14,298 research outputs found
X-ray spectral complexity in narrow-line Seyfert 1 galaxies
We present a systematic analysis of the X-ray spectral properties of a sample
of 22 ``narrow-line'' Seyfert 1 galaxies for which data are available from the
ASCA public archive. Many of these sources, which were selected on the basis of
their relatively narrow H-beta line width (FWHM <= 2000 km/s), show significant
spectral complexity in the X-ray band. Their measured hard power-law continua
have photon indices spanning the range 1.6 - 2.5 with a mean of 2.1, which is
only slightly steeper than the norm for ``broad-line'' Seyfert 1s. All but four
of the sources exhibit a soft excess, which can be modelled as blackbody
emission (T_{bb} ~ 100 - 300 eV) superposed on the underlying power-law. This
soft component is often so strong that, even in the relatively hard bandpass of
ASCA, it contains a significant fraction, if not the bulk, of the X-ray
luminosity, apparently ruling out models in which the soft excess is produced
entirely through reprocessing of the hard continuum.
Most notably, 6 of the 22 objects show evidence for a broad absorption
feature centred in the energy range 1.1 - 1.4 keV, which could be the signature
of resonance absorption in highly ionized material. A further 3 sources exhibit
``warm absorption'' edges in the 0.7 - 0.9 keV bandpass. Remarkably, all 9
``absorbed'' sources have H-beta line widths below 1000 km/s, which is less
than the median value for the sample taken as a whole. This tendency for very
narrow line widths to correlate with the presence of ionized absorption
features in the soft X-ray spectra of NLS1s, if confirmed in larger samples,
may provide a further clue in the puzzle of active galactic nuclei.Comment: 13 pages, 5 figures, accepted for publication in MNRA
Photodissociation of NO2 by pulsed laser light at 6943 A
Two photon absorption in photodissociation of nitrogen dioxide using pulsed laser at 6943
Evidence for a circum-nuclear and ionised absorber in the X-ray obscured BroadLine Radio Galaxy 3C 445
Here we present the results of a Suzaku observation of the Broad Line Radio
Galaxy 3C 445. We confirm the results obtained with the previous X-ray
observations which unveiled the presence of several soft X-ray emission lines
and an overall X-ray emission which strongly resembles a typical Seyfert 2
despite of the optical classification as an unobscured AGN. The broad band
spectrum allowed us to measure for the first time the amount of reflection
(R~0.9) which together with the relatively strong neutral Fe Kalpha emission
line (EW ~ 100 eV) strongly supports a scenario where a Compton-thick mirror is
present. The primary X-ray continuum is strongly obscured by an absorber with a
column density of NH =2-3 x10^{23} cm^{-2}. Two possible scenarios are proposed
for the absorber: a neutral partial covering or a mildly ionised absorber with
an ionisation parameter log\xi ~ 1.0 erg cm s^{-1}. A comparison with the past
and more recent X-ray observations of 3C 445 performed with XMM-Newton and
Chandra is presented, which provided tentative evidence that the ionised and
outflowing absorber varied. We argue that the absorber is probably associated
with an equatorial disk-wind located within the parsec scale molecular torus.Comment: Accepted by MNRAS; 13 pages, 6 figures, 4 table
Chandra detection of a parsec scale wind in the Broad Line Radio Galaxy 3C 382
We present unambiguous evidence for a parsec scale wind in the Broad-Line
Radio Galaxy (BLRG) 3C 382, the first radio-loud AGN, with , whereby an outflow has been measured with
X-ray grating spectroscopy. A 118 ks Chandra grating (HETG) observation of 3C
382 has revealed the presence of several high ionization absorption lines in
the soft X-ray band, from Fe, Ne, Mg and Si. The absorption lines are
blue-shifted with respect to the systemic velocity of 3C 382 by -840\pm60 km/s
and are resolved by Chandra with a velocity width of 340\pm70 km/s. The outflow
appears to originate from a single zone of gas of column density cm and ionization parameter . From
the above measurements we calculate that the outflow is observed on parsec
scales, within the likely range from 10-1000 pc, i.e., consistent with an
origin in the Narrow Line Region.Comment: 11 pages, accepted for publication in Astrophysical Journal Letter
Probing the cool ISM in galaxies via 21cm HI absorption
Recent targeted studies of associated HI absorption in radio galaxies are
starting to map out the location, and potential cosmological evolution, of the
cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21
cm absorption profiles often show two distinct spectral-line components:
narrow, deep lines arising from cold gas in the extended disc of the galaxy,
and broad, shallow lines from cold gas close to the AGN (e.g. Morganti et al.
2011). Here, we present results from a targeted search for associated HI
absorption in the youngest and most recently-triggered radio AGN in the local
universe (Allison et al. 2012b). So far, by using the recently commissioned
Australia Telescope Compact Array Broadband Backend (CABB; Wilson et al. 2011),
we have detected two new absorbers and one previously-known system. While two
of these show both a broad, shallow component and a narrow, deep component (see
Fig. 1), one of the new detections has only a single broad, shallow component.
Interestingly, the host galaxies of the first two detections are classified as
gas-rich spirals, while the latter is an early-type galaxy. These detections
were obtained using a spectral-line finding method, based on Bayesian
inference, developed for future large-scale absorption surveys (Allison et al.
2012a).Comment: 1 page, 1 figure, published in Proceedings of IAU Symposium No. 29
Gamma-Ray Bursts observed by XMM-Newton
Analysis of observations with XMM-Newton have made a significant contribution
to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area,
bandpass and resolution of the EPIC instrument permit the study of a wide
variety of spectral features. In particular, strong, time-dependent, soft X-ray
emission lines have been discovered in some bursts. The emission mechanism and
energy source for these lines pose major problems for the current generation of
GRB models. Other GRBs have intrinsic absorption, possibly related to the
environment around the progenitor, or possible iron emission lines similar to
those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of
GRBs discovered by the Swift satellite should help unlock the origin of the GRB
phenomenon over the next few years.Comment: To appear in proceedings of the "XMM-Newton EPIC Consortium meeting,
Palermo, 2003 October 14-16", published in Memorie della Societa Astronomica
Italian
NASA/ESA CV-990 Spacelab Simulation (ASSESS 2)
To test the validity of the ARC approach to Spacelab, several missions simulating aspects of Spacelab operations have been conducted as part of the ASSESS Program. Each mission was designed to evaluate potential Shuttle/Spacelab concepts in increasing detail. For this mission, emphasis was placed on development and exercise of management techniques planned for Spacelab using management participants from NASA and ESA who have responsibilities for Spacelab 1 which will be launched in 1980
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