3,515 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
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
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
X-ray absorption and rapid variability of the dwarf Seyfert nucleus of NGC4395
We report the detection of an absorbed central X-ray source and its strong,
rapid variability in NGC4395, the least luminous Seyfert nucleus known. The
X-ray source exhibits a number of flares with factors of 3-4 flux changes
during a half day ASCA observation. Such X-ray variability is in constrast to
the behaviour of other low luminosity active galaxies. It provides further
support for an accreting black hole model rather than an extreme stellar
process in accounting for the nuclear activity of NGC4395. The soft X-ray
emission below 3 keV is strongly attenuated by absorption. The energy spectrum
in this absorption band shows a dramatic change in response to the variation in
continuum luminosity. A variable warm absorber appears to be an explanation for
the spectral change. The absorption-corrected 2-10 keV luminosity is 4e39 erg/s
for a source distance of 2.6 Mpc, and at 1 keV is one order of magnitude above
previous ROSAT estimates. Our X-ray results infer the nuclear source of NGC4395
to be a scaled-down version of higher luminosity Seyfert nuclei, with an
intermediate mass (10^4-10^5 Msun) black hole, unlike the nearby low luminosity
active galaxies in which underfed massive black holes are suspected to reside.Comment: 12 pages, accepted for publication in MNRA
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