27 research outputs found
The proper motion of the isolated neutron star RX J1605.3+3249
We obtained deep optical imaging of the thermally emitting X-ray bright and
radio-quiet isolated neutron star RX J1605.3+3249 with the Subaru telescope in
1999 and 2003. Together with archival HST images acquired in 2001 these data
reveal a proper motion of mu = 144.5 +/- 13.2 mas/yr. This implies a relatively
high spatial velocity and indicates that the star is unlikely to be re-heated
by accretion of matter from the interstellar medium. Assuming that RX
J1605.3+3249 is a young (10^5-10^6 yr) cooling neutron star, its apparent
trajectory is consistent with a birth in the nearby Sco OB2 OB association at a
location close to that derived for RX J1856.5-3754 and perhaps also to that of
RX J0720.4-3125. This suggests that the X-ray bright part of ROSAT-discovered
isolated neutron stars is dominated by the production of the Sco OB2 complex
which is the closest OB association and a part of the Gould belt. The B and R
magnitudes of the faint optical counterpart did not vary from 1999 to 2003 at B
= 27.22 +/- 0.10. Its B-R colour index of +0.32 +/- 0.17 is significantly
redder than that of other isolated neutron stars and the optical flux lies a
factor 11.5 above the extrapolation of the X-ray blackbody-like spectrum. The
red optical colour reveals the presence of an additional emitting component in
the optical regime over the main neutron star thermal emission. We also
discovered a small elongated Halpha nebula approximately centered on the
neutron star and aligned with the direction of motion. The width of the nebula
is unresolved and smaller than ~ 0.4" for a length of about 1". The shape of
the Balmer emitting nebula is very different from those seen close to other
neutron stars and should be confirmed by follow-up observations. We shortly
discuss the possible mechanisms which could give rise to such a geometry.Comment: 9 pages, 6 figures, resolution of some figures reduced to meet
astro-ph file size restriction, accepted for publication in A&
INTEGRAL observations of the Crab pulsar
The paper presents the timing and spectral analysis of several observations
of the Crab pulsar performed with INTEGRAL in the energy range 3-500 keV. All
these observations, when summed together provide a high statistics data set
which can be used for accurate phase resolved spectroscopy. A detailed study of
the pulsed emission at different phase intervals is performed. The spectral
distribution changes with phase showing a characteristic reverse S shape of the
photon index. Moreover the spectrum softens with energy, in each phase
interval, and this behavior is adequately modeled over the whole energy range
3-500 keV with a single curved law with a slope variable with Log(E),
confirming the BeppoSAX results on the curvature of the pulsed emission. The
bending parameter of the log-parabolic model is compatible with a single value
of 0.14+/-0.02 over all phase intervals. Results are discussed within the
three-dimensional outer gap model.Comment: 10 pages, 7 figures, accepted by Astronomy and Astrophysic
Symmetry of the Neutron and Proton Superfluidity Effects in Cooling Neutron Stars
We investigate the combined effect of neutron and proton superfluidities on
the cooling of neutron stars whose cores consist of nucleons and electrons. We
consider singlet-state pairing of protons and triplet-state pairing of neutrons
in the cores of neutron stars. The critical superfluid temperatures T_c are
assumed to depend on the density of matter. We study two types of neutron
pairing with different components of the total angular momentum of Cooper pairs
along the quantization axis (|m_J| =0 or 2). Our calculations are compared with
observations of thermal emission from isolated neutron stars. We show that the
observations can be interpreted by using two classes of superfluidity models:
(1) strong proton superfluidity with a maximum critical temperature in the
stellar core T_c^{max} > 4 \times 10^9 K and weak neutron superfluidity of any
type (T_c^{max} < 2 \times 10^8 K); (2) strong neutron superfluidity (pairing
with |m_J|=0) and weak proton superfluidity. The two types of models reflect an
approximate symmetry with respect to an interchange of the critical
temperatures of neutron and proton pairing.Comment: 20 pages, 8 figure
Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre
Most galactic nuclei are now believed to harbour supermassive black holes.
Studies of stellar motions in the central few light-years of our Milky Way
Galaxy indicate the presence of a dark object with a mass of about 2.6 million
solar masses. This object is spatially coincident with Sagittarius A* (Sgr A*),
the unique compact radio source located at the dynamical centre of our Galaxy.
By analogy with distant quasars and nearby active galactic nuclei (AGN), Sgr A*
is thought to be powered by the gravitational potential energy released by
matter as it accretes onto a supermassive black hole. However, Sgr A* is much
fainter than expected in all wavebands, especially in X-rays, casting some
doubt on this model. Recently, we reported the first strong evidence of X-ray
emission from Sgr A*. Here we report the discovery of rapid X-ray flaring from
the direction of Sgr A*. These data provide compelling evidence that the X-ray
emission is coming from accretion onto a supermassive black hole at the
Galactic Centre, and the nature of the variations provides strong constraints
on the astrophysical processes near the event horizon of the black hole.Comment: 4 pages, 3 figures (Figs 1 and 3 in color), LaTe
Multiwavelength observations of V407 Lupi (ASASSN-16kt) --- a very fast nova erupting in an intermediate polar
We present a detailed study of the 2016 eruption of nova V407 Lupi (ASASSN-16kt), including optical, near-infrared, X-ray, and ultraviolet data from SALT, SMARTS, SOAR, Chandra, Swift, and XMM-Newton. Timing analysis of the multiwavelength light-curves shows that, from 168 days post-eruption and for the duration of the X-ray supersoft source phase, two periods at 565 s and 3.57 h are detected. We suggest that these are the rotational period of the white dwarf and the orbital period of the binary, respectively, and that the system is likely to be an intermediate polar. The optical light-curve decline was very fast ( 2.9 d), suggesting that the white dwarf is likely massive ( M). The optical spectra obtained during the X-ray supersoft source phase exhibit narrow, complex, and moving emission lines of He II, also characteristics of magnetic cataclysmic variables. The optical and X-ray data show evidence for accretion resumption while the X-ray supersoft source is still on, possibly extending its duration
Assumption without representation: the unacknowledged abstraction from communities and social goods
We have not clearly acknowledged the abstraction from unpriceable “social goods” (derived from
communities) which, different from private and public goods, simply disappear if it is attempted to
market them. Separability from markets and economics has not been argued, much less established.
Acknowledging communities would reinforce rather than undermine them, and thus facilitate
the production of social goods. But it would also help economics by facilitating our understanding
of – and response to – financial crises as well as environmental destruction and many social problems,
and by reducing the alienation from economics often felt by students and the public