1,705 research outputs found
ROSAT monitoring of persistent giant and rapid variability in the narrow-line Seyfert 1 galaxy IRAS 13224-3809
We report evidence for persistent giant and rapid X-ray variability in the
radio-quiet, ultrasoft, strong Fe II, narrow-line Seyfert 1 galaxy IRAS
13224-3809. Within a 30 day ROSAT High Resolution Imager (HRI) monitoring
observation at least five giant amplitude count rate variations are visible,
with the maximum observed amplitude of variability being about a factor of 60.
We detect a rise by a factor of about 57 in just two days. IRAS 13224-3809
appears to be the most X-ray variable Seyfert known, and its variability is
probably nonlinear. We carefully check the identification of the highly
variable X-ray source with the distant galaxy, and it appears to be secure. We
examine possible explanations for the giant variability. Unusually strong
relativistic effects and partial covering by occulting structures on an
accretion disc can provide plausible explanations of the X-ray data, and we
explore these two scenarios. Relativistic boosting effects may be relevant to
understanding the strong X-ray variability of some steep spectrum Seyferts more
generally.Comment: 14 pages, submitted to MNRA
Predictions of the pseudo-complex theory of Gravity for EHT observations- II. Theory and predictions
We present a resum\'e on the modified theory of gravity, called
pseudo-complex General Relativity (pc-GR). It is the second in a series of
papers, where the first one (Boller et al. 2019, referred to as paper I)
discussed the observational consequences of pc-GR. In this paper, we
concentrate on the underlying theory. PC-GR involves an algebraic extension of
the standard theory of GR and it depends on two phenomenological parameters. An
element included in pc-GR that is not present in standard GR is the
energy-momentum tensor corresponding to an anisotropic ideal fluid, which we
call dark energy. The two parameters are related to the coupling of mass to the
dark energy and its fall-off as a function of r. The consequences and
predictions of this theory will be discussed in the context of the
observational results of the Even Horizon Telescope, expected soon. Our main
result is that due to the accumulation of dark energy near a large mass, the
modified theory predicts a dark ring followed by a bright ring in the emission
profile of the accretion disc. We also discuss the light ring in the equatorial
plane.Comment: 2 figure
Corrosion of copper electrode in sodium sulfide solution
AbstractThe electrochemical reactions of a copper electrode in Na2S solutions were studied using cyclic voltammetry, potentiostatic and galvanostatic measurements. In addition surface examination and morphological studies were applied using scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX). There are three anodic peaks were found in the anodic branch of the voltammogram’s. These peaks may be corresponding successively to the formation of Cu2S, CuS and Cu2O. On the other hand, the cathodic branch contains four peaks. These peaks correspond to the reduction of copper oxide and copper sulfide formed on the anodic branch
Inclinations and black hole masses of Seyfert 1 galaxies
A tight correlation of black hole mass and central velocity dispersion has
been found recently for both active and quiescent galaxies. By applying this
correlation, we develop a simple method to derive the inclination angles for a
sample of 11 Seyfert 1 galaxies that have both measured central velocity
dispersions and black hole masses estimated by reverberation mapping. These
angles, with a mean value of 36 degree that agrees well with the result
obtained by fitting the iron K lines of Seyfert 1s observed with ASCA,
provide further support to the orientation-dependent unification scheme of AGN.
A positive correlation of the inclinations with observed FWHMs of H line
and a possible anti-correlation with the nuclear radio-loudness have been
found. We conclude that more accurate knowledge on inclinations and broad line
region dynamics is needed to improve the black hole mass determination of AGN
with the reverberation mapping technique.Comment: 12 pages including 4 figures, accepted for publication in The
Astrophysical Journal Letter
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
Ponderomotive scattering of an electron-bunch before injection into a laser wakefield
For the purpose of laser wakefield acceleration, it turned out that also the
injection of electron bunches longer than a plasma wavelength can generate
accelerated femtosecond bunches with relatively low energy spread. This is of
high interest because such injecting bunches can be provided, e.g., by
state-of-the-art photo cathode RF guns. Here we point out that when an e-bunch
is injected in the wakefield it is important to take into account the
ponderomotive scattering of the injecting bunch by the laser pulse in the
vacuum region located in front of the plasma. At low energies of the injected
bunch this scattering results in a significant drop of the collection
efficiency. Larger collection efficiency can by reached with lower intensity
laser pulses and relatively high injection energies. We also estimate the
minimum trapping energy for the injected electrons and the length of the
trapped bunch.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
ISO observations of four active galaxies
We present ISO PHOT-S spectra of four galaxies known or suspected to host a
central AGN, selected from the initial Iras/Rosat sample of Boller et al.
(1992). Two of them had no obvious Seyfert features in their previous optical
spectra: IRAS 14201+2956, and IRAS 21582+1018. The latter was bright enough to
also allow SWS observations around selected neon lines, to establish its
excitation. While both PHOT-S spectra are characteristic of starburst-dominated
galaxies, the neon line ratios in IRAS 21582+1018 indicate the presence of a
hard excitation source. New, high-resolution, optical spectra show only a weak,
broad component around Halpha, classifying now these two objects as Sey 1.9
galaxies. The two other galaxies observed are the NLS1 galaxies Mrk 359 and Mrk
1388. Their ISO spectra however do not reveal the typical, strong PAH features
found in the starburst galaxies and are more like those of standard Seyferts.
These results show therefore that, although IR observations were expected to be
able to always reveal the presence of an active nucleus by piercing through the
central obscuration, the result may be ambiguous: the broad band IR energy
distribution can still be dominated by starburts located in a circumnuclear
region, and the AGN appear only in specific observations (high-excitation lines
in the IR, or optical spectra with better quality than classification spectra).
The obscuration needs however to be patchy rather than complete, to explain the
detection of the high-excitation lines or broad Balmer wings. Only high-energy
observations can then establish the strength of the central
AGN and the amount of extinction with certainty.Comment: 8 pages, 8 figures, accepted in Astronomy & Astrophysic
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