•For neutrino astronomy, the knowledge of the rate of core collapse supernovae is of essential importance.•We use the best available information to update its study and to obtain the state-of-the-art ...value: R = 1.63 ± 0.46/century.•We discuss the consistency of the results and point out the critical aspects in this inference.
Several large neutrino telescopes, operating at various sites around the world, have as their main objective the first detection of neutrinos emitted by a gravitational collapse in the Milky Way. The success of these observation programs depends on the rate of supernova core collapse in the Milky Way, R. In this work, standard statistical techniques are used to combine several independent results. Their consistency is discussed and the most critical input data are identified. The inference on R is further tested and refined by including direct information on the occurrence rate of gravitational collapse events in the Milky Way and in the Local Group, obtained from neutrino telescopes and electromagnetic surveys. A conservative treatment of the errors yields a combined rate R=1.63±0.46 (100 yr)−1; the corresponding time between core collapse supernova events turns out to be T=61−14+24 yr. The importance to update the analysis of the stellar birthrate method is emphasized.
Discovery of a kilonova and prospects for future hunts Cappellaro, Enrico
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
12/2019, Letnik:
30, Številka:
Suppl 1
Journal Article
Recenzirano
The discovery of the GW signal from the merging of two neutron stars (GW170817) and the detection of related electromagnetic radiations, namely a short GRB, an optical transient (kilonova) and a late ...afterglow emission at X-ray and radio wavelengths, opened the new era of multi-messenger astrophysics. I will briefly review the history of this discovery with an emphasis on the results of the optical/near-infrared follow-up. The lesson learned is used to get prepared for the forthcoming LIGO/Virgo runs.
Abstract
We study the production of very light elements (
Z
< 20) in the dynamical and spiral-wave wind ejecta of binary neutron star mergers by combining detailed nucleosynthesis calculations with ...the outcome of numerical relativity merger simulations. All our models are targeted to GW170817 and include neutrino radiation. We explore different finite-temperature, composition-dependent nuclear equations of state, and binary mass ratios, and find that hydrogen and helium are the most abundant light elements. For both elements, the decay of free neutrons is the driving nuclear reaction. In particular, ∼0.5–2 × 10
−6
M
⊙
of hydrogen are produced in the fast expanding tail of the dynamical ejecta, while ∼1.5–11 × 10
−6
M
⊙
of helium are synthesized in the bulk of the dynamical ejecta, usually in association with heavy
r
-process elements. By computing synthetic spectra, we find that the possibility of detecting hydrogen and helium features in kilonova spectra is very unlikely for fiducial masses and luminosities, even when including nonlocal thermodynamic equilibrium effects. The latter could be crucial to observe helium lines a few days after merger for faint kilonovae or for luminous kilonovae ejecting large masses of helium. Finally, we compute the amount of strontium synthesized in the dynamical and spiral-wave wind ejecta, and find that it is consistent with (or even larger than, in the case of a long-lived remnant) the one required to explain early spectral features in the kilonova of GW170817.
Abstract
We present 888 visual-wavelength spectra of 122 nearby type II supernovae (SNe II) obtained between 1986 and 2009, and ranging between 3 and 363 days post-explosion. In this first paper, we ...outline our observations and data reduction techniques, together with a characterization based on the spectral diversity of SNe II. A statistical analysis of the spectral matching technique is discussed as an alternative to nondetection constraints for estimating SN explosion epochs. The time evolution of spectral lines is presented and analyzed in terms of how this differs for SNe of different photometric, spectral, and environmental properties: velocities, pseudo-equivalent widths, decline rates, magnitudes, time durations, and environment metallicity. Our sample displays a large range in ejecta expansion velocities, from ∼9600 to ∼1500 km s
−1
at 50 days post-explosion with a median
value of 7300 km s
−1
. This is most likely explained through differing explosion energies. Significant diversity is also observed in the absolute strength of spectral lines, characterized through their pseudo-equivalent widths. This implies significant diversity in both temperature evolution (linked to progenitor radius) and progenitor metallicity between different SNe II. Around 60% of our sample shows an extra absorption component on the blue side of the
P-Cygni profile (“Cachito” feature) between 7 and 120 days since explosion. Studying the nature of Cachito, we conclude that these features at early times (before ∼35 days) are associated with Si
ii
, while past the middle of the plateau phase they are related to high velocity (HV) features of hydrogen lines.
