Space Cowboys Odissey: Beyond the Gould Belt

1. Space Cowboys Odissey:Beyond the Gould Belt Sergei Popov, Bettina Posselt (co-authors: F. Haberl, R. Neuhauser, J. Truemper, R. Turolla) astro-ph/0609275, 0710.1547 and A&A in press

2. The new zoo of neutron stars • During last>10 years • 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 ….

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

4. Population of close-by young NSs • Magnificent seven • Geminga and 3EG J1853+5918 • Four radio pulsars with thermal emission (B0833-45; B0656+14; B1055-52; B1929+10) • Seven older radio pulsars, without detected thermal emission. Where are the rest? UNCATCHABLES

5. calculations -3/2 sphere: number ~ r3 flux ~ r-2 -1 disc: number ~ r2 flux ~ r-2 Log N – Log S Log of the number of sources brighter than the given flux Log of flux (or number counts)

6. Population synthesis: ingredients • Birth rate of NSs • Initial spatial distribution • Spatial velocity (kick) • Mass spectrum • Thermal evolution • Interstellar absorption • Detector properties Task: To build an artificial model of a population of some astrophysical sources and to compare the results of calculations with observations. A brief review on population synthesis in astrophysics can be found in astro-ph/0411792 and in Physics-Uspekhi (2007).

7. Cooling curves by • Blaschke et al. • Mass spectrum Gould Belt : 20 NS Myr-1 Gal. Disk (3kpc) : 250 NS Myr-1 ROSAT 18° Gould Belt Arzoumanian et al. 2002 Population synthesis – I.

8. The Gould Belt • Poppel (1997) • R=300 – 500 pc • Age 30-50 Myrs • Center at 150 pc from the Sun • Inclined respect to the galactic plane at 20 degrees • 2/3 massive stars in 600 pc belong to the Belt

9. Population synthesis – II.recent improvements 1. Spatial distribution of progenitor stars We use the same normalization for NS formation rate inside 3 kpc: 270 per Myr. Most of NSs are born inOB associations. For stars <500 pc we eventry to take into accountif they belong to OB assoc.with known age. a) Hipparcos stars up to 500 pc [Age: spectral type & cluster age (OB ass)] b) 49 OB associations: birth rate ~ Nstar c) Field stars in the disc up to 3 kpc

10. Effects of the new spatial distribution on Log N – Log S There are no significanteffects on the Log N – Log Sdistribution due to moreclumpy initial distributionof NSs. But, as we’ll see below,the effect is strong forsky distribution. Solid – new initial XYZ Dashed – Rbelt = 500 pc Dotted – Rbelt = 300 pc

11. Mass spectrum of NSs • Mass spectrum of local young NSs can be different from the general one (in the Galaxy) • Hipparcos data onnear-by massive stars • Progenitor vs NS mass: Timmes et al. (1996); Woosley et al. (2002) (masses of secondary objects in NS+NS) astro-ph/0305599

12. Population synthesis – II.recent improvements 2. New cross sections & abundances and new mass spectrum Low mass progenitors for thedotted mass spectrum are treated following astro-ph/0409422. The new spectrum looksmore “natural”. But the effect is ....

13. Effects of the new mass spectrum and abundances on the Log N – Log S ... Effect is negligible We also introducednew abundances, andcalculated count ratemore accurately than before. Still,the effect is small. Solid – new abundances, old mass Dotted – old abundances, old mass Dashed – new abundances, new mass

14. Population synthesis – II.recent improvements 3. Spatial distribution of ISM (NH) instead of : NH inside 1 kpc (see astro-ph/0609275 for details) now : Modification of the old one Hakkila

15. Effects of the new ISM distribution Again, the effect is not very significant forLog N – Log S, butit is strong for thesky distribution(see below). Dot-dashed and dot-dot-dashed lines Represent two new models of the ISM distribution.

