adsabs/FOCAL huggingface dataset:
In view of the ultrahigh mass of the merger product of around 2.5 M⊙, it is undoubtedly necessary and important to further test the existence of post-merger NSs (Gao et al. 2016; Li et al. 2016, 2017; Ai et al. 2018; Zhu et al. 2018; Sarin et al. 2020; Beniamini & Lu 2021), which can provide a robust constraint on the equation of state of the NS matter and then improve our understanding of the low-energy feature of strong interaction. Besides the GRB 170817A/AT 2017gfo event, searches for possible kilonova emission have already been carried out in the afterglows of many SGRBs since 2013 (Berger et al. 2013; Tanvir et al. 2013; Yang et al. 2015; Jin et al. 2015, 2016, 2018, 2020; Gao et al. 2015, 2017; Kasliwal et al. 2017). Among the SGRBs with a kilonova candidate, GRB 160821B has one of the lowest redshifts, of namely z = 0.162. From its optical/near-infrared(NIR) afterglow, an obvious excess was found. Because of its close distance, the kilonova emission associated with GRB 160821B is in principle detectable and can provide a natural explanation for the observed optical/NIR excess (Lamb et al. 2019; Troja et al. 2019). In view of its luminosity, which is lower than that of AT 2017gfo, the kilonova after GRB 160821B can in principle be modeled with a pure radioactive power. However, it could still be necessary to mention that a significant internal plateau appeared in the early X-ray afterglow during the first few hundred seconds (see the insert in Fig. 1), which indicated that a post-merger NS also exists in this event. According to these observations, Ma et al. (2021) suggested that the post-merger NS could collapse into a black hole and then the subsequent kilonova could be powered by the accretion onto the black hole. Nevertheless, alternatively, as suggested by Yu et al. (2018), the steep decay after the internal plateau may not represent the collapse of the NS, but may simply be caused by the suppression of the magnetic dipole radiation of the NS. In this case, the spin-down of the NS of relatively low luminosity can still power the kilonova emission, which can be generally called a mergernovae (Yu et al. 2013). This scenario can provide a natural explanation for the AT 2017gfo emission. Therefore, in our opinion, this situation could also appear in the case of GRB 160821B. This paper is devoted to testing whether or not there is a nonthermal emission component arising from the interaction between the NS wind and the merger ejecta, as mentioned above for AT 2017gfo.
Citation: Gao et al. 2015
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As Parker Solar Probe (PSP) descends deeper into the solar corona on its succeeding orbits, its measurements reveal features of the heliospheric plasma that will significantly increase our fundamental understanding of the workings of the solar corona, the origins of the solar wind, and the behavior of heliospheric energetic particle populations (Fox et al. 2016). In the first several orbits, PSP approached progressively nearer to the range of altitudes at which the accelerating solar wind speed exceeds the Alfvén speed. This critical zone is not a simple surface, but a more irregularly defined region above which (incompressive) magnetohydrodynamic signals, such as Alfvén waves, can no longer return to the lower altitude corona. In this very region, the analysis of heliospheric imaging (HI; DeForest et al. 2016) has described a transition from striated images that appear to be highly collimated due to a structured magnetic field and lower plasma beta to higher altitude images that appeared to be more disordered and isotropic, a condition described as “flocculation.” A number of interesting features have been reported from observations in the region, including periods of near-corotation and, notably, the appearance of magnetic reversals or “switchbacks” (Bale et al. 2019) and accompanying plasma jets (Kasper et al. 2019). Switchbacks have received considerable attention, with a focus on understanding how various plasma properties respond in and near them (Bale et al. 2019; Kasper