Despite this Number, the Currently favored Model is not on This list! Table: Nemiroff, R. J. 1991, Comments on Astrophysics

On the 75 th anniversary of the great debate between Curtis and Shapley On the Scale of the Universe, Bohdan Paczynski (left) and Donald Lamb (right) debated The Distance Scale to Gamma Ray Bursts in the same Auditorium. Martin Rees (center) moderated. (Photo: Jerry Bonnell)

Credit: G. Fishman et al., BATSE, CGRO, NASA BATSE GRB Final Sky Map: Astronomy Picture of the Day 2000 June 28

S keV / S keV 90 % Width ( sec ) Soft Hard Two Duration Classes of GRBs

Gamma-Ray Burst Durations Two Populations: Short – s Long – s Possible third Population 1-10s

A GRB C Symphony Credit: Andrew Fruchter (STScI) et al., STIS, HST, NASA Astronomy Picture of the Day 2000 March 14 Explanation: 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 C 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?

Image Credit: S. Kulkarni, J. Bloom, P. Price, Caltech - NRAO GRB Collaboration Gamma-Ray Burst, Supernova Bump: Astronomy Picture of the Day 2002 May 17

A Slow Explosion Astronomy Picture of the Day: 2003 March 25 Credit: Y. Grosdidier (U. Montreal) et al., WFPC2, HST, NASA

Short Gamma-Ray Busts Localized Astronomy Picture of the Day: 2005 October 17 Illustration Credit : Dana Berry, NASA

On the Origin of Gold: Astronomy Picture of the Day: 2005 May 15

Credit & Copyright: Visualization: Ralf Kaehler (ZIB) & Tom Abel (Penn. State) Simulation: Tom Abel (Penn. State), Greg Bryan (Oxford) & Mike Norman (UCSD) Zooming in on the First Stars Astronomy Picture of the Day 2003 June 10

Relations Lag-Luminosity (Norris et al.): L   Variability-Luminosity (Fenimore & Ramirez-Ruiz, Reichart et al.):L  V 3.3 AtteiaN  /E pt /√T 90  f(z) Amati: E pt  E iso 1/2 Ghirlanda:E pt  E  0.7 Yonetoku:E pt  L 1/2

From Nemiroff & Tilvi 2005, in preparation: E_peak corrected for redshift Still appears to be a function of redshift.

Some Burst Terminology E p is E of peak of E 2 N(E)  f Peak of lightcurve Spectrum may be from lightcurve peak or entire burst (“fluence spectrum”) Integrate spectrum for bolometric flux or fluence Integrate over entire burst for total energy Spiky-ness can be quantified

But GRBs at low BATSE peak fluxes do look similar. Fraction of long-lag bursts increases approaching BATSE threshold. Fraction of long-lag bursts increases approaching BATSE threshold. Long-lag bursts: - lags > 0.5s - tend to be dim - simple, few pulses (Stern, Poutanen & Svensson 1999) - wide pulses - softer spectrum

A Main Sequence “HR Diagram for Gamma-Ray Bursts” L 53 ≈ 1.1  (  lag /0.01 s) Updated from Norris, Marani, Bonnell (2000). Woosley & MacFadyen (1999), Ioka & Nakamura (2001), others predicted subclass of numerous, nearby GRBs: low luminosity, soft-spectrum, long-lag. See Sazonov et al. (2004) for subluminous GRB See GCN 3484 (redshift, lag for GRB )

Beamed Burst Emission  External shock—origin of afterglow Internal shocks—origin of burst Central Engine Break in lightcurve resulting from jet’s finite width; modeling gives 

Possible Central Engine Unified Model SN IIM prog > 10 M o NS Long GRB & SNIcM prog > 20 M o NS + SN fallback to BH Dark CollapseM prog > 40 M o BH direct, no SN Long GRBM prog > 40 M o + some spinBH + GRB Short GRBNS+NS merger ??? From Gehrels, N., 2004, GSFC presentation

Credit: Nemiroff et al. 2001, PRL 86, 580 Millilensing Candidate GRB: BATSE Trigger 5457

Limits on Universe abundance of Compact Objects: Entire BATSE Sample Credit: Nemiroff et al. 2001, PRL 86, 580

GRB pulse structure at GeV energies + Gigaparsec distances may constrain E Quantum Gravity ~10 19 GeV Amelino-Camelia et al. (1998) predict energy-dependent dispersion: v  c{1 -  E photon /E QG )}  t = (1 GeV/E QG )(1 Gpc/c) ~ 10 ms LAT could look for the predicted energy- and distance-dependent effects. Lorentz Invariance Violation: Bounds on the energy dependence of the speed of light can constrain the effective energy scale for quantum gravity effects.

GRB as SETI Markers Search for ET signals in direction of GRBs just after GRB Send an ET-like signal in the opposite direction of a GRB, just after a GRB Identifies unique angles and times on the sky Might be found serendipitously by ETs studying GRBs See: Corbet, R. H. D. 1999, PASP, 111, 881:

X-Ray Rings Expand from a Gamma Ray Burst Astronomy Picture of the Day 2004 January 30 Credit: S. Vaughan, R. Willingale (U. Leicester) et al., XMM, ESA