16. Popov et al. 2005 Count rate > 0.05 cts/s b= +90° Cep?Per? Sco OB Ori b= -90° PSRs+ Geminga+ M7 PSRs- First results: new maps Clearly several rich OB associations start to dominate in the spatial distribution

17. INSs and local surrounding Massive star population in the Solar vicinity (up to 2 kpc) is dominated by OB associations. Inside 300-400 pc the Gould Belt is mostly important. Motch et al. 2006 De Zeeuw et al. 1999

18. 50 000 tracks, new ISM model Candidates: Agueros Chieregato radiopulsars Magn. 7

19. Age and distance distributions 0.01 < cts/s < 0.1 0.1 < cts/s < 1 1 < cts/s < 10 Age New cands. Distance

20. Different models: age distributions Bars with vertical lines:old model for Rbelt=500 pc White bars: new initial dist Black bars: new ISM (analyt.) andnew initial distribution Diagonal lines:new ISM (Hakkila) andnew initial distribution

21. Different models: distance distr.

22. Where to search for more cowboys? We do not expect to find much more candidates at fluxes >0.1 cts/s. Most of new candidates should be at fluxes 0.01< f < 0.1 cts/s. So, they are expected to be young NSs (<few 100 Mys) just outside the Belt. I.e., they should be in nearby OB associations and clusters. Most probable candidates are Cyg OB7, Cam OB1, Cep OB2 and Cep OB3. Orion region can also be promising. Name           l-      l+     b-    b+      Dist., pcCyg OB7     84      96    -5     9       600-700Cep OB2     96     108    -1   12       700Cep OB3    108    113     1     7       700-900Cam OB1   130    153    -3    8       800-900 90 130 L=110 10 0 -10 (ads.gsfc.nasa.gov/mw/)

23. 56 EGRET sources Recently Crawford et al. (astro-ph/0608225) presented a studyof 56 well-identified EGRET error boxes. The idea was to find radio pulsars. Nothing was found. Obviously, they can be geminga-like sources, or represent some other subpopulation of cooling NSs.

24. OB runaway stars Another possibility to find new ICoNSs is to search for (un)bound compact companions of OB runaway stars. More than one hundred OB runaway stars are known in 1 kpc around the Sun (astro-ph/9809227). Unbounded NSs Bounded NSs Sayer et al. 1996 and Philp et al. 1996looked for radio pulsars as companionsof runaway stars. It is reasonable to look for M7-likecompanions around young OB stars. Optical star bh (for BHs done in astro-ph/0511224)

25. 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.

26. CCO vs. M7 Gotthelf and Halpern (2007) presented evidence in favor of hypothesis that among CCOs there is a population of NSs born with long spin periods (few tenths of a second) and small magnetic fields (<1012 G). These sources are hot. The M7 sources are hot, too, but they seemto belong to different populations. This can be explained by accreted envelopes in CCOs (Kaminker et al. 2006). It is necessary to make a general population synthesis, which would include all types of isolated NSs.

27. Resume • New more detailed population synthesis model for local population of isolated NS is made • New results provide a hint to search for new coolers. • We predict that new objects can be identified at 0.01<cts/s<0.1 behind the Gould Belt in the directions of close-by rich OB associations, in particular Cep OB2. • These objects are expected to be younger and hotter than the Magnificent seven. • New ways to find candidates can be discussed.

28. That’s all! The Magnificent Seven Vs. Uncatchables Born in the Gould Belt. Bright. Middle-aged. Already observed. Born behind the Belt. Dimmer. Younger. Wanted.

29. Radio detection Malofeev et al. (2005) reported detection of 1RXS J1308.6+212708 (RBS 1223) in the low-frequency band (60-110 MHz) with the radio telescope in Pushchino. In 2006 Malofeev et al. reported radio detection of another one. (back)

30. NS+NS binaries Pulsar Pulsar mass Companion mass B1913+16 1.44 1.39 B2127+11C 1.35 1.36 B1534+12 1.33 1.35 J0737-3039 1.34 1.25 J1756-2251 1.40 1.18 (PSR+companion)/2 J1518+4904 1.35 J1811-1736 1.30 J1829+2456 1.25 (David Nice, talk at Vancouver 2005) (Back)