108,574 research outputs found
Chandra detection of diffuse hot gas in and around the M31 bulge
We report the detection of diffuse hot gas in M31, using archival Chandra
observations which allow us to map out a 30' by 30' field (covering a
galactocentric radius up to 4.5 kpc) and to detect sources in the galaxy down
to a 0.5-8 keV luminosity limit of ~10^35 ergs/s. We estimate the remaining
stellar contribution from fainter X-ray sources (primarily cataclysmic
variables and coronally active binaries), assuming that they spatially follow
the stellar distribution. Indeed, the near-IR K-band light of the galaxy
closely traces the 2-8 keV unresolved X-rays, indicating a collective stellar
X-ray emissivity consistent with those determined for the Galactic ridge and
M32, whereas the amount of the 0.5-2 keV unresolved emission is significantly
greater than the expected stellar contribution, especially within a
galactocentric radius of ~2 kpc. Morphologically, this soft X-ray excess
appears substantially rounder than the bulge as seen in K-band and is elongated
approximately along the minor-axis at large radii. The excess thus most likely
represents the emission of diffuse hot gas in and around the galactic bulge.
Furthermore, the near side of the M31 disk casts an apparent shadow against the
soft X-ray excess, indicating that the hot gas extends to at least 2.5 kpc from
the galactic plane. We briefly discuss the implications of these results on the
energy balance in the M31 bulge and on understanding the large-scale soft X-ray
enhancement observed toward the inner region of our own Galaxy.Comment: 10 pages, 2 figures, accepted by ApJ
The role of components in the N(1440) resonance
The role of 5-quark components in the pion and electromagnetic decays and
transition form factors of the N(1440) is explored. The
components, where the 4-quark subsystem has the flavor-spin symmetries
and , which are expected to have
the lowest energy of all configurations, are considered in detail
with a nonrelativistic quark model. The matrix elements between the 5-quark
components of the N(1440) and the nucleon, , play a
minor role in these decays, while the transition matrix elements and that involve quark antiquark annihilation are very
significant. Both for the electromagnetic and strong decay the change from the
valence quark model value is dominated by the confinement triggered
annihilation transitions. In the case of pion decay the calculated decay width
is enhanced substantially both by the direct and also by the
confinement triggered transitions. Agreement with the
empirical value for the pion decay width may be reached with a 30%
component in the N(1440).Comment: 23 pages revte
Five-quark components in decay
Five-quark components in the are shown to
contribute significantly to decay through
quark-antiquark annihilation transitions. These involve the overlap between the
and components and may be triggered by the confining
interaction between the quarks. With a 10% admixture of five-quark
components in the the decay width can be larger by factors 2 - 3
over that calculated in the quark model with 3 valence quarks, depending on the
details of the confining interaction. The effect of transitions between the
components themselves on the calculated decay width is however
small. The large contribution of the quark-antiquark annihilation transitions
thus may compensate the underprediction of the width of the by
the valence quark model, once the contains
components with 10% probability.Comment: accepted versio
Aggregation and the "Random Objective" Justification for Disturbances in Complete Demand Systems
Sea-quark effects in the pion charge form factor
It is shown that the data on the pion charge form factor admit the
possibility for a substantial sea-quark components in the pion wave function.
If the charge form factor is calculated with instant form kinematics in a
constituent quark model that is extended to include explicit
components in the pion wave function, that component will give the dominant
contribution to the calculated charge form factor at large values of
momentum transfer. The present experimental values can be described well
with component admixtures of up to 50%. The sensitivity of the
calculated charge form factor to whether one of the quarks or one of
the antiquarks is taken to be in the P-state is small.Comment: 14 page
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