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(left) Narrow-band H α image of the WR nebula around WR 16 taken from the Super COSMOS Sky Survey (Parker et al. 2005). (right) Color-composite mid-infrared WISE W2 4.6 μ m (blue), W3 12 μ m (green), and W4 22 μ m (red) picture of the WR nebula around WR 16. The central star, WR 16, is located at the center of each image. North is up, east to the left.
Source publication
We present the analysis of XMM-Newton archival observations towards the
Wolf-Rayet (WR) bubble around WR16. Despite the closed bubble morphology of
this WR nebula, the XMM-Newton observations show no evidence of diffuse
emission in its interior as in the similar WR bubbles NGC6888 and S308. We use
the present observations to estimate a 3-\sigma upp...
Contexts in source publication
Context 1
... WR nebula around WR 16 was first discovered by Marston et al. (1994), who described it as a round main neb- ula with multiple arc-like features towards the northwest (see Figure 1-left). The main nebula is classified as a wind-blown bubble (a W-type nebula according to the classification scheme developed by Chu 1981), whereas the outer features have been associated with multiple mass ejection episodes (Marston 1995). ...
Context 2
... optical and radio morphologies of the nebula around WR 16 are consistent with the mid-infrared morphology re- vealed by WISE observations (see Figure 1-right). In particular, the W4 band (red in Figure 1-right) shows a complete round shell with enhanced, limb-brightened emission towards the northwest direction. ...
Context 3
... optical and radio morphologies of the nebula around WR 16 are consistent with the mid-infrared morphology re- vealed by WISE observations (see Figure 1-right). In particular, the W4 band (red in Figure 1-right) shows a complete round shell with enhanced, limb-brightened emission towards the northwest direction. The round WR nebula seen in this WISE band matches that of the IRAS 60 µm image presented by Marston et al. (1999). ...
Context 4
... interpretation of this behaviour is that a disrupted shell cannot hold the hot gas which escapes away. Contrary to this trend, the nebula around WR 16 displays a complete shell morphology (Figure 1), but we have set a stringent upper limit for the X-ray emission from hot plasma in its interior. ...
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Citations
... They lie at a distances of a few parsec from the central star (Stock & Barlow 2010), with some lying as close as 0.7 pc (Cohen et al. 2005;Sirianni et al. 1998). In addition, the wind-blown bubbles form a low-density cavity with densities as low as 10 −3 -10 −2 cm −3 (Toalá & Guerrero 2013) and, in some cases, the nebula itself is located inside a cavity in the interstellar medium (Vamvatira-Nakou et al. 2016). ...
... However, in the mixing zone between the hot bubble and the cooler outer material the emission measure is expected to increase to detectable levels. Such a scenario is consistent with observations yielding upper limits to the density (e.g., Chu et al. 2003;Toalá & Guerrero 2013). Furthermore, we note that such tenious medium is consistent with several observations of GRB afterglows, which indicate circumburst medium which have very low densities (Piro et al. 2014;Ryde et al. 2022;Dereli-Bégué et al. 2022), in some cases, even as low as 10 −4 cm −3 (Oganesyan et al. 2023). ...
... • Characteristic density inside the cavity: n ∼ 10 −2 cm −3 (e.g., Chu et al. 2003;Toalá & Guerrero 2013). ...
Progenitor stars of long gamma-ray bursts (GRBs) could be surrounded by a significant and complex nebula structure lying at a parsec scale distance. After the initial release of energy from the GRB jet, the jet will interact with this nebula environment. We show here that for a large, plausible parameter space region, the interaction between the jet blastwave and the wind termination (reverse) shock is expected to be weak, and may be associated with a precursor emission. As the jet blast wave encounters the contact discontinuity separating the shocked wind and the shocked interstellar medium, we find that a bright flash of synchrotron emission from the newly-formed reverse shock is produced. This flash is expected to be observed at around ~100 s after the initial explosion and precursor. Such a delayed emission thus constitutes a circumburst medium (CBM) phase in a GRB, having a physically distinct origin from the preceding prompt phase and the succeeding afterglow phase. The CBM phase emission may thus provide a natural explanation to bursts observed to have a precursor followed by an intense, synchrotron-dominated main episode that is found in a substantial minority, ~10% of GRBs. A correct identification of the emission phase is thus required to infer the properties of the flow and of the immediate environment around GRB progenitors.
... Instabilities will cause elevation of the outer envelope potentially leading to occasional giant eruption events, with major mass ejections in several consecutive periods. These mass ejections lead to circumstellar nebulae and wind blown bubbles 66,67 . Observations of galactic Wolf-Rayet stars indicate shell structures and nebulae at 1-10 pc scales, and in some cases, reveals the existence of low density cavities within these nebulae 67 . ...
