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The Zoo Of Neutron Stars

The Zoo Of Neutron Stars. Sergei Popov ( SAI MSU ). ( www.bradcovington.com). Neutron stars. Superdense matter, strong gravity and superstrong magnetic fields. Magnetospheric activity. Cooling. Accretion. The old zoo of neutron stars. In 60s the first X-ray sources have been discovered.

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The Zoo Of Neutron Stars

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  1. The Zoo Of Neutron Stars Sergei Popov (SAI MSU) (www.bradcovington.com)

  2. Neutron stars Superdense matter, strong gravity and superstrong magnetic fields Magnetospheric activity Cooling Accretion

  3. The old zoo of neutron stars In 60s the first X-ray sources have been discovered. They were neutron stars in close binary systems, BUT ... .... theywere «notrecognized».... Now we know hundreds of X-ray binaries with neutron stars in the Milky Way and in other galaxies.

  4. The first detections in binaries Giacconi, Gursky, Hendel (1962) About ½ of massive stars are members of close binary systems. Now we know hundreds of close binary systems with neutron stars. UHURU was launched on December 12, 1970. 2-20keV The first sky survey. 339 sources.

  5. Crab nebula A binary system Good old classics Radio pulsars discovery 1967: JocelynBell.

  6. Evolution of neutron stars. I.: rotation + magnetic field Ejector → Propeller → Accretor → Georotator 1 – spin down 2 – passage through a molecular cloud 3 – magnetic field decay astro-ph/0101031 See the book by Lipunov (1987, 1992)

  7. Magnetorotational evolution of radio pulsars Spin-down. Rotational energy is released. The exact mechanism is still unknown.

  8. Evolution of NSs. II.:temperature [Yakovlev et al. (1999) Physics Uspekhi] First papers on the thermal evolution appeared already in early 60s, i.e. before the discovery of radio pulsars.

  9. The old Zoo: young pulsars & old accretors For years only two main types of NSs have been discussed:radio pulsars and accreting NSs in close binary systems

  10. The new zoo of neutron stars • During last~10-15years • it became clear that neutron stars • can be born very different. • In particular, absolutely • non-similar to the Crab pulsar. • Compact central X-ray sources • in supernova remnants. • Anomalous X-ray pulsars • Soft gamma repeaters • The Magnificent Seven • Unidentified EGRET sources • Transient radio sources (RRATs) • Calvera …. All together these NSs have total birth rate higher than normal radio pulsars(see discussion in Popov et al. 2006, Keane, Kramer 2008)

  11. Compact central X-ray sources in supernova remnants Cas A RCW 103 Puppis A No pulsations, small emitting area 6.7 hour period (de Luca et al. 2006) • Vkick=1500 km/s(Winkler, Petre 2006)

  12. CCOs in SNRs Age Distance J232327.9+584843 Cas A 0.32 3.3–3.7 J085201.4−461753 G266.1−1.2 1–3 1–2 J082157.5−430017Pup A 1–3 1.6–3.3 J121000.8−522628 G296.5+10.0 3–20 1.3–3.9 J185238.6+004020 Kes 79 ~9 ~10 J171328.4−394955 G347.3−0.5 ~10 ~6 [Pavlov, Sanwal, Teter: astro-ph/0311526, de Luca: arxiv:0712.2209] For two sources there are strong indications for large (>~100 msec) initial spin periods and low magnetic fields:1E 1207.4-5209 in PKS 1209-51/52 andPSR J1852+0040 in Kesteven 79 [see Halpern et al. arxiv:0705.0978]

  13. Magnetars • dE/dt > dErot/dt • By definition:The energy of the magnetic field is released • P-Pdot • “Direct” measurements of the field (spectral lines) Magnetic fields 1014–1015G

  14. Giant flares P, s 8.0 5 March 1979 (?) 18 June 1998 6.4 27 Dec 2004 7.5 5.2 27 Aug 1998 SGRs: periods and giant flares • 0526-66 • 1627-41 • 1806-20 • 1900+14 • 0501+45 5.7 See the review in Woods, Thompson astro-ph/0406133 and Mereghetti arXiv: 0804.0250

