41 research outputs found
Multi Wave Link: An interactive database for co-ordination of multiwavelength programs
Multi Wave Link is an operational database used by the international astronomical community to plan and coordinate multiwavelength observational campaigns on various celestial objects. This facility has been and continues to be an essential tool for the organization of numerous simultaneous ground-based and satellite observations. The Multi Wave Link system has both an interactive component and an electronic mail alert notice component. The interactive portion contains a database of schedules from several of the world's larger observatories and orbiting satellites. Lists of observers, observatories, and their available instrumentation are additionally contained in the system. Another feature added to the software allows the user to search the Royal Greenwich Observatory e-mail listing of international astronomers. This capability is often used by astronomers to find the electronic address of colleagues for improved communication. However, the most productive aspect of the Multi Wave Link system appears to be one of the simplest parts of the system: the electronic mail alert notices for observing campaigns. Information useful in planning the structure of future astronomical databases can be obtained by studying patterns of use of the Multi Wave Link system. This paper analyzes 22 months of Multi Wave Link usage from Sep. 1991 - Jul. 1993
XMM-Newton observes flaring in the polar UZ For during a low state
During an XMM-Newton observation, the eclipsing polar UZ For was found in a
peculiar state with an extremely low X-ray luminosity and occasional X-ray and
UV flaring. For most of the observation, UZ For was only barely detected in
X-rays and about 800 times fainter than during a high state previously observed
with ROSAT. A transient event, which lasted about 900 s, was detected
simultaneously by the X-ray instruments and, in the UV, by the Optical Monitor.
The transient was likely caused by the impact of 10^17-10^18 g of gas on the
main accretion region of the white dwarf. The X-ray spectrum of the transient
is consistent with 7 keV thermal bremsstrahlung from the shock-heated gas in
the accretion column. A soft blackbody component due to reprocessing of X-rays
in the white dwarf atmosphere is not seen. The likely origin of the UV emission
during the transient is cyclotron radiation from the accretion column. We
conclude from our analysis that the unusual flaring during the low state of UZ
For was caused by intermittent increases of the mass transfer rate due to
stellar activity on the secondary.Comment: To be published in MNRAS, 8 pages, 4 figure
Bright X-ray Transients in M31: 2004 July XMM-Newton Observations
We present the results of X-ray observations of four bright transients
sources detected in the July 2004 XMM-Newton observations of the central bulge
of M31. Two X-ray sources, XMMU J004315.5+412440 and XMMU J004144.7+411110,
were discovered for the first time. Two other sources, CXOM31 J004309.9+412332
and CXOM31 J004241.8+411635, were previously detected by Chandra. The
properties of the sources suggest their identification with accreting binary
systems in M31. The X-ray spectra and variability of two sources, XMMU
J004144.7+411110 and CXOM31 J004241.8+411635, are similar to that of the
Galactic black hole transients, making them a good black hole candidates. The
X-ray source XMMU J004315.5+412440 demonstrates a dramatic decline of the X-ray
flux on a time scale of three days, and a remarkable flaring behavior on a
short time scales. The X-ray data on XMMU J004315.5+412440 and CXOM31
J004309.9+412332 suggest that they can be either black hole or neutron star
systems. Combining the results of 2000-2004 XMM observations of M31, we
estimate a total rate of the bright transient outbursts in the central region
of M31 to be 6-12 per year, in agreement with previous studies.Comment: 8 pages, 3 figures, uses emulateapj style. Submitted to Ap
First XMM-Newton observations of strongly magnetic cataclysmic variables - II. Timing studies of DP Leo and WW Hor
XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables,
DP Leo and WW Hor, continuously for three orbital cycles each. Both systems
were in an intermediate state of accretion. For WW Hor we also obtained optical
light curves with the XMM-Newton Optical Monitor and from ground-based
observations. Our analysis of the X-ray and optical light curves allows us to
constrain physical and geometrical parameters of the accretion regions and
derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we
directly measure horizontal and vertical temperature variations in the
accretion column. From comparisons with previous observations we find that
changes in the accretion spot longitude are correlated with the accretion rate.
For DP Leo the shape of the hard X-ray light curve is not as expected for
optically thin emission, showing the importance of optical depth effects in the
post-shock region. We find that the spin period of the white dwarf is slightly
shorter than the orbital period and that the orbital period is decreasing
faster than expected for energy loss by gravitational radiation alone.Comment: Accepted for publication in MNRAS, 12 pages, 6 figure
The Nature of the Secondary Star in the Black Hole X-Ray Transient V616 Mon (=A0620-00)
We have used NIRSPEC on Keck II to obtain -band spectroscopy of the low
mass X-ray binary V616 Mon (= A062000). V616 Mon is the proto-typical soft
x-ray transient containing a black hole primary. As such it is important to
constrain the masses of the binary components. The modeling of the infrared
observations of ellipsoidal variations in this system lead to a derived mass of
11.0 M_{\sun} for the black hole. The validity of this derivation has been
called into question due to the possiblity that the secondary star's spectral
energy distribution is contaminated by accretion disk emission (acting to
dilute the variations). Our new -band spectrum of V616 Mon reveals a
late-type K dwarf secondary star, but one that has very weak CO
absorption features. Comparison of V616 Mon with SS Cyg leads us to estimate
that the accretion disk supplies only a small amount of -band flux, and the
ellipsoidal variations are not seriously contaminated. If true, the derived
orbital inclination of V616 Mon is not greatly altered, and the mass of the
black hole remains large. A preliminary stellar atmosphere model for the
-band spectrum of V616 Mon reveals that the carbon abundance is
approximately 50% of the solar value. We conclude that the secondary star in
V616 Mon has either suffered serious contamination from the accretion of
supernova ejecta that created the black hole primary, or it is the stripped
remains of a formerly more massive secondary star, one in which the CNO cycle
had been active.Comment: 20 pages, 5 figure