Status Report

Astrophysics astro-ph new abstracts 1 September 2000

By SpaceRef Editor
September 1, 2000
Filed under

Astrophysics


astro-ph new abstracts, Fri, 1 Sep 00 04:00:27 GMT
0008502 — 0008526 received




astro-ph/0008502 [abs, src, ps, other] :




Title: Effects of weak lensing on the topology of CMB maps

Authors:
Jens Schmalzing (1,2),
Masahiro Takada,
Toshifumi Futamase (Tohoku University, Sendai, (1) Teoretisk Astrofysik Center, Copenhagen, (2) Ludwig-Maximilians-Universitaet Muenchen)

Comments: 4 pages, 2 figures. Submitted to Astrophysical Journal Letters


We investigate the non-Gaussian signatures in Cosmic Microwave Background
(CMB) maps induced by the intervening large-scale structure of the universe
through weak lensing. In order to measure the deviation from the Gaussian
behavior of the intrinsic temperature anisotropies, we use a family of three
morphological descriptors, the so-called Minkowski functionals of
isotemperature contours. We show analytically how these quantities depend on
the temperature threshold, and compare the results to numerical experiments
including the instrumental effects of the Planck surveyor. It turns out that
Minkowski functionals can directly measure the statistical properties of the
displacement field and hence provide useful constraints on large-scale
structure formation in the past.
(37kb)




astro-ph/0008503 [abs, src, ps, other] :




Title: Warm Absorbing Gas in Cooling Flows

Authors:
David A. Buote (UC Santa Cruz)

Comments: 4 pages (1 figure), To Appear in “Gas & Galaxy Evolution”, ASP Conf.
Ser., eds Hibbard, Rupen, and van Gorkom


We summarize the discovery of oxygen absorption and warm (10^5-10^6 K) gas in
cooling flows. Special attention is given to new results for M87 for which we
find the strongest evidence to date for ionized oxygen absorption in these
systems. We briefly discuss implications for observations of cooling flows with
Chandra and XMM.
(29kb)




astro-ph/0008504 [abs, src, ps, other] :




Title: Galaxy Halo Masses from Galaxy-Galaxy Lensing

Authors:
Gillian Wilson,
Nick Kaiser,
Gerard A. Luppino,
Lennox L. Cowie (Institute for Astronomy, University of Hawaii, Honolulu)

Comments: 34 pages, 11 figs, 4 tables, submitted to Ap.J

We present measurements of the extended dark halo profiles of bright early
type galaxies at redshifts 0.1 to 0.9 obtained via galaxy-galaxy lensing
analysis of images taken at the CFHT using the UH8K CCD mosaic camera. Six half
degree fields were observed for a total of 2 hours each in I and V, resulting
in catalogs containing ~20 000 galaxies per field. We used V-I color and I
magnitude to select bright early type galaxies as the lens galaxies, yielding a
sample of massive lenses with fairly well determined redshifts and absolute
magnitudes M ~ M_* pm 1. We paired these with faint galaxies lying at angular
distances 20″ to 60″, corresponding to physical radii of 26 to 77 kpc (z = 0.1)
and 105 to 315 kpc (z = 0.9), and computed the mean tangential shear of the
faint galaxies. The shear falls off with radius roughly as expected for flat
rotation curve halos. The shear values were weighted in proportion to the
square root of the luminosity of the lens galaxy. Our results give a value for
the average mean rotation velocity of an L_* galaxy halo at r~50-200 kpc of v_*
= 238^{+27}_{-30} km per sec for a flat lambda (Omega_m0 = 0.3, Omega_l0 = 0.7)
cosmology (v_* = 269^{+34}_{-39} km per sec for Einstein-de Sitter), and with
little evidence for evolution with redshift. We compare to halo masses measured
by other groups/techniques. We find a mass-to-light ratio of ~121pm28h(r/100
kpc) and these halos constitute Omega ~0.04 pm 0.01(r/100 kpc) of closure
density. (abridged)
(114kb)




astro-ph/0008505 [abs, src, ps, other] :




Title: Complex Spectral Variability from Intensive Multi-wavelength Monitoring
of Mrk421 in 1998

Authors:
T. Takahashi,
J. Kataoka,
G. Madejski,
J. Mattox,
C.M. Urry,
S. Wagner,
F. Aharonian,
M. Catanese,
L. Chiappetti,
P. Coppi,
B. Degrange,
G. Fossati,
H. Kubo,
H. Krawczynski,
F. Makino,
H. Marshall,
L. Maraschi,
F. Piron,
R. Remillard,
F. Takahara,
M. Tashiro,
H. Terasranta,
T. Weekes

