1,674 research outputs found
Search for GRB afterglows in the ROSAT all-sky survey
We report on the status of our search for X-ray afterglows of gamma-ray
bursts (GRBs) using the ROSAT all-sky survey data. The number of potential
X-ray afterglow candidates with respect to the expected number of beamed GRBs
allows to constrain the relative beaming angles of GRB emission and afterglow
emission at about 1-5 hrs after the GRB.Comment: 3 pages A&A style, 1 color ps-figure; To appear in A&A Suppl. Series,
Proc. of Rome 1998 GRB workshop, also available from
http://www.aip.de/~jcg/publis.htm
Mrk 1014: An AGN Dominated ULIRG at X-rays
In this paper we report on an XMM-Newton observation of the ultraluminous
infrared QSO Mrk 1014. The X-ray observation reveals a power-law dominated
(photon index of about 2.2) spectrum with a slight excess in the soft energy
range. AGN and starburst emission models fit the soft excess emission equally
well, however, the most plausible explanation is an AGN component as the
starburst model parameter, temperature and luminosity, appear physically
unrealistic. The mean luminosity of Mrk 1014 is about 2 times 10^44 erg s^-1.
We have also observed excess emission at energies greater than 5 keV. This
feature could be attributed to a broadened and redshifted iron complex, but
deeper observations are required to constrain its origin. The light curve shows
small scale variability over the 11 ks observation. There is no evidence of
intrinsic absorption in Mrk 1014. The X-ray observations support the notion of
an AGN dominated central engine. We establish the need for a longer observation
to constrain more precisely the nature of the X-ray components.Comment: 5 pages incl. 3 figures, MNRAS in pres
Temporal extension of stable glow discharges in fluorine-based excimer laser gas mixtures by the addition of xenon
The effect of addition of xenon on the long term homogeneity of discharges in F2and ArF excimer laser gas mixtures was investigated in a small-volume discharge chamber. The gas mixture in the discharge chamber was preionized by X-rays. A special electrical excitation circuit containing a pulse forming line provided a long, square-shaped current pumping pulse of a predetermined duration to the discharge electrodes. The initiation and the development of the discharge was monitored via its fluorescence signal with an intensified CCD camera. We found that adding Xe up to partial pressures of 0.53 mbar extended the homogeneous phase of the discharge from 80 ns to approximately 200 ns in He/F2as well as in He/Ar/F2and Ne/Ar/F2excimer laser gas mixtures. Monitoring of the ArF and XeF spontaneous emission signals showed that the formation of ArF excimers remained unaffected by the addition of xenon (up to 1.3 mbar) to the laser gas mixture
The Largest Blueshifts of [O III] emission line in Two Narrow-Line Quasars
We have obtained optical intermediate resolution spectra (R = 3000) of the
narrow-line quasars DMS 0059-0055 and PG 1543+489. The [O III] emission line in
DMS 0059-0055 is blueshifted by 880 km/s relative to Hbeta. We also confirm
that the [O III] emission line in PG 1543+489 has a relative blueshift of 1150
km/s. These two narrow-line quasars show the largest [O III] blueshifts known
to date among type 1 active galactic nuclei (AGNs). The [O III] emission lines
in both objects are broad (1000 - 2000 km/s) and those in DMS 0059-0055 show
strong blue asymmetry. We interpret the large blueshift and the profile of the
[O III] lines as the result of an outflow interacting with circumnuclear gas.