et al. 2019; Dudok de Wit et al. 2020; McManus et al. 2020; Mozer et al. 2020; Whittlesey et al. 2019). Their origin is also a subject of active discussion, with ideas ranging from distant generation in the lower corona via interchange reconnection (Axford et al. 1999; Fisk & Kasper 2020; Zank et al. 2020) to a roll-up of the magnetic field by vortices in shear-driven turbulence (Ruffolo et al. 2020). Here we examine another important set of PSP observations and their behavior near switchbacks, namely the behavior of energetic particles as measured on PSP by the integrated Science Investigation of the Sun (IS⊙IS) instrument suite (McComas et al. 2016, 2019).
Citation: DeForest et al. 2016
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After a first part of ballistic, high-speed motion, the deceleration of RK1 was rather abrupt, which is something not observed in the majority of discrete ejecta from BH XRBs (e.g Mirabel & Rodríguez 1994; Fender et al. 1999; Miller-Jones et al. 2012). This scenario is consistent with a jet that travels first at constant speed in a low-density region of the ISM, which constitutes a large scale cavity around the system, before hitting the higher density wall of the cavity itself, as already proposed in Hao & Zhang (2009). Radio emission at late times would be produced by the external shocks between the plasma blob and the ISM cavity wall, in analogy with GRB afterglows (Wang et al. 2003). Those cavities have been suggested to exist at ∼pc scales at least for XTE J1550–564 and H1743–322 (Hao & Zhang 2009; Steiner & McClintock 2012; Steiner, McClintock & Reid 2012; Migliori et al. 2017). We obtained the best modelling for the RK1 motion by a combination of a linear motion and a Sedov phase (see Section 3.3), achieved at late times due to the jet sweeping up ISM material on its path, in a similar way as Miller-Jones et al. (2011), which derived it from Wang et al. (2003). We therefore suggest that MAXI J1348–630 is located in a similar cavity, possibly carved by previous jet activity, or resulting from the action of accretion disc winds. However, so far such winds have not been detected for MAXI J1348–630. If we take our estimate of α0 ∼ 25 arcsec, the upper limit on the inclination angle of the discrete ejection of θ1 ∼ 44○ and the lowest acceptable distance of 1.6 kpc, we obtain that RK1 travelled at least ∼0.3 pc before reaching the angular distance α0, which is consistent with what has been observed for other discrete ejections (Corbel et al. 2000; Gallo et al. 2004) and could be taken as a rough lower limit on the size of the cavity.7 As argued by Hao & Zhang (2009), the presence of an underdense cavity could be a common characteristic of BH XRBs environments (Heinz 2002), and its existence could be strictly required for the jet to travel such a long distance (Hao & Zhang 2009).
Citation: Steiner & McClintock 2012
Citation function: Uses
The short gamma-ray burst (GRB) 170817A was observed by the Fermi- Gamma-ray Burst Monitor (GBM; Goldstein et al. 2017). The fact that it was not detected by the Insight Hard X-ray Modulation Telescope (Li et al. 2017) suggests that the burst had a very weak fluence and a soft spectrum. The burst was highly noticeable because of its connection to gravitational-wave (GW) event GW170817, which was detected by the Laser Interferometer Gravitational-wave Observatory, about 1.7 s before the GBM was triggered (Abbott et al. 2017a). To understand the event, it is crucial that we obtain all of the object’s physical properties. Compared with other short GRBs, the luminosity of GRB 170817A was extremely weak, thus suggesting that the jet was off-axis to the line of sight (Albert et al. 2017; Burgess et al. 2017; Fong et al. 2017; Granot et al. 2017a; He et al. 2017; Jin et al. 2017; Margutti et al. 2017; Metzger 2017; Troja et al. 2017; Wang et al. 2017; Xiao et al. 2017). The GW fitting parameters suggest an angle of less than 28° (Abbott et al. 2017a). Given that no prompt X-rays were detected, a number of predictions have been made for the off-axis angle. From observations by the 





