214 research outputs found
Spectral variability in Cygnus X-3
We model the broad-band X-ray spectrum of Cyg X-3 in all states displayed by
this source as observed by the Rossi X-ray Timing Explorer. From our models, we
derive for the first time unabsorbed spectral shapes and luminosities for the
full range of spectral states. We interpret the unabsorbed spectra in terms of
Comptonization by a hybrid electron distribution and strong Compton reflection.
We study the spectral evolution and compare with other black hole as well as
neutron star sources. We show that a neutron star accretor is not consistent
with the spectral evolution as a function of Ledd and especially not with the
transition to a hard state. Our results point to the compact object in Cyg X-3
being a massive, ~30 Msun black hole.Comment: 14 pages, 9 figures, accepted for publication in MNRA
On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C +67.13
Here we analyze radio, optical, and X-ray data for a peculiar cluster Abell
578. This cluster is not fully relaxed and consists of two merging sub-systems.
The brightest cluster galaxy, CGPG 0719.8+6704, is a pair of interacting
ellipticals with projected separation 10 kpc, the brighter of which hosts
the radio source 4C +67.13. The Fanaroff-Riley type-II radio morphology of 4C
+67.13 is unusual for central radio galaxies in local Abell clusters. Our new
optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are
active, albeit at low accretion rates corresponding to the Eddington ratio
(for the estimated black hole masses of and ). The gathered X-ray ({\it Chandra})
data allowed us to confirm and to quantify robustly the previously noted
elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a
large spatial offset (\,kpc projected) between the position of the
brightest cluster galaxy and the cluster center inferred from the modeling of
the X-ray surface brightness distribution. Detailed analysis of the brightness
profiles and temperature revealed also that the cluster gas in the vicinity of
4C\,+67.13 is compressed (by a factor of about ) and heated (from
\,keV up to 2.7\,keV), consistent with the presence of a weak shock
(Mach number ) driven by the expanding jet cocoon. This would then
require the jet kinetic power of the order of \,erg\,s,
implying either a very high efficiency of the jet production for the current
accretion rate, or a highly modulated jet/accretion activity in the system.Comment: 12 pages, 11 figures, accepted for publication in Ap
On the Interaction of the PKS B1358-113 Radio Galaxy with the Abell 1836 Cluster
[abridged] Here we present the analysis of multifrequency data gathered for
the FRII radio galaxy PKS B1358-113, hosted in the brightest cluster galaxy of
Abell 1836. The galaxy harbors one of the most massive black holes known to
date and our analysis of the optical data reveals that this black hole is only
weakly active. Based on new Chandra and XMM-Newton X-ray observations and
archival radio data we derive the preferred range for the jet kinetic
luminosity erg s. This is above the values
implied by various scaling relations proposed for radio sources in galaxy
clusters, being instead very close to the maximum jet power allowed for the
given accretion rate. We constrain the radio source lifetime as
Myrs, and the total amount of deposited jet energy \,ergs. The detailed analysis of the X-ray data provides indication for
the presence of a bow-shock driven by the expanding radio lobes into the Abell
1836 cluster environment, with the corresponding Mach number . This,
together with the recently growing evidence that powerful FRII radio galaxies
may not be uncommon in the centers of clusters at higher redshifts, supports
the idea that jet-induced shock heating may indeed play an important role in
shaping the properties of clusters, galaxy groups, and galaxies in formation.
