843 research outputs found
Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars
The origin of the Nuclear Star Cluster in the centre of our Galaxy is still
unknown. One possibility is that it formed after the disruption of stellar
clusters that spiralled into the Galactic Centre due to dynamical friction. We
trace the formation of the Nuclear Star Cluster around the central black hole,
using state-of-the-art N-body simulations, and follow the dynamics of the
neutron stars born in the clusters. We then estimate the number of Millisecond
Pulsars (MSPs) that are released in the Nuclear Star Cluster, during its
formation. The assembly and tidal dismemberment of globular clusters lead to a
population of MSPs distributed over a radius of about 20 pc, with a peak near 3
pc. No clustering is found on the sub-parsec scale. We simulate the
detectability of this population with future radio telescopes like the MeerKAT
radio telescope and SKA1, and find that about of order ten MSPs can be observed
over this large volume, with a paucity of MSPs within the central parsec. This
helps discriminating this scenario from the in-situ formation model for the
Nuclear Star Cluster that would predict an over abundance of MSPs closer to the
black hole. We then discuss the potential contribution of our MSP population to
the gamma-ray excess at the Galactic Centre.Comment: 11 pages, 8 figures, accepted for publication in MNRA
The optical companion to the intermediate mass millisecond pulsar J1439-5501 in the Galactic field
We present the identification of the companion star to the intermediate mass
binary pulsar J1439-5501 obtained by means of ground-based deep images in the
B, V and I bands, acquired with FORS2 mounted at the ESO-VLT. The companion is
a massive white dwarf (WD) with B=23.57+-0.02, V=23.21+-0.01 and I=22.96+-0.01,
located at only ~0.05" from the pulsar radio position. Comparing the WD
location in the (B, B-V) and (V, V-I) Color-Magnitude diagrams with theoretical
cooling sequences we derived a range of plausible combinations of companion
masses (1<~Mcom<~1.3 Msun), distances (d<~1200 pc), radii (<~7.8 10^3 Rsun) and
temperatures (T=31350^{+21500}_{-7400}). From the PSR mass function and the
estimated mass range we also constrained the inclination angle i >~ 55 degrees
and the pulsar mass (Mpsr <~2.2 Msun). The comparison between the WD cooling
age and the spin down age suggests that the latter is overestimated by a factor
of about ten.Comment: Accepted for publication by ApJ; 19 pages, 5 figures, 1 tabl
Activation of kinase phosphorylation by heat-shift and mild heat-shock
Most cells activate intracellular signalling to recover from heat damage. An increase of temperature, known as HS (heat shock), induces two major signalling events: the transcriptional induction of HSPs (heat-shock proteins) and the activation of the MAPK (mitogen-activated protein kinase) cascade. We performed the present study to examine the effects of HS, induced by different experimental conditions, on various kinases [ERK (extracellular-signal-regulated kinase), JNK (c-Jun N-terminal kinase), p38, Akt, AMPK (AMP-activated protein kinase) and PKC (protein kinase C)]. We investigated by Western blot analysis the phosphorylation of MAPK as a measure of cellular responsiveness to heat shift (37°C) and mild HS (40°C) in different cell lines. The results of the study indicate that every cell line responded to heat shift, and to a greater extent to HS, increasing ERK and JNK phosphorylation, whereas variable effects on activation or inhibition of PKC, AMPK, Akt and p38 were observed. Besides the implications of intracellular signalling activated by heat variations, these data may be of technical relevance, indicating possible sources of error due to different experimental temperature conditions
Pulsars in Globular Clusters with the SKA
Globular clusters are highly efficient radio pulsar factories. These pulsars
can be used as precision probes of the clusters' structure, gas content,
magnetic field, and formation history; some of them are also highly interesting
in their own right because they probe exotic stellar evolution scenarios as
well as the physics of dense matter, accretion, and gravity. Deep searches with
SKA1-MID and SKA1-LOW will plausibly double to triple the known population.
Such searches will only require one to a few tied-array beams, and can be done
during early commissioning of the telescope - before an all-sky pulsar survey
using hundreds to thousands of tied-array beams is feasible. With SKA2 it will
be possible to observe most of the active radio pulsars within a large fraction
of the Galactic globular clusters, an estimated population of 600 - 3700
observable pulsars (those beamed towards us). This rivals the total population
of millisecond pulsars that can be found in the Galactic field; fully
characterizing it will provide the best-possible physical laboratories as well
as a rich dynamical history of the Galactic globular cluster system.Comment: 15 pages, 5 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
Pulsar Wind Nebulae in the SKA era
Neutron stars lose the bulk of their rotational energy in the form of a
pulsar wind: an ultra-relativistic outflow of predominantly electrons and
positrons. This pulsar wind significantly impacts the environment and possible
binary companion of the neutron star, and studying the resultant pulsar wind
nebulae is critical for understanding the formation of neutron stars and
millisecond pulsars, the physics of the neutron star magnetosphere, the
acceleration of leptons up to PeV energies, and how these particles impact the
interstellar medium. With the SKA1 and the SKA2, it could be possible to study
literally hundreds of PWNe in detail, critical for understanding the many open
questions in the topics listed above.Comment: Comments: 10 pages, 3 figures, to be published in: "Advancing
Astrophysics with the Square Kilometre Array", Proceedings of Science,
PoS(AASKA14
Synchrotron radiation μ X-ray diffraction in transmission geometry for investigating the penetration depth of conservation treatments on cultural heritage stone materials
The assessment of the penetration depth of conservation treatments applied to cultural heritage stone
materials is a burning issue in conservation science. Several analytical approaches have been proposed
