1

Soft gamma repeaters outside the Local group

S.B. Popov, B.E. Stern

(astro-ph/0502391; astro-ph/0503532)

Physics of Neutron Stars–200527 June 2005. St-Petersburg.

2

Abstract

We propose that the best sites to search for SGRs outside the Local group are galaxies with active massive star formation.

We searched for giant flares from near-by starforming galaxies (M82, M83, NGC 253, NGC 4945) and from “supernova factories” (Arp 299 and NGC 3256) in the BATSE catalogue. No good candidates are found.

We discuss this result.

3

SGRs: periods and giant flares

0526-66 1627-41 1806-20 1900+14

+candidates

P, sec Giant flare

8.0

6.4

7.5

5.2

5 March 1979

27 Aug 1998

24 Dec 2004

18 June 1998 (?)

See a review inWoods, Thompsonastro-ph/0406133

History was reported by Prof. Clineand observational data by Dr. Palshin

4

Main types of activity of SGRs

Weak burst. L<1041 erg/s Intermediate bursts. L=1041–1043 erg/s Giant bursts. L<1045 erg/s Hyperflares. L>1046 erg/s

See a review inWoods, Thompsonastro-ph/0406133

History was reported by Prof. Clineand observational data by Dr. Palshin

5

SGR flares vs. GRBs

Woods et al.

6

SGRs and starformation

Possibility of a SGR detection outside the Local group of galaxies

Starforming galaxies are the best sites to search for extragalactic SGRs

<5 Mpc. M82, M83, NGC 253, NGC 4945 About 40 Mpc. Arp 299, NGC 3256 Possible candidates in the BATSE catalogue

of short GRBs

(Popov, Stern 2005)

See also the poster by A.Pozanenko

7

BATSE GRBs associated with near-by starbursts

8

BATSE GRBs associated with “supernova factories”

9

Virgo cluster analysis

We also searched for GFs and HFs fromthe Virgo cluster direction in BATSE data.Nothing was found (see astro-ph/0503352).Renormalizing this result to our Galaxywe obtain that HFs should be as rare asone in 1000 years. This estimate is in correspondence with results obtained by other authors (Palmer et al. 2005, Ghirlanda et al. 2005).

10

Assumed time profiles of the initial spike of the 05 March 1979 event

11

The probability of detection by BATSE of a giant flare

12

The probability of detection by BATSE of a hyperflare

13

Other ideas about relations between SGR and SF galaxies

Eichler (2005) discussed a possible connection between SGRs and high energy cosmic rays.

In this sense it is interesting to remember that several groups (for example, Giller et al.) reported the discovery of associationsbetween UHECR and starforming galaxies.

In particular, Giller et al. discussed Arp 299 and NGC 3256.

14

Evolution of SGR activity

Usually the rate of GFs is assumed to be constant.

However, all types of activity of NSs normally decay with timeFor example, the rate of starquakes is expected to evolve as t5/2

If the rate of GFs evolves proportionally to time or faster then:1. The probability to detect a SGR is higher for younger objects2. We can face “an energy crisis”, i.e. there is not enough energy to support strong burst in SGRs youth. All these items can be important in estimation of theprobability of detection of extragalactic SGRs.

15

Conclusions

Close galaxies with enhanced starformation

rate are the best sites to search for extragalactic SGRs

Our search in the BATSE catalogue did not provide good candidates

Reasons for the non-detection

- overestimates of the peak flux

- naïve scaling of the SGRs number is not valid

- ??????