1,158 research outputs found
SN contributions to GRB lightcurves
Several of the nearer GRB afterglows (up to z ⌠1) show bumps in their lightcurves that have been interpreted as contributions from associated SNae. Thebumps arecustomarily modelled likethet ype-Ic SN 1998bw, but wein vestigate
here, for several low-z GRBs, whether other SN types might offer alternatives. While several SN types are ruled out, or are unlikely, a type âII-blâ could also explain the
observations
Black Hole Mass, Velocity Dispersion and the Radio Source in AGN
The recent discovery of a correlation between nuclear black hole mass, M_bh,
and the stellar velocity dispersion (Gebhardt et al. 2000, Ferrarese and
Merritt 2000), in elliptical galaxies and spiral bulges, has raised the
question whether such a relationship exists for AGN. Estimates of M_bh for many
AGN, made using reverberation mapping techniques, allow exploration of the
relationship between black hole mass, the host galaxy and the energetics of
nuclear emission. However, since only a few AGN have both M_bh and velocity
dispersion measurements, we use the [OIII] 5007 emission line widths on the
assumption that for most AGN the forbidden line kinematics are dominated by
virial motion in the host galaxy bulge. We find that a relation does exist
between M_bh and [OIII] line width for AGN which is similar to the one found by
Gebhardt et al. 2000, although with more scatter as expected if secondary
influences on the gas kinematics are also present. Our conclusion is that both
active and inactive galaxies follow the same relationship between black hole
mass and bulge gravitational potential. We find no compelling evidence for
systematic differences in the mass estimates from reverberation mapping and
stellar dynamics. We also find that for radio quiet AGN the radio power and
black hole mass are highly correlated linking emission on scales of kiloparsecs
with the nuclear energy source.Comment: 4 pages, uses emulateapj5.sty and aastex, 2 figures, 1 table accepted
for publication in the Astrophysical Journa
UVES/VLT High Resolution Spectroscopy of Gamma Ray Burst Afterglows
We present early time, high resolution spectroscopy of three GRB afterglows:
GRB050730, 050922C and 060418. These data give us precious information on the
kinematics, ionization and metallicity of the interstellar matter of GRB host
galaxies up to a redshift z = 4, and of intervening absorbers along the line of
sight.Comment: 2 pages, 1 ps figure. Proceedings of the Swift-Venice 2006 meeting to
be published by "Il Nuovo Cimento
Statistical Properties of Radio Emission from the Palomar Seyfert Galaxies
We have carried out an analysis of the radio and optical properties of a
statistical sample of 45 Seyfert galaxies from the Palomar spectroscopic survey
of nearby galaxies. We find that the space density of bright galaxies (-22 mag
<= M_{B_T} <= -18 mag) showing Seyfert activity is (1.25 +/- 0.38) X 10^{-3}
Mpc^{-3}, considerably higher than found in other Seyfert samples. Host galaxy
types, radio spectra, and radio source sizes are uncorrelated with Seyfert
type, as predicted by the unified schemes for active galaxies. Approximately
half of the detected galaxies have flat or inverted radio spectra, more than
expected based on previous samples. Surprisingly, Seyfert 1 galaxies are found
to have somewhat stronger radio sources than Seyfert 2 galaxies at 6 and 20 cm,
particularly among the galaxies with the weakest nuclear activity. We suggest
that this difference can be accommodated in the unified schemes if a minimum
level of Seyfert activity is required for a radio source to emerge from the
vicinity of the active nucleus. Below this level, Seyfert radio sources might
be suppressed by free-free absorption associated with the nuclear torus or a
compact narrow-line region, thus accounting for both the weakness of the radio
emission and the preponderance of flat spectra. Alternatively, the flat spectra
and weak radio sources might indicate that the weak active nuclei are fed by
advection-dominated accretion disks.Comment: 18 pages using emulateapj5, 13 embedded figures, accepted by Ap
UVES - VLT High Resolution Spectroscopy of GRB Afterglows
We present early time, high resolution spectroscopy of three GRB afterglows:
GRB050730, GRB050922C and GRB060418. These data give us precious information on
the kinematics, ionization and metallicity of the interstellar matter of GRB
host galaxies up to a redshift z = 4, and of intervening absorbers along the
line of sight. The absorption spectra show that elements are present both with
high and low ionization states, and even forbidden, fine structure levels are
commonly observed. These features allow us to evaluate the physical parameters
of the absorbing gas. In details, the density of the gas regions lie in the
range n = 10 - 10^6 cm-3, and the temperatures are of the order of T = 10^3 -
10^4 K. The metallicity of the GRB host galaxies is computed using the hydrogen
absorption features. We find undersolar abundances for our GRBs, namely, Z =
0.001 - 0.01. However, depletion has not been considered. It can be taken into
account using as metallicity indicators Zn and Cr, which tend to remain in the
gas phase. We find metallicities higher than the previous values and in
agreement with other measurements for GRB host galaxies. Finally, the observed
[C/Fe] ratio for GRB050730 (z = 3.967) agrees with values expected for a galaxy
younger than a Gyr undergoing bursts of star-formation. In addition, the [C/Fe]
ratio evaluated component by component can give informations on the relative
distances of the components from the GRB explosion site, since Fe dust is more
efficiently destroyed than graphite.Comment: 8 pages, 11 figure, To appear in "The Multicoloured Landscape of
Compact Objects and their Explosive Progenitors: Theory vs Observations"
(Cefalu, Sicily, June 2006). Eds. L. Burderi et al. (New York: AIP
Tomographic Separation of Composite Spectra. IX. The Massive Close Binary HD 115071
We present the first orbital elements for the massive close binary, HD