... These mass ejections lead to circumstellar nebulae and wind blown bubbles 66,67 . Observations of galactic Wolf-Rayet stars indicate shell structures and nebulae at 1-10 pc scales, and in some cases, reveals the existence of low density cavities within these nebulae 67 . We thus view one of the merits of this work as providing further information that could potentially help understanding the nature of these objects. ...
Gamma-ray bursts (GRBs) are known to have the most relativistic jets, with initial Lorentz factors in the order of a few hundreds. Many GRBs display an early X-ray light-curve plateau, which was not theoretically expected and therefore puzzled the community for many years. Here, we show that this observed signal is naturally obtained within the classical GRB fireball model, provided that the initial Lorentz factor is rather a few tens, and the expansion occurs into a medium-low density wind. The range of Lorentz factors in GRB jets is thus much wider than previously thought and bridges an observational gap between mildly relativistic jets inferred in active galactic nuclei, to highly relativistic jets deduced in few extreme GRBs. Furthermore, long GRB progenitors are either not Wolf-Rayet stars, or the wind properties during the final stellar evolution phase are different than at earlier times. Our model has predictions that can be tested to verify or reject it in the future, such as lack of GeV emission, lack of strong thermal component and long (few seconds) variability during the prompt phase characterizing plateau bursts.
... Instabilities will cause elevation of the outer envelope potentially leading to occasional giant eruption events, with major mass ejections in several consecutive periods. These mass ejections lead to circumstellar nebulae and wind blown bubbles 64,65 . Observations of galactic Wolf-Rayet stars indicate shell structures and nebulae at 1-10 pc scales, and in some cases, reveals the existence of low density cavities within these nebulae 65 . ...
... These mass ejections lead to circumstellar nebulae and wind blown bubbles 64,65 . Observations of galactic Wolf-Rayet stars indicate shell structures and nebulae at 1-10 pc scales, and in some cases, reveals the existence of low density cavities within these nebulae 65 . We thus view one of the merits of this work as providing further information that could potentially help understanding the nature of these objects. ...
Gamma-ray bursts (GRBs) are known to have the most relativistic jets, with initial Lorentz factors in the order of a few hundreds. Many GRBs display an early X-ray light-curve plateau, which was not theoretically expected and therefore puzzled the community for many years. Here, we show that this observed signal is naturally obtained within the classical GRB "fireball" model, provided that the initial Lorentz factor is rather a few tens, and the expansion occurs into a medium-low density "wind". The range of Lorentz factors in GRB jets is thus much wider than previously thought and bridges an observational gap between mildly relativistic jets inferred in active galactic nuclei, to highly relativistic jets deduced in few extreme GRBs. Furthermore, long GRB progenitors are either not Wolf-Rayet stars, or the wind properties during the final stellar evolution phase are different than at earlier times. We discuss several testable predictions of this model.
... Up to a third of WR stars observed in the galaxy have a narrow ring nebula (Marston 1997) lying at a typical distance of 1 pc from the central star, and some have much smaller sizes (Stock & Barlow 2010). The existence of a lowdensity cavity within such wind-blown bubbles (Toalá & Guerrero 2013) would lead to very little interaction with the blast wave before it encounters the circumstellar ring itself. This fact is supported by the quiescent period observed just before the 130 s flare in GRB 160821A. . ...
The physical processes of gamma-ray emission and particle acceleration during the prompt phase in gamma-ray bursts (GRBs) are still unsettled. In order to perform unambiguous physical modeling of observations, a clear identification of the emission mechanism is needed. An instance of a clear identification is the synchrotron emission during the very strong flare in GRB 160821A, which occurred during the prompt phase at 135 s. Here we show that the distribution of the radiating electrons in this flare is initially very narrow but later develops a power-law tail of accelerated electrons. We thus identify for the first time the onset of particle acceleration in a GRB jet. The flare is consistent with a late energy release from the central engine causing an external shock as it encounters a preexisting ring nebula of a progenitor Wolf–Rayet star. Relativistic forward and reverse shocks develop, leading to two distinct emission zones with similar properties. The particle acceleration only occurs in the forward shock, moving into the dense nebula matter. Here, the magnetization also decreases below the critical value, which allows for Fermi acceleration to operate. Using this fact, we find a bulk Lorentz factor of 420 ≲ Γ ≲ 770 and an emission radius of R ∼ 10 ¹⁸ cm, indicating a tenuous gas of the immediate circumburst surroundings. The observation of the onset of particle acceleration thus gives new and independent constraints on the properties of the flow as well as on theories of particle acceleration in collisionless astrophysical shocks.
... Up to a third of WR stars observed in the Galaxy have a narrow ring nebula (Marston 1997) lying at a typical distance of 1 pc from the central star, and some having much smaller sizes (Stock & Barlow 2010). The existence of a low-density cavity within such wind-blown bubbles (Toalá & Guerrero 2013) would lead to very little interaction with the blast wave before it encounters the circumstellar ring itself. This fact is supported by the quiescent period observed just before the 130 s flare in GRB160821A. ...
