SOFT GAMMA REPEATERS Kevin Hurley UC Berkeley Space Sciences Laboratory THE SGR-SHORT BURST CONNECTION Kevin Hurley UC Berkeley Space Sciences Laboratory

ARE SOME SHORT GRBs ACTUALLY MAGNETAR FLARES IN NEARBY GALAXIES? GIANT FLARE FROM SGR RHESSI DATA SGR giant flares begin with a ~0.2 s long, hard spectrum spike The spike is followed by a pulsating tail, but it only contains ~1/1000 th of the energy Viewed from a large distance, only the initial spike would be visible It would resemble a short duration, hard spectrum GRB It could be detected out to ~100 Mpc

Some short GRBs are almost certainly giant magnetar flares, but how many? The answer depends on giant magnetar flare luminosities and rates (their number-intensity distribution), which are poorly known Two approaches: statistical, and burst-by-burst

HOW MANY ARE THERE? (STATISTICAL. I) Lazzati et al. (2005) studied BATSE short bursts with blackbody- like energy spectra They found only 3 Their conclusions: –Up to 4% of short bursts could be SGR giant flares (2σ limit), or –We have overestimated the energy of the galactic giant flares, or –We have overestimated the rate of galactic giant flares

HOW MANY ARE THERE? (STATISTICAL. II) Nakar et al. (2006) searched for nearby galaxies in the error boxes of 6 short duration hard spectrum GRBs Their conclusions: –<15% of BATSE short/hard GRBs are SGR giant flares, or –SGR giant flares can be much more energetic and more distant, or –SGR giant flares are very rare, possibly once in a magnetar lifetime, or –The distance to SGR1806 is smaller than previously thought

HOW MANY ARE THERE? (STATISTICAL. III) Popov & Stern (2005) looked for BATSE bursts from four nearby (<3.7 Mpc) galaxies undergoing star formation, and from the Virgo cluster (17 Mpc) Their conclusions –< a few percent of BATSE bursts are giant flares, and giant flares are very rare (1/1000 years/magnetar), or –Distance to SGR has been overestimated

GRB – A POSSIBLE EXTRAGALACTIC GIANT MAGNETAR FLARE FROM M81 (3.6 Mpc) IPN Error Ellipse M81 M82 Swift BAT keV (Not imaged) E γ =7x10 46 erg Frederiks et al. 2007

GRB – A POSSIBLE EXTRAGALACTIC MAGNETAR FLARE FROM M31 (780 kpc) IPN Error Box M31 E γ =1.5x10 45 erg LIGO measurements indicate that this could not have been a binary merger in M31 (Abbott et al. 2008) Mazets et al. 2008

GRB – A POSSIBLE SGR GIANT FLARE FROM IC 328 (130 Mpc) GRB was a 0.26 s long, very weak (6x10 -9 erg cm -2 ) Swift burst It had no fading X-ray or optical counterpart The BAT error circle includes a z=0.43 cluster (130 Mpc), with a starburst galaxy, IC 328 If this was its origin, E γ ~1.5x10 46 erg Levan et al. 2008

6 GIANT FLARE ENERGIES Assumed distance, kpcE γ, erg SGR August x10 44 SGR March (LMC)7x10 44 SGR February (M31)1.5x10 45 SGR December x10 45 SGR September (IC 328)1.5x10 46 SGR November (M81)7x10 46

NUMBER-INTENSITY RELATION FOR 6 SGR GIANT FLARES* *not to be taken too seriously

CONCLUSIONS A small percentage of short GRBs are extragalactic giant magnetar flares Their number is small enough that it does not contradict anything we know about short GRBs But it is not zero, so it is important to understand them from the SGR point of view A definitive search through existing data has not been carried out yet