735 research outputs found
Follow-up of X-ray transients detected by SWIFT with COLORES using the BOOTES network
The Burst Observer and Optical Transient Exploring System (BOOTES) is a
network of telescopes that allows the continuous monitoring of transient
astrophysical sources. It was originally devoted to the study of the optical
emission from gamma-ray bursts (GRBs) that occur in the Universe. In this paper
we show the initial results obtained using the spectrograph COLORES (mounted on
BOOTES-2), when observing compact objects of diverse nature.Comment: 6 pages, 2 figues, to appear in "Swift: 10 years of discovery",
Proceedings of Scienc
Invasion Through Quantitative Effects: Intense Shade Drives Native Decline and Invasive Success
The effects of invasive nonnative species on community composition are well documented. However, few studies have determined the mechanisms by which invaders drive these changes. The literature indicates that many nonnative plant species alter light availability differently than natives in a given community, suggesting that shading may be such a mechanism. We compared light quantity (photosynthetically active radiation, PAR) and quality (red : far-red ratio, R:Fr) in riparian reaches heavily invaded by a nonnative tree (Acer platanoides) to that in an uninvaded forest and experimentally tested the effects of our measured differences in PAR and R:Fr on the survival, growth, and biomass allocation of seedlings of the dominant native species and Acer platanoides. Light conditions representative of the understory of Acer platanoides-invaded forest decreased survival of the native maple Acer glabrum by 28%; Amelanchier alnifolia by 32%; Betula occidentalis by 55%; Elymus glaucus by 46%; and Sorbus aucuparia by 52%, relative to seedlings growing in PAR similar to that of native understories. In contrast, Acer platanoides and the native shrub Symphoricarpos albus were not affected by reductions in PAR.
Acer platanoides seedlings and saplings are uniquely adapted to shade relative to native species. Acer platanoides was the only species tested that decreased allocation to roots relative to shoots in the invaded forest vs. the native forest light conditions. Therefore it was the only species to demonstrate an adaptive response to the particular light environment associated with Acer platanoides invasion as predicted by optimal partitioning theory.
The profound change in light quantity associated with Acer platanoides canopies appears to act as an important driver of native suppression and conspecific success in invaded riparian communities. Further research is necessary to determine whether the effect of nonnative plant-driven changes on light quantity and quality is a widespread mechanism negatively affecting resident species and facilitating invasion by nonnatives
INITIAL FOLLOW-UP OF OPTICAL TRANSIENTS WITH COLORES USING THE BOOTES NETWORK
The Burst Observer and Optical Transient Exploring System (BOOTES) is a network of telescopes that allows the continuous monitoring of transient astrophysical sources. It was originally devoted to the study of the optical emissions from gamma-raybursts (GRBs) that occur in the Universe. In this paper we show the initial results obtained using the spectrograph COLORES (mounted on BOOTES-2), when observing optical transients (OTs) of a diverse nature
The Host Galaxy and Optical Light Curve of the Gamma-Ray Burst GRB 980703
We present deep HST/STIS and ground-based photometry of the host galaxy of
the gamma-ray burst GRB 980703 taken 17, 551, 710, and 716 days after the
burst. We find that the host is a blue, slightly over-luminous galaxy with
V_gal = 23.00 +/- 0.10, (V-R)_gal = 0.43 +/- 0.13, and a centre that is
approximately 0.2 mag bluer than the outer regions of the galaxy. The galaxy
has a star-formation rate of 8-13 M_sun/yr, assuming no extinction in the host.
We find that the galaxy is best fit by a Sersic R^(1/n) profile with n ~= 1.0
and a half-light radius of 0.13 arcsec (= 0.72/h_100 proper kpc). This
corresponds to an exponential disk with a scale radius of 0.22 arcsec (=
1.21/h_100 proper kpc). Subtracting a fit with elliptical isophotes leaves
large residuals, which suggests that the host galaxy has a somewhat irregular
morphology, but we are unable to connect the location of GRB 980703 with any
special features in the host. The host galaxy appears to be a typical example
of a compact star forming galaxy similar to those found in the Hubble Deep
Field North. The R-band light curve of the optical afterglow associated with
this gamma-ray burst is consistent with a single power-law decay having a slope
of alpha = -1.37 +/- 0.14. Due to the bright underlying host galaxy the late
time properties of the light-curve are very poorly constrained. The decay of
the optical light curve is consistent with a contribution from an underlying
Type Ic supernova like SN1998bw, or a dust echo, but such contributions cannot
be securely established.Comment: 9 pages, 5 figures, LaTeX using A&A Document Class v4.05, to appear
in A&
The short-duration GRB 050724 host galaxy in the context of the long-duration GRB hosts
We report optical and near-infrared broad band observations of the
short-duration GRB 050724 host galaxy, used to construct its spectral energy
distribution (SED). Unlike the hosts of long-duration gamma-ray bursts (GRBs),
which show younger stellar populations, the SED of the GRB 050724 host galaxy
is optimally fitted with a synthetic elliptical galaxy template based on an
evolved stellar population (age ~2.6 Gyr). The SED of the host is difficult to
reproduce with non-evolving metallicity templates. In contrast, if the short
GRB host galaxy metallicity enrichment is considered, the synthetic templates
fit the observed SED satisfactorily. The internal host extinction is low (A_v
\~< 0.4 mag) so it cannot explain the faintness of the afterglow. This short
GRB host galaxy is more massive (~5x10^10 Mo) and luminous (~1.1 L*) than most
of the long-duration GRB hosts. A statistical comparison based on the ages of
short- and long-duration GRB host galaxies strongly suggests that
short-duration GRB hosts contain, on average, older progenitors. These findings
support a different origin for short- and long-duration GRBs.Comment: A&A in pres
The optical/near-IR spectral energy distribution of the GRB 000210 host galaxy
We report on UBVRIZJsHKs-band photometry of the dark GRB 000210 host galaxy.