Comments: 10 pages, 4 figures, accepted for publication in ApJ Letters


We conducted a multi-frequency campaign for the TeV blazar Mrk~421 in 1998
April. The campaign started from a pronounced high amplitude flare recorded by
SAX and Whipple; ASCA observation started three days later. In the X-ray data,
we detected multiple flares, occuring on time scales of about one day. ASCA
data clearly reveal spectral variability. The comparison of the data from ASCA,
EUVE and RXTE indicates that the variability amplitudes in the low energy
synchrotron component are larger at higher photon energies. In TeV Gamma-rays,
large intra-day variations — which were correlated with the X-ray flux — were
observed when results from three Cherenkov telescopes are combined. The RMS
variability of TeV Gamma–rays was similar to that observed in hard X-rays,
above 10 keV. The X-ray light curve reveals flares which are almost symmetric
for most of cases, implying the dominant time scale is the light crossing time
through the emitting region. The structure function analysis based on the
continuous X-ray light curve of seven days indicates that the characteristic
time scale is ~0.5 day. The analysis of ASCA light curves in various energy
bands appears to show both soft (positive) and hard (negative) lags. These may
not be real, as systematic effects could also produce these lags, which are all
much smaller than an orbit. If the lags of both signs are real, these imply
that the particle acceleration and X-ray cooling time scales are similar.
(306kb)




astro-ph/0008506 [abs, src, ps, other] :




Title: Very Large Telescope Observations of the peculiar globular cluster
NGC6712. Discovery of a UV, H-alpha excess star in the core

Authors:
Francesco R. Ferraro (Bologna Observatory),
Barbara Paltrinieri (Rome University – “La Sapienza”),
Francesco Paresce (ESO),
Guido De Marchi (ESO)

Comments: 15 pages, 3 figures. ApJL in press


We present results from multi-band observations in the central region of the
cluster NGC6712 with the ESO-Very Large Telescope. Using high resolution images
we have identified three UV-excess stars. In particular two of them are within
the cluster core, a few arcsec apart: the first object is star “S” which
previous studies identified as the best candidate to the optical counterpart to
the luminous X-ray source detected in this cluster. The other UV object shows
clearcut H-alpha emission and, for this reason, is an additional promising
interacting binary candidate (a quiescent LMXB or a CV). The presence of two
unrelated interacting binary systems a few arcsec apart in the core of this
low-density cluster is somewhat surprising and supports the hypothesis that the
(internal) dynamical history of the cluster and/or the (external) interaction
with the Galaxy might play a fundamental role in the formation of these
peculiar objects.
(143kb)




astro-ph/0008507 [abs, src, ps, other] :




Title: Hierarchical clustering and formation of power-law correlation in
1-dimensional self-gravitating system

Authors:
Hiroko Koyama,
Tetsuro Konishi

Comments: 9pages,4figures


The process of formation of fractal structure in one-dimensional
self-gravitating system is examined numerically. It is clarified that
structures created in small spatial scale grow up to larger scale through
clustering of clusters, and form power-law correlation.
(80kb)




astro-ph/0008508 [abs, src, ps, other] :




Title: The compact core-jet region of the superluminal quasar 3C216

Authors:
Z. Paragi (SGO),
S. Frey (SGO),
I. Fejes (SGO),
T. Venturi (IRA),
R.W. Porcas (MPIfR),
R.T. Schilizzi (JIVE/Leiden Obs.)

Comments: 6 pages, 3 figures, accepted for publication by PASJ


Space very long baseline interferometry (VLBI) observations of the quasar
3C216 with the VLBI Space Observatory Programme (VSOP) reveal that the parsec
scale structure of the source can be well described by compact jet models
developed for interpreting the core region of radio-loud active galactic nuclei
(AGN). The measured brightness temperature of T_(b) = 7.9*10^{11} K is
comparable to the inverse Compton limit, from which we determine a lower limit
of delta ~ 3.17 for the Doppler-boosting factor. The apparent transvers
velocity of the superluminal component is beta_(app) = (3.0+-0.2) h^{-1}
asuming a constant velocity, but deceleration of the jet material cannot be
excluded from our data. A combination of the above values indicates that the
viewing angle of the core-jet to the line-of-sight is less than 18.4 degrees,
and the jet Lorentz-factor exceeds 3.16. The observed small size of the source
is probably caused by both interaction with the interstellar medium, and a
projection effect.
(192kb)




astro-ph/0008509 [abs, src, ps, other] :




Title: WSRT Observations of the Hubble Deep Field Region

Authors:
M.A. Garrett (JIVE),
A.G. de Bruyn (ASTRON),
M. Giroletti (JIVE/U of Bologna),
W.A. Baan (ASTRON),
R.T. Schilizzi (JIVE)

Comments: To appear in Astronomy and Astrophysics Letters (accepted); 4 Pages,
1 figure. See this http URL for a useful but preliminary web
based catalogue, colour (pretty) figures and more information