115071, a double-lined spectroscopic binary in a circular orbit with a period
of 2.73135 +/- 0.00003 days. The orbital semiamplitudes indicate a mass ratio
of M_2/M_1 = 0.58 +/- 0.02 and yet the stars have similar luminosities. We used
a Doppler tomography algorithm to reconstruct the individual component optical
spectra, and we applied well known criteria to arrive at classifications of
O9.5 V and B0.2 III for the primary and secondary, respectively. We present
models of the Hipparcos light curve of the ellipsoidal variations caused by the
tidal distortion of the secondary, and the best fit model for a Roche-filling
secondary occurs for an inclination of i = 48.7 +/- 2.1 degrees. The resulting
masses are 11.6 +/- 1.1 and 6.7 +/- 0.7 solar masses for the primary and
secondary, respectively, so that both stars are very overluminous for their
mass. The system is one of only a few known semi-detached, Algol-type binaries
that contain O-stars. We suggest that the binary has recently emerged from
extensive mass transfer (possibly through a delayed contact and common envelope
process).Comment: Submitted to Ap
A flash in the dark: UVES/VLT high resolution spectroscopy of GRB afterglows
We present the first high resolution (R=20000--45000, corresponding to 14
km/s at 4200A to 6.6 km/s at 9000A) observations of the optical afterglow of
Gamma Ray Bursts. GRB020813 and GRB021004 were observed by UVES@VLT 22.19 hours
and 13.52 hours after the trigger, respectively. These spectra show that the
inter--stellar matter of the GRB host galaxies is complex, with many components
contributing to each main absorption system, and spanning a total velocity
range of up to about 3000 km/s. Several narrow components are resolved down to
a width of a few tens of km/s. In the case of GRB021004 we detected both low
and high ionization lines. Combined with photoionization results obtained with
CLOUDY, the ionization parameters of the various systems are consistent with a
remarkably narrow range with no clear trend with system velocity. This can be
interpreted as due to density fluctuations on top of a regular R^-2 wind
density profile.Comment: Most figure improved, a few typos corrected, added a new subsection.
ApJ in pres
Simultaneous Swift and REM monitoring of the blazar PKS0537-441 in 2005
The blazar PKS0537-441 has been observed by Swift between the end of 2004 and
November 2005. The BAT monitored it recurrently for a total of 2.7 Ms, and the
XRT and UVOT pointed it on seven occasions for a total of 67 ks, making it one
of the AGNs best monitored by Swift. The automatic optical and infrared
telescope REM has monitored simultaneously the source at all times. In
January-February 2005 PKS0537-441 has been detected at its brightest in optical
and X-rays: more than a factor of 2 brighter in X-rays and about a factor 60
brighter in the optical than observed in December 2004. The July 2005
observation recorded a fainter X-ray state. The simultaneous optical state,
monitored by both Swift UVOT and REM, is high, and in the VRI bands it is
comparable to what was recorded in early January 2005, before the outburst. In
November 2005, the source subsided both in X-rays and optical to a quiescent
state, having decreased by factors of ~4 and ~60 with respect to the
January-February 2005 outburst, respectively. Our monitoring shows an overall
well correlated optical and X-ray decay. On the shorter time scales (days or
hours), there is no obvious correlation between X-ray and optical variations,
but the former tend to be more pronounced, opposite to what is observed on
monthly time scales. The widely different amplitude of the long term
variability in optical and X-rays is very unusual and makes this observation a
unique case study for blazar activity. The spectral energy distributions are
interpreted in terms of the synchrotron and inverse Compton mechanisms within a
jet where the plasma radiates via internal shocks and the dissipation depends
on the distance of the emitting region from the central engine (abridged).Comment: 24 pages, 7 figures, 3 tables, in press in the Ap
The X-ray Source Population of "The Antennae" Galaxies: X-ray Properties from Chandra and Multiwavelength Associations
[abridged] We investigate the nature of the luminous X-ray source population
detected in a (72 ks) Chandra ACIS-S observation of NGC 4038/39, the Antennae
galaxies. We derive the average X-ray spectral properties of sources in
different luminosity ranges, and we correlate the X-ray positions with radio,
IR, and optical HST data. The X-ray sources are predominantly associated with
young stellar clusters, indicating that they belong to the young stellar
population. Based on both their co-added X-ray spectrum, and on the lack of
associated radio emission, we conclude that the Ultra Luminous X-ray sources
(ULXs), with Lx>10^{39} erg\s, are not young compact Supernova Remnants (SNR),
but accretion binaries. While their spectrum is consistent with those of ULXs
studied in nearby galaxies, and interpreted as the counterparts of intermediate
mass black-holes (M >10-1000 \msun), comparison with the position of
star-clusters suggests that some of the ULXs may be runaway binaries, thus
suggesting lower-mass binary systems. The co-added spectrum of the sources in
the 3x10^{38}-10^{39} erg\s luminosity range is consistent with those of
Galactic black-hole candidates. These sources are also on average displaced
from neighboring star clusters. The softer spectrum of the less luminous
sources suggests the presence of SNRs or of hot interstellar medium (ISM) in
the Chandra source extraction area. Comparison with HI and CO observations
shows that most sources are detected in the outskirts of large concentrations
of gas. The absorbing columns inferred from these observations would indeed
absorb X-rays up to 5 keV, so there may be several hidden X-ray sources.
Associated with these obscured regions we find 6 sources with heavily absorbed
X-ray spectra and absorption-corrected luminosities in the ULX range.Comment: 18 pages, submitted to Ap
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