but, at present, many of them are not fully exhaustive to define in a direct way the composition and
location of the conservation products formed after inorganic mineral treatments. Here, we explored, for
the first time, the analytical capability of synchrotron radiation m X-ray diffraction in transmission
geometry (SR-mTXRD) for the study of the crystal chemistry and penetration depth of the consolidating
phases formed after the application of diammonium hydrogen phosphate (DAP) treatments on a porous
carbonatic stone (Noto limestone). The SR-mTXRD approach provided unambiguous information on the
nature of the newly formed calcium phosphates (hydroxyapatite, HAP, and octacalcium phosphate, OCP)
with depth, supplying important indications of the diffusion mechanism and the reactivity of the
substrate. Qualitative and semi-quantitative data were obtained at the microscale with a non-destructive
protocol and an outstanding signal-to-noise ratio. The SR-mTXRD approach opens a new analytical
scenario for the investigation of a wide range of cultural heritage materials, including natural and artificial
stone materials, painted stratigraphies, metals, glasses and their decay products. Furthermore, it can
potentially be used to characterize the penetration depth of a phase \u201cA\u201d (or more crystalline phases) in
a matrix \u201cB\u201d also beyond the cultural heritage field, demonstrating the potential wide impact of the study
Aqueye optical observations of the Crab Nebula pulsar
We observed the Crab pulsar in October 2008 at the Copernico Telescope in
Asiago - Cima Ekar with the optical photon counter Aqueye (the Asiago Quantum
Eye) which has the best temporal resolution and accuracy ever achieved in the
optical domain (hundreds of picoseconds). Our goal was to perform a detailed
analysis of the optical period and phase drift of the main peak of the Crab
pulsar and compare it with the Jodrell Bank ephemerides. We determined the
position of the main peak using the steepest zero of the cross-correlation
function between the pulsar signal and an accurate optical template. The pulsar
rotational period and period derivative have been measured with great accuracy
using observations covering only a 2 day time interval. The error on the period
is 1.7 ps, limited only by the statistical uncertainty. Both the rotational
frequency and its first derivative are in agreement with those from the Jodrell
Bank radio ephemerides archive. We also found evidence of the optical peak
leading the radio one by ~230 microseconds. The distribution of phase-residuals
of the whole dataset is slightly wider than that of a synthetic signal
generated as a sequence of pulses distributed in time with the probability
proportional to the pulse shape, such as the average count rate and background
level are those of the Crab pulsar observed with Aqueye. The counting
statistics and quality of the data allowed us to determine the pulsar period
and period derivative with great accuracy in 2 days only. The time of arrival
of the optical peak of the Crab pulsar leads the radio one in agreement with
what recently reported in the literature. The distribution of the phase
residuals can be approximated with a Gaussian and is consistent with being
completely caused by photon noise (for the best data sets).Comment: 7 pages, 7 figures. Accepted for publication in Astronomy and
Astrophysic
A Double-Pulsar System - A Rare Laboratory for Relativistic Gravity and Plasma Physics
The clock-like properties of pulsars moving in the gravitational fields of
their unseen neutron-star companions have allowed unique tests of general
relativity and provided evidence for gravitational radiation. We report here
the detection of the 2.8-sec pulsar J0737-3039B as the companion to the 23-ms
pulsar J0737-3039A in a highly-relativistic double-neutron-star system,
allowing unprecedented tests of fundamental gravitational physics. We observe a
short eclipse of J0737-3039A by J0737-3039B and orbital modulation of the flux
density and pulse shape of J0737-3039B, probably due to the influence of
J0737-3039A's energy flux upon its magnetosphere. These effects will allow us
to probe magneto-ionic properties of a pulsar magnetosphere.Comment: 21 pages, 5 figures, Science, in pres
The Double Pulsar System J0737-3039: Modulation of the radio emission from B by radiation from A
We have analyzed single pulses from PSR J0737-3039B, the 2.8-s pulsar in the
recently discovered double pulsar system, using data taken with the Green Bank
Telescope at 820 and 1400 MHz. We report the detection of features similar to
drifting subpulses, detectable over only a fraction of the pulse window, with a
fluctuation frequency of 0.196 cycles/period. This is exactly the beat
frequency between the periods of the two pulsars. In addition, the drifting
features have a separation within a given pulse of 23 ms, equal to the pulse
period of A. These features are therefore due to the direct influence of PSR
J0737-3039A's 44-Hz electromagnetic radiation on PSR J0737-3039B's
magnetosphere. We only detect them over a small range of orbital phases, when
the radiation from the recycled pulsar PSR J0737-3039A meets our line of sight
to PSR J0737-3039B from the side.Comment: 4 pages, 5 figures, Accepted by ApJ Letters 11 August 200
The optical companion to the binary millisecond pulsar J1824-2452H in the globular cluster M28
We report on the optical identification of the companion star to the
eclipsing millisecond pulsar PSR J1824-2452H in the galactic globular cluster
M28 (NGC 6626). This star is at only 0.2" from the nominal position of the
pulsar and it shows optical variability (~ 0.25 mag) that nicely correlates
with the pulsar orbital period. It is located on the blue side of the cluster
main sequence, ~1.5 mag fainter than the turn-off point. The observed light
curve shows two distinct and asymmetric minima, suggesting that the companion
star is suffering tidal distortion from the pulsar. This discovery increases
the number of non-degenerate MSP companions optically identified so far in
globular clusters (4 out of 7), suggesting that these systems could be a common
outcome of the pulsar recycling process, at least in dense environments where
they can be originated by exchange interactions.Comment: accepted for publication on ApJ, 17 pages, 5 figure
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