102 research outputs found
A spectroscopic look at the gravitationally lensed type Ia SN 2016geu at z=0.409
The spectacular success of type Ia supernovae (SNe Ia) in SN-cosmology is
based on the assumption that their photometric and spectroscopic properties are
invariant with redshift. However, this fundamental assumption needs to be
tested with observations of high-z SNe Ia. To date, the majority of SNe Ia
observed at moderate to large redshifts (0.4 < z < 1.0) are faint, and the
resultant analyses are based on observations with modest signal-to-noise ratios
that impart a degree of ambiguity in their determined properties. In rare cases
however, the Universe offers a helping hand: to date a few SNe Ia have been
observed that have had their luminosities magnified by intervening galaxies and
galaxy clusters acting as gravitational lenses. In this paper we present
long-slit spectroscopy of the lensed SNe Ia 2016geu, which occurred at a
redshift of z=0.409, and was magnified by a factor of ~55 by a galaxy located
at z=0.216. We compared our spectra, which were obtained a couple weeks to a
couple months past peak light, with the spectroscopic properties of
well-observed, nearby SNe Ia, finding that SN 2016geu's properties are
commensurate with those of SNe Ia in the local universe. Based primarily on the
velocity and strength of the Si II 6355 absorption feature, we find that SN
2016geu can be classified as a high-velocity, high-velocity gradient and
"core-normal" SN Ia. The strength of various features (measured though their
pseudo-equivalent widths) argue against SN 2016geu being a faint, broad-lined,
cool or shallow-silicon SN Ia. We conclude that the spectroscopic properties of
SN 2016geu imply that it is a normal SN Ia, and when taking previous results by
other authors into consideration, there is very little, if any, evolution in
the observational properties of SNe Ia up to z~0.4. [Abridged]Comment: 12 pages, 5 figures, 4 tables. Submitted to MNRAS. Comments welcome
Four Years of Realtime GRB Followup by BOOTES-1B (2005-2008)
Four years of BOOTES-1B GRB follow-up history are summarised for the first
time in the form of a table. The successfully followed events are described
case by case.
Further, the data are used to show the GRB trigger rate in Spain on a
per-year basis, resulting in an estimate of 18 triggers and about 51 h of
telescope time per year for real time triggers. These numbers grow to about 22
triggers and 77 h per year if we include also the GRBs observable within 2
hours after the trigger.Comment: 16 pages, Accepted into Proceedings of AstroRob Malaga 200
Polarimetry of the superluminous supernova LSQ14mo: no evidence for significant deviations from spherical symmetry
We present the first polarimetric observations of a Type I superluminous
supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at five different epochs
in the V band, with the observations starting before maximum light and spanning
26 days in the rest frame (z=0.256). During this period, we do not detect any
statistically significant evolution (< 2) in the Stokes parameters. The
average values we obtain, corrected for interstellar polarisation in the
Galaxy, are Q = -0.01% ( 0.15%) and U = - 0.50% ( 0.14%). This low
polarisation can be entirely due to interstellar polarisation in the SN host
galaxy. We conclude that, at least during the period of observations and at the
optical depths probed, the photosphere of LSQ14mo does not present significant
asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c.
Alternatively, it is possible that we may have observed LSQ14mo from a special
viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a
typical SLSN I. Further studies of the polarisation of Type I SLSNe are
required to determine whether the low levels of polarisation are a
characteristic of the entire class and to also study the implications for the
proposed explosion models.Comment: ApJ Letters, 4 Figures, 3 Tables. The previous version was accepted.
This version contains minor modifications to match proofs (as much as
possible
NGC 2770: high supernova rate due to interaction
Galaxies which hosted many core-collapse supernovae (SN) explosions can be
used to study the conditions necessary for the formation of massive stars. NGC
2770 was dubbed a SN factory, because it hosted four core-collapse SNe in 20
years (three type Ib and one type IIn). Its star formation rate (SFR) was
reported not to be enhanced and therefore not compatible with such a high SN
rate. We aim at explaining the high SN rate of NGC 2770. We used archival HI
line data for NGC 2770 and reinterpret the Halpha and optical continuum data.
