ABSTRACT We present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum (OAM). This physical observable allows ...a direct measurement of the rotation of the black hole. We extracted the OAM spectra from the radio intensity data collected by the Event Horizon Telescope from around the black hole M87* by using wavefront reconstruction and phase recovery techniques and from the visibility amplitude and phase maps. This method is robust and complementary to black hole shadow circularity analyses. It shows that the M87* rotates clockwise with an estimated rotation parameter a = 0.90 ± 0.05 with an $\sim 95{{\ \rm per\ cent}}$ confidence level (c.l.) and an inclination i = 17° ± 2°, equivalent to a magnetic arrested disc with an inclination i = 163° ± 2°. From our analysis, we conclude that, within a 6σ c.l., the M87* is rotating.
The recent GAIA DR2 measurements of distances to galactic novae have allowed to re-analyse some properties of nova populations in the Milky Way and in external galaxies on new and more solid ...empirical bases. In some cases, we have been able to confirm results previously obtained, such as the concept of nova populations into two classes of objects, that is
disk
and
bulge
novae and their link with the Tololo spectroscopic classification in Fe II and He/N novae. The recent and robust estimates of nova rates in the Magellanic Clouds galaxies provided by the OGLE team have confirmed the dependence of the normalized nova rate (i.e., the nova rate per unit of luminosity of the host galaxy) with the colors and/or class of luminosity of the parent galaxies. The nova rates in the Milky Way and in external galaxies have been collected from literature and critically discussed. They are the necessary ingredient to asses the contribution of novae to the nucleosynthesis of the respective host galaxies, particularly to explain the origin of the overabundance of lithium observed in young stellar populations. A direct comparison between distances obtained via GAIA DR2 and maximum magnitude vs. rate of decline (MMRD) relationship points out that the MMRD can provide distances with an uncertainty better than 30%. Multiwavelength observations of novae along the whole electromagnetic spectrum, from radio to gamma rays, have revealed that novae undergo a complex evolution characterized by several emission phases and a non-spherical geometry for the nova ejecta.
Nova neutrinos in the multi-messenger era Guetta, Dafne; Hillman, Yael; Della Valle, Massimo
Journal of cosmology and astroparticle physics,
03/2023, Letnik:
2023, Številka:
3
Journal Article
ABSTRACT
The joint observation of core-collapse supernovae with gamma-ray bursts shows that jets can be launched in the aftermath of stellar core collapse, likely by a newly formed black hole that ...accretes matter from the star. Such gamma-ray bursts have only been observed accompanying Type Ibc supernovae, indicating a stellar progenitor that lost its hydrogen envelope before collapse. According to recent hypothesis, it is possible that jets are launched in core-collapse events even when the progenitors still retain their hydrogen envelopes; however, such jets are not able to burrow through the star and will be stalled into the interior of the progenitor star before escaping. These jets are called choked jets. High-energy neutrinos produced by such choked jets could escape the stellar envelope and could be observed. Here, we examine how multimessenger searches for high-energy neutrinos and core-collapse supernovae can detect or limit the fraction of stellar collapses that produce jets. We find that a high fraction of jet production is already limited by previous observational campaigns. We explore possibilities with future observations using Large Synoptic Survey Telescope, IceCube, and Km3NET.
ABSTRACT The recent LIGO event GW170817 is the merger of a double neutron star system with an associated short GRB170817A with 2.9 ± 0.3 s soft emission over 8–70 keV. This association has a Gaussian ...equivalent level of confidence of 5.1σ. The merger produced a hypermassive neutron star or stellar mass black hole with prompt or continuous energy output powering GRB170817A. Here, we report on a possible detection of extended emission (EE) in gravitational radiation during GRB170817A: a descending chirp with characteristic time-scale $\tau _s=3.01\pm 0.2\,$ s in a (H1,L1)-spectrogram up to 700 Hz with Gaussian equivalent level of confidence greater than 3.3σ based on causality alone following edge detection applied to (H1,L1)-spectrograms merged by frequency coincidences. Additional confidence derives from the strength of this EE. The observed frequencies below 1 kHz indicate a hypermassive magnetar rather than a black hole, spinning down by magnetic winds and interactions with dynamical mass ejecta.
Predicted rates of merging neutron stars in galaxies Molero, Marta; Simonetti, Paolo; Matteucci, Francesca ...
Monthly notices of the Royal Astronomical Society,
01/2021, Letnik:
500, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We compute rates of merging neutron stars (MNS) in different galaxies, as well as the cosmic MNS rate in different cosmological scenarios. Our aim is to provide predictions of kilonova rates ...for future observations both at low and high redshift. In the adopted galaxy models, the production of r-process elements either by MNS or core-collapse supernovae is taken into account. To compute the MNS rates, we adopt either a constant total time delay for merging (10 Myr) or a distribution function of such delays. We conclude (i) the observed present time MNS rate in our Galaxy is well reproduced either with a constant time delay or a distribution function ∝t−1. (ii) The Eu/Fe versus Fe/H relation can be well reproduced with only MNS, if the time delay is short and constant. If a distribution function of delays is adopted, core-collapse supernovae are also required. (iii) The present time cosmic MNS rate can be well reproduced in several cosmological scenarios. (iv) Spiral galaxies are the major contributors to the cosmic MNS at all redshifts in hierarchical scenarios. In the pure luminosity evolution scenario, the spirals are the major contributors locally, whereas at high redshift ellipticals dominate. (v) The predicted cosmic MNS rate well agrees with the cosmic rate of short gamma-ray bursts, if the distribution function of delays is adopted in a cosmological hierarchical scenario observationally derived. (vi) Future observations of kilonovae in ellipticals will allow us to disentangle among constant or a distribution of time delays and among different cosmological scenarios.
