4,074 research outputs found
Revisiting the radio/X-ray flux correlation in the black hole V404 Cyg: from outburst to quiescence
We report results of Chandra X-ray and VLA radio observations of the Galactic
accreting black hole V404 Cyg (GS 2023+338) in its quiescent state. V404 Cyg is
detected at its faintest level of radio and X-ray emission with a 0.5-10 keV
unabsorbed luminosity of 8.3 x 10^32 (d/3.5 kpc)^2 erg/s. The X-ray spectrum
fit with an absorbed power-law model yields a photon index of 2.17 +/- 0.13.
Contrary to previous findings, this clearly indicates that V404 Cyg undergoes -
like most black holes in quiescence - a softening of its X-ray spectrum at very
low luminosity compared to the standard hard state. The quiescent radio
emission is consistent with the presence of self-absorbed compact jets. We have
also reanalyzed archival data from the decay of the 1989 outburst of V404 Cyg
in order to quantify more precisely the correlation between radio and X-ray
emission in the hard state of V404 Cyg. We show that this correlation extends
over five decades in X-ray flux and holds down to the quiescent state of V404
Cyg. The index of this correlation (~0.5) may suggest that synchrotron
self-Compton emission is the dominant physical process at high energy in V404
Cyg. However, this index is also consistent with scale invariant jet models
coupled to an inefficiently radiating accretion disc. We discuss the properties
of the quiescent state of black holes and highlight the fact that some of their
properties are different from the standard hard state.Comment: 7 pages, Accepted for publication in MNRA
The variable radio counterpart and possible large-scale jet of the new Z-source XTE J1701-462
We report radio observations, made with the Australia Telescope Compact
Array, of the X-ray transient XTE J1701-462. This system has been classified as
a new `Z' source, displaying characteristic patterns of behaviour probably
associated with accretion onto a low magnetic field neutron star at close to
the Eddington limit. The radio counterpart is highly variable, and was detected
in six of sixteen observations over the period 2006 January -- April. The
coupling of radio emission to X-ray state, despite limited sampling, appears to
be similar to that of other `Z' sources, in that there is no radio emission on
the flaring branch. The mean radio and X-ray luminosities are consistent with
the other Z sources for a distance of 5--15 kpc. The radio spectrum is
unusually flat, or even inverted, in contrast to the related sources, Sco X-1
and Cir X-1, which usually display an optically thin radio spectrum. Deep
wide-field observations indicate an extended structure three arcminutes to the
south which is aligned with the X-ray binary. This seems to represent a
significant overdensity of radio sources for the field and so, although a
background source remains a strong possibility, we consider it plausible that
this is a large-scale jet associated with XTE J1701-462.Comment: Accepted for publication as a Letter in MNRA
On the Origin of Radio Emission in the X-ray States of XTE J1650-500 during the 2001-2002 Outburst
We report on simultaneous radio and X-ray observations of the black hole
candidate XTE J1650-500 during the course of its 2001-2002 outburst. The
scheduling of the observations allowed us to sample the properties of XTE
J1650-50 in different X-ray spectral states, namely the hard state, the steep
power-law state and the thermal dominant state, according to the recent
spectral classification of McClintock & Remillard. The hard state is consistent
with a compact jet dominating the spectral energy distribution at radio
frequencies; however, the current data suggest that its contribution as direct
synchrotron emission at higher energies may not be significant. In that case,
XTE J1650-50 may be dominated by Compton processes (either inverse
Comptonization of thermal disk photons and/or SSC from the base of the compact
jet) in the X-ray regime. We, surprisingly, detect a faint level of radio
emission in the thermal dominant state that may be consistent with the emission
of previously ejected material interacting with the interstellar medium,
similar (but on a smaller angular scale) to what was observed in XTE J1550-564
by Corbel and co-workers. Based on the properties of radio emission in the
steep power-law state of XTE J1650-50, and taking into account the behavior of
other black hole candidates (namely GX 339-4, XTE J1550-564, and XTE J1859+226)
while in the intermediate and steep power-law states, we are able to present a
general pattern of behavior for the origin of radio emission in these two
states that could be important for understanding the accretion-ejection
coupling very close to the black hole event horizon.Comment: Accepted for publication in The Astrophysical Journal. 33 pages, 10
figure
The evolution of patent functions: New trends, main challenges and implications for firm strategy
Recent publications in the field of Intellectual Property (IP) have shown that the previous literature did not grasp how complex patents are. The goal of this paper is to present an overview of all identified functions of patents and of the main strategic implications of such a complex picture. We first survey the main patent functions : innovation protection, functions related to trade and finance, defensive roles, and patent as an input in the innovation process. We then define each function and analyse their main evolution trends in relation with the current environment. We finally identify the strategic implications of each function. We focus on the implications of the newly identified functions and on the interaction between the different functions.Patent ; Intellectual Property ; Strategic Management ; Functions ; Motives to patent
Near-infrared synchrotron emission from the compact jet of GX339-4
We have compiled contemporaneous broadband observations of the black hole
candidate X-ray binary GX 339-4 when in the low/hard X-ray state in 1981 and
1997. The data clearly reveal the presence of two spectral components, with
thermal and non-thermal spectra, overlapping in the optical -- near-infrared
bands. The non-thermal component lies on an extrapolation of the radio spectrum
of the source, and we interpret it as optically thin synchrotron emission from
the powerful, compact jet in the system. Detection of this break from
self-absorbed to optically thin synchrotron emission from the jet allows us to
place a firm lower limit on the ratio of jet (synchrotron) to X-ray
luminosities of %. We further note that extrapolation of the optically
thin synchrotron component from the near-infrared to higher frequencies
coincides with the observed X-ray spectrum, supporting models in which the
X-rays could originate via optically thin synchrotron emission from the jet
(possibly instead of Comptonisation).Comment: Accepted for publication in ApJ Lette
A UV flux drop preceding the X-ray hard-to-soft state transition during the 2010 outburst of GX 339-4
The black hole X-ray transient GX 3394 was observed with the {\it Swift}
satellite across the hard-to-soft state transition during its 2010 outburst.