  15. Historical notes • 05 March 1979. The ”Konus” experiment & Co. Venera-11,12 • Events in the LMC. SGR 0520-66. • Fluence: about 10-3 erg/cm2 Mazets et al. 1979 N49 – supernova remnant in the Large Magellanic cloud (G.Vedrenne et al. 1979)

  16. Soft Gamma Repeaters: main properties Saturationof detectors • Energetic “Giant Flares” (GFs, L ≈ 1045-1047 erg/s) detected from 3 (4?) sources • No evidence for a binary companion, association with a SNR at least in one case • Persistent X-ray emitters, L ≈ 1035 - 1036 erg/s • Pulsations discovered both in GFs tails and persistent emission, P ≈ 5 -10 s • Huge spindown rates, Ṗ ≈ 10-10 –10-11 ss-1

  17. Main types of activity of SGRs • Weak bursts. L<1042 erg/s • Intermediate.L~1042–1043 erg/s • Giant. L<1045 erg/s • Hyperflares. L>1046 erg/s (fromWoods, Thompson 2004)

  18. Extragalactic SGRs It was suggested long ago (Mazets et al. 1982) that present-day detectors could alredy detectgiant flares from extragalactic magnetars. However, all searches in, for example,BATSE databse did not provide clear candidates(Lazzati et al. 2005, Popov & Stern 2006, etc.). Finally, recently several good candidates have been proposed by different groups (Mazets et al., Frederiks et al., Golenetskii et al., Ofek et al, Crider ...., see arxiv:0712.1502andreferences therein, for example). Burstin M31 [D. Frederiks et al. astro-ph/0609544]

  19. Anomalous X-ray pulsars Identified as a separate group in 1995. (Mereghetti, Stella 1995Van Paradijs et al.1995) • Similar periods (5-10 sec) • Constant spin down • Absence of optical companions • Relatively weak luminosity • Constant luminosity

  20. Known AXPs Sources Periods, s

  21. SGRs and AXPs

  22. Are SGRs and AXPs brothers? • Bursts of AXPs (from 6 now) • Spectral properties • Quiescent periods of SGRs (0525-66 since1983) Gavriil et al. 2002

  23. Magnetic field estimates • Spin down • Long spin periods • Energy to support bursts • Field to confine a fireball (tails) • Duration of spikes (alfven waves) • Direct measurements of magnetic field (cyclotron lines) Ibrahim et al. 2002 Gavriil et al. (2002, 2004)

  24. Transient radio emission from AXP ROSAT and XMM images.The X-ray outburst happened in 2003. AXP has spin period 5.54 s Radio emission was detected from XTE J1810-197during its active state. Clear pulsations have been detected. Large radio luminosity. Strong polarization. Precise Pdot measurement.Important for limting models, better distanceand coordinates determination etc. (Camilo et al. astro-ph/0605429)

  25. Transient radiopulsar PSR J1846-0258 P=0.326 sec B=5 1013 G However,no radio emissiondetected. Due to beaming? Among all rotation poweredPSRs it has the largest Edot.Smallest spindown age (884 yrs). The pulsar increased its luminosity in X-rays. Increase of pulsed X-ray flux. Magnetar-like X-ray bursts (RXTE). Timing noise. See additional info about this pulsar at the web-site http://hera.ph1.unikoeln.de/~heintzma/SNR/SNR1_IV.htm 0802.1242, 0802.1704

  26. Twisted Magnetospheres – I • The magnetic field inside a magnetar is “wound up” • The presence of a toroidal component induces a rotation of the surface layers • The crust tensile strength resists • A gradual (quasi-plastic ?) deformation of the crust • The external field twists up (Thompson, Lyutikov & Kulkarni 2002) (by R. Turolla) (Mereghetti arXiv: 0804.0250) (Thompson & Duncan 2001)

