3,087 research outputs found
Discovery of a 6.4 h black hole binary in NGC 4490
We report on the discovery with Chandra of a strong modulation (~90% pulsed
fraction) at ~6.4 h from the source CXOU J123030.3+413853 in the star-forming,
low-metallicity spiral galaxy NGC 4490, which is interacting with the irregular
companion NGC 4485. This modulation, confirmed also by XMM-Newton observations,
is interpreted as the orbital period of a binary system. The spectra from the
Chandra and XMM-Newton observations can be described by a power-law model with
photon index ~1.5. During these observations, which span from 2000 November to
2008 May, the source showed a long-term luminosity variability by a factor of
~5, between ~2E+38 and 1.1E+39 erg/s (for a distance of 8 Mpc). The maximum
X-ray luminosity, exceeding by far the Eddington limit of a neutron star,
indicates that the accretor is a black hole. Given the high X-ray luminosity,
the short orbital period and the morphology of the orbital light curve, we
favour an interpretation of CXOU J123030.3+413853 as a rare high-mass X-ray
binary system with a Wolf-Rayet star as a donor, similar to Cyg X-3. This would
be the fourth system of this kind known in the local Universe. CXOU
J123030.3+413853 can also be considered as a transitional object between high
mass X-ray binaries and ultraluminous X-ray sources (ULXs), the study of which
may reveal how the properties of persistent black-hole binaries evolve entering
the ULX regime.Comment: Fig. 1 in reduced quality; minor changes to match the MNRAS versio
Ultraluminous X-ray Sources forming in low metallicity natal environments
In the last few years multiwavelength observations have boosted our
understanding of Ultraluminous X-ray Sources (ULXs). Yet, the most fundamental
questions on ULXs still remain to be definitively answered: do they contain
stellar or intermediate mass black holes? How do they form? We investigate the
possibility that the black holes hosted in ULXs originate from massive (40-120
) stars in low metallicity natal environments. Such black holes have a
typical mass in the range and may account for the
properties of bright (above erg s) ULXs. More than massive black holes might have been generated in this way in the metal
poor Cartwheel galaxy during the last years and might power most of the
ULXs observed in it. Support to our interpretation comes from NGC 1313 X-2, the
first ULX with a tentative identification of the orbital period in the optical
band, for which binary evolution calculations show that the system is most
likely made by a massive donor dumping matter on a black hole.Comment: 4 pages. To appear in the Proceedings of the Conference "X-Ray
Astronomy 2009: Present Status, Multiwavelength Approach and Future
Perspectives", Bologna, Italy, September 2009, Eds. A. Comastri, M. Cappi, L.
Angelini, 2010 AIP (in press)
Periodic signals from the Circinus region: two new cataclysmic variables and the ultraluminous X-ray source candidate GC X-1
The examination of two 2010 Chandra ACIS exposures of the Circinus galaxy
resulted in the discovery of two pulsators: CXO J141430.1-651621 and CXOU
J141332.9-651756. We also detected 26-ks pulsations in CG X-1, consistently
with previous measures. For ~40 other sources, we obtained limits on periodic
modulations. In CXO J141430.1-651621, which is ~2 arcmin outside the Circinus
galaxy, we detected signals at 6120(1) s and 64.2(5) ks. In the longest
observation, the source showed a flux of ~1.1e-13 erg/cm^2/s (absorbed, 0.5-10
keV) and the spectrum could be described by a power-law with photon index ~1.4.
From archival observations, we found that the luminosity is variable by ~50 per
cent on time-scales of weeks-years. The two periodicities pin down CXO
J141430.1-651621 as a cataclysmic variable of the intermediate polar subtype.
The period of CXOU J141332.9-651756 is 6378(3) s. It is located inside the
Circinus galaxy, but the low absorption indicates a Galactic foreground object.
The flux was ~5e-14 erg/cm^2/s in the Chandra observations and showed ~50 per
cent variations on weekly/yearly scales; the spectrum is well fit by a power
law ~0.9. These characteristics and the large modulation suggest that CXOU
J141332.9-651756 is a magnetic cataclysmic variable, probably a polar. For CG
X-1, we show that if the source is in the Circinus galaxy, its properties are
consistent with a Wolf-Rayet plus black hole binary. We consider the
implications of this for ultraluminous X-ray sources and the prospects of
Advanced LIGO and Virgo. In particular, from the current sample of WR-BH
systems we estimate an upper limit to the detection rate of stellar BH-BH
mergers of ~16 events per yr.Comment: 17 pages, 7 figures, 6 tables; accepted for publication in MNRA
The ACS LCID project VII: the blue stragglers population in the isolated dSph galaxies Cetus and Tucana
We present the first investigation of the Blue Straggler star (BSS)
population in two isolated dwarf spheroidal galaxies of the Local Group, Cetus
and Tucana. Deep HST/ACS photometry allowed us to identify samples of 940 and
1214 candidates, respectively. The analysis of the star formation histories of
the two galaxies suggests that both host a population of BSSs. Specifically, if
the BSS candidates are interpreted as young main sequence stars, they do not
conform to their galaxy's age-metallicity relationship. The analysis of the
luminosity function and the radial distributions support this conclusion, and
suggest a non-collisional mechanism for the BSS formation, from the evolution
of primordial binaries. This scenario is also supported by the results of new
dynamical simulations presented here. Both galaxies coincide with the
relationship between the BSS frequency and the absolute visual magnitude Mv
found by Momany et al (2007). If this relationship is confirmed by larger
sample, then it could be a valuable tool to discriminate between the presence
of BSSs and galaxies hosting truly young populations.Comment: Accepted for publication on ApJ. 15 pages, 3 tables, 13 figures. A
version with high resolution figure can be downloaded from
http://rialto.ll.iac.es/proyecto/LCID/?p=publication
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Development of interconnected silicon micro-evaporators for the on-detector electronics cooling of the future ITS detector in the ALICE experiment at LHC
