1. LONDON - April 20061 Persistent and Transient Blank Field Sources A. Treves Insubria University, Italy S. Campana Brera Observatory, Italy M. Chieregato Insubria University, Italy – Zürich University, Switzerland T. Nelson Wisconsin University M. Orio Torino, Italy – Wisconsin University

2. LONDON - April 2006 2 Dim Isolated Neutron Stars (DINS) Residual Internal Energy Interaction with the surrounding N ~ 10 8 – 10 9

3. LONDON - April 2006 3 ROSAT – DINS Blank Field Sources Low X-ray Luminosity: L x ~ 10 30 erg/s T < 100 eV d ~ 100 pc P ~ 5 – 10 s Absorption lines < 1 KeV

4. LONDON - April 2006 4 Outline of the Contribution BFS in the ROSAT HRI Wavelet Catalogue (Chieregato et al., 2005, A&A 444, 69) Progress in ROSAT BFS Transient Blank Field Sources Future perspectives

5. LONDON - April 2006 5 BFS from HRI Catalogue Blank Field Sources f x > 2.7 x 10 -13 erg/s N ph >25

6. LONDON - April 2006 6 BFS – HRI SourceFlux 10 -13 erg cm -2 s -1 Prob. σ Ctsf x / f opt Opt. σ 0421-51 persistent 6.514.0742>1415.3 1357+18 transient 3.54.2112>476.3 2007-48 transient 3.04.355>655.2 0433+15 transient 2.94.234>404.9

7. LONDON - April 2006 7 0421-57 X-ray position and blue image

8. LONDON - April 2006 8 1357+18 X-ray position and blue image

9. LONDON - April 2006 9 0421-57 Spectral fits for PSPC observation

10. LONDON - April 2006 10 0421-57 Power law spectral fits for PSPC observation

11. LONDON - April 2006 11 Progress in BSF – HRI Reconsideration of 4 sources: 0433+15 is a fake 1357+18, 2007-48 are not spiky X-ray (SWIFT – Campana) 1357+18f x < 10 -14 erg / s Optical (WIYN – Orio) 1357+18R > 23.4

12. LONDON - April 2006 12 If the two TBSF were real… Total Number: T HRI ~ 3 x 10 7 s Ω ~ 0.2 deg 2 Isotropic N ~ 10 5 y -1  Extragalactic: unlikely Gamma Ray Burst: unlikely

13. LONDON - April 2006 13 TBSF Non Collapsed Companions: unlikely White Dwarfs Neutron Stars Relation with transient PSR? Hiccups?

14. LONDON - April 2006 14 Progress Search for BFS with f x ~ 10 -14 erg / s (Chandra, XMM, SWIFT) X- and optical archives

15. LONDON - April 2006 15 What we expect (dreams?) DINS: accretion powered TBFS DINS cousins Isolated Black Holes Intermediate Mass Black Holes (ULX)