Origin of magnetars and observability of soft gamma repeaters outside the Local group

1. Origin of magnetars andobservability of soft gamma repeaters outside the Local group S.B. Popov (Sternberg Astronomical Institute) Co-authors: M.E. Prokhorov, B.E. Stern (astro-ph/0502391; astro-ph/0503532; astro-p/0505406)

2. Plan of the talk • Introduction: magnetars (Woods, Thompson 2004) • Origin of magnetars (astro-ph/0505406) • Search for extragalactic magnetars (astro-ph/0502391; astro-ph/0503532)

3. Introduction: magnetars Magnetars are neutron stars powered by their magnetic fields (i.e. not by rotation, thermal evolution, etc.) Usually they have high magnetic fields. There are two main types of magnetars: Soft gamma repeaters (SGRs) and Anomalous X-ray pulsars (AXPs). (см. «В мире науки» N6 2003 г. + более новый Elementy.ru)

4. Magnetic field measurements Large fields: 1014 – 1015 G • Direct measurement of the magnetic field of the SGR • Spin-down • Long periods Ibrahim et al. 2002

5. Alternative theory • Fossil disk • Mereghetti, Stella 1995 • Van Paradijs et al.1995 • Alpar 2001 • Marsden et al. 2001 • Problems ….. • How to generate strong bursts?

6. Magnetars in the Galaxy • 4 SGRs, 8 AXPs, plus candidates, plus radio pulsars with high magnetic fields … • Young objects (about 104 yrs). • Probably about 10% of all NSs.

7. Historical notes • 05 March 1979. Cone experiment. Venera-11,12 (Mazets et al.) • Event in LMC. SGR 0520-66. • Fluence: about 10-3 erg/cm2 Mazets et al. 1979

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

9. 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

10. Common (weak) bursts from SGRS and AXPs • Typical burst from SGR 1806-29, SGR 1900+14 and from AXP 1E 2259+586 observed by RXTE (from Woods, Thompson, 2004, astro-ph/0406133) from Woods, Thompson 2004

11. Intermediate SGR bursts • Four intermediate bursts. However, the forth is sometimes considered as a giant one from Woods, Thompson 2004

12. Giant flare from SGR 1900+14 (27 Aug 1998) • Data from Ulysses (figure from Hurley et al. 1999a) • Spike 0.35 sec • P=5.16 sec • L>3 1044 erg/s • ETOTAL>1044 erg • Influenced the Earth ionosphere Hurley et al. 1999

13. 27 Dec 2004 giant outburst of SGR 1806-20 • Spike 0.2 sec • Fluence 1 erg/cm2 • E(spike)3.5 1046 erg • L(spike)1.8 1047 erg/s • Long tail (400 s) • P=7.65 s • E(tail) 1.6 1044 erg • Distance 15 kpc Подборка статей в обзоре Архива www.astronet.ru; Scientific.Ru

14. The greatest flare of a Soft Gamma Repeater • On December 27 2004 the greatest flare from SGR 1806-20 was detected by many satellites: Swift, RHESSI, Konus-Wind, Coronas-F, Integral, HEND, … • 100 times brighter than ever! Palmer et al. astro-ph/0503030

15. Konus-Wind data om SGR 1806-20 27 Dec 2004 flare Mazets et al. 2005

16. AXP: anomalous X-ray pulsars These sources were recognized as a separate class in 1995 • They are characterized by: • Continuous spin down • Period about 5-10 sec • Small and stable X-ray luminosities • about 1035 erg/s • Soft spectra • Absence of secondary companions • Recently bursts (similar to weak bursts of SGRs) • were discovered.

17. Known AXPs and candidates Name Period, s

18. Are SGRs and AXPs relatives? • SGR-like bursts from AXPs • Spectral properties • Quiet periods of SGRs (0525-66 since 1983) Gavriil et al. 2002

19. I. Origin of magnetars: abstract •We present population synthesis calculations of binary systems. • Our goal is to estimate the number of neutron stars originated from progenitors with enhanced rotation, as such compact objects can be expected to have large magnetic fields, i.e. they can be magnetars. • The fraction of such neutron stars in our calculations is about 13-16 %. • Most of these objects are isolated due to coalescences of components prior to a neutron star formation, or due to a system disruption after a supernova explosion. • The fraction of such neutron stars in survived binaries is about 1% or lower, i.e. magnetars are expected to be isolated objects. Their most numerous companions are black holes.

20. • 10 % of NSs are expected to be binary. • All known magnetars (or candidates) are single objects. • At the moment from the statistical point of view it is not a miracle, however, it’s time to ask this question. A question: Why do all magnetars are isolated? Two possible explanations • Large kick velocities • Particular evolutionary path

21. Theory of magnetars • Thompson, Duncan ApJ 408, 194 (1993) • Entropy-driven convection in young NSs generate strong magnetic field • Twist of magnetic field lines

22. Magnetars origin • Probably, magnetars are isolated due to their origin • Fast rotation is necessary (Thompson, Duncan) • Two possibilities to spin-up during evolution in a binary 1) Spin-up of a progenitor star in a binary via accretion or synchronization 2) Coalescence

23. The code We use the “Scenario Machine” code. Developed in SAI (Moscow) since 1983 by Lipunov, Postnov, Prokhorov et al. (http://xray.sai.msu.ru/~mystery/articles/review/) We run the population synthesis of binaries to estimate the fraction of NS progenitors with enhanced rotation.

24. The model Among all possible evolutionary paths that result in formation of NSs we select those that lead to angular momentum increase of progenitors. • Coalescence prior to a NS formation. • Roche lobe overflow by a primary. • Roche lobe overflow by a primary with a common envelope. • Roche lobe overflow by a secondary without a common envelope. • Roche lobe overflow by a secondary with a common envelope.

25. Parameters We run the code for two values of the parameter αqwhich characterizes the mass ratio distribution of components, f(q), where q is the mass ratio. At first, the mass of a primary is taken from the Salpeter distribution, and then the q distribution is applied.f(q)~q αq , q=M2/M1<1 We use αq=0 (flat distribution, i.e. all variants of mass ratio are equally probable) and αq=2 (close masses are more probable, so numbers of NS and BH progenitors are increased in comparison with αq=0).

26. Results of calculations

27. II. Extragalactic SGRs: 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 star forming galaxies (M82, M83, NGC 253, NGC 4945), from the Virgo cluster and from “supernova factories” (Arp 299 and NGC 3256) in the BATSE catalogue. No good candidates are found. We discuss this result.

28. SGR flares vs. GRBs Woods et al.

29. 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

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

31. The probability of detection by BATSE of a giant flare

32. BATSE GRBs associated with near-by starbursts

33. The probability of detection by BATSE of a hyperflare

34. BATSE GRBs associated with “supernova factories”

35. 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).

36. 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.

37. 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.

38. Conclusions.I. • We made population synthesis of binary systems to derive the relative number of NSs originated from progenitors with enhanced rotation -``magnetars''. • With an inclusion of single stars (with the totalnumber equal to the total number of binaries) the fraction of ``magnetars'‘ is ~13-16%. • Most of these NSs are isolated due to coalescences of components prior to NS formation, or due to a system disruption after a SN explosion. • The fraction of ``magnetars'' in survived binaries is about 1% or lower. • The most numerous companions of ``magnetars'' are BHs.

39. Conclusions. II. • 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 - ??????

40. THAT’S ALL. THANK YOU!