14,234 research outputs found
Surgery on -manifolds
We show that although closed -manifolds
do not admit metrics of nonpositive sectional curvature, the arguments of
Farrell and Jones can be extended to show that such manifolds are topologically
rigid, if .Comment: 7 pages, AMS-LaTeX file, To appear in the Canadian Mathematical
Bulletin
Superorbital Period in the High Mass X-ray Binary 2S 0114+650
We report the detection of a superorbital period in the high-mass X-ray
binary 2S 0114+650. Analyses of data from the Rossi X-ray Timing Explorer
(RXTE) All-Sky Monitor (ASM) from 1996 January 5 to 2004 August 25 reveal a
superorbital period of 30.7 +/- 0.1 d, in addition to confirming the previously
reported neutron star spin period of 2.7 h and the binary orbital period of
11.6 d. It is unclear if the superorbital period can be ascribed to the
precession of a warped accretion disc in the system.Comment: 5 pages, 5 figures, submitted to MNRAS 27th January 2005. Manuscript
expanded to include discussion of evolution of periods, and hardness ratio
variability. Number of figures increased from 5 to 9. Accepted for
publication 19th December 200
A Multicoloured View of 2S 0114+650
We report the results of radio and X-ray observations of the high mass X-ray
binary 2S 0114+650, made with the Giant Meterwave Radio Telescope and the Rossi
X-ray Timing Explorer respectively. No emission was detected at radio
wavelengths. The neutral hydrogen column density was found to vary over the
orbital period, while no variability over the the super-orbital period was
observed. We discuss the causes of the observed relationships and the
implications for the underlying mechanisms.Comment: 4 pages, 2 figures; to appear in proceedings for "The multicoloured
landscape of compact objects and their explosive progenitors", Cefalu,
Sicily, 2006 June 11-24, AIP, submitte
GRO J1744-28, search for the counterpart: infrared photometry and spectroscopy
Using VLT/ISAAC, we detected 2 candidate counterparts to the bursting pulsar
GRO J1744-28, one bright and one faint, within the X-ray error circles of
XMM-Newton and Chandra. In determining the spectral types of the counterparts
we applied 3 different extinction corrections; one for an all-sky value, one
for a Galactic Bulge value and one for a local value. We find the local value,
with an extinction law of alpha = 3.23 +- 0.01 is the only correction that
results in colours and magnitudes for both bright and faint counterparts
consistent with a small range of spectral types, and for the bright
counterpart, consistent with the spectroscopic identification. Photometry of
the faint candidate indicates it is a K7/M0 V star at a distance of 3.75 +- 1
kpc. This star would require a very low inclination angle (i < 9deg) to satisfy
the mass function constraints; however it cannot be excluded as the counterpart
without follow-up spectroscopy to detect emission signatures of accretion.
Photometry and spectroscopy of the bright candidate indicate it is most likely
a G/K III star. The spectrum does not show Br-gamma emission, a known indicator
of accretion. The bright star's magnitudes are in agreement with the
constraints placed on a probable counterpart by the calculations of Rappaport &
Joss (1997) for an evolved star that has had its envelope stripped. The mass
function indicates the counterpart should have M < 0.3 Msol for an inclination
of i >= 15deg; a stripped giant, or a main sequence M3+ V star are consistent
with this mass-function constraint. In both cases mass-transfer, if present,
will be by wind-accretion as the counterpart will not fill its Roche lobe given
the observed orbital period. The derived magnetic field of 2.4 x 10^{11} G will
inhibit accretion by the propeller effect, hence its quiescent state.Comment: 12 pages, 6 figures, 4 table, MNRAS accepted Changes to the content
and an increased analysis of the Galactic centre extinctio
Formation of a Nematic Fluid at High Fields in Sr3Ru2O7
In principle, a complex assembly of strongly interacting electrons can
self-organise into a wide variety of collective states, but relatively few such
states have been identified in practice. We report that, in the close vicinity
of a metamagnetic quantum critical point, high purity Sr3Ru2O7 possesses a
large magnetoresistive anisotropy, consistent with the existence of an
electronic nematic fluid. We discuss a striking phenomenological similarity
between our observations and those made in high purity two-dimensional electron
fluids in GaAs devices.Comment: 14 pages, 3 figures, 11 extra pages of supplementary informatio
Some general classes of comatching graphs
Some sufficient conditions are given for two graphs to have the same matching polynomial (comatching graphs). Several general classes of comatching graphs are given. Also, techniques are discussed for extending certain pairs of comatching graphs to larger pairs of comatching graphs
Surgery groups of the fundamental groups of hyperplane arrangement complements
Using a recent result of Bartels and Lueck (arXiv:0901.0442) we deduce that
the Farrell-Jones Fibered Isomorphism conjecture in L-theory is true for any
group which contains a finite index strongly poly-free normal subgroup, in
particular, for the Artin full braid groups. As a consequence we explicitly
compute the surgery groups of the Artin pure braid groups. This is obtained as
a corollary to a computation of the surgery groups of a more general class of
groups, namely for the fundamental group of the complement of any fiber-type
hyperplane arrangement in the complex n-space.Comment: 11 pages, AMSLATEX file, revised following referee's comments and
suggestions, to appear in Archiv der Mathemati
Further Observations of the Intermediate Mass Black Hole Candidate ESO 243-49 HLX-1
The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49
currently provides strong evidence for the existence of intermediate mass black
holes. Here we present the latest multi-wavelength results on this intriguing
source in X-ray, UV and radio bands. We have refined the X-ray position to
sub-arcsecond accuracy. We also report the detection of UV emission that could
indicate ongoing star formation in the region around HLX-1. The lack of
detectable radio emission at the X-ray position strengthens the argument
against a background AGN.Comment: 4 pages, 2 figures. Accepted 11th of Feb 2010. Contributed talk to
appear in Proceedings of "X-ray Astronomy 2009: Present Status,
Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September
7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin
Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst
We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large
Telescope (VLT), V- and R-band) observations of the intermediate mass black
hole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We show
that the V-band magnitudes vary with time, thus proving that a portion of the
observed emission originates in the accretion disk. Using the first quiescent
optical observations of HLX-1, we show that the stellar population surrounding
HLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission may
increase before the X-ray emission consistent with the scenario proposed by
Lasota et al. (2011) in which the regular outbursts could be related to the
passage at periastron of a star circling the intermediate mass black hole in an
eccentric orbit, which triggers mass transfer into a quasi-permanent accretion
disk around the black hole. Further, if there is indeed a delay in the X-ray
emission we estimate the mass-transfer delivery radius to be ~1e11 cm.Comment: 9 pages, 2 figures, accepted for publication in ApJ
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