216 research outputs found
Type IIP Supernova 2009kf: Explosion Driven by Black Hole Accretion?
Unusually bright type IIP supernova (SN) 2009kf is studied employing the
hydrodynamic modelling. We derived optimal values of the ejecta mass of 28.1
Msun, explosion energy of 2.2x10^{52} erg, and presupernova radius of 2x10^3
Rsun assuming that Ni-56 mass is equal to the upper limit of 0.4 Msun. We
analyzed effects of the uncertainties in the extinction and Ni-56 mass and
concluded that both the ejecta mass and explosion energy cannot be
significantly reduced compared with the optimal values. The huge explosion
energy of SN 2009kf indicates that the explosion is caused by the same
mechanism which operates in energetic SNe Ibc (hypernovae), i.e., via a rapid
disk accretion onto black hole. The ejecta mass combined with the black hole
mass and the mass lost by stellar wind yields the progenitor mass of about 36
Msun. We propose a scenario in which massive binary evolution might result in
the SN 2009kf event.Comment: 14 pages, 4 figures, 1 table, accepted for publication in ApJ Letter
Supernova 2009kf: An Ultraviolet Bright Type IIP Supernova Discovered with Pan-STARRS 1 and GALEX
We present photometric and spectroscopic observations of a luminous Type IIP Supernova (SN) 2009kf discovered by the Pan-STARRS 1 (PS1) survey and also detected by the Galaxy Evolution Explorer. The SN shows a plateau in its optical and bolometric light curves, lasting approximately 70 days in the rest frame, with an absolute magnitude of M_V = -18.4 mag. The P-Cygni profiles of hydrogen indicate expansion velocities of 9000 km s^(-1) at 61 days after discovery which is extremely high for a Type IIP SN. SN 2009kf is also remarkably bright in the near-ultraviolet (NUV) and shows a slow evolution 10-20 days after optical discovery. The NUV and optical luminosity at these epochs can be modeled with a blackbody with a hot effective temperature (T ~ 16,000 K) and a large radius (R ~ 1 × 10^(15) cm). The bright bolometric and NUV luminosity, the light curve peak and plateau duration, the high velocities, and temperatures suggest that 2009kf is a Type IIP SN powered by a larger than normal explosion energy. Recently discovered high-z SNe (0.7 < z < 2.3) have been assumed to be IIn SNe, with the bright UV luminosities due to the interaction of SN ejecta with a dense circumstellar medium. UV-bright SNe similar to SN 2009kf could also account for these high-z events, and its absolute magnitude M_(NUV) = -21.5 ± 0.5 mag suggests such SNe could be discovered out to z ~ 2.5 in the PS1 survey
VLT Spectropolarimetry of the optical transient in NGC300. Evidence for asymmetry in the circumstellar dust
AIMS: The main goal of this work is to study possible signs of asymmetry in
the bright optical transient in NGC300, with the aim of getting independent
information on the explosion mechanism, the progenitor star and its
circumstellar environment.
METHODS: Using VLT-FORS1 we have obtained low-resolution optical linear
spectropolarimetry of NGC300 OT2008-1 on two epochs, 48 and 55 days after the
discovery, covering the spectral range 3600--9330A.
RESULTS: The data show a continuum polarization at a very significant level.
