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Register a new userDynamical formation of the GW190814 merger
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Added by
Manuel Arca Sedda Dr.
Publication date
2021
fields
Physics
and research's language is
English
Authors
Manuel Arca Sedda
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We investigate the possible dynamical origin of GW190814, a gravitational wave (GW) source discovered by the LIGO-Virgo-Kagra collaboration (LVC) associated with a merger between a stellar black hole (BH) with mass $23.2$ M$_odot$ and a compact object, either a BH or a neutron star (NS), with mass $2.59$ M$_odot$. Using a database of 240,000 $N$-body simulations modelling the formation of NS-BH mergers via dynamical encounters in dense clusters, we find that systems like GW190814 are likely to form in young, metal-rich clusters. Our model suggests that a little excess ($sim 2-4%$) of objects with masses in the range $2.3-3$ M$_odot$ in the compact remnants mass spectrum leads to a detection rate for dynamically formed GW190814 -like mergers of $Gamma_{rm GW190814} simeq 1-6$ yr Gpc$^{-3}$, i.e. within the observational constraints set by the GW190814 discovery, $Gamma_{rm LVC} sim 1-23$ yr Gpc$^{-3}$. Additionally, our model suggests that $sim 1.8-4.8%$ of dynamical NS-BH mergers are compatible with GW190426_152155, the only confirmed NS-BH merger detected by the LVC. We show that the relative amount of light and heavy NS-BH mergers can provide clues about the environments in which they developed.
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On 2017 August 17, gravitational waves were detected from a binary neutron star merger, GW170817, along with a coincident short gamma-ray burst, GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a), was subsequently identified as the counterpart of this event. We present ultraviolet, optical and infrared light curves of SSS17a extending from 10.9 hours to 18 days post-merger. We constrain the radioactively-powered transient resulting from the ejection of neutron-rich material. The fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. The late-time light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in r-process nucleosynthesis in the Universe.
Merging neutron stars offer an exquisite laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart EM170817 to gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic dataset, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma-rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultra-relativistic jets. Instead, we suggest that breakout of a wide-angle, mildly-relativistic cocoon engulfing the jet elegantly explains the low-luminosity gamma-rays, the high-luminosity ultraviolet-optical-infrared and the delayed radio/X-ray emission. We posit that all merging neutron stars may lead to a wide-angle cocoon breakout; sometimes accompanied by a successful jet and sometimes a choked jet.
We present a near-infrared spectral sequence of the electromagnetic counterpart to the binary neutron star merger GW170817 detected by Advanced LIGO/Virgo. Our dataset comprises seven epochs of J+H spectra taken with FLAMINGOS-2 on Gemini-South between 1.5 and 10.5 days after the merger. In the initial epoch, the spectrum is dominated by a smooth blue continuum due to a high-velocity, lanthanide-poor blue kilonova component. Starting the following night, all subsequent spectra instead show features that are similar to those predicted in model spectra of material with a high concentration of lanthanides, including spectral peaks near 1.07 and 1.55 microns. Our fiducial model with 0.04 M_sun of ejecta, an ejection velocity of v=0.1c, and a lanthanide concentration of X_lan=1e-2 provides a good match to the spectra taken in the first five days, although it over-predicts the late-time fluxes. We also explore models with multiple fitting components, in each case finding that a significant abundance of lanthanide elements is necessary to match the broad spectral peaks that we observe starting at 2.5 d after the merger. These data provide direct evidence that binary neutron star mergers are significant production sites of even the heaviest r-process elements.
We report on our observing campaign of the compact binary merger GW190814, detected by the Advanced LIGO and Advanced Virgo detectors on August 14th, 2019. This signal has the best localisation of any observed gravitational wave (GW) source, with a 90% probability area of 18.5 deg$^2$, and an estimated distance of ~ 240 Mpc. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering 88% of the probability area down to a limiting magnitude of $w$ = 19.9 AB. Nearby galaxies within the high probability region were targeted with the Lowell Discovery Telescope (LDT), whereas promising candidate counterparts were characterized through multi-colour photometry with the Reionization and Transients InfraRed (RATIR) and spectroscopy with the Gran Telescopio de Canarias (GTC). We use our optical and near-infrared limits in conjunction with the upper limits obtained by the community to constrain the possible electromagnetic counterparts associated with the merger. A gamma-ray burst seen along its jets axis is disfavoured by the multi-wavelength dataset, whereas the presence of a burst seen at larger viewing angles is not well constrained. Although our observations are not sensitive to a kilonova similar to AT2017gfo, we can rule out high-mass (> 0.1 M$_{odot}$) fast-moving (mean velocity >= 0.3c) wind ejecta for a possible kilonova associated with this merger.
The aim of this review is to describe the nature, formation and evolution of the three kinds of high mass X-ray binary (HMXB) population: i. systems hosting Be stars (BeHMXBs), ii. systems accreting the stellar wind of supergiant stars (sgHMXBs), and iii. supergiant stars overflowing their Roche lobe. There are now many new observations, from the high-energy side (mainly from the INTEGRAL satellite), complemented by multi-wavelength observations (mainly in the optical, near and mid-infrared from ESO facilities), showing that a new population of supergiant HMXBs has been recently revealed. New observations also suggest the existence of evolutionary links between Be and stellar wind accreting supergiant X-ray binaries. I describe here the observational facts about the different categories of HMXBs, discuss the different models of accretion in these sources (e.g. transitory accretion disc versus clumpy winds), show the evidences of a link between different kinds of HMXBs, and finally compare observations with population synthesis models.
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