2,878 research outputs found
Warm absorber, reflection and Fe K line in the X-ray spectrum of IC 4329A
Results from the X-ray spectral analysis of the ASCA PV phase observation of
the Seyfert 1 galaxy IC 4329A are presented. We find that the 0.4 - 10 keV
spectrum of IC 4329A is best described by the sum of a steep () power-law spectrum passing through a warm absorber plus a strong
reflection component and associated Fe K line, confirming recent results
(Madejski et al. 1995, Mushotsky et al. 1995). Further cold absorption in
excess of the Galactic value and covering the entire source is also required by
the data, consistent with the edge-on galactic disk and previous X-ray
measurements. The effect of the warm absorber at soft X-ray energies is best
parameterized by two absorption edges, one consistent with OVI, OVII or NVII,
the other consistent with OVIII. A description of the soft excess in terms of
blackbody emission, as observed in some other Seyfert 1 galaxies, is ruled out
by the data. A large amount of reflection is detected in both the GIS and SIS
detectors, at similar intensities. We find a strong correlation between the
amount of reflection and the photon index, but argue that the best solution
with the present data is that given by the best statistical fit. The model
dependence of the Fe K line parameters is also discussed. Our best fit gives a
slightly broad ( keV) and redshifted (E keV) Fe K line, with equivalent width 89 33 eV.
The presence of a weak Fe K line with a strong reflection can be reconciled if
one assumes iron underabundances or ionized reflection. We also have modeled
the line with a theoretical line profile produced by an accretion disk. This
yields results in better agreement with the constraints obtained from the
reflection component.Comment: Accepted for publication in The Astrophysical Journal, 10th February
1996 issue; 24 pages and 8 figures + 1 table tared, compressed and uuencoded
(with uufiles
The variable OVIII Warm Absorber in MCG-6-30-15
We present the results of a 4 day ASCA observation of the Seyfert galaxy
MCG-6-30-15, focussing on the nature of the X-ray absorption by the warm
absorber, characterizd by the K-edges of the intermediately ionized oxygen,
OVII and OVIII. We confirm that the column density of OVIII changes on a
timescale of ~s when the X-ray continuum flux decreases. The
significant anti-correlation of column density with continuum flux gives direct
evidence that the warm absorber is photoionized by the X-ray continuum. From
the timescale of the variation of the OVIII column density, we estimate that it
originates from gas within a radius of about 10^{17}\cm of the central
engine. In contrast, the depth of the OVII edge shows no response to the
continuum flux, which indicates that it originates in gas at larger radii. Our
results strongly suggest that there are two warm absorbing regions; one located
near or within the Broad Line Region, the other associated with the outer
molecular torus, scattering medium or Narrow Line Region.Comment: 8 pages (including figures) uuencoded gziped PS file. Submitted to
Publications of the Astronomical Society of Japa
Implications of a Possible Clustering of Highest Energy Cosmic Rays
Very recently, a possible clustering of a subset of observed ultrahigh energy
cosmic rays above about 40EeV (4x10^19eV) in pairs near the supergalactic plane
was reported. We show that a confirmation of this effect would provide
information on origin and nature of these events and, in case of charged
primaries, imply interesting constraints on the extragalactic magnetic field.
The observed time correlation would most likely rule out an association of
these events with cosmological gamma ray bursts. If no prominent astrophysical
source candidates such as powerful radiogalaxies can be found, the existence of
a mechanism involving new fundamental physics would be favored.Comment: 10 latex pages, 1 postscript figure, uses aaspp4.sty, submitted to
Astrophysical Journal Letter
Probing Exotic Physics With Cosmic Neutrinos
Traditionally, collider experiments have been the primary tool used in
searching for particle physics beyond the Standard Model. In this talk, I will
discuss alternative approaches for exploring exotic physics scenarios using
high energy and ultra-high energy cosmic neutrinos. Such neutrinos can be used
to study interactions at energies higher, and over baselines longer, than those
accessible to colliders. In this way, neutrino astronomy can provide a window
into fundamental physics which is highly complementary to collider techniques.