At least two separate components are identified. The first is characterized by
a strong wavelength dependency and a constant position angle (68.6+/-0.3
degrees), which is parallel to the local spiral arm of the host galaxy. The
second shows a completely different position angle (151.3+/-0.4) and displays a
mild but statistically significant evolution between the two epochs. While the
former is identified as arising in the interstellar dust associated with
NGC300, the latter is most likely due to continuum polarization by dust
scattering in the circumstellar environment. No line depolarization is detected
in correspondence of the most intense emission lines, disfavoring electron
scattering as the source of intrinsic polarization. This implies a very small
deviation from symmetry in the continuum-forming region. Given the observed
level of intrinsic polarization, the transient must be surrounded by a
significant amount of dust (>4x10^-5 Msun), asymmetrically distributed within a
few thousand AU. This most likely implies that one or more asymmetric outflow
episodes took place during the past history of the progenitor.Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 16
figure
GW170817: implications for the local kilonova rate and for surveys from ground-based facilities
We compute the local rate of events similar to GRB 170817A, which has been
recently found to be associated with a kilonova (KN) outburst. Our analysis
finds an observed rate of such events of R
Gpcyr. After comparing at their face values this density of sGRB
outbursts with the much higher density of Binary Neutron Star (BNS) mergers of
1540 Gpcyr, estimated by LIGO-Virgo
collaboration, one can conclude, admittedly with large uncertainty that either
only a minor fraction of BNS mergers produces sGRB/KN events or the sGRBs
associated with BNS mergers are beamed and observable under viewing angles as
large as . Finally we provide preliminary estimates
of the number of sGRB/KN events detected by future surveys carried out with
present/future ground-based/space facilities, such as LSST, VST, ZTF, SKA and
THESEUS.Comment: MNRAS accepted, 6 pages, 1 figur
Explosion of a massive, He-rich star at z=0.16
We present spectroscopic and photometric data of the peculiar SN 2001gh,
discovered by the 'Southern inTermediate Redshift ESO Supernova Search'
(STRESS) at a redshift z=0.16. SN 2001gh has relatively high luminosity at
maximum (M_B = -18.55 mag), while the light curve shows a broad peak. An
early-time spectrum shows an almost featureless, blue continuum with a few weak
and shallow P-Cygni lines that we attribute to HeI. HeI lines remain the only
spectral features visible in a subsequent spectrum, obtained one month later. A
remarkable property of SN 2001gh is the lack of significant spectral evolution
over the temporal window of nearly one month separating the two spectra. In
order to explain the properties of SN 2001gh, three powering mechanism are
explored, including radioactive decays of a moderately large amount of 56Ni,
magnetar spin-down, and interaction of SN ejecta with circumstellar medium. We
favour the latter scenario, with a SN Ib wrapped in a dense, circumstellar
shell. The fact that no models provide an excellent fit with observations,
confirms the troublesome interpretation of the nature of SN 2001gh. A rate
estimate for SN 2001gh-like event is also provided, confirming the intrinsic
rarity of these objects.Comment: 11 pages, 8 figures, 3 tables. Accepted by MNRA
The Type IIP SN 2007od in UGC 12846: from a bright maximum to dust formation in the nebular phase
Ultraviolet (UV), optical and near infrared (NIR) observations of the type
IIP supernova (SN) 2007od are presented, covering from the maximum light to the
late phase, allowing to investigate in detail different physical phenomena in
the expanding ejecta. These data turn this object into one of the most peculiar
IIP ever studied. The early light curve of SN 2007od is similar to that of a
bright IIPs with a short plateau, a bright peak (MV = -18 mag), but a very
faint optical light curve at late time. However, with the inclusion of mid
infrared (MIR) observations during the radioactive decay we have estimate a
M(56Ni) ~ 2\times10^-2 M\odot. Modeling the bolometric light curve, ejecta
expansion velocities and black-body temperature, we estimate a total ejected
mass was 5 - 7.5 M\odot with a kinetic energy of at least 0.5 \times 10^51 erg.
The early spectra reveal a boxy H{\alpha} profile and high velocities features
of the Balmer series that suggest interaction between the ejecta and a close
circum-stellar matter (CSM). SN 2007od may be, therefore, an intermediate case
between a Type IIn SN and a typical Type IIP SN. Also late spectra show a clear
evidence of CSM and the presence of dust formed inside the ejecta. The episodes
of mass loss short before explosion, the bright plateau, along with the
relatively small amount of 56Ni and the faint [O I] observed in the nebular
spectra are consistent with a super-asympthotic giant branch (super-AGB)
progenitor (M~9.7 - 11 M\odot).Comment: V2, some test added and three figures changed from the first version.
21 pages, 18 figures, accepted for publication in MNRAS on May 24, 201
Moderately Luminous type II Supernovae
Core-collapse Supernovae (CC-SNe) descend from progenitors more massive than
about 8 Msun. Because of the young age of the progenitors, the ejecta may
eventually interact with the circumstellar medium (CSM) via highly energetic
processes detectable in the radio, X-ray, ultraviolet (UV) and, sometimes, in
the optical domains. In this paper we present ultraviolet, optical and near
infrared observations of five type II SNe, namely SNe 2009dd, 2007pk, 2010aj,
1995ad, and 1996W. Together with few other SNe they form a group of moderately
luminous type II events. We collected photometry and spectroscopy with several
telescopes in order to construct well-sampled light curves and spectral
evolutions from the photospheric to the nebular phases. Both photometry and
spectroscopy indicate a degree of heterogeneity in this sample. The light
curves have luminous peak magnitudes (). The ejected
masses of ^56\ni for three SNe span a wide range of values
(MsunM(\ni)Msun), while for a fourth
(SN2010aj) we could determine a stringent upper limit (Msun).
