Recent Publications
10 most recent research publications
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ADS (authors="STEEGHS, D")
We present the semi-analytical light curve modelling of 13 supernovae
associated with gamma-ray bursts (GRB-SNe) along with two relativistic
broad-lined (Ic-BL) SNe without GRBs association (SNe 2009bb and
2012ap), considering millisecond magnetars as central-engine-based power
sources for these events. The bolometric light curves of all 15 SNe in
our sample are well-regenerated utilising a $\chi^2-$minimisation code,
$\texttt{MINIM}$, and numerous parameters are constrained. The median
values of ejecta mass ($M_{\textrm{ej}}$), magnetar's initial spin
period ($P_\textrm{i}$) and magnetic field ($B$) for GRB-SNe are
determined to be $\approx$ 5.2 M$_\odot$, 20.5 ms and 20.1 $\times$
10$^{14}$ G, respectively. We leverage machine learning (ML) algorithms
to comprehensively compare the 3-dimensional parameter space
encompassing $M_{\textrm{ej}}$, $P_\textrm{i}$, and $B$ for GRB-SNe
determined herein to those of H-deficient superluminous SNe (SLSNe-I),
fast blue optical transients (FBOTs), long GRBs (LGRBs), and short GRBs
(SGRBs) obtained from the literature. The application of unsupervised ML
clustering algorithms on the parameters $M_{\textrm{ej}}$,
$P_\textrm{i}$, and $B$ for GRB-SNe, SLSNe-I, and FBOTs yields a
classification accuracy of $\sim$95%. Extending these methods to
classify GRB-SNe, SLSNe-I, LGRBs, and SGRBs based on $P_\textrm{i}$ and
$B$ values results in an accuracy of $\sim$84%. Our investigations show
that GRB-SNe and relativistic Ic-BL SNe presented in this study occupy
different parameter spaces for $M_{\textrm{ej}}$, $P_\textrm{i}$, and
$B$ than those of SLSNe-I, FBOTs, LGRBs and SGRBs. This indicates that
magnetars with different $P_\textrm{i}$ and $B$ can give birth to
distinct types of transients.
MAXI J1348-630 is a low mass X-ray binary discovered in 2019 during a
bright outburst. During this event, the system experienced both hard and
soft states following the standard evolution. We present multi-epoch
optical and near-infrared spectroscopy obtained with X-shooter at the
Very Large Telescope. Our dataset includes spectra taken during the
brightest phases of the outburst as well as the decay towards
quiescence. We study the evolution of the main emission lines, paying
special attention to the presence of features commonly associated with
accretion disc winds, such as blueshifted absorptions, broad emission
line wings and flat-top profiles. We find broad emission line wings in
Hα during the hard-to-soft transition and blueshifted absorption
troughs at ∼ ‒ 500 km s‒1 in Hβ, He
I-5876, Hα and Paβ during the bright soft-intermediate state.
In addition, flat-top profiles are seen throughout the outburst. We
interpret these observables as signatures of a cold (i.e.,
optical-to-infrared) accretion disc wind present in the system. We
discuss the properties of the wind and compare them with those seen in
other X-ray transients. In particular, the wind velocity that we observe
is low when compared to those of other systems, which might be a direct
consequence of the relatively low binary inclination, as suggested by
several observables. This study strengthens the hypothesis that cold
winds are a common feature in low mass X-ray binaries and that they can
also be detected in low inclination objects via high-quality optical and
infrared spectroscopy.
The discovery of the electromagnetic counterpart to the binary neutron
star (NS) merger GW170817 has opened the era of gravitational-wave
multimessenger astronomy. Rapid identification of the optical/infrared
kilonova enabled a precise localization of the source, which paved the
way to deep multiwavelength follow-up and its myriad of related science
results. Fully exploiting this new territory of exploration requires the
acquisition of electromagnetic data from samples of NS mergers and other
gravitational-wave sources. After GW170817, the frontier is now to map
the diversity of kilonova properties and provide more stringent
constraints on the Hubble constant, and enable new tests of fundamental
physics. The Vera C. Rubin Observatory's Legacy Survey of Space and Time
can play a key role in this field in the 2020s, when an improved network
of gravitational-wave detectors is expected to reach a sensitivity that
will enable the discovery of a high rate of merger events involving NSs
(~tens per year) out to distances of several hundred megaparsecs. We
design comprehensive target-of-opportunity observing strategies for
follow-up of gravitational-wave triggers that will make the Rubin
Observatory the premier instrument for discovery and early
characterization of NS and other compact-object mergers, and yet unknown
classes of gravitational-wave events.
The Gravitational-wave Optical Transient Observer (GOTO) is an array of
wide-field optical telescopes, designed to exploit new discoveries from
the next generation of gravitational wave detectors (LIGO, Virgo, and
KAGRA), study rapidly evolving transients, and exploit multimessenger
opportunities arising from neutrino and very high energy gamma-ray
triggers. In addition to a rapid response mode, the array will also
perform a sensitive, all-sky transient survey with few day cadence. The
facility features a novel, modular design with multiple 40-cm wide-field
reflectors on a single mount. In 2017 June, the GOTO collaboration
deployed the initial project prototype, with 4 telescope units, at the
Roque de los Muchachos Observatory (ORM), La Palma, Canary Islands.
Here, we describe the deployment, commissioning, and performance of the
prototype hardware, and discuss the impact of these findings on the
final GOTO design. We also offer an initial assessment of the science
prospects for the full GOTO facility that employs 32 telescope units
across two sites.
Despite being bright (V ≃ 11.8) and nearby (d = 212 pc) ASAS
J071404+7004.3 has only recently been identified as a nova-like
cataclysmic variable. We present time-resolved optical spectroscopy
obtained at the Isaac Newton and the Hiltner and McGraw-Hill Telescopes,
together with Swift X-ray and ultraviolet observations. We combined
these with TESS photometry and find a period of 3.28 h and a mass
transfer rate of $4\!-\!9\times 10^{-9}\, {\mathrm{M_{\odot }\,
yr}^{-1}}$. Historical photometry shows at least one low state
establishing the system as a VY Scl star. Our high-cadence spectroscopy
also revealed rapidly changing winds emanating from the accretion disc.
We have modelled these using the Monte Carlo PYTHON code and shown that
all the emission lines could emanate from the wind - which would explain
the lack of double-peaked lines in such systems. In passing, we discuss
the effect of variability on the position of cataclysmic variables in
the Gaia Hertzsprung-Russell diagram.