Soft gamma repeaters outside the Local group S.B. Popov, B.E. Stern (astro-ph/0502391; astro-ph/0503532)

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.

SGRs: periods and giant flares P, sec Giant flare 0526-66 1627-41 1806-20 1900+14 +candidates 8.0 5 March 1979 6.4 18 June 1998 (?) 7.5 24 Dec 2004 5.2 27 Aug 1998 See a review in Woods, Thompson astro-ph/0406133

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 in Woods, Thompson astro-ph/0406133

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

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

The probability of detection by BATSE of a giant flare

BATSE GRBs associated with near-by starbursts

The probability of detection by BATSE of a hyperflare

BATSE GRBs associated with “supernova factories”

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

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 associations between UHECR and starforming galaxies. In particular, Giller et al. discussed Arp 299 and NGC 3256.

Evolution of SGR activity Usually the rate of GFs is assumed to be constant. However, all types of activity of NSs normally decay with time For example, the rate of starquakes is expected to evolve as t5/2 If the rate of GFs evolves proportionally to time or faster then: The probability to detect a SGR is higher for younger objects 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 the probability of detection of extragalactic SGRs.

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 - ??????