The progenitor system of the compact binary merger GW190425 had a total mass of $3.4^{+0.3}_{-0.1}$ M$_\odot$ (90th-percentile confidence region) as measured from its gravitational wave signal. This mass is significantly different from the Milky Way (MW) population of binary neutron stars (BNSs) that are expected to merge in a Hubble time and from that of the first BNS merger, GW170817. Here we explore the expected electromagnetic signatures of such a system. We make several astrophysically motivated assumptions to further constrain the parameters of GW190425. By simply assuming that both components were NSs, we reduce the possible component masses significantly, finding $m_1 = 1.85^{+0.27}_{-0.19}$ M$_\odot$ and $m_2 = 1.47^{+0.16}_{-0.18}$ M$_\odot$. However if the GW190425 progenitor system was a NS-black hole merger, we find best-fitting parameters $m_1 = 2.19^{+0.21}_{-0.17}$ M$_\odot$ and $m_2 = 1.26^{+0.10}_{-0.08}$ M$_\odot$. For a well-motivated BNS system where the lighter NS has a mass similar to the mass of non-recycled NSs in MW BNS systems, we find $m_1 = 2.03^{+0.15}_{-0.14}$ M$_\odot$ and $m_2 = 1.35 \pm 0.09$ M$_\odot$, corresponding to only 7% mass uncertainties. For all scenarios, we expect a prompt collapse of the resulting remnant to a black hole. Examining detailed models with component masses similar to our best-fitting results, we find the electromagnetic counterpart to GW190425 is expected to be significantly redder and fainter than that of GW170817. We find that almost all reported observations used to search for an electromagnetic counterpart for GW190425 were too shallow to detect the expected counterpart. If the LIGO-Virgo Collaboration promptly provides the chirp mass, the astronomical community can adapt their observations to improve the likelihood of detecting a counterpart for similarly "high-mass" BNS systems. (abridged)
The stochastic gravitational wave background produced by supernovas, magnetars and merger of binaries constituted by a pair of compact objects is reviewed and updated. The merger of systems composed by two black holes dominates by far the background signal, whose amplitude in the range 10-100 Hz is above the sensitivity of the planned Einstein laser interferometer (ET). The background signal at 25 Hz estimated by the LIGO-VIRGO collaboration, based on the available merger detection data, is in good agreement with the present theoretical predictions.
In this paper we study two newly discovered classes of radio sources: the highly energetic, short-lived events, known as Fast Radio Bursts (FRBs), and a new category of compact sources known as Fanaroff-Riley type 0 radio galaxies (FR0s). Due to a possible catastrophic event origin for the FRBs and a previous correlation found with an FR0 in the gamma ray spectrum, it is possible that these radio sources could also emit high energy photons in the Fermi-LAT satellite energy range (20 MeV - 300GeV). Here we present an exhaustive time-dependent and spatial search of all up-to-date observed FRBs a…
We investigate the possibility of detection of the VHE gamma-ray counterparts to the neutrino astrophysical sources within the Neutrino Target of Opportunity (NToO) program of CTA using the populations simulated by the FIRESONG software to resemble the diffuse astrophysical neutrino flux measured by IceCube. We derive the detection probability for different zenith angles and geomagnetic field configurations. The difference in detectability of sources between CTA-North and CTA-South for the average geomagnetic field is not substantial. We investigate the effect of a higher night-sky background …
In the next decade, the Laser Interferometer Space Antenna (LISA) will detect the coalescence of massive black hole binaries (MBHBs) in the range $[10^4, 10^8] \, \rm M_{\odot}$, up to $z\sim10$. Their gravitational wave (GW) signal is expected to be accompanied by an electromagnetic counterpart (EMcp), generated by the gas accreting on the binary or on the remnant BH. In this work, we present the number and characteristics (such as redshift and mass distribution, apparent magnitudes or fluxes) of EMcps detectable jointly by LISA and some representative EM telescopes. We combine state-of-the-a…
