281 research outputs found
Herschel PACS and SPIRE observations of blazar PKS 1510-089: a case for two blazar zones
We present the results of observations of blazar PKS 1510-089 with the
Herschel Space Observatory PACS and SPIRE instruments, together with
multiwavelength data from Fermi/LAT, Swift, SMARTS and SMA. The source was
found in a quiet state, and its far-infrared spectrum is consistent with a
power-law with a spectral index of alpha ~ 0.7. Our Herschel observations were
preceded by two 'orphan' gamma-ray flares. The near-infrared data reveal the
high-energy cut-off in the main synchrotron component, which cannot be
associated with the main gamma-ray component in a one-zone leptonic model. This
is because in such a model the luminosity ratio of the External-Compton and
synchrotron components is tightly related to the frequency ratio of these
components, and in this particular case an unrealistically high energy density
of the external radiation would be implied. Therefore, we consider a
well-constrained two-zone blazar model to interpret the entire dataset. In this
framework, the observed infrared emission is associated with the synchrotron
component produced in the hot-dust region at the supra-pc scale, while the
gamma-ray emission is associated with the External-Compton component produced
in the broad-line region at the sub-pc scale. In addition, the optical/UV
emission is associated with the accretion disk thermal emission, with the
accretion disk corona likely contributing to the X-ray emission.Comment: 13 pages, 8 figures, 7 tables; accepted for publication in the
Astrophysical Journa
Tracing colliding winds in the UV line orbital variability of gamma-ray binaries
Gamma-ray binaries emit most of their radiated power beyond ~10 MeV. The
non-thermal emission is thought to arise from the interaction of the
relativistic wind of a rotation-powered pulsar with the stellar wind of its
massive (O or Be) companion star. A powerful pulsar creates an extended cavity,
filled with relativistic electrons, in the radiatively-driven wind of the
massive star. As a result, the observed P Cyg profiles of UV resonant lines
from the stellar wind should be different from those of single massive stars.
We propose to use UV emission lines to detect and constrain the colliding wind
region in gamma-ray binaries. We compute the expected orbital variability of P
Cyg profiles depending upon the interaction geometry (set by the ratio of
momentum fluxes from the winds) and the line-of-sight to the system. We predict
little or no variability for the case of LS 5039 and PSR B1259-63, in agreement
with currently available HST observations of LS 5039. However, variability
between superior and inferior conjunction is expected in the case of LS I+61
303.Comment: Accepted for publication in MNRA
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
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
Extremelt low rates of hypoglycemia following transfer of tight glucose control management to ICU nurses
Effects of the stellar wind on X-ray spectra of Cygnus X-3
We study X-ray spectra of Cyg X-3 from BeppoSAX, taking into account
absorption and emission in the strong stellar wind of its companion. We find
the intrinsic X-ray spectra are well modelled by disc blackbody emission, its
upscattering by hot electrons with a hybrid distribution, and by Compton
reflection. These spectra are strongly modified by absorption and reprocessing
in the stellar wind, which we model using the photoionization code cloudy. The
form of the observed spectra implies the wind is composed of two phases. A hot
tenuous plasma containing most of the wind mass is required to account for the
observed features of very strongly ionized Fe. Small dense cool clumps filling
<0.01 of the volume are required to absorb the soft X-ray excess, which is
emitted by the hot phase but not present in the data. The total mass-loss rate
is found to be (0.6--1.6) x 10^-5 solar masses per year. We also discuss the
feasibility of the continuum model dominated by Compton reflection, which we
find to best describe our data. The intrinsic luminosities of our models
suggest that the compact object is a black hole.Comment: MNRAS, in pres
- …