We present deep WSRT 1.4 GHz observations of the Hubble Deep Field region. At
the 5 sigma level, the WSRT clearly detects 85 regions of radio emission in a
10′ x 10′ field centred on the HDF. Eight of these regions fall within the HDF
itself, four of these are sources that have not previously been detected at 1.4
GHz, although two of these are VLA detections at 8.5GHz. The two new radio
sources detected by the WSRT are identified with relatively bright (I<21m)
moderate redshift spiral and irregular type galaxies. In the full field, the
WSRT detects 22 regions of emission that were not previously detected by the
VLA at 1.4GHz. At least two of these are associated with nearby, extended
star-forming galaxies.
(475kb)




astro-ph/0008510 [abs, src, ps, other] :




Title: Electromagnetic Radiation and Motion of Real Particle

Authors:
Jozef Klacka

Relativistically covariant equation of motion for real dust particle under
the action of electromagnetic radiation is derived. The particle is neutral in
charge. Equation of motion is expressed in terms of particle’s optical
properties, standardly used in optics for stationary particles.
(5kb)




astro-ph/0008511 [abs, src, ps, other] :




Title: Changing Molecular Gas Properties in the Bar and Canter of NGC7479

Authors:
S. Huettemeister (RAIUB, Bonn, Germany),
S. Aalto (OSO, Sweden),
M. Das (UMD, USA),
W.F. Wall (INAOE, Mexico)

Comments: 16 pages, 12 ps figures included, accepted by A&A


We present sensitive interferometric 12CO, 13CO and HCN observations of the
barred spiral galaxy NGC7479, known to be one of the few barred galaxies with a
continuous gas-filled bar. We focus on the investigation and interpretation of
12CO/13CO line intensity ratios, which is facilitated by having more than 90%
of the flux in our interferometer maps. The global (9kpc by 2.5kpc) value of
the 12CO/13CO ratio is high at 20 – 40. On smaller scales (~ 750 pc), the ratio
is found to vary dramatically, reaching values > 30 in large parts of the bar,
but dropping to values ~ 5, typical for galactic disks, at a 13CO condensation
in the southern part of the bar. We interpret these changes in terms of the
relative importance of the contribution of a diffuse molecular component,
characterized by unbound gas that has a moderate optical depth in the 12CO(1 –
0) transition. This component dominates the 12CO along the bar and is also
likely to play an important role in the center of NGC7479. In the center, the
12CO and the HCN intensity peaks coincide, while the 13CO peak is slightly
offset. This can be explained in terms of high gas temperature and density at
the 12CO peak position. Along the bar, the relation between the distribution of
12CO, 13CO, dust lanes and velocity gradient is complex. A southern 13CO
condensation is found offset from the 12CO ridge that generally coincides with
the most prominent dust lanes. It is possible that strong 13CO detections along
the bar indicate quiescent conditions, downstream from the major bar shock.
Still, these condensations are found close to high velocity gradients. In the
central region, the velocity gradient is traced much more closely by 13CO than
by 12CO.
(572kb)




astro-ph/0008512 [abs, src, ps, other] :




Title: Numerical hydrodynamics: SPH vs. AMR

Authors:
Tomek Plewa (Copernicus Astronomical Center, Warsaw, Poland)

Comments: 4 pages, LaTeX, requires newpasp.sty. To appear in H. Zinnecker and
R.D. Mathieu, eds, Proceedings of the IAU Symposium 200 “The Formation of
Binary Stars”, held in Potsdam, Germany, April 10-15 2000


The advantages and disadvantages of two approaches to astrophysical
hydrodynamics, Smoothed Particle Hydrodynamics and Adaptive Mesh Refinement,
are briefly discussed together with some current problems of computational
hydrodynamics.
(9kb)




astro-ph/0008513 [abs, src, ps, other] :




Title: Near-infrared imaging of the host galaxies of intermediate redshift
steep spectrum radio quasars

Authors:
J.K. Kotilainen (Tuorla Observatory, Finland),
R. Falomo (Padova Observatory, Italy)

Comments: 14 pages, accepted for publication in A&A


We present the results of near-infrared H-band (1.65 microns) imaging of 19
steep spectrum radio quasars (SSRQ) in the redshift range 0.5 < z < 1.0. This
sample of SSRQs is matched with our previously studied complete sample of 20
flat spectrum radio quasars (FSRQ) with respect to redshift and optical and
radio luminosity. We are able to clearly detect the host galaxy in 10 (53 %)
SSRQs and marginally in 6 (32 %) others, while the host remains unresolved in 3
(16 %) SSRQs. The galaxies hosting the SSRQs are large (average bulge
scale-length R(e) = 9.0+-1.7 kpc) and luminous (average M(H) = -27.2+-1.1).
They are, therefore, about 2 mag more luminous than the typical galaxy
luminosity L* (M*(H) = -25.0+-0.2), and about 1 mag more luminous than the
brightest cluster galaxies (M(H) = -26.3+-0.3). The SSRQ hosts appear to have
similar luminosity to those of the FSRQ hosts (M(H) = -27), and they fall
between the luminosities of lower redshift (M(H) = -26) and higher redshift
(M(H) = -29) radio-loud quasars. The average nucleus-to-galaxy luminosity ratio
of SSRQs (LN/LG = 3.8+-3.2) is much smaller than that found for the FSRQs
(LN/LG = 21+-11), in good agreement with the current unified models. We confirm
for the most luminous SSRQs the trend noted for the FSRQs between the host and
nuclear luminosity. This trend supports the suggestion based on studies of
lower redshift AGN, that there is a minimum host galaxy luminosity which
increases linearly with the quasar luminosity. Finally, FSRQs seem to reside in
richer environments than SSRQs, as evidenced by a larger number of close
companion galaxies.
(141kb)




astro-ph/0008514 [abs, src, ps, other] :