The ultraviolet (UV) flux measured with the filter UVW2 of the {\it Swift}/UVOT
started to decrease nearly 10 days before the drop in the hard X-ray flux when
the hard-to-soft state transition started. The UV flux
correlated with the X-ray flux as before the drop in the UV flux. During the UV drop
lasting about 16 days, the X-ray flux in 0.4--10 keV was increasing. The drop
in the UV flux indicates that the jet started to quench 10 days before the
hard-to-soft state transition seen in X-rays, which is unexpected.Comment: accepted for publication in MNRAS Lette
Radio Emission from an Ultraluminous X-Ray Source
The physical nature of ultraluminous x-ray sources is uncertain. Stellar mass
black holes with beamed radiation and intermediate mass black holes with
isotropic radiation are two plausible explanations. We discovered radio
emission from an ultraluminous x-ray source in the dwarf irregular galaxy NGC
5408. The x-ray, radio and optical fluxes as well as the x-ray spectral shape
are consistent with beamed relativistic jet emission from an accreting stellar
black hole. If confirmed, this would suggest that the ultraluminous x-ray
sources may be stellar-mass rather than intermediate mass black holes. However,
interpretation of the source as a jet-producing intermediate-mass black hole
cannot be ruled out at this time.Comment: 8 pages, one color figure. appeared in Science 299: 365-367 (January
17, 2003
On the role of the magnetic field on jet emission in X-ray binaries
Radio and X-ray fluxes of accreting black holes in their hard state are known
to correlate over several orders of magnitude. This correlation however shows a
large scatter: black hole candidates with very similar X-ray luminosity,
spectral energy distribution and variability, show rather different radio
luminosities. This challenges theoretical models that aim at describing both
the radio and the X-ray fluxes in terms of radiative emission from a
relativistic jet. More generally, it opens important questions on how similar
accretion flows can produce substantially different outflows. Here we present a
possible explanation for this phenomenon, based on the strong dependency of the
jet spectral energy distribution on the magnetic field strength, and on the
idea that the strength of the jet magnetic field varies from source to source.
Because of the effect of radiative losses, sources with stronger jet magnetic
field values would have lower radio emission. We discuss the implications of
this scenario, the main one being that the radio flux does not necessarily
provide a direct measure of the jet power. We further discuss how a variable
jet magnetic field, reaching a critical value, can qualitatively explain the
observed spectral transition out of the hard state.Comment: 4 pages, 2 figures. Accepted for publication on ApJ Letter
Spectral evolution of the microquasar XTE J1550-564 over its entire 2000 outburst
We report on RXTE observations of the microquasar XTE J1550-564 during a ~70
day outburst in April-June 2000. We study the evolution of the PCA+HEXTE
spectra over the outburst. The source transited from an initial Low Hard State
(LS), to an Intermediate State (IS), and then back to the LS. The source shows
an hysteresis effect similar to what is observed in other sources, favoring a
common origin for the state transitions in soft X-ray transients. The first
transition occurs at a ~ constant 2-200 keV flux, which probably indicates a
change in the relative importance of the emitting media. The second transition
is more likely driven by a drop in the mass accretion rate.
In both LS, the spectra are characterized by the presence of a strong
power-law tail (Compton corona) with a variable high energy cut-off. During the
IS, the spectra show the presence of a ~0.8 keV thermal component (accretion
disk). We discuss the apparently independent evolution of the two media, and
show that right after the X-ray maximum on MJD 51662, the decrease of the
source luminosity is due to a decrease of the power-law luminosity, at a
constant disk luminosity. This, together with the detection of radio emission
(with a spectrum typical of optically thin synchrotron emission), may suggest
that the corona is ejected and further detected as a discrete radio ejection.Comment: Accepted for publication in ApJ. 9 pages, 4 figures, abstract
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