Clues of interaction, such as the presence of high velocity (HV) features of
the Balmer lines, are visible in the photospheric spectra of SNe 2009dd and
1996W. For SN2007pk we observe a spectral transition from a type IIn to a
standard type II SN. Modelling the observations of SNe 2009dd, 2010aj and
1995ad with radiation hydrodynamics codes, we infer kinetic plus thermal
energies of about 0.2-0.5 foe, initial radii of 2-5 cm and
ejected masses of 5.0-9.5 Msun. These values suggest moderate-mass,
super-asymptotic giant branch (SAGB) or red super-giants (RSG) stars as SN
precursors, in analogy with other luminous type IIP SNe 2007od and 2009bw.Comment: 28 pages, 27 fig, accepted by A&A, 3 pages of online material,
abstract abridged. revised significantly with respect to the previous versio
The Unusually Luminous Extragalactic Nova SN 2010U
We present observations of the unusual optical transient SN 2010U, including
spectra taken 1.03 days to 15.3 days after maximum light that identify it as a
fast and luminous Fe II type nova. Our multi-band light curve traces the fast
decline (t_2 = 3.5 days) from maximum light (M_V = -10.2 mag), placing SN 2010U
in the top 0.5% of the most luminous novae ever observed. We find typical
ejecta velocities of approximately 1100 km/s and that SN 2010U shares many
spectral and photometric characteristics with two other fast and luminous Fe II
type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme
luminosity of this nova, the maximum magnitude vs. rate of decline relationship
indicates a massive white dwarf progenitor with a low pre-outburst accretion
rate. However, this prediction is in conflict with emerging theories of nova
populations, which predict that luminous novae from massive white dwarfs should
preferentially exhibit an alternate spectral type (He/N) near maximum light.Comment: 16 pages, 16 figures. Submitted to the Astrophysical Journa
Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field
The analysis of the variability of active galactic nuclei (AGNs) at different
wavelengths and the study of possible correlations among different spectral
windows are nowadays a major field of inquiry. Optical variability has been
largely used to identify AGNs in multivisit surveys. The strength of a
selection based on optical variability lies in the chance to analyze data from
surveys of large sky areas by ground-based telescopes. However the
effectiveness of optical variability selection, with respect to other
multiwavelength techniques, has been poorly studied down to the depth expected
from next generation surveys. Here we present the results of our r-band
analysis of a sample of 299 optically variable AGN candidates in the VST survey
of the COSMOS field, counting 54 visits spread over three observing seasons
spanning > 3 yr. This dataset is > 3 times larger in size than the one
presented in our previous analysis (De Cicco et al. 2015), and the observing
baseline is ~8 times longer. We push towards deeper magnitudes (r(AB) ~23.5
mag) compared to past studies; we make wide use of ancillary multiwavelength
catalogs in order to confirm the nature of our AGN candidates, and constrain
the accuracy of the method based on spectroscopic and photometric diagnostics.
We also perform tests aimed at assessing the relevance of dense sampling in
view of future wide-field surveys. We demonstrate that the method allows the
selection of high-purity (> 86%) samples. We take advantage of the longer
observing baseline to achieve great improvement in the completeness of our
sample with respect to X-ray and spectroscopically confirmed samples of AGNs
(59%, vs. ~15% in our previous work), as well as in the completeness of
unobscured and obscured AGNs. The effectiveness of the method confirms the
importance to develop future, more refined techniques for the automated
analysis of larger datasets.Comment: 21 pages, 10 figures; accepted for publication in A&
Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO
We present the identification of the progenitor of the Type IIP SN 2012ec in
archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of
the progenitor are further constrained by non-detections in pre-explosion WFPC2
F450W and F606W images. We report a series of early photometric and
spectroscopic observations of SN 2012ec. The r'-band light curve shows a
plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN
1999em, with the expansion velocity measured at Halpha absorption minimum of
-11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic
evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days
post-explosion (<6d). We derive a luminosity for the progenitor, in comparison
with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an
initial mass range of 14-22Msun. This is the first SN with an identified
progenitor to be followed by the Public ESO Spectroscopic Survey of Transient
Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte
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