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 => 10 8 -10 9 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, L x = 1 x 10 31 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, isolated neutron stars (XDINs) (Zane et al. 2005) Radio quiet X-ray to optical flux ratio (10 4 ) Low hydrogen column densities (n H ~10 20 cm -2 )

5. Quiescent neutron star low mass X-ray binaries (qNSLMXBs) Without assuming mass M NS = 1.19 0.21 0.69 M solar T  = 1.13 0.47 0.25 x10 6 K R  = 7.5 5.1 0.60 km  2 = 1.12, 45 d.o.f. Adapted from Gendre, Barret & Webb (2003a)

6. 2XMMp (and all preceding versions) Used temperatures and n H 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. kT 1 =0.0390.002 keV kT 2 =0.1680.002 keV  2 =2.17 (111 dof) All looking good ? Flux ~ 7x10 -13 erg cm -2 s -1

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

11. kT 1 =0.080.05 keV kT 2 =0.440.02 keV kT 3 =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!