Even though the continuum-based SFR indicators do not yield high values, the
dust-corrected Halpha luminosity implies a high SFR, consistent with the high
SN rate. Such disparity between the SFR estimators is an indication of recently
enhanced star formation activity, because the continuum indicators trace long
timescale of the order of 100 Myr, unlike the line indicators, which trace
timescales of the order of 10 Myr. Hence, the unique feature of NGC 2770
compared to other galaxies is the fact that it is observed very recently after
the enhancement of the SFR. It also has high dust extinction, E(B-V) above 1
mag. We provide support for the hypothesis that the increased SFR in NGC 2770
is due to the interaction with its companion galaxies. We report an HI bridge
between NGC 2770 and its closest companion and the existence of a total of four
companions within 100 kpc (one identified for the first time). There are no
clear HI concentrations close to the positions of SNe in NGC 2770 such as those
detected for hosts of gamma-ray bursts (GRBs) and broad-lined SNe type Ic
(IcBL). This suggests that the progenitors of type Ib SNe are not born out of
recently accreted atomic gas, as was suggested for GRB and IcBL SN progenitors.Comment: Astronomy & Astrophysics, in press, 8 pages, 3 figures, 1 tabl
EIFIS: a modular extreme integral field spectrograph for the 10.4m GTC
EIFIS (Extreme Integral FIeld Spectrograph) is a modular integral field
spectrograph, based on image slicers, and makes use of new, large format
detectors. The concept is thought to cover the largest possible field of view
while producing spectroscopy over the complete optical range (3 000 - 10 000
\r{A}) at a medium resolving power of about 2400. In the optimal concept, each
module covers a field of view of 38" x 38" with 0.3" spaxels, which is fed into
a double spectrograph with common collimator optics. The blue arm covers the
spectral range between 3000 and 5600 \r{A} and the red arm between 5400 and
10100 \r{A}, allowing for an overlap range. The spectra are imaged onto 9.2k x
9.2k detectors using a double pseudoslit. The proposed design for the 10.4m
Gran Telescopio Canarias uses a total of 6 such modules to cover a total of
2.43 square arcminutes. Here we will present the conceptual design of the
instrument and a feasibility study of the optical and mechanical design of the
spectrographs. We discuss the limitations and alternative designs and its
potential to produce leading edge science in the era of extremely large
telescopes and the James Webb Space Telescope.Comment: Submitted to the Proceedings of the SPIE, Astronomical Telescopes and
Instrumentatio
Recent GRBs observed with the 1.23m CAHA telescope and the status of its upgrade
We report on optical observations of Gamma-Ray Bursts (GRBs) followed up by
our collaboration with the 1.23m telescope located at the Calar Alto
observatory. The 1.23m telescope is an old facility, currently undergoing
upgrades to enable fully autonomous response to GRB alerts. We discuss the
current status of the control system upgrade of the 1.23m telescope. The
upgrade is being done by the ARAE our group, based on members of IAA (Instituto
de Astrofiisica de Andalucia). Currently the ARAE group is responsible to
develop the BOOTES network of robotic telescopes based on the Remote Telescope
System, 2nd Version (RTS2), which controls the available instruments and
interacts with the EPICS database of Calar Alto. Currently the telescope can
run fully autonomously or under observer supervision using RTS2. The fast
reaction response mode for GRB reaction (typically with response times below 3
minutes from the GRB onset) still needs some development and testing. The
telescope is usually operated in legacy interactive mode, with periods of
supervised autonomous runs under RTS2. We show the preliminary results of
several GRBs followed up with observer intervention during the testing phase of
the 1.23m control software upgrade.Comment: 15 pages, 7 figures. Accepted for publication in the Special issue
"Robotic Astronomy" of Advances in Astronomy. It includes two iterations with
the referee
The host-galaxy response to the afterglow of GRB 100901A
For Gamma-Ray Burst 100901A, we have obtained Gemini-North and Very Large
Telescope optical afterglow spectra at four epochs: one hour, one day, three
days and one week after the burst, thanks to the afterglow remaining unusually
bright at late times. Apart from a wealth of metal resonance lines, we also
detect lines arising from fine-structure levels of the ground state of Fe II,
and from metastable levels of Fe II and Ni II at the host redshift (z =
1.4084). These lines are found to vary significantly in time. The combination
of the data and modelling results shows that we detect the fall of the Ni II 4
F9/2 metastable level population, which to date has not been observed. Assuming
that the population of the excited states is due to the UV-radiation of the
afterglow, we estimate an absorber distance of a few hundred pc. This appears
to be a typical value when compared to similar studies. We detect two
intervening absorbers (z = 1.3147, 1.3179). Despite the wide temporal range of
the data, we do not see significant variation in the absorption lines of these
two intervening systems.Comment: 17 pages, 9 figures. Accepted by Monthly Notices of the Royal
Astronomical Society on Jan 11th 201
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