  27. Generation of the magnetic field or fossil field? The mechanism of the magnetic field generation is still unknown. α-Ω dynamo (Duncan,Thompson) α2 dynamo (Bonanno et al.) or their combination In any case, initial rotation of a protoNS is the critical parameter. There are reasons to suspect that the magnetic fields of magnetars are not due to any kind of dynamo mechanism, but just due to flux conservation: • Study of SNRs with magnetars (Vink and Kuiper 2006). • 2. There are few examples of massive stars with field strong enough to produce magnetars (Ferrario and Wickramasinghe 2006)

  28. What is special about magnetars? Link withmassive stars There are reasons to suspect that magnetars are connected to massive stars (astro-ph/0611589). Link to binary stars There is a hypothesis that magnetars are formed in close binary systems (astro-ph/0505406). AXP in Westerlund 1 most probably hasa very massive progenitor >40 Msolar. The question is still on the list.

  29. ROSAT ROentgen SATellite German satellite (with participation of US and UK). Launched 01June 1990. The program was successfully ended on 12 Feb 1999.

  30. Close-by radioquiet NSs • Discovery: Walter et al. (1996) • Proper motion and distance: Kaplan et al. • No pulsations • Thermal spectrum • Later on: six brothers RX J1856.5-3754

  31. Magnificent Seven Radioquiet (?) Close-by Thermal emission Absorption features Long periods

  32. RX J0420.0-5022 (Haberl et al 2004) Pulsating ICoNS • Quite large pulsed fractions • Skewed lightcurves • Harder spectrum at pulse minimum • Phase-dependent absorption features

  33. The Optical Excess • In the four sources with a confirmed optical counterpart Fopt  5-10 x B(TBB,X) • Fopt  2 ? • Deviations from a Rayleigh-Jeans continuum in RX J0720 (Kaplan et al 2003) and RX J1605 (Motch et al 2005). A non-thermal power law ? RX J1605 multiwavelength SED (Motch et al 2005)

  34. Period Evolution • RX J0720.4-3125: bounds on derived by Zane et al. (2002) and Kaplan et al (2002) • Timing solution by Cropper et al (2004), further improved by Kaplan & Van Kerkwijk (2005): = 7x10-14 s/s, B = 2x1013 G • RX J1308.6+2127: timing solution by Kaplan & Van Kerkwijk (2005a), = 10-13 s/s, B = 3x1013 G • Spin-down values of B in agreement with absorption features being proton cyclotron lines B ~ 1013 -1014 G

  35. RX J0720.4-3125 (Haberl et al 2004) Featureless ? No Thanks ! • RX J1856.5-3754 is convincingly featureless(Chandra 500 ks DDT; Drake et al 2002; Burwitz et al 2003) • A broad absorption feature detected in all other ICoNS(Haberl et al 2003, 2004, 2004a; Van Kerkwijk et al 2004; Zane et al 2005) • Eline ~ 300-700 eV; evidence for two lines with E1 ~ 2E2 in RBS 1223 (Schwope et al 2006) • Proton cyclotron lines ? H/He transitions at high B ?

  36. De Vries et al. 2004 Long Term Variations in RX J0720.4-3125 • A gradual, long term change in the shape of the X-ray spectrum AND the pulse profile (De Vries et al 2004; Vink et al 2004) • Steady increase of TBB and of the absorption feature EW (faster during 2003) • Evidence for a reversal of the evolution in 2005 (Vink et al 2005)

  37. Unidentified EGRET sources Grenier (2000), Gehrels et al. (2000) Unidentified sources are divided into several groups. One of them has sky distribution similar to the Gould Belt objects. It is suggested that GLAST (and, probably, AGILE) Can help to solve this problem. Actively studied subject (see for example papers byHarding, Gonthier) no radio pulsars in 56 EGRET error boxes (Crawford et al. 2006) However, Keith et al. (0807.2088) found a PSR at high frequency.