Among type 1 AGNs with large blueshifted [O III], there is no correlation
between the Eddington ratios and the amount of [O III] blueshifts. Combining
our new data with published results, we confirm that the Eddington ratios of
the such AGNs are the highest among AGNs with the same black hole masses. These
facts suggest that the Eddington ratio is a necessary condition or the [O III]
blueshifts weakly depend on the Eddington ratio. Our new sample suggests that
there are possible necessary conditions to produce an outflow besides a high
Eddington ratio: large black hole mass (> 10^7 M_solar) or high mass accretion
rate (> 2 M_solar/yr) or large luminosity (lambda L_{lambda} (5100A) > 10^44.6
erg/s).Comment: Accepted for publication in The Astrophysical Journa
HST STIS Ultraviolet Spectral Evidence for Outflow in Extreme Narrow-line Seyfert 1 Galaxies: I. Data and Analysis
We present HST STIS observations of two extreme NLS1s, IRAS 13224-3809 and 1H
0707-495. The spectra are characterized by very blue continua, broad, strongly
blueshifted high-ionization lines (including \ion{C}{4} and \ion{N}{5}), and
narrow, symmetric intermediate- (including \ion{C}{3}], \ion{Si}{3}],
\ion{Al}{3}) and low-ionization (e.g., \ion{Mg}{2}) lines centered at their
rest wavelengths. The emission-line profiles suggest that the high-ionization
lines are produced in a wind, and the intermediate- and low-ionization lines
are produced in low-velocity gas associated with the accretion disk or base of
the wind. In this paper, we present the analysis of the spectra from these two
objects; in a companion paper we present photoionization analysis and a toy
dynamical model for the wind. The highly asymmetric profile of \ion{C}{4}
suggests that it is dominated by emission from the wind, so we develop a
template for the wind from the \ion{C}{4} line. We model the bright emission
lines in the spectra using a combination of this template, and a narrow,
symmetric line centered at the rest wavelength. We also analyzed a comparison
sample of HST spectra from 14 additional NLS1s, and construct a correlation
matrix of emission line and continuum properties. A number of strong
correlations were observed, including several involving the asymmetry of the
\ion{C}{4} line.Comment: 26 pages, 10 figures, accepted for publication in ApJ with no change
Search for X-ray Afterglows from Gamma-Ray Bursts in the RASS
We report on a search for X-ray afterglows from gamma-ray bursts using the
ROSAT all-sky survey (RASS) data. If the emission in the soft X-ray band is
significantly less beamed than in the gamma-ray band, we expect to detect many
afterglows in the RASS. Our search procedure generated 23 afterglow candidates,
where about 4 detections are predicted. Follow-up spectroscopy of several
counterpart candidates strongly suggests a flare star origin of the RASS events
in many, if not all, cases. Given the small number of events we conclude that
the data are consistent with comparable beaming angles in the X-ray and
gamma-ray bands. Models predicting a large amount of energy emerging as a
nearly isotropic X-ray component, and a so far undetected class of ``dirty
fireballs'' and re-bursts are constrained.Comment: 5 pages, LATEX with aipproc.sty, incl. 1 ps-Fig., Proc. of the 5th
Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AIP; also
available at http://www.aip.de/~jcg/publis.htm
An intense soft-excess and evidence for light bending in the luminous narrow-line quasar PHL 1092
The narrow-line quasar PHL 1092 was observed by XMM-Newton at two epochs
separated by nearly thirty months. Timing analyses confirm the extreme
variability observed during previous X-ray missions. A measurement of the
radiative efficiency is in excess of what is expected from a Schwarzschild
black hole. In addition to the rapid X-ray variability, the short UV light
curves (< 4 hours) obtained with the Optical Monitor may also show
fluctuations, albeit at much lower amplitude than the X-rays. In general, the
extreme variability is impressive considering that the broad-band (0.4-10 keV
rest-frame) luminosity of the source is ~10^45 erg/s. During at least one of
the observations, the X-ray and UV light curves show common trends, although
given the short duration of the OM observations, and low significance of the UV
light curves it is difficult to comment on the importance of this possible
correlation. Interestingly, the high-energy photons (> 2 keV) do not appear
highly variable. The X-ray spectrum resembles that of many narrow-line Seyfert
1 type galaxies: an intense soft-excess modelled with a multi-colour disc
blackbody, a power-law component, and an absorption line at ~1.4 keV. The ~1.4
keV feature is curious given that it was not detected in previous observations,
and its presence could be related to the strength of the soft-excess. Of
further interest is curvature in the spectrum above ~2 keV which can be
described by a strong reflection component. The strong reflection component,
lack of high-energy temporal variability, and extreme radiative efficiency
measurements can be understood if we consider gravitational light bending
effects close to a maximally rotating black hole.Comment: To appear in MNRAS. Submitted March 01, 2004. 9 page
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