8,205 research outputs found
Weak Reprocessed Features in the Broad Line Radio Galaxy 3C382
We present a detailed X-ray study of the Broad Line Radio Galaxy 3C382,
observed with the BeppoSAX satellite in a very bright state. The continuum
emission is well modeled with a power law that steepens at high energies, with
an e-folding energy of about 120 keV. At soft energies a clear excess of
emission is detected, which can not be explained solely by the extended thermal
halo seen in a ROSAT HRI image. A second, more intense soft X-ray component,
possibly related to an accretion disk, is required by the data. Both a
reflection component (R=0.3) and an iron line (EW \sim 50) are detected, at
levels much weaker than in Seyfert galaxies, suggesting a common origin.
Combining our measurements with results from the literature we find that the
iron line has remained approximately constant over 9 years while the continuum
varied by a factor of 5. Thus the fluorescent gas does not respond promptly to
the variations of the X-ray primary source, suggesting that the reprocessing
site is located away, likely at parsec distances. While the continuum shape
indicates that X-rays derive from a thermal Comptonization process, the
weakness of other spectral features implies that either the upper layers of the
optically thick accretion disk are completely ionized or the corona above the
disk is outflowing with mildly relativistic velocity.Comment: 11 pages, 4 figures. Accepted for publication in the Astrophysical
Journa
Extended X-ray emission in radio galaxies: the peculiar case of 3C 305
Extended X-ray structures are common in Active Galactic Nuclei (AGNs). Here
we present the first case of a Compact Steep Spectrum (CSS) radio galaxy, 3C
305, in which the X-ray radiation appears to be associated with the optical
emission line region, dominated by the [O III]5007. On the basis of a
morphological study, performed using the comparison between the X-rays, the
optical and the radio band, we argue that the high energy emission has a
thermal nature and it is not directly linked to the radio jet and hotspots of
this source. Finally, we discuss the origin of the extended X-ray structure
connected with the optical emission line region following two different
interpretations: as due to the interaction between matter outflows and
shock-heated environment gas, or as due to gas photoionized by nuclear
emission.Comment: 5 pages, 2 figures, Accepted for publication in The ApJL Comments:
references and affilitations correcte
High Energy Break and Reflection Features in the Seyfert Galaxy MCG+8-11-11
We present the results from ASCA and OSSE simultaneous observations of the
Seyfert 1.5 galaxy MCG+8-11-11 performed in August-September 1995. The ASCA
observations indicate a modest flux increase (20%) in 3 days, possibly
correlated to a softening of the 0.6-9 keV spectrum. The spectrum is well
described by a hard power law (Gamma=1.64) absorbed by a column density
slightly larger than the Galactic value, with an iron line at 6.4 keV of EW=400
eV. The simultaneous OSSE data are characterized by a much softer power law
with photon index Gamma=3.0, strongly suggesting the presence of a spectral
break in the hard X/soft gamma-ray band. A joint fit to OSSE and ASCA data
clearly shows an exponential cut-off at about 300 keV, and strong reflection
component. MCG+8-11-11 features a spectral break in the underlying continuum
unambiguously. This, together with the inferred low compactness of this source,
favours thermal or quasi-thermal electron Comptonization in a structured Corona
as the leading process of high energy radiation production.Comment: 13 pages, + 4 figure.ps AAS LateX [11pt,aasms4]{article} To be
published in ApJ, Main Journa
CHANDRA reveals galaxy cluster with the most massive nearby cooling core, RXCJ1504.1-0248
A CHANDRA follow-up observation of an X-ray luminous galaxy cluster with a
compact appearance, RXCJ1504.1-0248 discovered in our REFLEX Cluster Survey,
reveals an object with one of the most prominent cluster cooling cores. With a
core radius of ~30 kpc smaller than the cooling radius with ~140 kpc more than
70% of the high X-ray luminosity of Lbol = 4.3 10e45 erg s-1 of this cluster is
radiated inside the cooling radius. A simple modeling of the X-ray morphology
of the cluster leads to a formal mass deposition rate within the classical
cooling flow model of 1500 - 1900 Msun yr-1 (for h=0.7), and 2300 - 3000 Msun
yr-1 (for h=0.5). The center of the cluster is marked by a giant elliptical
galaxy which is also a known radio source. Thus it is very likely that we
observe one of the interaction systems where the central cluster AGN is heating
the cooling core region in a self-regulated way to prevent a massive cooling of
the gas, similar to several such cases studied in detail in more nearby
clusters. The interest raised by this system is then due to the high power
recycled in RXCJ1504-0248 over cooling time scales which is about one order of
magnitude higher than what occurs in the studied, nearby cooling core clusters.
