33 research outputs found
The Broad-lined Type Ic SN 2003jd
The results of a world-wide coordinated observational campaign on the
broad-lined Type Ic SN 2003jd are presented. In total, 74 photometric data
points and 26 spectra were collected using 11 different telescopes. SN 2003jd
is one of the most luminous SN Ic ever observed. A comparison with other Type
Ic supernovae (SNe Ic) confirms that SN 2003jd represents an intermediate case
between broad-line events (2002ap, 2006aj), and highly energetic SNe (1997ef,
1998bw, 2003dh, 2003lw), with an ejected mass of M_{ej} = 3.0 +/- 1 Mo and a
kinetic energy of E_{k}(tot) = 7_{-2}^{+3} 10^{51} erg. SN 2003jd is similar to
SN 1998bw in terms of overall luminosity, but it is closer to SNe 2006aj and
2002ap in terms of light-curve shape and spectral evolution. The comparison
with other SNe Ic, suggests that the V-band light curves of SNe Ic can be
partially homogenized by introducing a time stretch factor. Finally, due to the
similarity of SN 2003jd to the SN 2006aj/XRF 060218 event, we discuss the
possible connection of SN 2003jd with a GRB.Comment: 19 pages, 19 figures, Accepted for publication in MNRA
The death of massive stars - I. Observational constraints on the progenitors of type II-P supernovae
We present the results of a 10.5 yr, volume limited (28 Mpc) search for
supernova (SN) progenitor stars. We compile all SNe discovered within this
volume (132, of which 27% are type Ia) and determine the relative rates of each
sub-type from literature studies : II-P (59%), Ib/c (29%), IIb (5%), IIn (4%)
and II-L (3%). Twenty II-P SNe have high quality optical or near-IR
pre-explosion images that allow a meaningful search for the progenitor stars.
In five cases they are clearly red supergiants, one case is unconstrained, two
fall on compact coeval star clusters and the other twelve have no progenitor
detected. We review and update all the available data for the host galaxies
(distance, metallicity and extinction) and determine masses and upper mass
estimates using the STARS stellar evolutionary code and a single consistent
homogeneous method. A maximum likelihood calculation suggests that the minimum
stellar mass for a type II-P to form is m(min)=8.5 +1/-1.5 Msol and the maximum
mass for II-P progenitors is m(max)=16.5 +/- 1.5 Msol, assuming a Salpeter
initial mass function (in the range Gamma = -1.35 +0.3/-0.7). The minimum mass
is consistent with current estimates for white dwarf progenitor masses, but the
maximum mass does not appear consistent with massive star populations. Red
supergiants in the Local Group have masses up to 25Msol and the minimum mass to
produce a Wolf-Rayet star in single star evolution (between solar and LMC
metallicity) is similarly 25-30 Msol. We term this discrepancy the "red
supergiant problem" and speculate that these stars could have core masses high
enough to form black holes and SNe which are too faint to have been detected.
Low luminosity SNe with low 56Ni production seem to arise from explosions of
low mass progenitors near the mass threshold for core-collapse. (abridged).Comment: 37 pages, 9 figs, accepted for publication in MNRA
SN 2004aw: Confirming Diversity of Type Ic Supernovae
Optical and near-infrared observations of the Type Ic supernova (SN) 2004aw
are presented, obtained from day -3 to day +413 with respect to the B-band
maximum. The photometric evolution is characterised by a comparatively slow
post-maximum decline of the light curves. The peaks in redder bands are
significantly delayed relative to the bluer bands, the I-band maximum occurring
8.4 days later than that in B. With an absolute peak magnitude of -18.02 in the
V band the SN can be considered fairly bright, but not exceptional. This also
holds for the U through I bolometric light curve, where SN 2004aw has a
position intermediate between SNe 2002ap and 1998bw. Spectroscopically SN
2004aw provides a link between a normal Type Ic supernova like SN 1994I and the
group of broad-lined SNe Ic. The spectral evolution is rather slow, with a
spectrum at day +64 being still predominantly photospheric. The shape of the
nebular [O I] 6300,6364 line indicates a highly aspherical explosion. Helium
cannot be unambiguously identified in the spectra, even in the near-infrared.