 and 





 telescopes, Evans et al. (2017) suggested that the viewing angle was 





. Constraints from deep Chandra observations suggest that it was greater than 23° (Haggard et al. 2017), whereas constraints from radio-frequency observations of a relativistic jet (Alexander et al. 2017) suggested it was 





. On the basis of the upper limit from the Atacama Large Millimeter/submillimeter Array (ALMA) and Giant Metrewave Radio Telescope (GMRT) at radio bands, Kim et al. (2017) found the angle to be 41° (or 17°) but did not rule out other values. The modeling for several different bands suggested that the viewing angle was 





 (Ioka & Nakamura 2017), 





 (Granot et al. 2017a), or 





 (Guidorzi et al. 2017). The 





 versus 





 plot in Pozanenko et al. (2017) shows that GRB 170817A belongs to neither the long nor short GRB groups, thus supporting the idea that it was triggered by an off-axis jet. However, the exact off-axis angle is still hard to predict. If it was derived from the relativistic beaming effect, it would have degenerated with the jet’s Lorentz factor; if it was derived from the parameter fitting of the GW signal, it would have degenerated with the distance.
Citation: Metzger 2017
Citation function: Compare/Contrast
Among the suggestedmechanisms responsible for the strong damping of the coronal loop oscillations (e.g., Ruderman & Roberts 2002; Ofman 2005, 2009; Morton & Erdélyi 2009) resonant absorption of the MHD waves, which was established first by Ionson (1978), is a strong candidate. Several works developed this theory (e.g., Davila 1987; Sakurai et al. 1991a, 1991b; Goossens et al. 1995; Goossens & Ruderman 1995; Erdélyi 1997; Cally & Andries 2010). The necessary condition for the resonant absorption is a continuum of Alfvén or slow frequency across the loop (Ionson 1978; Hollweg 1984, 1987; Davila 1987; Sakurai et al. 1991a). Resonant absorption occurs when the frequency of the global MHD mode matches at least with one of the frequencies of the background Alfvén or slow continuum at a location called he resonance point. As a result, the energy of the global MHD mode transfers to the local Alfvén modes in a layer around the resonance point, named the resonance layer (Lee & Roberts 1986; see also Goossens et al. 2013; Soler & Terradas 2015). In the absence of dissipation mechanisms, the amplitude of the oscillations diverges at the resonance point. Dissipation is important in the resonance layer, where the oscillations make large gradients. The background Alfvén or slow continuum can be due to the variation of the plasma density (e.g., Davila 1987; Ofman et al. 1994; Ruderman & Roberts 2002; Terradas et al. 2006; Soler & Terradas 2015), twisted magnetic field (Ebrahimi & Karami 2016), or both of them together (Karami & Bahari 2010; Giagkiozis et al. 2016). There are a variety of theoretical works related to the damping of the coronal loop oscillations based on the theory of resonant absorption of MHD waves (e.g., Goossens et al. 2002, 2009; Ruderman & Roberts 2002; Van Doorsselaere et al. 2004; Andries et al. 2005; Terradas et al. 2006; Karami et al. 2009; Karami & Bahari 2010; Soler et al. 2013; Soler & Terradas 2015; Ebrahimi & Karami 2016; Giagkiozis et al. 2016; Jung Yu & Van Doorsselaere 2016). For a good review about the theory of resonant absorption, see also Goossens et al. (2011).
Citation: Soler & Terradas 2015
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Citation: Soler & Terradas 2015
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The dust condensations could not arise from a thermal Jeans fragmentation process. If that is the case, with a density of 104–105 cm−3 for the surrounding medium, one may expect the mass of the condensations on the order of 20–50 M⊙ (the Jeans mass at 105–104 cm−3) and the nearest separations between the condensations around 0.2–0.5 pc (the Jeans length at 105–104 cm−3); both are clearly inconsistent with the observations. Alternatively, small dense structures can be temporary density fluctuations frequently created and destroyed by supersonic turbulence (e.g., Elmegreen 1999; Biskamp 2003; Falgarone & Passot 2003). However, σnth is found to be subsonic or at most transonic. Goicoechea et al. (2016) also found that there is only a gentle level of turbulence in the Bar. So the turbulence does not seem to be strong enough to produce the condensations. Another force that could potentially compress the cloud and produce high-density structures is a high-pressure wave from the expansion of the H ii region. Goicoechea et al. (2016) detected a fragmented ridge of