SGR activity in time Sergei Popov (SAI MSU) (HEA-2006, December 2006 Moscow, IKI)

2 Four giant bursts 05 Mar Aug Dec Jun 1998?

3 Energy output of SGRs Thermal emission. L≈10 35 erg/s. E < erg/year. Short bursts. Hundreds of bursts per source with L<10 41 erg/s during ≈ 30 years. E<10 42 erg/year. Giant bursts. E ≈ erg/year if the 27 Dec hyperflare is taken into account. Giant bursts seem to dominate in the energy release. (Review in Woods, Thompson 2004)

4 Burst rate In 30 years of observations four very powerful flares have been detected. 18 Jun 1998 burst is often not included into the list of giant flares. To be conservative, one can assume the rate as one in 50 years per source. Usually burst rate is taken to be constant during the lifetime of a source.

5 Bursts vs. Glitches Bursts of magnetars are known to be related to glitches (Kaspi et al. 2003, Woods et al. 2004). What comes first: bursts or glitches? Here I propose that glitches and bursts are closely related and the burst rate evolves similar to the changes in glitch rate. Most probably, the evolution of core-quake glitches can be similar to the evolution of the burst rate.

6 Glitches Long-period pulsars are known to demonstrate glitch activity. PSR B P=3.75 sec. Age ≈ years. PSR J P≈3.98 sec. Age ≈ years. Two models: vortex unpinning and core-quakes (Alpar, Baykal 1994): vortex unpinning: core-quakes:

7 Extragalactic giant flares Initial enthusiasm that most of short GRBs can be explained as giant flares of extraG SGRs disappeared. At the moment, we have a definite deficit of extraG SGR bursts, especially in the direction of Virgo cluster (Popov, Stern 2006; Lazzatti et al. 2006). However, there are several good candidates (for the latest one see Frederiks et al. 2006).

8 ExtraG flares and evolution Absence of numerous extraG giant flares argues against frequent and energetic bursts of young magnetars, i.e. against significant increase of the rate of giant bursts for small SGR ages with the same (or even larger) energy in comparison with the known galactic SGRs. Still, evolutionary law cannot help to solve the problem of the deficit of giant flares from the Virgo region.

9 Total energy storage E therm <10 46 erg magnetic energy In magnetars, by definition, magnetic energy dominates.

10 Evolution and energy storage Let both, flare energy and flare rate, evolve as powers laws: Total energy release due to flares should be below total magnetic energy storage. For b=0 the energy crises appear for a>2.5 for k 0 =50 yrs and E 0 = erg. For b<0 and when hyperflares are taken into account, the crises appears even for smaller values of a.

11 Galactic population If the rate of flares decreases with time, then there are no younger SGRs in the Galaxy, but some older objects, which do not show any strong activity now, can produce giant flares in the future.

12 Some uncertain conclusions It seems inevitable that the rate of giant flares decreases with time, as for young SGRs all timescales are shorter. But then, if rate~t a and a>2 there is not enough energy to support flares of the same (or larger) energy that we observe from SGRs. So, young SGRs should burst often, but produce less powerful flares.