  38. Discovery of RRATs • 11 sources detected in the Parkes Multibeam survey (McLaughlin et al 2006) • Burst duration 2-30 ms, interval 4 min-3 hr • Periods in the range 0.4-7 s • Period derivative measured in 3 sources: B ~ 1012-1014 G, age ~ 0.1-3 Myr • RRAT J1819-1458 detected in X-rays, spectrum soft and thermal, kT ~ 120 eV (Reynolds et al 2006)

  39. RRATs • P, B, ages and X-ray properties of RRATs very similar to those of XDINSs • Estimated number of RRATs: ~ 3-5 times that of PSRs • If τRRAT ≈ τPSR, βRRAT ≈ 3-5 βPSR • βXDINS > 3 βPSR (Popov et al 2006) • Are RRATs far away XDINSs ?

  40. RRAT in X-rays X-ray pulses overlaped onradio data of RRAT J1819-1458. Thermally emitting NS kT ~ 120 eV (Reynolds et al 2006) (arXiv: 0710.2056)

  41. Calvera et al. Recently, Rutledge et al. reported the discovery of an enigmatic NS candidated dubbed Calvera. It can be an evolved (aged) version of Cas A source, but also it can be a M7-like object, who’s progenitor was a runaway (or, less probably, hypervelocity) star. No radio emission was found.

  42. CCO vs. M7. New population? Gotthelf & Halpern (arXiv:0704.2255) recently suggested that 1E 1207.4-5209 and PSR J1852+0040 (in Kes 79) can beprototypes of a different subpopulation of NSs born withlow magnetic field (< few 1011 G) and relatively long spin periods (few tenths of a second). These NSs are relatively hot, and probably not very rare. Surprisingly, we do not see objects of this type in our vicinity. In the solar neighbourhood we meet a different class of object. This can be related to accreted envelopes (see, for example, Kaminker et al. 2006). Sources in CCOs have them, so they look hotter,but when these envelopes disappear, they are colderthan NSs which have no envelopes from the very beginning.So, we do not see such sources among close-by NSs.

  43. CCOs Temperature M7 Age M7 and CCOs Both CCOs and M7 seem to bethe hottest at their ages (103 and 106 yrs). However, the former cannot evolve to become the latter ones! • Accreted envelopes (presented in CCOs, absent in the M7) • Heating by decaying magnetic field in the case of the M7

  44. Accreted envelopes, B or heating? (Yakovlev & Pethick 2004) It is necessary to make population synthesis studies to test all these possibilities. • Related to e-capture SN? • low-mass objects • low kicks • ~10% of all NSs However, small emitting area remains unexplained.Accretion???

  45. M7 and RRATs Similar periods and Pdots In one case similar thermal properties Similar birth rate? (arXiv: 0710.2056)

  46. M7 and RRATs: pro et contra Based on similarities between M7 and RRATs it was proposed that they can bedifferent manifestations of the same type of INSs (astro-ph/0603258).To verify it a very deep search for radio emission (including RRAT-like bursts)was peformed on GBT (Kondratiev et al.).In addition, objects have been observed with GMRT (B.C.Joshi, M. Burgay et al.). In both studies only upper limits were derived. Still, the zero result can be just due to unfavorable orientations(at long periods NSs have very narrow beams).It is necessary to increase statistics. (Kondratiev et al, in press, see also arXiv: 0710.1648)

  47. M7 and high-B PSRs Strong limits on radio emission from the M7are established (Kondratiev et al. 2008). However, observationally it is still possible thatthe M7 are just misaligned high-B PSRs. Are there any other considerations to verify a link between thesetwo popualtions of NSs? In most of population synthesis studies of PSRsthe magnetic field distribution is described as agaussian, so that high-B PSRs appear to be notvery numerous.On the other hand, population synthesis of thelocal population of young NSs demonstrate thatthe M7 are as numerous as normal-B PSRs. So, for standard assumptionsit is much more probable, thathigh-B PSRs and the M7 are not related.

  48. Magnetars Pdot B=const M7 PSRs P Magnetars, field decay, heating A model based on field-dependent decay of the magnetic moment of NSscan provide an evolutionary link between different populations. Magnetic fields of NSs are expected to decay due to decay ofcurrents which support them.

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