14 research outputs found
The Optical Gravitational Lensing Experiment. Monitoring of QSO 2237+0305
We present results from 2 years of monitoring of Huchra's lens (QSO
2237+0305) with the 1.3 m Warsaw telescope on Las Campanas, Chile. Photometry
in the V band was done using a newly developed method for image subtraction.
Reliable subtraction without Fourier division removes all complexities
associated with the presence of a bright lensing galaxy. With positions of
lensed images adopted from HST measurements it is relatively easy to fit the
variable part of the flux in this system, as opposed to modeling of the
underlying galaxy. For the first time we observed smooth light variation over a
period of a few months, which can be naturally attributed to microlensing. We
also describe automated software capable of real time analysis of the images of
QSO 2237+0305. It is expected that starting from the next observing season in
1999 an alert system will be implemented for high amplification events (HAE) in
this object. Time sampling and photometric accuracy achieved should be
sufficient for early detection of caustic crossings.Comment: 8 pages (including 4 figures and table), latex, emulateapj, submitted
to ApJ, revised version - minor change
Optical Gravitational Lensing Experiment. OGLE-1999-BUL-32: the Longest Ever Microlensing Event -- Evidence for a Stellar Mass Black Hole?
We describe the discovery of the longest microlensing event ever observed,
OGLE-1999-BUL-32, also independently identified by the MACHO collaboration as
MACHO-99-BLG-22. This unique event has an Einstein radius crossing time of 641
days. The high quality data obtained with difference image analysis shows a
small but significant parallax signature. This parallax effect allows one to
determine the Einstein radius projected onto the observer plane as rE^hat ~
29.2AU. The transverse velocity projected onto the observer plane is about
79km/s. We argue that the lens is likely to be have a mass of at least a few
solar masses, i.e., it could be a stellar black hole. The black hole hypothesis
can be tested using the astrometric microlensing signature with the soon-to-be
installed Advanced Camera for Surveys on board the Hubble Space Telescope. Deep
X-ray and radio images may also be useful for revealing the nature of the
object.Comment: submitted to Monthly Notice
Combined Analysis of the Binary-Lens Caustic-Crossing Event MACHO 98-SMC-1
We fit the data for the binary-lens microlensing event MACHO 98-SMC-1 from 5
different microlensing collaborations and find two distinct solutions
characterized by binary separation d and mass ratio q: (d,q)=(0.54,0.50) and
(d,q)=(3.65,0.36), where d is in units of the Einstein radius. However, the
relative proper motion of the lens is very similar in the two solutions, 1.30
km/s/kpc and 1.48 km/s/kpc, thus confirming that the lens is in the Small
Magellanic Cloud. The close binary can be either rotating or approximately
static but the wide binary must be rotating at close its maximum allowed rate
to be consistent with all the data. We measure limb-darkening coefficients for
five bands ranging from I to V. As expected, these progressively decrease with
rising wavelength. This is the first measurement of limb darkening for a
metal-poor A star.Comment: 29 pages + 9 figures + 2 tables, submitted to Ap