Binary neutron star mergers are important in understanding stellar evolution, the chemical enrichment of the universe via the r-process, the physics of short gamma-ray bursts, gravitational waves, ...and pulsars. The rates at which these coalescences happen is uncertain, but it can be constrained in different ways. One of those is to search for the optical transients produced at the moment of the merging, called a kilonova, in ongoing supernova (SN) searches. However, until now, only theoretical models for a kilonova light curve were available to estimate their rates. The recent kilonova discovery of AT 2017gfo/DLT17ck gives us the opportunity to constrain the rate of kilonovae using the light curve of a real event. We constrain the rate of binary neutron star mergers using the DLT40 Supernova search and the native AT 2017gfo/DLT17ck light curve obtained with the same telescope and software system. Excluding AT 2017gfo/DLT17ck due to visibility issues, which was only discovered thanks to the aLIGO/aVirgo trigger, no other similar transients were detected during the 13 months of daily cadence observations of ∼2200 nearby (<40 Mpc) galaxies. We find that the rate of BNS mergers is lower than 0.47-0.55 kilonovae per 100 years per 1010 L B (depending on the adopted extinction distribution). In volume, this translates to < 0.99 × 10 − 4 − 0.15 + 0.19 , Mpc − 3 yr − 1 (SNe Ia-like extinction distribution), consistent with previous BNS coalescence rates. Based on our rate limit, and the sensitivity of aLIGO/aVirgo during O2, it is very unlikely that kilonova events are lurking in old pointed galaxy SN search data sets.
Abstract
We present the discovery and studies of the helium-rich, fast-evolving supernova (SN) 2021agco at a distance of ∼40 Mpc. Its early-time flux is found to rise from half peak to the peak of ...−16.06 ± 0.42 mag in the
r
band within
2.4
−
1.0
+
1.5
days, and the post-peak light curves also decline at a much faster pace relative to normal stripped-envelope supernovae (SNe) of Type Ib/Ic. The early-time spectrum of SN 2021agco (
t
≈ 1.0 days after the peak) is characterized by a featureless blue continuum superimposed with a weak emission line of ionized C
iii
, and the subsequent spectra show prominent He
i
lines. Both the photometric and spectroscopic evolution show close resemblances to SN 2019dge, which is believed to have an extremely stripped progenitor. We reproduce the multicolor light curves of SN 2021agco with a model combining shock-cooling emission with
56
Ni decay. The best-fit results give an ejecta mass of ≈0.3
M
⊙
and a synthesized nickel mass of ≈2.2 × 10
−2
M
⊙
. The progenitor is estimated to have an envelope radius of
R
env
≈ 80
R
⊙
and a mass of
M
env
≈ 0.10
M
⊙
. All these suggest that SN 2021agco can be categorized as an ultra-stripped SN Ib, representing the closest object of this rare subtype. This SN is found to explode in the disk of a Sab-type galaxy with an age of ∼10.0 Gyr and low star-forming activity. Compared to normal SNe Ib/c, the host galaxies of SN 2021agco and other ultra-stripped SNe tend to have relatively lower metallicity, which complicates the properties of their progenitor populations.
It is well known that massive stars (M > 8 M☉) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different ...configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN 2010bt, which was classified as a Type IIn SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L☉ 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (∼5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.
Supernovae (SNe) are luminous optical transients, which, despite being rare events in a single galaxy, nowadays are discovered at a rate of ten per day. They populate a growing zoo of different types ...linked to a variety of progenitors and explosion mechanisms. Through a biased selection of a century of researches, I will review how SNe have became a leading tool to probe the cosmic expansion. I will mainly focus on SNe of type Ia, originating from the thermonuclear explosion of white dwarfs, that were demonstrated to be excellent distance indicators after proper calibration and standardisation. Two decades ago, SNe Ia provided the surprising result that the cosmic expansion is accelerated by a misterious dark energy. Recently, with the decisive contribution of Cepheids variables as primary distance indicators, SN Ia allowed to measure the value of the Hubble-Lemaître constant,
H
0
, with an error of only 1%. It turned out that the value of
H
0
based on SNe Ia is in tension with the one measured through the fit of the CMB fluctuations. If confirmed, this finding requires a deep revision of the standard cosmological model.
The only supernovae (SNe) to show gamma-ray bursts (GRBs) or early x-ray emission thus far are overenergetic, broad-lined type Ic SNe (hypernovae, HNe). Recently, SN 2008D has shown several unusual ...features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E almost equal to 6x10⁵¹ erg) and ejected mass ~7 times the mass of the Sun (Formula: see text) are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a ~30 Formula: see text star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.
We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta ...velocities and with a very slow spectroscopic and photometric evolution (more than twice as slow as SN 1998bw). The Pan-STARRS1 retrospective detection shows that the rise time from explosion to peak was ~40 days in the R band. Through an analysis of the light curve and the spectral sequence, we estimate a kinetic energy of ~7-17 foe and a total ejected mass of ~7-17 M sub(middot in circle), 5-10 M sub(middot in circle) of which is oxygen and 0.6-0.7 M sub(middot in circle) is super(56)Ni. The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 M sub(middot in circle). The profile of the forbidden oxygen lines in the nebular spectra shows no evidence of a bi-polar geometry in the ejected material.
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