Context.
LIGO–Virgo–KAGRA observations may identify the remnant of compact binary coalescence and core-collapse supernovae associated with gamma-ray bursts. The multimessenger event ...GW170817–GRB170817A appears ripe for this purpose thanks to its fortuitous close proximity at 40 Mpc. Its post-merger emission, ℰ
GW
, in a descending chirp can potentially break the degeneracy in spin-down of a neutron star or black hole remnant by the relatively large energy reservoir in the angular momentum,
E
J
, of the latter according to the Kerr metric.
Aims.
The complex merger sequence of GW170817 is probed for the central engine of GRB170817A by multimessenger calorimetry and event timing.
Methods.
We used model-agnostic spectrograms with equal sensitivity to ascending and descending chirps generated by time-symmetric butterfly matched filtering. The sensitivity was calibrated by response curves generated by software injection experiments, covering a broad range in energies and timescales. The statistical significance for candidate emission from the central engine of GRB170817A is expressed by probabilities of false alarm (PFA; type I errors) derived from an event-timing analysis. Probability density functions (PDF) were derived for start-time
t
s
, identified via high-resolution image analyses of the available spectrograms. For merged (H1,L1)-spectrograms of the LIGO detectors, a PFA
p
1
derives from causality in
t
s
given GW170817–GRB17081A (contextual). A statistically independent confirmation is presented in individual H1 and L1 analyses, quantified by a second PFA
p
2
of consistency in their respective observations of
t
s
(acontextual). A combined PFA derives from their product since the mean and (respectively) the difference in timing are statistically independent.
Results.
Applied to GW170817–GRB170817A, PFAs of event timing in
t
s
produce
p
1
= 8.3 × 10
−4
and
p
2
= 4.9 × 10
−5
of a post-merger output ℰ
GW
≃ 3.5%
M
⊙
c
2
(
p
1
p
2
= 4.1 × 10
−8
, equivalent
Z
-score 5.48). ℰ
GW
exceeds
E
J
of the hyper-massive neutron star in the immediate aftermath of GW170817, yet it is consistent with
E
J
rejuvenated in gravitational collapse to a Kerr black hole. Similar emission may be expected from energetic core-collapse supernovae producing black holes of interest to upcoming observational runs by LIGO–Virgo–KAGRA.
Recovery of the supernova (SN) delay-time distribution (DTD) - the SN rate versus time that would follow a hypothetical brief burst of star formation - can shed light on SN progenitors and physics, ...as well as on the time-scales of chemical enrichment. Previous attempts to reconstruct the DTD have been based either on comparison of mean SN rates versus redshift to cosmic star-formation history (SFH), or on the comparison of SN rates among galaxies with different mean ages. Here, we present an approach to recover the SN DTD that avoids the averaging and loss of information of other schemes. We compare the SFHs of individual galaxies to the numbers of SNe discovered by a survey in each galaxy (generally zero, sometimes one SN, rarely a few). We apply the method to a subsample of 3505 galaxies, hosting 82 type-Ia SNe (SNe Ia) and 119 core-collapse supernovae (CC SNe), from the Lick Observatory Supernova Search (LOSS), that have SFHs reconstructed from Sloan Digital Sky Survey (SDSS) spectra. We find a >2σ SN Ia DTD signal in our shortest-delay, 'prompt' bin at <420 Myr. We identify and study a systematic error, due to the limited aperture of the SDSS spectroscopic fibres, that causes some of the prompt signal to leak to the later bins of the DTD. After accounting for this systematic error, we demonstrate that a prompt SN Ia contribution is required by the data at the >99 per cent confidence level. We further find a 4σ indication of SNe Ia that are 'delayed' by >2.4 Gyr. Thus, the data support the existence of both prompt and delayed SNe Ia. We measure the time integral over the SN DTD. For CC SNe we find a total yield of 0.010 ± 0.002 SNe per M⊙ formed, in excellent agreement with expectations, if all stars more massive than 8 M⊙ lead to visible SN explosions. This argues against scenarios in which the minimum mass for core-collapse SNe is ≳10 M⊙, or in which a significant fraction of massive stars collapse without an accompanying explosion. For SNe Ia, the time-integrated yield is 0.0023 ± 0.0006 SNe per M⊙ formed, most of them with delays <2.4 Gyr. Finally, we show the robust performance of the method on simulated samples, and demonstrate that its application to already existing SN samples, such as the full LOSS sample, but with complete and unbiased SFH estimates for the survey galaxies, could provide an accurate and detailed measurement of the SN Ia DTD.
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