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2XMMp and Galactic neutron stars Natalie Webb Stéphanie Dupuy

2XMMp and Galactic neutron stars Natalie Webb Stéphanie Dupuy. Why search for X-ray emitting neutron stars?. Almost 2000 known neutron stars (NS) (1627 pulsars, ~70 NS X-ray binaries , the magnificent seven …) Expect a NS to be born every 30-100 yrs in Milky Way

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2XMMp and Galactic neutron stars Natalie Webb Stéphanie Dupuy

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  1. 2XMMp and Galactic neutron stars Natalie Webb Stéphanie Dupuy

  2. Why search for X-ray emitting neutron stars? • Almost 2000 known neutron stars (NS) (1627 • pulsars, ~70 NS X-ray binaries, the magnificent • seven …) • Expect a NS to be born every 30-100 yrs in Milky • Way • => 108-109 NS in our Galaxy (Neuhäuser & • Trümper 1999) – depends on star formation • Only youngest detected as radio pulsars • Expect ~1000 radio quiet NSs for every pulsar • (Kulkarni & van Kerkwijk 1998) • 7 X-ray emitting radio quiet NSs found with Rosat • NS detection important for: star formation rate • physics of dense matter • stellar core collapse

  3. From Rosat to XMM-Newton • XMM-Newton has >10x collecting area • to detect 100 cts from a NS, Lx = 1 x 1031 erg s-1, 1.9 kpc Rosat ~ 30 ks XMM-Newton ~ 3 ks • Dramatic increase of observable population! Median flux of 2XMMp sources is ~10x fainter than the Rosat All Sky Survey limit => Huge resource with which to detect NSs

  4. X-ray emitting, dim, isolatedneutron stars (XDINs) (Zane et al. 2005) Radio quiet X-ray to optical fluxratio (104) Lowhydrogen column densities (nH~1020 cm-2)

  5. Quiescent neutron star low mass X-ray binaries (qNSLMXBs) Adapted from Gendre, Barret & Webb (2003a) Without assuming mass MNS = 1.190.210.69 Msolar T= 1.130.470.25 x106K R = 7.55.10.60 km 2 = 1.12, 45 d.o.f.

  6. 2XMMp (and all preceding versions) • Used temperatures and nH of XDINs and qNSLMXBs • Determined ranges of fluxes in 2XMMp bands using: • xspec blackbody model  • neutron star atmosphere model (Zavlin et al. 1996)  • colour diagrams  • ratios fluxes  • screening • important • Check: • Found all observed • XDINs/qNSLMXBs • observed in 2XMMp

  7. Results • 346 candidate NSs based on X-ray properties • 98 candidates without optical counterparts 55% false sources => 44 NS candidates Proposed 3 candidates to be observed in AO6/VLT

  8. A strange object … 0.2-0.5 keV: 1.730.87 x 10-16 erg cm-2 s-1 0.5-1.0 keV : 1.490.02 x 10-13 erg cm-2 s-1 1.0-2.0 keV : 5.190.16 x 10-14 erg cm-2 s-1 2.0-4.5 keV : 3.370.26 x 10-16 erg cm-2 s-1 4.5-12.0 keV : 0.421.13 x 10-16 erg cm-2 s-1 No optical counterpart

  9. kT1=0.0390.002 keV kT2=0.1680.002 keV 2=2.17 (111 dof) All looking good ? Flux ~ 7x10-13 erg cm-2 s-1

  10. kT1=0.0390.003 keV kT2=0.1950.050 keV 2=7.8 (103 dof) … but Flux ~ 5x10-12 erg cm-2 s-1

  11. kT1=0.080.05 keV kT2=0.440.02 keV kT3=1.310.03 keV 2=4.54 (215 dof) … and Rosat (early ’90s) Flux ~ 1.5x10-12 erg cm-2 s-1

  12. … and in fact … The bright star is the optical counterpart (M2 V) B=9, V=7.5, proper motion=4.8’’/yr, d=2.5 pc!!! Although, The temperatures seem to be low for a flare star But no significant radial velocity (N’dever et al 2002) Summary 43 candidate neutron stars Hoping for three to be followed up with XMM/VLT One very strange object!

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