high-density substructures at the molecular cloud surface and three periodic emission maxima in HCO+ (4–3) from the cloud edge to the interior of the Bar, providing evidence that a high-pressure wave has compressed the cloud surface and moved into the cloud to a distance of ∼15″ from the dissociation front. The dust condensations are also located within a distance of 15″ from the dissociation front, and thus are very likely over-dense structures created as the compressive wave passed by. The complex clumpy appearance of the condensations is probably related to the front instability of the compressive wave (Goicoechea et al. 2016), or an instability developed across different layers of the Bar (e.g., the thin-shell instability, García-Segura & Franco 1996). The velocity structure of dense gas around the dust condensations may provide insights into the feasibility of this scenario. Figure 10 shows the intensity-weighted velocity map of the H2CS (71,7–61,6) emission. A velocity gradient in a northwest–southeast direction (i.e., along the direction of the propagation of the compressive wave) is seen in the map, and is consistent with the scenario that the gas is being compressed by a high-pressure wave.
Citation: Falgarone & Passot 2003
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Figure 9 presents Fourier power spectrum for wave period P versus height. The initial pulse has a Gaussian spectrum of wave number k which results in a spectrum of period P. The steepening of the magnetoacoustic waves results from the growing wave amplitude with height. Hence, waves with shorter wavelengths and wave periods are present for higher y-values in their Fourier spectra. For the pulse launched from y = y0 = 0 Mm (top), the main wave period of the downward-propagating waves becomes approximately the same for all values of y  0 Mm and is equal to about 250 s. Higher up, however, the period P decays with increasing y, and attains values close to 200 s. As a result of the cut-off only short-period waves can propagate upwards while long-period waves become evanescent. Hence, the relative contribution of long P waves weakens with increasing y. We note that some of our data fits the observational findings of Wiśniewska et al. (2016), represented by diamonds over-plotted on the power spectra, and Kayshap et al. (2018), denoted by dots. The agreement of the theory with the observational data indicates that the results can be used to determine the background structure of the solar atmosphere and confirms that wave generation by the solar granulation in the partially ionized plasma dominates the behavior of the waves. For a pulse at the bottom of the photosphere (y = y0 = 0 Mm, Fig. 9 (top)), a jump in the dominant wave period is observed close to the height y = 1.5 Mm, which reaches a magnitude of 300 s. The signal launched from the bottom of the photosphere with the main period P = 250 s thus reaches the corona with P = 300 s. The wave periods in the photosphere are lower than Pac in this region, because max Pac = 240 s at y = 0.5 Mm, which means that magnetoacoustic waves are evanescent. However, in the corona above y = 2.3 Mm the acoustic cut-off period reaches values larger than P = 300 s. However, this is not the case for a pulse launched at a somewhat greater height, in the middle of the photosphere, namely for y = y0 = 0.25 Mm (see Fig. 9 (bottom)). Moreover, in this case the layers below the photosphere (y  0) oscillate with a dominant wave period of 225 s. In the photosphere, this wave period is also dominant and this time it increases slightly with height in the photosphere. Moreover, in this case there is a second dominant period, namely 250 s. In fact, this wave period is also the dominant one in the upper chromosphere and low corona in this case.
Citation: Wiśniewska et al. (2016)
Citation function: Similarities; Uses; Compare/Contrast
The aforementioned fluid description offers a good starting point to understand the global electric circuit made of charge and current densities. However, it neglects some fundamental kinetic aspects required to self-consistently include single particle acceleration as well as radiation feedback. As kinetic simulations are much more demanding than fluid models, this approach was only scarcely investigated in the last century. Let us mention Krause-Polstorff & Michel (1985) who computed axisymmetric dead pulsar magnetospheres called electrospheres. Due to the axisymmetry of the problem they used rings of charges instead of point particles. Later with the advent on computational power, Smith, Michel & Thacker (2001) showed with