We speculate on a possible bias against detecting jet-driven shocks in poorer
environments, resulting from an inefficient electron heating at the shock
front, combined with a relatively long electron-ion equilibration timescale.Comment: Version accepted to Ap
The Hardness-Intensity Diagram of Cygnus X-3: Revisiting the Radio/X-Ray States
Cygnus X-3 is one of the brightest X-ray and radio sources in the Galaxy, and
is well known for its erratic behaviour in X-rays as well as in the radio,
occasionally producing major radio flares associated with relativistic
ejections. However, even after many years of observations in various wavelength
bands Cyg X-3 still eludes clear physical understanding. Studying different
emission bands simultaneously in microquasars has proved to be a fruitful
approach towards understanding these systems, especially by shedding light on
the accretion disc/jet connection. We continue this legacy by constructing a
hardness-intensity diagram (HID) from archival Rossi X-ray Timing Explorer data
and linking simultaneous radio observations to it. We find that surprisingly
Cyg X-3 sketches a similar shape in the HID to that seen in other transient
black hole X-ray binaries during outburst but with distinct differences.
Together with the results of this analysis and previous studies of Cyg X-3 we
conclude that the X-ray states can be assigned to six distinct states. This
categorization relies heavily on the simultaneous radio observations and we
identify one new X-ray state, the hypersoft state, similar to the ultrasoft
state, which is associated to the quenched radio state during which there is no
or very faint radio emission. Recent observations of GeV flux observed from Cyg
X-3 (Tavani et al. 2009; Fermi LAT Collaboration et al. 2009) during a soft
X-ray and/or radio quenched state at the onset of a major radio flare hint that
a very energetic process is at work during this time, which is also when the
hypersoft X-ray state is observed. In addition, Cyg X-3 shows flaring with a
wide range of hardness.Comment: 17 pages, 9 figures, accepted for publication in MNRA
Extremelt low rates of hypoglycemia following transfer of tight glucose control management to ICU nurses
Correlated radio/X-ray behaviour of Cyg X-3
In order to test the recently proposed classification of the radio/X-ray states of the X-ray binary Cyg X-3, we present an analysis of the radio data available for the system at much higher spatial resolutions than used for defining the states. The radio data set consists of archival VLBA data at 5 and 15 GHz and new e-EVN data at 5 GHz. In the X-ray regime we use data that are quasi-simultaneous with radio, monitoring and pointed RXTE observations. We find that when the radio emission from both jet and core is globally considered, the behaviour of Cyg X-3 at milliarcsecond scales is consistent with that described at arcsecond scales. However, when the radio emission is disentangled in a core component and a jet component the situation changes. It becomes clear that in active states the radio emission from the jet is dominating that from the core. This shows that in these states the overall radio flux cannot be used as a direct tracer of the accretion state
The bright unidentified gamma-ray source 1FGL J1227.9-4852: Can it be associated with an LMXB?
We present an analysis of high energy (HE; 0.1-300 GeV) gamma-ray
observations of 1FGL J1227.9-4852 with the Fermi Gamma-ray Space Telescope,
follow-up radio observations with the Australia Telescope Compact Array, Giant
Metrewave Radio Telescope and Parkes radio telescopes of the same field and
follow-up optical observations with the ESO VLT. We also examine archival
XMM-Newton and INTEGRAL X-ray observations of the region around this source.
The gamma-ray spectrum of 1FGL J1227.9-4852 is best fit with an exponentially
cutoff power-law, reminiscent of the population of pulsars observed by Fermi. A
previously unknown, compact radio source within the 99.7% error circle of 1FGL
J1227.9-4852 is discovered and has a morphology consistent either with an AGN
core/jet structure or with two roughly symmetric lobes of a distant radio
galaxy. A single bright X-ray source XSS J12270-4859, a low-mass X-ray binary,
also lies within the 1FGL J1227.9-4852 error circle and we report the first
detection of radio emission from this source. The potential association of 1FGL
J1227.9-4852 with each of these counterparts is discussed. Based upon the
available data we find the association of the gamma-ray source to the compact
double radio source unlikely and suggest that XSS J12270-4859 is a more likely
counterpart to the new HE source. We propose that XSS J12270-4859 may be a
millisecond binary pulsar and draw comparisons with PSR J1023+0038.Comment: Accepted for publication in MNRAS; 9 pages, 8 figures, 2 table
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