421 research outputs found
Dust-to-metal ratios in damped Lyman-alpha absorbers: Fresh clues to the origins of dust and optical extinction towards gamma-ray bursts
Motivated by the anomalous dust-to-metal ratios derived in the literature for
gamma-ray burst (GRB) damped Lyman-alpha absorbers (DLAs), we measure these
ratios using the dust-depletion pattern observed in UV/optical afterglow
spectra associated with the ISM at the GRB host-galaxy redshifts. Our sample
consists of 20 GRB absorbers and a comparison sample of 72 QSO-DLAs with
redshift 1.2 < z < 4.0 and down to Z = 0.002 Z_Sol metallicities. The
dust-to-metal ratio in QSO- and GRB-DLAs increases both with metallicity and
metal column density, spanning ~10--110% of the Galactic value and pointing to
a non universal dust-to-metal ratio. The low values of dust-to-metal ratio
suggest that low-metallicity systems have lower dust fractions than typical
spiral galaxies and perhaps that the dust in these systems is produced
inefficiently, i.e. by grain growth in the low-metallicity regime with
negligible contribution from supernovae (SNe) and asymptotic giant branch (AGB)
stars. On the other hand, some GRB- and QSO-DLAs show high dust-to-metal ratio
values out to z ~ 4, requiring rapid dust production, such as in SN ejecta, but
also in AGB winds and via grain growth for the highest metallicity systems.
GRB-DLAs overall follow the dust-to-metal-ratio properties of QSO-DLAs, GRBs
probing up to larger column and volume densities. For comparison, the
dust-to-metal ratio that we derive for the SMC and LMC are ~82--100% and ~98%
of the Galactic value, respectively. The literature dust-to-metal ratio of the
low-metallicity galaxy I Zw 18 (< 37%) is consistent with the distribution that
we find. The dust extinction Av increases steeply with the column density of
iron in dust, N(Fe)dust, calculated from relative metal abundances, confirming
that dust extinction is mostly occurring in the host galaxy ISM. Most GRB-DLAs
display log N(Fe)dust > 14.7, above which several QSO-DLAs reveal H2
(abridged).Comment: 14 pages, 9 figures. A&A, in pres
The bumpy light curve of supernova iPTF13z
A Type IIn supernova (SN) is dominated by the interaction of SN ejecta with
the circumstellar medium (CSM). Some SNe IIn (e.g., SN 2006jd) have episodes of
re-brightening ("bumps") in their light curves. We present iPTF13z, a SN IIn
discovered by the intermediate Palomar Transient Factory (iPTF) and
characterised by several bumps in its light curve. We analyse this peculiar
behaviour trying to infer the properties of the CSM and of the SN explosion, as
well as the nature of its progenitor star. We obtained multi-band optical
photometry for over 1000 days after discovery with the P48 and P60 telescopes
at Palomar Observatory. We obtained low-resolution optical spectra in the same
period. We did an archival search for progenitor outbursts. We analyse our
photometry and spectra, and compare iPTF13z to other SNe IIn. A simple
analytical model is used to estimate properties of the CSM. iPTF13z was a SN
IIn showing a light curve with five bumps during its decline phase. The bumps
had amplitudes between 0.4 and 0.9 mag and durations between 20 and 120 days.
The most prominent bumps appeared in all our different optical bands. The
spectra showed typical SN IIn characteristics, with emission lines of H
(with broad component FWHM ~ and narrow
component FWHM ~) and He I, but also with Fe II, Ca II,
Na I D and H P-Cygni profiles (with velocities of ~ ). A pre-explosion outburst was identified lasting days,
with mag around 210 days before discovery. Large, variable
progenitor mass-loss rates (~> 0.01 ) and CSM densities
(~> 10 g cm) are derived. We suggest that the light curve bumps
of iPTF13z arose from SN ejecta interacting with denser regions in the CSM,
possibly produced by the eruptions of a luminous blue variable star.Comment: Version 2: Update to match published paper. 21 pages, 14 figures,
abstract abridged to comply with arXiv length limit. In version 1 of the
paper on arXiv, Table 3 had some erroneous entries. Table 3 is now corrected
and available via VizieR. Version 1 comment: Accepted for publication in
Astronomy & Astrophysics (24 pages, 14 figures, abstract abridged by 20 % not
to exceed the arXiv length limit
Far-UV HST Spectroscopy of an Unusual Hydrogen-poor Superluminous Supernova: SN2017egm
SN2017egm is the closest (z = 0.03) H-poor superluminous supernova (SLSN-I) detected to date, and a rare example of an SLSN-I in a massive, metal-rich galaxy. We present the HST UV and optical spectra covering 1000–5500 Å, taken at +3 day relative to the peak. Our data reveal two absorption systems at redshifts matching the host galaxy NGC 3191 (z = 0.0307) and its companion galaxy (z = 0.0299) 73'' apart. Weakly damped Lyα absorption lines are detected at these two redshifts, with H i column densities of (3.0 ± 0.8) × 1019 and (3.7 ± 0.9) × 1019 cm−2, respectively. This is an order of magnitude smaller than the H i column densities in the disks of nearby galaxies (>1010 M ⊙) and suggests that SN2017egm is on the near side of NGC 3191 and has a low host extinction (E(B − V) ~ 0.007). Using unsaturated metal absorption lines, we find that the host of SN2017egm probably has a solar or higher metallicity and is unlikely to be a dwarf companion to NGC 3191. Comparison of early-time UV spectra of SN2017egm, Gaia16apd, iPTF13ajg, and PTF12dam finds that the continuum at λ > 2800 Å is well fit by a blackbody, whereas the continuum at λ < 2800 Å is considerably below the model. The degree of UV suppression varies from source to source, with the 1400–2800 Å continuum flux ratio of 1.5 for Gaia16apd and 0.4 for iPTF13ajg. This cannot be explained by the differences in magnetar power or blackbody temperature. Finally, the UV spectra reveal a common set of seven broad absorption features and their equivalent widths are similar (within a factor of 2) among the four events
Time-dependent excitation and ionization modelling of absorption-line variability due to GRB 080310