I will discuss the role of neutrino astronomy in fundamental physics,
considering the use of such techniques in studying several specific scenarios
including low scale gravity models, Standard Model electroweak instanton
induced interactions, decaying neutrinos and quantum decoherence.Comment: 11 pages, 6 figures; For the proceedings of From Colliders To Cosmic
Rays, Prague, Czech Republic, September 7-13, 200
Properties of 10 (18)-10 (19)eV EAS at far core distance
The properties of 10 to the 18th power - 10 to the 19th power eV EAS showers such as the electron lateral distribution, the muon lateral distribution ( 1Gev), the ratio of muon density to a electron density, the shower front structure and the transition effects in scintillator of 5cm thickness are investigated with the Akeno 4 sq km/20sq km array at far core distances between 500m and 3000m. The fluctuation of densities and arrival time increase rapidly at core distances greater than 2km
Akeno 20 km (2) air shower array (Akeno Branch)
As the first stage of the future huge array, the Akeno air shower array was expanded to about 20 sq. km. by adding 19 scintillation detectors of 2.25 sq m area outside the present 1 sq. km. Akeno array with a new data collection system. These detectors are spaced about 1km from each other and connected by two optical fiber cables. This array has been in partial operation from 8th, Sep. 1984 and full operation from 20th, Dec. 1984. 20 sq m muon stations are planned to be set with 2km separation and one of them is now under construction. The origin of the highest energy cosmic rays is studied
A variability study of the Seyfert 2 galaxy NGC 6300 with XMM-Newton
We present the results of timing analysis of the XMM-Newton observation of
the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of
a Compton-thin-absorbed power law, as is often seen in Seyfert 2 galaxies. We
clearly detected rapid time variability on a time scale of about 1000 s from
the light curve above 2 keV. The excess variance of the time variability
(sigma2_RMS) is calculated to be ~0.12, and the periodogram of the light curve
is well represented by a power law function with a slope of 1.75. In contrast
with previous results from Seyfert 2 nuclei, these variability characteristics
are consistent with those of Seyfert 1 galaxies. This consistency suggests that
NGC 6300 has a similar black hole mass and accretion properties as Seyfert 1
galaxies. Using the relation between time variability and central black hole
mass by Hayashida et al. (1998), the black hole mass of NGC 6300 is estimated
to be ~2.8x10^5 Mo. Taking uncertainty of this method into account, the black
hole mass is less than 10^7 Mo. Taking the bolometric luminosity of 3.3x10^43
erg/s into consideration, this yields an accretion rate of > 0.03 of the
Eddington value, and comparable with estimates from Seyfert 1 galaxies using
this method. The time variability analysis suggests that NGC 6300 actually has
a Seyfert 1 nucleus obscured by a thick matter, and more generally provides a
new pillar of support for the unified model of Seyfert galaxies based on
obscuration.Comment: 11 pages, 6 figures, accepted for publication in Ap
X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku
We report results from a Suzaku observation of the narrow-line Seyfert 1 NGC
4051. During our observation, large amplitude rapid variability is seen and the
averaged 2--10 keV flux is 8.1x10^-12 erg s^-1 cm^-2, which is several times
lower than the historical average. The X-ray spectrum hardens when the source
flux becomes lower, confirming the trend of spectral variability known for many
Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high and
low flux intervals are analyzed. The spectra are first fitted with a model
consisting of a power-law component, a reflection continuum originating in cold
matter, a blackbody component, two zones of ionized absorber, and several
Gaussian emission lines. The amount of reflection is rather large (R ~ 7, where
R=1 corresponds to reflection by an infinite slab), while the equivalent width
of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We
then model the overall spectra by introducing partial covering for the
power-law component and reflection continuum independently. The column density
for the former is 1x10^23 cm^-2, while it is fixed at 1x10^24 cm-2 for the
latter. By comparing the spectra in different flux states, we identify the
causes of spectral variability. (abridged)Comment: 19 pages, 18 figures, accepted for publication in PASJ (Suzaku 3rd
special issue
Correlation between Compact Radio Quasars and Ultra-High Energy Cosmic Rays
Some proposals to account for the highest energy cosmic rays predict that
they should point to their sources. We study the five highest energy events
(E>10^20 eV) and find they are all aligned with compact, radio-loud quasars.
The probability that these alignments are coincidental is 0.005, given the
accuracy of the position measurements and the rarity of such sources. The
source quasars have redshifts between 0.3 and 2.2. If the correlation pointed
out here is confirmed by further data, the primary must be a new hadron or one
produced by a novel mechanism.Comment: 8 pages, 3 tables, revtex. with some versions of latex it's necessary
to break out the tables and latex them separately using article.sty rather
than revtex.st
Cosmic Rays and Large Extra Dimensions
We have proposed that the cosmic ray spectrum "knee", the steepening of the
cosmic ray spectrum at energy E \gsim 10^{15.5} eV, is due to "new physics",
namely new interactions at TeV cm energies which produce particles undetected
by the experimental apparatus. In this letter we examine specifically the
possibility that this interaction is low scale gravity. We consider that the
graviton propagates, besides the usual four dimensions, into an additional
, compactified, large dimensions and we estimate the graviton
production in collisions in the high energy approximation where graviton
emission is factorized. We find that the cross section for graviton production
rises as fast as , where is the fundamental
scale of gravity in dimensions, and that the distribution of
radiating a fraction of the initial particle's energy into gravitational
energy (which goes undetected) behaves as . The missing
energy leads to an underestimate of the true energy and generates a break in
the {\sl inferred} cosmic ray spectrum (the "kne"). By fitting the cosmic ray
spectrum data we deduce that the favorite values for the parameters of the
theory are TeV and .Comment: 8 pages, 1 figur
- …