538 research outputs found
Nuclear activity and massive star formation in the low luminosity AGN NGC4303: Chandra X-ray observations
We present evidence of the co-existence of either an AGN or an ultraluminous
X-ray source (ULX), together with a young super stellar cluster in the 3
central parsecs of NGC4303. The galaxy contains a low luminosity AGN and hosts
a number of starburst regions in a circumnuclear spiral, as well as in the
nucleus itself. A high spatial resolution Chandra image of this source reveals
that the soft X-ray emission traces the ultraviolet nuclear spiral down to a
core, which is unresolved both in soft and hard X-rays. The astrometry of the
X-ray core coincides with the UV core within the Chandra positioning accuracy.
The total X-ray luminosity of the core, 1.5*10^{39} erg/s, is similar to that
from some LINERs or from the weakest Seyferts detected so far. The soft X-rays
in both the core and the extended structure surrounding it can be well
reproduced by evolutionary synthesis models (which include the emission
expected from single stars, the hot diffuse gas, supernova remnants and binary
systems), consistent with the properties of the young stellar clusters
identified in the UV. The hard X-ray tail detected in the core spectrum,
however, most likely requires the presence of an additional source. This
additional source could either be a weak active nucleus black hole or an
ultraluminous X-ray object. The implications of these results are discussed.Comment: 37 pages, 7 figures, ApJ accepte
Early Science with the Large Millimeter Telescope: an energy-driven wind revealed by massive molecular and fast X-ray outflows in the Seyfert Galaxy IRAS 17020+4544
We report on the coexistence of powerful gas outflows observed in millimeter
and X-ray data of the Radio-Loud Narrow Line Seyfert 1 Galaxy IRAS 17020+4544.
Thanks to the large collecting power of the Large Millimeter Telescope, a
prominent line arising from the 12CO(1-0) transition was revealed in recent
observations of this source. The complex profile is composed by a narrow
double-peak line and a broad wing. While the double-peak structure may be
arising in a disk of molecular material, the broad wing is interpreted as the
signature of a massive outflow of molecular gas with an approximate bulk
velocity of -660 km/s. This molecular wind is likely associated to a
multi-component X-ray Ultra-Fast Outflow with velocities reaching up to ~0.1c
and column densities in the range 10^{21-23.9} cm^-2 that was reported in the
source prior to the LMT observations. The momentum load estimated in the two
gas phases indicates that within the observational uncertainties the outflow is
consistent with being propagating through the galaxy and sweeping up the gas
while conserving its energy. This scenario, which has been often postulated as
a viable mechanism of how AGN feedback takes place, has so far been observed
only in ULIRGs sources. IRAS 17020+4544 with bolometric and infrared luminosity
respectively of 5X10^{44} erg/s and 1.05X10^{11} L_sun appears to be an example
of AGN feedback in a NLSy1 Galaxy (a low power AGN). New proprietary
multi-wavelength data recently obtained on this source will allow us to
corroborate the proposed hypothesis.Comment: Accepted for publication on ApJ Letters, 9 pages, 4 figure
High resolution X-ray spectroscopy of the Seyfert 1 Mrk841: insights into the warm absorber and warm emitter
The Seyfert 1 galaxy Mrk841 was observed five times between 2001 and 2005 by
the XMM-Newton X-ray observatory. The source is well known for showing spectral
complexity in the variable iron line and in the soft X-ray excess. This paper
reports on the first study of Mrk841 soft X-ray spectrum at high spectral
resolution. The availability of multiple exposures obtained by the Reflection
Grating Spectrometer (RGS) cameras allows a thorough study of the complex
absorption and emission spectral features in the soft X-ray band.The three
combined exposures obtained in January 2001 and the two obtained in January and
July 2005 were analysed using the SPEX software. We detect a two-phase warm
absorber: a medium ionisation component (logxi~1.5-2.2 ergs s cm^{-1}) is
responsible for a deep absorption feature in the Unresolved Transition Array of
the Fe M-shell and for several absorption lines in the OVI-VIII band; a higher
ionisation phase with logxi~3 ergs s cm^{-1} is required to fit absorption in
the NeIX-X band. The ionisation state and the column density of the gas present
moderate variation from 2001 to 2005 for both phases. The high ionisation
component of the warm absorber has no effect in the Fe K band. No significant
velocity shift of the absorption lines is measured in the RGS data. Remarkably,
the 2005 spectra show emission features consistent with photoionisation in a
high density (n_e>10^{11} cm^{-3}) gas: a prominent OVII line triplet is
clearly observed in January 2005 and narrow Radiative Recombination Continua
(RRC) of OVII and CVI are observed in both 2005 data sets. A broad Gaussian
line around 21.7 Angstrom is also required to fit all the data sets. The
derived radial distance for the emission lines seems to suggest that the
photoionisation takes place within the optical Broad Line Region of the source.Comment: In press on A&A, replaced version includes language editing and typo
on velocities corrected in Table
New constraints on the continuum-emission mechanism of AGN: Intensive monitoring of NGC 7469 in the X-ray and ultraviolet
We have undertaken near-continuous monitoring of the Seyfert 1 galaxy NGC
7469 in the X-ray with RXTE over a ~30d baseline. The source shows strong
variability with a root-mean-square (rms) amplitude of ~16 per cent, and
peak-to-peak variations of a factor of order 2. Simultaneous data over this
period were obtained in the ultraviolet (UV) using IUE, making this the most
intensive X-ray UV/X-ray variability campaign performed for any active galaxy.