The physical processes of the gamma-ray emission and particle acceleration during the prompt phase in GRBs are still unsettled. In order to perform an unambiguous physical modelling of observations, a clear identification of the emission mechanism is needed. An instance of a clear identification is the synchrotron emission during the very strong flare in GRB160821A, that occurs during the prompt phase at 135 s. Here we show that the distribution of the radiating electrons in this flare is initially very narrow, but later develops a power-law tail of accelerated electrons. We thus identify for the first time the onset of particle acceleration in a GRB jet. The flare is consistent with a late energy release from the central engine causing an external-shock as it encounters a preexisting ring nebula of a progenitor Wolf-Rayet star. Relativistic forward and reverse shocks develop, leading to two distinct emission zones with similar properties. The particle acceleration only occurs in the forward shock, moving into the dense nebula matter. Here, the magnetisation also decreases below the critical value, which allows for Fermi acceleration to operate. Using this fact, we find a bulk Lorentz factor of $420 \simleq \Gamma \simleq 770$, and an emission radius of $R \sim 10^{18}$ cm, indicating a tenuous gas of the immediate circumburst surrounding. The observation of the onset of particle acceleration thus gives new and independent constraints on the properties of the flow as well as on theories of particle acceleration in collisionless astrophysical shocks.
... We also compared the X-ray (0.3-1.5 keV) luminosities of K1 and Wolf-Rayet nebulae. Figure 11 shows X-ray luminosity of Wolf-Rayet nebulae as a function of distance from the Earth (Toalá & Guerrero 2013;Toalá et al. 2015), together with that of K1 as a cross. The X-ray luminosity of WR nebulae is in the range of 10 33 -10 34 erg s −1 (Chu et al. 2003;Toalá et al. 2012Toalá et al. , 2015Toalá et al. , 2016. ...
... Comparison of X-ray luminosity between K1 and Wolf-Rayet nebulae. The blue dots indicate X-ray luminosity(Toalá & Guerrero 2013;Toalá et al. 2015Toalá et al. , 2017 of Wolf-Rayet nebulae, and the orange cross line indicates the X-ray luminosity from K1 at the WR 85 assumed distance of ...
We report on a discovery of an X-ray emitting circumstellar material (CSM) knot inside the synchrotron dominant supernova remnant RX J1713.7−3946. This knot was previously thought to be a Wolf–Rayet star (WR 85), but we realized that it is in fact ∼40″ away from WR 85, indicating no relation to WR 85. We performed high-resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The RGS spectrum clearly resolves a number of emission lines, such as N Ly α , O Ly α , Fe xviii , Ne x , Mg xi , and Si xiii . The spectrum can be well represented by an absorbed thermal-emission model with a temperature of k B T e = 0.65 ± 0.02 keV. The elemental abundances are obtained to be N / H = 3.5 ± 0.8 N / H ⊙ , O / H = 0.5 ± 0.1 O / H ⊙ , Ne / H = 0.9 ± 0.1 Ne / H ⊙ , Mg / H = 1.0 ± 0.1 Mg / H ⊙ , Si / H = 1.0 ± 0.2 Si / H ⊙ , and Fe / H = 1.3 ± 0.1 Fe / H ⊙ . The enhanced N abundance with others being about the solar values allows us to infer that this knot is CSM ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to O is obtained to be N / O = 6.8 − 2.1 + 2.5 N / O ⊙ . By comparing this to those in outer layers of red supergiant stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be 15 M ⊙ ≲ M ≲ 20 M ⊙ .
... We also compared the X-ray (0.3-1.5keV) luminosities of K1 and Wolf-Rayet nebulae. Figure 11 shows X-ray luminosity of Wolf-Rayet nebulae as a function of distance from the Earth (Toalá & Guerrero 2013;Toalá et al. 2015), together with that of K1 as a cross. The X-ray luminosity of WR nebulae is in the range of 10 33 -10 34 erg s −1 (Chu et al. 2003;Toalá et al. 2012Toalá et al. , 2015Toalá et al. , 2016. ...
... Comparison of X-ray luminosity between K1 and Wolf-Rayet nebulae. The blue dots indicate X-ray luminosity (Toalá & Guerrero 2013;Toalá et al. 2015Toalá et al. , 2017 of Wolf-Rayet nebulae, and the orange cross line indicates the X-ray luminosity from K1 at the WR 85 assumed distance of 2.1 +0.3 −0.2 kpc. WR 7 shows the luminosity at 0.3-2.0 ...