Title: Tidally-induced angular momentum transport in disks

Authors:
Caroline E. J. M. L. J. Terquem (Institut d’Astrophysique de Paris, France)

Comments: 4 pages, LaTeX, uses newpasp.sty, to be published in ‘The Formation
of Binary Stars’, eds. R.D. Mathieu and H. Zinnecker (ASP Conference Series)


We discuss the transport of angular momentum induced by tidal effects in a
disk surrounding a star in a pre-main sequence binary system. We consider the
effect of both density and bending waves. Although tidal effects are important
for truncating protostellar disks and for determining their size, it is
unlikely that tidally-induced angular momentum transport plays a dominant role
in the evolution of protostellar disks. Where the disk is magnetized, transport
of angular momentum is probably governed by MHD turbulence. In a non
self-gravitating laminar disk, the amount of transport provided by tidal waves
is probably too small to account for the lifetime of protostellar disks. In
addition, tidal effects tend to be localized in the disk outer regions.
(8kb)




astro-ph/0008515 [abs, src, ps, other] :




Title: The Global-Normal Disk Oscillations and the Persistent Low Frequency QPO
in X-ray Binaries

Authors:
Lev Titarchuk (GMU/NRL/NASA/GSFC),
Vladimir Osherovich (GSFC/Ritss)

Comments: 14 pages, 1 figure, to appear in the Astrophysical Journal Letters


We suggest that persistent low-frequency quasi-periodic oscillations (QPOs)
detected in X-ray, ultraviolet, optical energy ranges the black hole (BH)
sources XTE J1118+480, GRO J1655-40 LMC X-1 at ~ 0.1 Hz, and QPOs in HZ Her/Her
X-1 at ~ 0.05 Hz and in Neutron Star (NS) binaries 4U 1323-62, 4U 1746-31 and
EXO 0748-76 at ~ 1 Hz are caused by the global disk oscillations in the
direction normal to the disk (normal mode). We argue that these disk
oscillations are a result of the gravitational interaction between the central
compact object and the disk. A small displacement of the disk from the
equatorial plane results in a linear gravitational restoring force opposite to
this displacement. Our analysis shows that the frequency of this mode is a
function of the mass of the central object and it also depends on the inner and
outer radii of the disk which in turn are related to the rotation period of the
binary system. We derive an analytical formula for the frequency of the normal
disk mode and show that these frequencies can be related to the persistent
lower QPO frequencies observed in the NS and BH sources. We offer a new
independent approach to the black hole mass determination by interpreting this
low QPO frequency as the global disk oscillation frequency. The implementation
of this method combined with the independent method which uses the X-ray energy
spectra (Shrader & Titarchuk 1999) results in stringent constraints for the
black hole masses.
(17kb)




astro-ph/0008516 [abs, src, ps, other] :




Title: Asteroseismology for the Masses

Authors:
Travis S. Metcalfe (University of Texas-Austin)

Comments: To appear in Proceedings of the 12th European Workshop on White
Dwarfs


For many years, astronomers interested in white dwarf stars have promised
that the study of these relatively simple compact objects would ultimately lead
to useful information about the physics under extreme conditions of temperature
and pressure. We are finally ready to make good on that promise. Using the
observational techniques of the Whole Earth Telescope developed over the past
decade, and a new analytical method only recently made feasible by the
availability of fast inexpensive computers, we demonstrate that meaningful
constraints can now be made on the rates of important nuclear fusion reactions
which cannot presently be measured in the laboratory.
(486kb)




astro-ph/0008517 [abs, src, ps, other] :




Title: Chandra measurements of the distribution of mass in the luminous lensing
cluster Abell 2390

Authors:
S.W. Allen,
S. Ettori,
A.C. Fabian (IoA, Cambridge, UK)