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The design of the future High Energy Physics (HEP) particle detectors for the upgrade of the LHC (Large Hadron Collider) experiments at CERN (European Organization for Nuclear Research) is pushing technological frontiers to the limit trying to reach unprecedented accuracy in particles identification and particle production dynamics in ultra-relativistic hadron collisions. The thermal management of the on-detector electronics and the development of low mass integrated cooling systems have become a crucial task in the design of silicon tracking detectors for HEP applications. In this paper, we present a novel concept of low mass interconnected silicon microchannel devices for the future Inner Tracking System of the ALICE (A Large Ion Collider Experiment) detector at LHC. This innovative design achieves the requirements of the detector while minimizing the total material budget
UGC 7069: The largest ring galaxy
We find that UGC 7069 is the largest ring galaxy known to date. In this
Letter, we present a multiwavelength study of this galaxy (combining radio,
2MASS, optical and ultraviolet data). The ring of UGC 7069, whose diameter
measures ~115 kpc, is also warped at its edges. The nucleus appears
double-peaked and hosts a possible LINER. The ultraviolet data indicate a
strong blue colour and suggest that UGC 7069 is a starburst galaxy. We also
present N-body simulation results, which indicate that galaxy collisions can
produce such huge rings. Large inclination angles between the target and the
intruder galaxy may account for the formation of warped rings. Multiwavelength
observations are highly essential to constrain our simulation results, which
will address the formation and evolution of such a rare galaxy.Comment: 6 pages, 5 figures, MNRAS Letters, in pres
Swift J201424.9+152930: discovery of a new deeply eclipsing binary with 491 s and 3.4 h modulations
We report on the discovery of a new X-ray pulsator, Swift J201424.9+152930
(Sw J2014). Owing to its X-ray modulation at 491 s, it was discovered in a
systematic search for coherent signals in the archival data of the Swift X-ray
Telescope. To investigate the nature of Sw J2014, we performed multi-wavelength
follow-up observations with space-borne (Swift and XMM-Newton) and ground-based
(the 1.5-m Loiano Telescope and the 3.6-m Telescopio Nazionale Galileo)
instruments. The X-ray spectrum of Sw J2014 can be described by a hard and
highly absorbed power law. The optical observations made it possible to single
out the optical counterpart to this source, which displays several variable
emission lines and total eclipses lasting ~20 min. Total eclipses of similar
length were observed also in X-rays. The study of the eclipses, allowed us to
infer a second periodicity of 3.44 h, which we interpret as the orbital period
of a close binary system. We also found that the period has not significantly
changed over a ~7 yr timespan. Based on the timing signatures of Sw J2014, and
its optical and X-ray spectral properties, we suggest that it is a close binary
hosting an accreting magnetic white dwarf. The system is therefore a
cataclysmic variable of the intermediate polar type and one of the very few
showing deep eclipses.Comment: 12 pages, 8 figures, 5 tables; minor changes to match the final MNRAS
versio
Deeper, Wider, Sharper: Next-Generation Ground-Based Gravitational-Wave Observations of Binary Black Holes
Next-generation observations will revolutionize our understanding of binary
black holes and will detect new sources, such as intermediate-mass black holes.
Primary science goals include: Discover binary black holes throughout the
observable Universe; Reveal the fundamental properties of black holes; Uncover
the seeds of supermassive black holes.Comment: 14 pages, 3 figures, White Paper Submitted to Astro2020 (2020
Astronomy and Astrophysics Decadal Survey) by GWIC 3G Science Case Team
(GWIC: Gravitational Wave International Committee
Gravitational Wave Bursts from Collisions of Primordial Black Holes in Clusters
The rate of gravitational wave bursts from the mergers of massive primordial
black holes in clusters is calculated. Such clusters of black holes can be
formed through phase transitions in the early Universe. The central black holes
in clusters can serve as the seeds of supermassive black holes in galactic
nuclei. The expected burst detection rate by the LISA gravitational wave
detector is estimated.Comment: 10 pages, 2 figure
Tonic activation of GABA-B receptors reduces release probability at inhibitory connections in the cerebellar glomerulus
Mapelli L, Rossi P, Nieus T, D'Angelo E. Tonic activation of GABA(B) receptors reduces release probability at inhibitory connections in the cerebellar glomerulus. J Neurophysiol 101: 3089-3099, 2009. First published April 1, 2009; doi:10.1152/jn.91190.2008. In the cerebellum, granule cells are inhibited by Golgi cells through GABAergic synapses generating complex responses involving both phasic neurotransmitter release and the establishment of ambient gamma-aminobutyric acid (GABA) levels. Although at this synapse the mechanisms of postsynaptic integration have been clarified to a considerable extent, the mechanisms of neurotransmitter release remained largely unknown. Here we have investigated the quantal properties of release during repetitive neurotransmission, revealing that tonic GABA(B) receptor activation by ambient GABA regulates release probability. Blocking GABA(B) receptors with CGP55845 enhanced the first inhibitory postsynaptic current (IPSC) and short-term depression in a train while reducing trial-to-trial variability and failures. The changes caused by CGP55845 were similar to those caused by increasing extracellular Ca2+ concentration, in agreement with a presynaptic GABA(B) receptor modulation of release probability. However, the slow tail following IPSC peak demonstrated a remarkable temporal summation and was not modified by CGP55845 or extracellular Ca2+ increase. This result shows that tonic activation of presynaptic GABA(B) receptors by ambient GABA selectively regulates the onset of inhibition bearing potential consequences for the dynamic regulation of signal transmission through the mossy fibergranule cell pathway of the cerebellum
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