Title: New Black Hole X-ray Novae in the Glactic Halo
Proposal ID: 0120098
Subject category: Compact Object
Principal investigator: Mirabel
Institute: CEA/Saclay
Abstract
Black Holes (BH) in the thick disk and/or halo of the Milky Way galaxy appear sporadically as X-ray Novae
with very hard spectra. The origin and nature of these objects is one of the most intriguing problems in
high energy astrophysics. They could have been shot out from the galactic plane, or be pristine BHs formed
in the Galactic Halo before the Milky Way disk. At galactic latitudes |b|>5 degrees BH X-ray Novae are
likely to be close to the Sun, bright, optically unobscured, and the compact radio counterpart subject to
low interstellar scattering. This will allow to: 1) probe the connection between accretion disk
instabilities and the formation of relativistic jets in all wavelength bands, 2) know whether the radio,
infrared, and optical non-thermal component and the gamma-ray events originate - as recently found in
quasars - within the same shocked area downstream the relativistic jet, and 3) determine the space velocity
of the binary centre of mass, and therefore know where these BHs come from. The recent discovery of
XTEJ1118+48, which is 62 degrees off hte galactic plane, and had its peak at L(X) < 1e36
erg/s, rises the
suspicion that we may have so far missed a large population of BHs in the galactic thick disk and/or the
Milky Way disk. Furtehrmore, some of these accreting BHs in Low MAss Binaries could be micro-blazars and it
is an open question their possbile relation to a subset of soft and variable unidentified EGRET sources that
are spread at medium and high latitude, most assembled within 30 degrees from the galactic centre.
We will
perform Multiwavelength Target of Opportunity (ToO) observations, from space with INTEGRAL and HST and from
ground with opt/IR/radio telescopes, of new BH X-ray Novae at |b| > 5 degrees (which at the galactic centre
would correspond to a distance > 700 pc above the plane not subject to INTEGRAL Core Program ToO.