SGR activity in time

Sergei Popov (SAI MSU)

(HEA-2006, 25-27 December 2006 Moscow, IKI)

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Four giant bursts

05 Mar 1979 27 Aug 199827 Dec 2004 18 Jun 1998?

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Energy output of SGRs

Thermal emission. L≈1035 erg/s. E < 1043 erg/year.

Short bursts. Hundreds of bursts per source with L<1041 erg/sduring ≈ 30 years. E<1042 erg/year.

Giant bursts. E ≈ 1044 erg/year if the 27 Dec. 2004 hyperflare is taken into account.

Giant bursts seem to dominate in the energy release.Giant bursts seem to dominate in the energy release.

(Review in Woods, Thompson 2004)

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Burst rate

In 30 years of observations four very powerful flareshave 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.

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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?What comes first: bursts or glitches?

Here I propose that glitches and bursts are closely related andthe burst rate evolves similar to the changes in glitch rate.

Most probably, the evolution of core-quake glitches can besimilar to the evolution of the burst rate.

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Glitches

Long-period pulsars are known to demonstrate glitch activity.PSR B0525+21 P=3.75 sec. Age ≈ 1.5 106 years.PSR J1814-1744 P≈3.98 sec. Age ≈ 8.5 104 years.

Two models: vortex unpinning and core-quakes (Alpar, Baykal 1994):

vortex unpinning:

core-quakes:

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Extragalactic giant flares

Initial enthusiasm that most of short GRBs can be explainedas 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).

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ExtraG flares and evolution

Absence of numerous extraG giant flares argues againstfrequent and energetic bursts of young magnetars, i.e.against significant increase of the rate of giant bursts for smallSGR ages with the same (or even larger) energy in comparisonwith the known galactic SGRs.

Still, evolutionary law cannot help to solve the problem ofthe deficit of giant flares from the Virgo region.

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Total energy storage

Etherm<1046 erg

magnetic energy

In magnetars, by definition, magnetic energy dominates.

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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 k0=50 yrs andE0=3 1044 erg. For b<0 and when hyperflares are taken intoaccount, the crises appears even for smaller values of a.

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Galactic population

If the rate of flares decreases with time, then there are no youngerSGRs in the Galaxy, but some older objects, which do not showany strong activity now, can produce giant flares in the future.

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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~ta and a>2 there is not enough energy to supportflares of the same (or larger) energy that we observe from SGRs.

So, young SGRs should burst often, but produce less powerful flares.