Fitting a grid of spectral templates to its Spectral Energy Distribution (SED),
we derived a photometric redshift (z=0.842\+0.0540.042) which is in excellent
agreement with the spectroscopic one (z=0.8463+/-0.0002; Piro et al. 2002). The
best fit to the SED is obtained with a blue starburst template with an age of
0.181\+0.0370.026 Gyr. We discuss the implications of the inferred low value of
Av and the age of the dominant stellar population for the non detection of the
GRB 000210 optical afterglow.Comment: 4 pages, 1 figure, contribution to the Rome 2002 GRB worksho
The central engine of GRB 130831A and the energy breakdown of a relativistic explosion
Gamma-ray bursts (GRBs) are the most luminous explosions in the universe, yet
the nature and physical properties of their energy sources are far from
understood. Very important clues, however, can be inferred by studying the
afterglows of these events. We present optical and X-ray observations of GRB
130831A obtained by Swift, Chandra, Skynet, RATIR, Maidanak, ISON, NOT, LT and
GTC. This burst shows a steep drop in the X-ray light-curve at s
after the trigger, with a power-law decay index of . Such a rare
behaviour cannot be explained by the standard forward shock (FS) model and
indicates that the emission, up to the fast decay at s, must be of
"internal origin", produced by a dissipation process within an
ultrarelativistic outflow. We propose that the source of such an outflow, which
must produce the X-ray flux for day in the cosmological rest frame,
is a newly born magnetar or black hole. After the drop, the faint X-ray
afterglow continues with a much shallower decay. The optical emission, on the
other hand, shows no break across the X-ray steep decrease, and the late-time
decays of both the X-ray and optical are consistent. Using both the X-ray and
optical data, we show that the emission after s can be explained
well by the FS model. We model our data to derive the kinetic energy of the
ejecta and thus measure the efficiency of the central engine of a GRB with
emission of internal origin visible for a long time. Furthermore, we break down
the energy budget of this GRB into the prompt emission, the late internal
dissipation, the kinetic energy of the relativistic ejecta, and compare it with
the energy of the associated supernova, SN 2013fu.Comment: Accepted for publication by MNRAS. 21 pages, 3 figures, 8 tables.
Extra table with magnitudes in the sourc
A multi-colour study of the dark GRB 000210 host galaxy and its environment
We present UBVRIZJsHKs broad band photometry of the host galaxy of the dark
gamma-ray burst (GRB) of February 10, 2000. These observations represent the
most exhaustive photometry given to date of any GRB host galaxy. A grid of
spectral templates have been fitted to the Spectral Energy Distribution (SED)
of the host. The derived photometric redshift is z=0.842^+0.054_-0.042, which
is in excellent agreement with the spectroscopic redshift (z=0.8463+/-0.0002)
proposed by Piro et al. (2002) based on a single emission line. Furthermore, we
have determined the photometric redshift of all the galaxies in an area of
6'x6' around the host galaxy, in order to check for their overdensity in the
environment of the host. We find that the GRB 000210 host galaxy is a
subluminous galaxy (L ~ 0.5+/-0.2 L*), with no companions above our detection
threshold of 0.18+/-0.06 L*. Based on the restframe ultraviolet flux a star
formation rate of 2.1+/-0.2 Solar Masses per year is estimated. The best fit to
the SED is obtained for a starburst template with an age of 0.181^+0.037_-0.026
Gyr and a very low extinction (Av~0). We discuss the implications of the
inferred low value of Av and the age of the dominant stellar population for the
non detection of the GRB 000210 optical afterglow.Comment: 10 pages with 4 encapsulated PostScript figures included. Accepted
for publication in Astronomy & Astrophysic
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