The cluster is also found to be very massive, with a global X-ray temperature
of about 10.5 keV and a total mass of about 1.7 10e15 Msun inside 3 Mpc.Comment: accepted for publication in Astrophys. Journal, 10 figure
The MURALES survey II. Presentation of MUSE observations of 20 3C low-z radio galaxies and first results
We present observations of a complete sub-sample of 20 radio galaxies from
the Third Cambridge Catalog (3C) with redshift <0.3 obtained from VLT/MUSE
optical integral field spectrograph. These data have been obtained as part of
the survey MURALES (a MUse RAdio Loud Emission line Snapshot survey) with the
main goal of exploring the Active Galactic Nuclei (AGN) feedback process in a
sizeable sample of the most powerful radio sources at low redshift. We present
the data analysis and, for each source, the resulting emission line images and
the 2D gas velocity field. Thanks to their unprecedented depth (the median 3
sigma surface brightness limit in the emission line maps is 6X10^-18 erg s-1
cm-2 arcsec-2, these observations reveal emission line structures extending to
several tens of kiloparsec in most objects. In nine sources the gas velocity
shows ordered rotation, but in the other cases it is highly complex. 3C sources
show a connection between radio morphology and emission line properties.
Whereas, in three of the four Fanaroff and Riley Class I radio galaxies (FRIs),
the line emission regions are compact, ~1 kpc in size; in all but one of the
Class II radiogalaxies FRIIs, we detected large scale structures of ionized gas
with a median extent of 17 kpc. Among the FRIIs, those of high and low
excitation show extended gas structures with similar morphological properties,
suggesting that they both inhabit regions characterized by a rich gaseous
environment on kpc scale.Comment: Accepted for publication in A&
Long-Term, Continuous Monitoring of the Broad Line Radio Galaxies 3C 390.3 and 3C 120 With the Rossi X-Ray Timing Explorer
We present a study of the flux and spectral variability of the two broad-line
radio galaxies (BLRGs) 3C 390.3 and 3C 120, observed almost daily with RXTE for
nearly two months each in 1996 and 1997, respectively. Our original motivation
for this study was to search for systematic differences between BLRGs and their
radio-quiet counterparts, the Seyfert galaxies, whose temporal and spectral
behavior is better studied. We find that both 3C 390.3 and 3C 120 are highly
variable, but in a different way, and quantify this difference by means of a
structure function analysis. 3C 390.3 is significantly more variable than 3C
120, despite its jet larger inclination angle, implying either that the X-ray
variability is not dominated by the jet or that two different variability
processes are simultaneously at work in 3C 390.3. We performed an
energy-selected and time-resolved analysis based on the fractional variability
amplitude and found that the variability amplitude of both objects is strongly
anticorrelated with the energy. This last result, along with the correlated
change of the photon index with the X-ray continuum flux, can be qualitatively
explained within the scenario of thermal Comptonization, generally invoked for
radio-quiet active galaxies. Moreover, the time-resolved and energy-selected
fractional variability analyses show a trend opposite to that observed in
jet-dominated AGN (blazars), suggesting only a minor contribution of the jet to
the X-ray properties of BLRGs. Time-averaged spectral analysis indicates the
presence of a strong, resolved iron line with centroid at 6.4 keV and a weak
reflection component in both objects. The overall PCA+HEXTE spectra are best
fitted with the constant density ionization model of Ross & Fabian, but with a
modest ionization parameter(abridged).Comment: 37 pages, 13 figures, accepted for publication on Ap
Gamma-loud quasars: a view with BeppoSAX
We present SAX observations of the -ray emitting quasars
0836+710, 1510-089 and 2230+114. All the objects have been detected in the PDS
up to 100 keV and have extremely flat power-law spectra above 2 keV (=0.3--0.5). 0836+710 shows absorption higher than the galactic value and
marginal evidence for the presence of the redshifted 6.4 keV Iron line.
1510-089 shows a spectral break around 1 keV, with the low energy spectrum
steeper (=1.6) than the high energy power-law (=0.3). The
data are discussed in the light of current Inverse Compton models for the high
energy emission.Comment: 4 pages, 2 figures, to appear in the proceedings of the conference
"X-Ray Astronomy '99", Bologna, Italy, September 199
Ultraviolet and Multiwavelength Variability of the Blazar 3C 279: Evidence for Thermal Emission
The gamma-ray blazar 3C 279 was monitored on a nearly daily basis with IUE,
ROSAT and EGRET for three weeks between December 1992 and January 1993. During
this period, the blazar was at a historical minimum at all wavelengths. Here we
present the UV data obtained during the above multiwavelength campaign. A
maximum UV variation of ~50% is detected, while during the same period the
X-ray flux varied by no more than 13%. At the lowest UV flux level the average
spectrum in the 1230-2700 A interval is unusually flat for this object
(~1). The flattening could represent the lowest energy tail of the
inverse Compton component responsible for the X-ray emission, or could be due
to the presence of a thermal component at ~20000 K possibly associated with an
accretion disk. The presence of an accretion disk in this blazar object, likely
observable only in very low states and otherwise hidden by the beamed, variable
synchrotron component, would be consistent with the scenario in which the seed
photons for the inverse Compton mechanism producing the gamma-rays are external
to the relativistic jet. We further discuss the long term correlation of the UV
flux with the X-ray and gamma-ray fluxes obtained at various epochs. All UV
archival data are included in the analysis. Both the X- and gamma-ray fluxes
are generally well correlated with the UV flux, approximately with square root
and quadratic dependences, respectively.Comment: 22 pages, Latex, 7 PostScript figures, to appear in The Astrophysical
Journa
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