Comments: 24 pages, 12 figs, 3 tables, submitted to MNRAS


We present spatially-resolved X-ray spectroscopy of the luminous lensing
cluster Abell 2390, using observations made with the Chandra observatory. The
temperature of the X-ray gas is shown to rise with increasing radius within the
central ~200 kpc of the cluster, and then remains approximately isothermal,
with kT =11.5^{+1.5}_{-1.6} keV, out to the limits of the observations at r~1.0
Mpc. The total mass profile determined from the Chandra data has a form in good
agreement with the predictions from numerical simulations. Using the
parameterization of Navarro, Frenk & White (1997), we measure a scale radius
r_s~0.7 Mpc and a concentration parameter c~5. The best-fit X-ray mass model is
in excellent agreement with independent measurements from strong and weak
lensing studies and optical measurements of the galaxy velocity dispersion in
the cluster. The X-ray gas-to-total-mass ratio rises with increasing radius
within the central ~0.7 Mpc with f_gas approxpropto r^{0.3}. At r = 0.9 Mpc,
we measure f_gas = 15.7^{+5.6}_{-4.1} per cent (90 per cent confidence limits).
The azimuthally-averaged 0.3-7.0 keV surface brightness profile exhibits a
small core radius and a clear `break’ at r~500 kpc, where the slope changes
from S_X approxpropto r^{-1.4} to S_X approxpropto r^{-3.7}. The data for the
central ~70 kpc radius indicate the presence of a strong cooling flow with a
mass deposition rate of 200-250 Msunpyr and an age of ~3 Gyr.
(105kb)




astro-ph/0008518 [abs, src, ps, other] :




Title: Particle reacceleration in Coma cluster: radio properties and hard X-ray
emission

Authors:
G. Brunetti,
G. Setti,
L. Feretti,
G. Giovannini

Comments: 15 pages, 13 figures, accepted for publication in MNRAS


The radio spectral index map of the Coma halo shows a progressive steepening
of the spectral index with increasing radius. Such a steepening cannot be
simply justified by models involving continuous injection of fresh particles in
the Coma halo or by models involving diffusion of fresh electrons from the
central regions. We propose a {it two phase} model in which the relativistic
electrons injected in the Coma cluster by some processes (starbursts, AGNs,
shocks, turbulence) during a {it first phase} in the past are systematically
reaccelerated during a {it second phase} for a relatively long time ($sim$ 1
Gyr) up to the present time. We show that for reacceleration time scales of
$sim 0.1$ Gyr this hypothesis can well account for the radio properties of
Coma C. For the same range of parameters which explain Coma C we have
calculated the expected fluxes from the inverse Compton scattering of the CMB
photons finding that the hard X-ray tail discovered by BeppoSAX may be
accounted for by the stronger reacceleration allowed by the model. The
possibility of extending the main model assumptions and findings to the case of
the other radio haloes is also discussed, the basic predictions being
consistent with the observations.
(217kb)




astro-ph/0008519 [abs, src, ps, other] :




Title: Massive star populations and the IMF in metal-rich starbursts

Author:
Daniel Schaerer (OMP, Toulouse),
Natalia G. Guseva,
Yuri I. Izotov (Main Astronomical Observatory, Kiev),
Trinh X. Thuan (University of Virginia, Charlottesville)

Comments: Accepted for publication in A&A. LaTeX, 18 pages including 8 figures.
Also available at this http URL


We present new spectroscopic observations of Mkn 309, a starburst galaxy with
one of the largest WR populations known. A highly super solar metallicity is
derived. Using additional objects we analyse a sample of five metal-rich WR
galaxies with the main goal of constraining the basic properties of the massive
star populations (IMF slope, M_up) and the star formation history (age, burst
duration) of these objects by quantitative comparisons with evolutionary
synthesis models. The following main results are obtained: 1) The observations
are well explained by extended bursts of star formation or a superposition of
several bursts. Ages and burst durations are estimated. This naturally explains
both the observed WR populations (including WN and WC stars) and the presence
of red supergiants. 2) The fitted SEDs indicate that the stellar light suffers
from a smaller extinction than that of the gas, confirming independent earlier
findings. 3) All the considered observational constraints are compatible with a
Salpeter IMF extending to masses >~ 40 Msun. Adopting a conservative approach
we derive a LOWER LIMIT of Mup >~ 30 Msun for the Salpeter IMF. From more
realistic assumptions on the metallicity and SF history we favour a lower limit
Mup >~ 30-40 Msun, which is also in agreement with Hbeta equivalent width
measurements of metal-rich HII regions in spiral galaxies indicating an upper
mass cut-off of at least ~ 35 – 50 Msun. Steep IMF slopes (alpha >~ 3.3) are
very unlikely. (abridged/modified abstract)
(88kb)




astro-ph/0008520 [abs, src, ps, other] :




Title: Infrared Observations of AR Ursa Majoris: Modeling the Ellipsoidal
Variations

Authors:
Steve B. Howell,
Dawn M. Gelino,
Thomas E. Harrison

Comments: Submitted to AJ


We have obtained time-series infrared photometry for the highly magnetic
cataclysmic variable AR UMa. Our J and K’ band observations occurred during a
low state and they show a distinctive double-humped structure. Using detailed
models for the expected ellipsoidal variations in the infrared due to the
non-spherical secondary star, we find that the most likely value for the system
inclination is 70 degrees. We also model low state V band photometry and find
that its observed double-humped structure is not caused by ellipsoidal
variations, as they have been ascribed to, but are due to beamed cyclotron
radiation. We use this result to estimate the magnetic field strength of the
active southern accretion region (B <= 190 MG) and its magnetic longitude (330
degrees).
(63kb)




astro-ph/0008521 [abs, src, ps, other] :