We model the time-variable absorption of FeII, FeIII, SiII, CII and CrII
detected in UVES spectra of GRB 080310, with the afterglow radiation exciting
and ionizing the interstellar medium in the host galaxy at a redshift of
z=2.42743. To estimate the rest-frame afterglow brightness as a function of
time, we use a combination of the optical VRI photometry obtained by the
RAPTOR-T telescope array -- which are presented in this paper -- and Swift's
X-Ray Telescope observations. Excitation alone, which has been successfully
applied for a handful of other GRBs, fails to describe the observed
column-density evolution in the case of GRB 080310. Inclusion of ionization is
required to explain the column-density decrease of all observed FeII levels
(including the ground state 6D9/2) and increase of the FeIII 7S3 level. The
large population of ions in this latter level (up to 10% of all FeIII) can only
be explained through ionization of FeII, whereby a large fraction of the
ionized FeII ions -- we calculate 31% using the Flexible Atomic (FAC) and Cowan
codes -- initially populate the 7S3 level of FeIII rather than the ground
state. This channel for producing a significant FeIII 7S3 level population may
be relevant for other objects in which absorption lines from this level -- the
UV34 triplet -- are observed, such as BAL quasars and Eta Carinae. This
provides conclusive evidence for time-variable ionization in the circumburst
medium, which to date has not been convincingly detected. However, the best-fit
distance of the neutral absorbing cloud to the GRB is 200--400 pc, i.e. similar
to GRB-absorber distance estimates for GRBs without any evidence for
ionization. We find that the presence of time-varying ionization in GRB 080310
is likely due to a combination of the super-solar iron abundance ([Fe/H]=+0.2)
and the low HI column density (log N(HI)=18.7). [abridged]Comment: 14 pages, 6 figures; accepted for publication in A&A (on August 8,
2012
Interaction-powered supernovae: Rise-time vs. peak-luminosity correlation and the shock-breakout velocity
Interaction of supernova (SN) ejecta with the optically thick circumstellar
medium (CSM) of a progenitor star can result in a bright, long-lived shock
breakout event. Candidates for such SNe include Type IIn and superluminous SNe.
If some of these SNe are powered by interaction, then there should be a
relation between their peak luminosity, bolometric light-curve rise time, and
shock-breakout velocity. Given that the shock velocity during shock breakout is
not measured, we expect a correlation, with a significant spread, between the
rise time and the peak luminosity of these SNe. Here, we present a sample of 15
SNe IIn for which we have good constraints on their rise time and peak
luminosity from observations obtained using the Palomar Transient Factory. We
report on a possible correlation between the R-band rise time and peak
luminosity of these SNe, with a false-alarm probability of 3%. Assuming that
these SNe are powered by interaction, combining these observables and theory
allows us to deduce lower limits on the shock-breakout velocity. The lower
limits on the shock velocity we find are consistent with what is expected for
SNe (i.e., ~10^4 km/s). This supports the suggestion that the early-time light
curves of SNe IIn are caused by shock breakout in a dense CSM. We note that
such a correlation can arise from other physical mechanisms. Performing such a
test on other classes of SNe (e.g., superluminous SNe) can be used to rule out
the interaction model for a class of events.Comment: Accepted to ApJ, 6 page
Light curves of hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
We investigate the light-curve properties of a sample of 26 spectroscopically
confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar
Transient Factory (PTF) survey. These events are brighter than SNe Ib/c and SNe
Ic-BL, on average, by about 4 and 2~mag, respectively. The peak absolute
magnitudes of SLSNe-I in rest-frame band span ~mag, and these peaks are not powered by radioactive Ni,
unless strong asymmetries are at play. The rise timescales are longer for SLSNe
than for normal SNe Ib/c, by roughly 10 days, for events with similar decay
times. Thus, SLSNe-I can be considered as a separate population based on
photometric properties. After peak, SLSNe-I decay with a wide range of slopes,
with no obvious gap between rapidly declining and slowly declining events. The
latter events show more irregularities (bumps) in the light curves at all
times. At late times, the SLSN-I light curves slow down and cluster around the
Co radioactive decay rate. Powering the late-time light curves with
radioactive decay would require between 1 and 10 of Ni masses.
Alternatively, a simple magnetar model can reasonably fit the majority of
SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay
of Co, up to days from explosion. The resulting spin values do
not correlate with the host-galaxy metallicities. Finally, the analysis of our
sample cannot strengthen the case for using SLSNe-I for cosmology.Comment: 120 pages, 48 figures, 78 tables. ApJ in pres
Effects of a localized beam on the dynamics of excitable cavity solitons
We study the dynamical behavior of dissipative solitons in an optical cavity
filled with a Kerr medium when a localized beam is applied on top of the
homogeneous pumping. In particular, we report on the excitability regime that
cavity solitons exhibits which is emergent property since the system is not
locally excitable. The resulting scenario differs in an important way from the
case of a purely homogeneous pump and now two different excitable regimes, both
Class I, are shown. The whole scenario is presented and discussed, showing that
it is organized by three codimension-2 points. Moreover, the localized beam can
be used to control important features, such as the excitable threshold,
improving the possibilities for the experimental observation of this
phenomenon.Comment: 9 Pages, 12 figure
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