The recent discovery of electromagnetic signals in coincidence with gravitational waves from neutron-star mergers has solidified the importance of multimessenger campaigns for studying the most energetic astrophysical events. Pioneering multimessenger observatories, such as the LIGO/Virgo gravitational wave detectors and the IceCube neutrino observatory, record many candidate signals that fall short of the detection significance threshold. These sub-threshold event candidates are promising targets for multimessenger studies, as the information provided by these candidates may, when combined wi…
Current status and desired accuracy of the isotopic production cross-sections relevant to astrophysics of cosmic rays II. Fluorine to Silicon (and updated LiBeB)
Mergers of binaries consisting of two neutron stars, or a black hole and a neutron star, offer a unique opportunity to study a range of physical and astrophysical processes using two different and almost orthogonal probes - gravitational waves (GW) and electromagnetic (EM) emission. The GW signal probes the binary and the physical processes that take place during the last stages of the merger, while the EM emission provides clues to the material that is thrown out following the merger. The accurate localization, which only the EM emission can provide, also indicates the astrophysical setting i…
Joint multi-messenger observations with gravitational waves and electromagnetic data offer new insights into the astrophysical studies of compact objects. The third Advanced LIGO and Advanced Virgo observing run began on April 1, 2019; during the eleven months of observation, there have been 14 compact binary systems candidates for which at least one component is potentially a neutron star. Although intensive follow-up campaigns involving tens of ground and space-based observatories searched for counterparts, no electromagnetic counterpart has been detected. Following on a previous study of th…
Discovery of a variable X-ray counterpart to HESS J1832-093: A new gamma-ray binary?
TeV γ射线点源HESSJ 1832 -093尽管进行了广泛的多波长研究，但仍未确定。伽马射线的发射可能来自一个非常致密的脉冲星风星云，或者是一个由X射线源XMMU J183245-0921539和伴星（2 MASS J18324516-0921545）组成的X射线双星系统。为了揭示XMMUJ 183245 -0921539的性质及其与HESSJ 1832 -093的关系，我们使用Chandra和Swift对X射线进行了更深入的后续观察，以改善源定位并研究时间变异性。我们观察到的X射线通量增加了一个因素~6的钱德拉数据相比，以前的意见。钱德拉的源是点状的，它的更新位置距离2 MASS J18324516-0921545只有0.3”的偏移，证实了与这个红外源的关联。随后的Swift ToO观测结果表明，通量较低，再次与之前用XMM-牛顿测量的通量一致，表明变化时间尺度为两个月或更短。现在建立的XMMU J183245-0921539和2 MASS J18324516-0921545的关联以及观察到的X射线变化是HESS J1832-093二元性质的有力证据。需要进一步的观测来确定光学对应物以及寻找轨道周期性来证实这种情况。
Searches for electromagnetic counterparts of gravitational-wave signals have redoubled since the first detection in 2017 of a binary neutron star merger with a gamma-ray burst, optical/infrared kilonova, and panchromatic afterglow. Yet, one LIGO/Virgo observing run later, there has not yet been a second, secure identification of an electromagnetic counterpart. This is not surprising given that the localization uncertainties of events in LIGO and Virgo's third observing run, O3, were much larger than predicted. We explain this by showing that improvements in data analysis that now allow LIGO/Vi…
We investigate the properties of the host galaxies of compact binary mergers across cosmic time. To this end, we combine population synthesis simulations together with galaxy catalogues from the hydrodynamical cosmological simulation EAGLE to derive the properties of the host galaxies of binary neutron star (BNS), black hole-neutron star (BHNS) and binary black hole (BBH) mergers. Within this framework, we derive the host galaxy probability, i.e., the probability that a galaxy hosts a compact binary coalescence as a function of its stellar mass, star formation rate, $K_s$ magnitude and $B$ mag…