Comparison of the continuum light curves reveals very similar amplitudes of
variability, but different variability characteristics, with the X-rays showing
much more rapid variations. The data are not strongly correlated at zero lag.
The largest absolute value of the correlation coefficient occurs for an
anticorrelation between the two bands, with the X-ray variations leading the UV
by ~4d. The largest positive correlation is for the ultraviolet to lead the
X-rays by ~4d. Neither option appears to be compatible with any simple
interband transfer function. The peak positive correlation at ~4d occurs
because the more prominent peaks in the UV light curve appear to lead those in
the X-rays by this amount. However, the minima of the light curves are
near-simultaneous. These observations provide new constraints on theoretical
models of the central regions of active galactic nuclei. Models in which the
observed UV emission is produced solely by re-radiation of absorber X-rays are
ruled out by our data, as are those in which the X-rays are produced solely by
Compton upscattering of the observed UV component by a constant distribution of
particles.Comment: 33 pages, 8 figures. LaTeX with encapsulated postscript. To appear in
the Astrophysical Journal. Also available via
http://lheawww.gsfc.nasa.gov/users/nandra/pubs/7469/abstract.htm
Complex resonance absorption structure in the X-ray spectrum of IRAS13349+2438
The luminous infrared-loud quasar IRAS 13349+2438 was observed with the
XMM-Newton Observatory as part of the Performance Verification program. The
spectrum obtained by the Reflection Grating Spectrometer (RGS) exhibits broad
(v ~ 1400 km/s FWHM) absorption lines from highly ionized elements including
hydrogen- and helium-like carbon, nitrogen, oxygen, and neon, and several iron
L-shell ions (Fe XVII - XX). Also shown in the spectrum is the first
astrophysical detection of a broad absorption feature around lambda = 16 - 17
Ang identified as an unresolved transition array (UTA) of 2p - 3d inner-shell
absorption by iron M-shell ions in a much cooler medium; a feature that might
be misidentified as an O VII edge when observed with moderate resolution
spectrometers. No absorption edges are clearly detected in the spectrum. We
demonstrate that the RGS spectrum of IRAS 13349+2438 exhibits absorption lines
from at least two distinct regions, one of which is tentatively associated with
the medium that produces the optical/UV reddening.Comment: 6 pages. Accepted for publication in Astronomy and Astrophysics
Letters, XMM issu
Asymmetric data acquisition system for an endoscopic PET-US detector
According to current prognosis studies of pancreatic cancer, survival rate nowadays is still as low as 6% mainly due to late detections. Taking into account the location of the disease within the body and making use of the level of miniaturization in radiation detectors that can be achieved at the present time, EndoTOFPET-US collaboration aims at the development of a multimodal imaging technique for endoscopic pancreas exams that combines the benefits of high resolution metabolic information from time-of- flight (TOF) positron emission tomography (PET) with anatomical information from ultrasound (US). A system with such capabilities calls for an application-specific high-performance data acquisition system (DAQ) able to control and readout data from different detectors. The system is composed of two novel detectors: a PET head extension for a commercial US endoscope placed internally close to the region-of-interest (ROI) and a PET plate placed over the patient's abdomen in coincidence with the PET head. These two detectors will send asymmetric data streams that need to be handled by the DAQ system. The approach chosen to cope with these needs goes through the implementation of a DAQ capable of performing multi-level triggering and which is distributed across two different on-detector electronics and the off-detector electronics placed inside the reconstruction workstation. This manuscript provides an overview on the design of this innovative DAQ system and, based on results obtained by means of final prototypes of the two detectors and DAQ, we conclude that a distributed multi-level triggering DAQ system is suitable for endoscopic PET detectors and it shows potential for its application in different scenarios with asymmetric sources of data
The nature of the X-ray transient SAX J1711.6-3808
SAX J1711.6-3808 is an X-ray transient in the Galactic bulge that was active
from January through May of 2001 and whose maximum 1-200 keV luminosity was
measured to be 5X10-9 erg/s/cm2 which is less than ~25% of the Eddington limit,
if placed at a distance equal to that of the galactic center. We study the
X-ray data that were taken of this moderately bright transient with instruments
on BeppoSAX and RXTE. The spectrum shows two interesting features on top of a
Comptonized continuum commonly observed in low-state X-ray binaries: a broad
emission feature peaking at 7 keV and extending from 4 to 9 keV, and a soft
excess with a color temperature below 1 keV which reveals itself only during
one week of data. High time-resolution analysis of 412 ksec worth of data fails
to show bursts, coherent or high-frequency quasi-periodic oscillations. Given
the dynamic range of the flux measurements, this would be unusual if a neutron
star were present. SAX J1711.6-3808 appears likely to contain a black hole. No
quiescent optical counterpart could be identified in archival data within the
5"-radius XMM error circle, but the limits are not very constraining because of
heavy extinction (Av=16).Comment: Accepted for publication in Astronomy & Astrophysic
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