Title: Assessing the state of galaxy formation

Authors:
D.J. Pisano,
Eric M. Wilcots (UW-Madison)

Comments: 5 pages, 4 figures, to appear in ASP conference series “Gas & Galaxy
Evolution” eds. Hibbard, Rupen, and van Gorkom


We present the results of a survey of nearby, quiescent, non-peculiar,
extremely isolated galaxies to search for the gaseous remnants of galaxy
formation. Such remnants are predicted to persist around galaxies into the
present day by galaxy formation models. We find low-mass HI companions around 7
of 34 galaxies surveyed. In addition we find 5 galaxies with lopsided HI
distributions. The implications for galaxy formation and the nature of high
velocity clouds are discussed.
(130kb)




astro-ph/0008522 [abs, src, ps, other] :




Title: Variable Iron K-alpha Lines in Seyfert 1 Galaxies

Authors:
K. A. Weaver,
J. Gelbord,
T. Yaqoob

Comments: 26 pages, 30 figures, accepted for publication in the Astrophysical
Journal


We find that variability of the iron K-alpha line is common in Seyfert 1
galaxies. Using data from the ASCA archive for objects that have been observed
more than once during the mission, we study the time-averaged spectra from
individual observations, thereby probing variability on timescales that range
from days to years. Since the statistics of the data do not warrant searches
for line variability in terms of a complex physical model, we use a a simple
Gaussian to model the gross shape of the line, and then use the centroid
energy, intensity and equivalent width as robust indicators of changes in the
line profile. We find that ~70% of Seyfert 1s (ten out of fifteen) show
variability in at least one of these parameters: the centroid energy,
intensity, and equivalent width vary in six, four, and eight sources
respectively. Due to the low S/N, limited sampling and time averaging, we
consider these results to represent lower limits to the rate of incidence of
variability. In most cases changes in the line do not appear to track changes
in the continuum. In particular, we find no evidence for variability of the
line intensity in NGC 4151, suggesting an origin in a region larger than the
putative accretion disk, where most of the iron line has been thought to
originate. Mkn 279 is investigated on short timescales. The time-averaged
effective line energy is 6.5 keV in the galaxy rest frame. As the continuum
flux increases by 20% in a few hours, the Fe K line responds with the effective
line energy increasing by 0.22 keV (~10,500 km s^-1). Problems with the ASCA
and Rosat calibration that affect simultaneous spectral fits are discussed in
an appendix.
(229kb)




astro-ph/0008523 [abs, src, ps, other] :




Title: Pulsar Astronomy: the HST Contribution

Authors:
P.A. Caraveo (1),
R. P. Mignani (2),
G.G.Pavlov (3),
G.F. Bignami (4) ((1) IFC-CNR, Milan, Italy, (2) STECF-ESO, Garching, Germany, (3) Pennsylvania State Univ., USA, (4) ASI, Rome, Italy)

Comments: 4 pages, 1 figure, uses psfig.sty. To appear in the proceedings of A
Decade of HST Science (Baltimore, USA, April 2000)


HST observations have contributed significantly to our knowledge on the
behaviour of Isolated Neutron Stars (INSs) as optical emitters. First, HST has
been instrumental both to discover new optical counterparts (PSR B1055-52, PSR
B1929+10, PSR B0950+08) and to confirm proposed identifications (PSR B0656+14).
Second, HST multicolor photometry provided useful information to characterize
the optical emission mechanism(s) at work in middle-aged INSs like PSR B0656+14
and Geminga. Last, but not least, the superior angular resolution of the HST
allowed both to perform a very accurate morphological study of the plerionic
environments of young pulsars (e.g. the Crab and PSR B0540-69) and to perform
very accurate astrometric measurements yielding proper motions (Crab, Vela,
Geminga, PSR B0656+14) and parallaxes (Geminga).
(28kb)




astro-ph/0008524 [abs, src, ps, other] :




Title: Kinematic Evidence of Minor Mergers in Normal Sa Galaxies

Authors:
Martha P. Haynes

Comments: To appear in proceedings of Gas and Galaxy Evolution, (VLA 20th
Anniversary Conference), ASP Conf. Series, ed. J. Hibbard, M. Rupen, & J. van
Gorkom. 4 pages, 1 figure, uses newpasp.sty


A detailed study of nearby, morphologically normal Sa galaxies reveals that
about half show some spectrocopic evidence for kinematically distinct
components despite their undisturbed optical appearance. In eight of nine
objects mapped in the 21 cm HI line, the HI distribution extends far outside
the optical disk and warps of the HI disk are complex. The multiwavelength
evidence can be interpreted in terms of the kinematic “memory” of past minor
mergers in objects that otherwise exhibit no morphological signs of
interaction.
(230kb)




astro-ph/0008525 [abs, src, ps, other] :




