4 research outputs found
Stellar-Mass Black Holes in the Solar Neighborhood
We search for nearby, isolated, accreting, ``stellar-mass'' (3 to
) black holes. Models suggest a synchrotron spectrum in visible
wavelengths and some emission in X-ray wavelengths. Of 3.7 million objects in
the Sloan Digital Sky Survey Early Data Release, about 150,000 objects have
colors and properties consistent with such a spectrum, and 87 of these objects
are X-ray sources from the ROSAT All Sky Survey. Thirty-two of these have been
confirmed not to be black-holes using optical spectra. We give the positions
and colors of these 55 black-hole candidates, and quantitatively rank them on
their likelihood to be black holes. We discuss uncertainties the expected
number of sources, and the contribution of blackholes to local dark matter.Comment: Replaced with version accepted by ApJ. 40 pages, 8 figure
Out of the darkness: the infrared afterglow of the INTEGRAL burst GRB 040422 observed with the VLT
GRB 040422 was detected by the INTEGRAL satellite at an angle of only 3
degrees from the Galactic plane. Analysis of the prompt emission observed with
the SPI and IBIS instruments on INTEGRAL are presented. The IBIS spectrum is
well fit by the Band model with a break energy of Eo=56+/-2 keV and
Epeak=41+/-3 keV. The peak flux is 1.8 10^(-7) erg/cm2/s and fluence 3.4
10^(-7) erg/cm2 in the range 20-200 keV. We then present the observations of
the afterglow of GRB 040422, obtained with the ISAAC and FORS 2 instruments at
the VLT less than 2 hours after the burst. We report the discovery of its
near-infrared afterglow, for which we give here the astrometry and photometry.
No detection could have been obtained in the R and I bands, partly due to the
large extinction in the Milky Way. We re-imaged the position of the afterglow
two months later in the Ks band, and detected a likely bright host galaxy. We
compare the magnitude of the afterglow with a those of a compilation of
promptly observed counterparts of previous GRBs, and show that the afterglow of
GRB 040422 lies at the very faint end of the distribution, brighter only than
that of GRB 021211, singled out later and in the optical bands, and GRB 040924
after accounting for Milky Way extinction. This observation suggests that the
proportion of dark GRBs can be significantly lowered by a more systematic use
of 8-m class telescopes in the infrared in the very early hours after the
burst.Comment: 9 pages, 7 figures, accepted in A&