slightly more sophisticated simulations that a fully field magnetosphere is unstable and collapse to an electrosphere. The first full three-dimensional electrosphere was constructed by McDonald & Shearer (2009), using an electromagnetic Particle in Cell (PIC) code. They neglect pair creation and therefore did not add any particle injection process. Eventually Philippov & Spitkovsky (2014) computed the first two-dimensional axisymmetric pulsar magnetosphere for an aligned rotator by permanently injecting particle supposed to be released from the surface, avoiding to end to an electrosphere configuration (Pétri, Heyvaerts & Bonazzola 2002). Depending on the volume injection rate, they were able to find any equilibrium between the force-free and the fully charge separated state. Chen & Beloborodov (2014) improved this model by adding a prescription for the pair creation, putting a threshold on the lepton Lorentz factor. Following the same lines, Cerutti et al. (2015) assumed particle injection only from the vicinity of the stellar surface. Belyaev (2015) injected particles from regions where a parallel electric field exists. The first full three-dimensional PIC simulations of a pulsar magnetosphere were performed by Philippov, Spitkovsky & Cerutti (2015b). For an aligned rotator Philippov et al. (2015a) also included general-relativistic corrections with frame-dragging. Soon after some observational signature predictions were added to compute light curves and spectra emanating from curvature and or synchrotron radiation like for instance Cerutti, Philippov & Spitkovsky (2016b) who then included polarization (Cerutti, Mortier & Philippov 2016a). This PIC simulations were then extended to the striped wind well outside the light-cylinder to study its dissipation (Cerutti & Philippov 2017; Cerutti, Philippov & Dubus 2020). The oblique magnetosphere with radiation and general-relativistic correction was eventually computed by Philippov & Spitkovsky (2018). Several other groups performed similar simulations like Brambilla et al. (2018) or Kalapotharakos et al. (2017, 2018) who tried to explicitly connect their simulation results to gamma-ray observations. Alternatively, more simply test particle trajectories can be explored within a fluid code (see for instance Brambilla et al. 2015).
Citation: Pétri, Heyvaerts & Bonazzola 2002
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The chemistry of C4H3N isomers in cold molecular clouds was discussed by Balucani et al. (2000), and more specifically by Balucani et al. (2002), based on crossed molecular beam experiments and ab initio calculations. In these studies, it was pointed out that reactions of the CN radical with methyl acetylene and allene are barrier-less and exothermic when producing CH3C3N and CH2CCHCN in the methyl acetylene reaction, and CH2CCHCN and HCCCH2CN in the reaction involving allene. Indeed, the reactions of CN with CH3CCH and CH2CCH2 were measured to be rapid at low temperatures (Carty et al. 2001). This chemical scheme was implemented in a chemical model by Quan & Herbst (2007) to explain the abundance of cyanoallene in TMC-1. Later on, Abeysekera et al. (2015) measured the product branching ratios of the reaction between CN and methyl acetylene at low temperatures using a chirped-pulse uniform flow and found that HC3N is the major product, while CH3C3N accounts for 22% of the products and CH2CCHCN is not formed. These results are in contrast with those obtained from crossed molecular beam experiments (Huang et al. 1999; Balucani et al. 2000, 2002), where CH2CCHCN is observed as a product of the CN + CH3CCH reaction. Therefore, the most stable isomer, CH3C3N, can be formed in the reaction of CN and methyl acetylene, the second most stable isomer, CH2CCHCN, can be formed when CN reacts with CH2CCH2 – and perhaps also with CH3CCH, depending on whether one gives credit to the chirped-pulse uniform flow experiment or to the crossed molecular beam ones – and the least stable isomer, HCCCH2CN, can only be formed in the reaction between CN and allene. These neutral-neutral reactions involving CN are therefore likely routes to the three C4H3N isomers in cold interstellar clouds such as TMC-1, where abundant CN, CH3CCH, and probably CH2CCH2 (non-polar and thus cannot be detected at radio wavelengths) are present. Moreover, the presence of HCCCH2CN (and perhaps also CH2CCHCN) can be used as a proxy of the non-polar C3H4 isomer allene since this isomer is only formed from CH2CCH2 in the aforementioned reactions of CN.
Citation: Quan & Herbst (2007)
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