Title: Comparison of UHECR spectra from necklaces and vortons

Authors:
Luis Masperi,
Milva Orsaria

Comments: 11 pages, standard latex, 3 postscript figures. Presented at the
Chacaltaya Meeting on Cosmic Rays Physics, La Paz, 23-27 July 2000


Cosmic rays of energy higher than 10^19 eV may be explained by topological
defects produced in the early stages of universe. Two suitable alternatives
are: necklaces formed by magnetic monopoles connected by strings, and vortons
which are loops stabilized by superconducting currents. The former are
uniformly distributed in the universe, may account for cosmic rays above the
ankle, suffer a transient GZK cutoff with a subsequent recovery and isotropy of
observations is expected. The latter are concentrated in the galactic halo,
require an additional extragalactic contribution between the ankle and the GZK
cutoff, beyond which give a harder component and predict anisotropy related to
mass concentration.
(20kb)




astro-ph/0008526 [abs, src, ps, other] :




Title: Discovery of nearly coherent oscillations with a frequency of ~567 Hz
during type-I X-ray bursts of the X-ray transient and eclipsing binary X
1658-298

Authors:
Rudy Wijnands,
Tod Strohmayer,
Lucia M. Franco

Comments: Submitted to ApJ Letters, 31 August 2000


We report the discovery of nearly coherent oscillations with a frequency of
567 Hz during type-I X-ray bursts from the X-ray transient and eclipsing binary
X 1658-298. If these oscillations are directly related to the neutron star
rotation then the spin period of the neutron star in X 1658-298 is ~1.8 ms. The
oscillations can be present during the rise or decay phase of the bursts.
Oscillations during the decay phase of the bursts show an increase in the
frequency of ~0.5 to 1 Hz, however, in one particular burst the oscillations
reappear at the end of the decay phase at about 571.5 Hz. This represents an
increase in oscillation frequency of about 5 Hz which is the largest frequency
change seen so far in a burst oscillation. It is unclear if such a large change
can be accommodated by present models used to explain the frequency evolution
of the oscillations. We also observed several bursts during which the
oscillations are detected at much lower significance or not at all. Most of
these bursts happen during periods of X-ray dipping behavior, strongly
suggesting that the X-ray dipping decreases the amplitude of the oscillations.
The two bursts without oscillations which did not happen during X-ray dips
exhibit other differences (one burst is only half as bright and the other burst
has an unusual decay profile) from the bursts which exhibit oscillations, and
these differences might conceivably account for their lack of oscillations. We
discuss our discovery in the framework of the neutron star spin interpretation
and the possibility of constraining the binary X-ray mass function in this
system for which the orbital period and the inclination are well constrained.
(40kb)




Cross-listings




gr-qc/0008028 [abs, src, ps, other] :




Title: Gravitational instabilities in helicity-1 waves propagating through
matter in equilibrium

Authors:
Luis Bento,
Jose P. S. Lemos

Comments: 12 pages, latex, 1 figure ps file, final version to appear in CQG


It is shown that the interaction of helicity-1 waves of gravity and matter in
a thin slab configuration produces new types of instabilities. Indeed, a
transverse spin-2 helicity-1 mode interacts strongly with the shear motion of
matter. This mode is unstable above a critical wavelength which reminds the
Jeans wavelength but with the speed of sound interchanged by the speed of
light. The two instabilities are of course different. For the case analyzed, a
plane parallel configuration, Jeans instability appears through a density wave
perturbation, the material collapsing into a set of plane-parallel slabs. On
the other hand, the helicity-1 wave instability induces a transverse motion in
the fluid that tends to shear in the material along the node of the
perturbation.
(16kb)




gr-qc/0008051 [abs, src, ps, other] :




Title: Cosmological Constant or Cosmological Potential

Authors:
P.Fiziev

Comments: 33 pages, latex, slides, no figures. Three new slides added with: 1)
qualitative analysis of the $10^122$-problem based on classical action; 2)
Acknowledgments. Talk at conference “Problems of Vacuum Energy”, Copenhagen,
23-26 August 2000

In the framework of a model of minimal of dilatonic gravity (MDG) with
cosmological potential we consider: the relations of MDG with nonlinear gravity
and string theory; natural cosmological units, defined by cosmological
constant; the properties of cosmological factor, derived from solar system and
Earth-surface gravitational experiments; universal anty-gravitational
interactions, induced by positive cosmological constant and by Nordtved effect;
a new formulation of cosmological constant problem using the ratio of
introduced cosmological action and Planck constant $sim 10 ^{122}$;qualitative
analysis of this huge number based on classical action of effective Bohr
hydrogen atoms; inverse cosmological problem: to find cosmological potential
which yields given evolution of the RW Universe; and comment other general
properties of MDG.
(14kb)




hep-ph/0008318 [abs, src, ps, other] :




Title: Primordial Galactic Magnetic Fields from the QCD Phase Transition

Authors:
Michael McNeil Forbes,
Ariel R. Zhitnitsky (University of British Columbia, Canada)