Using an analytical description of the light curve peak we find that the total
mass of the ejecta in SN 2004aw is 3.5-8.0 M_Sun, significantly larger than in
SN 1994I, although not as large as in SN 1998bw. The same model suggests that
about 0.3 M_Sun of {56}Ni has been synthesised in the explosion. No connection
to a GRB can be firmly established.Comment: 22 pages, 15 figures, 6tables, LaTeX, MNRAS online-early, references
and affiliations updated, style correction
Death rate of massive stars at redshift ~0.3
We report the first result of a supernova search program designed to measure
the evolution of the supernova rate with redshift. To make the comparison with
local rates more significant we copied, as much as possible, the same
computation recepies as for the measurements of local rates. Moreover, we
exploited the multicolor images and the photometric redshift technique to
characterize the galaxy sample and accurately estimate the detection
efficiency.
Combining our data with the recently published meaurements of the SN Ia rate
at different redshifts, we derived the first, direct measurement of the core
collapse supernova rate at z = 0.26 as r_cc = 1.45^{+0.55}{-0.45} h^2 SNu
[h=H_0/75]. This is a factor three {+/- 50%)} larger than the local estimate.
The increase for a look back time of "only" 2.8 Gyr is more rapid than
predicted by most of the published models of the SN rate evolution.
Core-collapse SN rates measure the death rate of massive star and, because of
the short time scale of evolution, can be translated in a measurement of the
ongoing SFR. Assuming a Salpeter IMF and the standard scenario for
core-collapse progenitors we derived to an estimate of the star formation rate
at redshift 3.1^{+1.1}{-1.0} 10^-2 h^3 M_sun yr^-1 Mpc^{-3} which compare very
well with a recent estimate based on the measurement of the Halpha luminosity
density at the same redshift.Comment: Revised following referee's comments. Accepted for publication in A&
Low luminosity TypeII supernovae-II. Pointing towards moderate mass precursors
We present new data for five under-luminous type II-plateau supernovae (SNe
IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new
sample of low-luminosity SNe IIP (LL SNe IIP) is analyzed together with similar
objects studied in the past. All of them show a flat light curve plateau
lasting about 100 days, an under luminous late-time exponential tail, intrinsic
colours that are unusually red, and spectra showing prominent and narrow
P-Cygni lines. A velocity of the ejected material below 10^3 km/s is inferred
from measurements at the end of the plateau. The 56Ni masses ejected in the
explosion are very small (less than 10^-2 solar masses). We investigate the
correlations among 56Ni mass, expansion velocity of the ejecta and absolute
magnitude in the middle of the plateau, confirming the main findings of Hamuy
(2003), according to which events showing brighter plateau and larger expansion
velocities are expected to produce more 56Ni. We propose that these faint
objects represent the low luminosity tail of a continuous distribution in
parameters space of SNe IIP. The physical properties of the progenitors at the
explosion are estimated through the hydrodynamical modeling of the observables
for two representative events of this class, namely SN 2005cs and SN 2008in. We
find that the majority of LL SNe IIP, and quite possibly all, originate in the
core-collapse of intermediate mass stars, in the mass range 10-15 solar masses.Comment: 20 pages, 19 figures, accepted for publication in MNRA
Low luminosity Type II supernovae - II. Pointing towards moderate mass precursors
We present new data for five underluminous Type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) is analysed together with similar objects studied in the past. All of them show a flat light-curve plateau lasting about 100 d, an underluminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P Cygni lines. A velocity of the ejected material below 10(3) km s(-1) is inferred from measurements at the end of the plateau. The Ni-56 masses ejected in the explosion are very small (< 10(-2) M-circle dot). We investigate the correlations among Ni-56 mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy, according to which events showing brighter plateau and larger expansion velocities are expected to produce more Ni-56. We propose that these faint objects represent the LL tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modelling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core collapse of intermediate-mass stars, in the mass range 10-15 M-circle dot.</p
Velocity-resolved reverberation mapping of five bright Seyfert 1 galaxies
We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one AGN (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-Hβ reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure Hbeta time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity dependent Hβ lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.PostprintPeer reviewe
Low luminosity type II supernovae-II. Pointing towards moderate mass precursors
We present new data for five underluminous Type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of lowluminosity SNe IIP (LL SNe IIP) is analysed together with similar objects studied in the past. All of them show a flat light-curve plateau lasting about 100 d, an underluminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P Cygni lines. A velocity of the ejected material below 103 km s-1 is inferred from measurements at the end of the plateau. The 56Ni masses ejected in the explosion are very small (≤10-2 M⊙). We investigate the correlations among 56Ni mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy, according to which events showing brighter plateau and larger expansion velocities are expected to produce more 56Ni. We propose that these faint objects represent the LL tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modelling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core collapse of intermediate-mass stars, in the mass range 10-15 M⊙