LONDON - April 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

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

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

LONDON - April 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

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

LONDON - April BFS – HRI SourceFlux erg cm -2 s -1 Prob. σ Ctsf x / f opt Opt. σ persistent > transient > transient > transient >404.9

LONDON - April X-ray position and blue image

LONDON - April X-ray position and blue image

LONDON - April Spectral fits for PSPC observation

LONDON - April Power law spectral fits for PSPC observation

LONDON - April Progress in BSF – HRI Reconsideration of 4 sources: is a fake , are not spiky X-ray (SWIFT – Campana) f x < erg / s Optical (WIYN – Orio) R > 23.4

LONDON - April 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

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

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

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