Comments: 13 pages, (LaTeX), uses sprocl.sty. To be published in the
proceedings of the Fourth Workshop on Continuous Advances in QCD,
Minneapolis, MN, May 2000


In this paper, we propose a mechanism to generate large-scale magnetic fields
with correlations lengths of 100 kpc. Domain walls with QCD scale internal
structure form and coalesce obtaining Hubble size correlations and align
nucleon spins. Due to strong CP violation, nucleons in these walls have
anomalous electric and magnetic dipole moments and thus the walls are
ferromagnetic. This induces electromagnetic fields with Hubble size
correlations. The same CP violation also induces maximal helicity
(Chern-Simons) correlated through the Hubble volume which supports an “inverse
cascade” allowing the initial correlations to grow to 100 kpc today. We
estimate the generated electromagnetic fields in terms of the QCD parameters
and discuss the effects of the resulting fields.
(14kb)




Replacements




astro-ph/0005551 [abs, src, ps, other] :




Title: Towards global-phase-delay VLBI astrometry: observations of QSO 1150+812
and BL 1803+784

Authors:
M.A.Perez-Torres,
J.M. Marcaide,
J.C. Guirado,
E. Ros,
I.I. Shapiro,
M.I. Ratner,
E. Sardon

Comments: 12 pages, 5 figures

Journal-ref: Astronomy & Astrophysics, 360, 161-170 (2000)

Note: replaced with revised version Thu, 31 Aug 2000 07:39:46 GMT (99kb)



astro-ph/0007187 [abs, src, ps, other] :




Title: Cosmological Parameters 2000

Authors:
Joel R. Primack (UC Santa Cruz)

Comments: 16 pages, including one postscript figure; talk presented at 4th
International Symposium on Sources and Detection of Dark Matter in the
Universe (DM 2000), Marina del Rey, California, 20-23 Feb 2000 Replaced
version has identical text, but updated references

Note: replaced with revised version Thu, 31 Aug 2000 22:10:24 GMT (62kb)



astro-ph/0008393 [abs, src, ps, other] :




Title: A Monte Carlo Study of the 6.4 keV Emission at the Galactic Center

Authors:
M. J. Fromerth (U. of Arizona),
F. Melia (U. of Arizona),
D. Leahy (U. of Calgary)

Comments: 11 pages, 4 EPS figures, uses epsfig.sty, amssym.sty, psfig.sty

Note: replaced with revised version Thu, 31 Aug 2000 15:44:40 GMT (17kb)



astro-ph/0008451 [abs, src, ps, other] :




Title: Massive warm dark matter

Authors:
Steen Hannestad

Comments: 5 pages, Revtex, 1 figure, reference corrected

Note: replaced with revised version Thu, 31 Aug 2000 11:22:45 GMT (12kb)



astro-ph/0008469 [abs, src, ps, other] :




Title: Secondary CMB Anisotropies from Cosmological Reionization

Authors:
Nickolay Y. Gnedin,
Andrew H. Jaffe

Comments: submitted to ApJ

Note: replaced with revised version Thu, 31 Aug 2000 14:41:03 GMT (296kb)



astro-ph/0008479 [abs, src, ps, other] :




Title: On the occurrence of dwarf nova outbursts in post novae

Authors:
M.R. Schreiber,
B.T. Gaensicke,
J.K. Cannizzo

Comments: accepted for publication in Astronomy and Astrophysics

Note: replaced with revised version Thu, 31 Aug 2000 09:22:19 GMT (41kb)



astro-ph/0008486 [abs, src, ps, other] :




Title: Multiwaveband studies of the hard ROSAT SMC transient 1WGA J0053.8-7226:
a new X-ray pulsar

Authors:
D.A.H. Buckley (SAAO),
M.J. Coe (Southampton),
J.B. Stephens (Southampton),
K. van der Heyden (SAAO),
L. Angelini (NASA/GSFC),
N. White (NASA/GSFC),
P. Giommi (NASA/GSFC)

Comments: Accepted for publication in MNRAS

Note: replaced with revised version Thu, 31 Aug 2000 11:00:41 GMT (287kb)



hep-ph/0005310 [abs, src, ps, other] :




Title: Tau Neutrinos Underground: Signals of $
u_mu o
u_ au$
Oscillations with Extragalactic Neutrinos

Authors:
Sharada Iyer Dutta (University of Arizona),
Mary Hall Reno (University of Iowa),
Ina Sarcevic (University of Arizona)

Comments: section added and two new figs; accepted for publication in Physical
Review D

Note: replaced with revised version Thu, 31 Aug 2000 19:52:32 GMT (457kb)



hep-th/0006007 [abs, src, ps, other] :




Title: Gravitational waves from inflation on the brane

Authors:
David Langlois,
Roy Maartens,
David Wands

Comments: 7 pages, revtex; minor corrections and modifications; to appear in
Phys. Lett. B

Note: replaced with revised version Thu, 31 Aug 2000 10:58:39 GMT (13kb)




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