We report on a discovery of an X-ray emitting circumstellar material knot inside the synchrotron dominant supernova remnant (SNR) RX J1713.7-3946. This knot was previously thought to be a Wolf-Rayet star (WR 85), but we realized that it is in fact $\sim$40$^{\prime\prime}$ away from WR 85, indicating no relation to WR 85. We performed high-resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The RGS spectrum clearly resolves a number of emission lines, such as N Ly$\alpha$, O Ly$\alpha$, Fe XVIII, Ne X, Mg XI, and Si XIII. The spectrum can be well represented by an absorbed thermal emission model with a temperature of $k_{\rm B}T_{\rm e} = 0.65\pm 0.02$ keV. The elemental abundances are obtained to be ${\rm N/H} = 3.5\pm 0.8{\rm \left(N/H\right)_{\odot}}$, ${\rm O/H} = 0.5\pm0.1{\rm \left(O/H\right)_{\odot}}$, ${\rm Ne/H} = 0.9\pm0.1{\rm \left(Ne/H\right)_{\odot}}$, ${\rm Mg/H} = 1.0\pm0.1{\rm \left(Mg/H\right)_{\odot}}$, ${\rm Si/H} = 1.0\pm0.2{\rm \left(Si/H\right)_{\odot}}$, and ${\rm Fe/H} = 1.3\pm0.1{\rm \left(Fe/H\right)_{\odot}}$. The enhanced N abundance with others being about the solar values allows us to infer that this knot is circumstellar material ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to O is obtained to be $\rm N/O = 6.8_{-2.1}^{+2.5}\left(N/O\right)_{\odot}$. By comparing this to those in outer layers of red supergiant stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be $15\, \rm M_{\odot} \lesssim \rm M \lesssim 20\, \rm M_{\odot}$.
... The powerful winds from WR stars (v ∞ 1500 km s −1 , M ≈ 10 −5 M yr −1 ; Hamann, Gräfener & Liermann 2006) interact with slow and dense material ejected on a previous evolutionary stage (either a red supergiant or luminous blue variable), creating the WR nebula. Interestingly, WR nebulae that display diffuse Xray emission harbour early nitrogen-rich (WNE) type stars, whilst late WN stars do not (Gosset et al. 2005;Toalá & Guerrero 2013;Toalá et al. 2018). Although hot gas can be easily produced by the strong winds of massive O stars, not many wind-blown bubbles (WBBs) within the H II regions around single hot stars have been detected by X-ray satellites. ...
We present a multiwavelength study of the iconic Bubble Nebula (NGC 7635) and its ionizing star BD+60○2522. We obtained XMM–Newton EPIC X-ray observations to search for extended X-ray emission as in other similar wind-blown bubbles around massive stars. We also obtained San Pedro Mártir spectroscopic observations with the Manchester Echelle Spectrometer to study the dynamics of the Bubble Nebula. Although our EPIC observations are deep, we do not detect extended X-ray emission from this wind-blown bubble. On the other hand, BD+60○2522 is a bright X-ray source similar to other O stars. We used the stellar atmosphere code PoWR to characterize BD+60○2522 and found that this star is a young O-type star with stellar wind capable of producing a wind-blown bubble that in principle could be filled with hot gas. We discussed our findings in line with recent numerical simulations proposing that the Bubble Nebula has been formed as the result of the fast motion of BD+60○2522 through the medium. Our kinematic study shows that the Bubble Nebula is composed by a series of nested shells, some showing blister-like structures, but with little signatures of hydrodynamical instabilities that would mix the material producing diffuse X-ray emission as seen in other wind-blown bubbles. Its morphology seems to be merely the result of projection effects of these different shells.
... This nebula consists of matter ejected by the star, and thus the mechanism of its formation is different from the WR nebulae around such WNE stars as WR 6, WR 7, WR 18, and WR 136 (see Toalá et al. 2017, and references therein), in which a fast-wind-slowwind interaction is thought to take place (e.g., Garcia-Segura & Mac Low 1995). M1-67 around WR 124 is the third WR nebula around a WN8 star without any hint of diffuse X-ray emission, along with RCW 58 (WR 40) and the nebula around WR 16 (Gosset et al. 2005;Toalá & Guerrero 2013). ...
Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using ∼100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L X ∼ 10³¹ erg s⁻¹ is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems. © 2018. The American Astronomical Society. All rights reserved..
Massive stars leave their imprint on the interstellar medium as they radiate their energy and undergo episodes of mass ejection throughout their lives. In this paper, we analyse the case of the Wolf–Rayet star WR16 combining archival multiwavelength data with new molecular observations obtained with the Atacama Submillimeter Telescope Experiment (ASTE). Our results suggest that during the main-sequence phase, WR16 swept up the surrounding gas creating a molecular structure (which we call Component 1) which also contains very cold dust observed in the infrared band. In a subsequent stage of evolution, as an LBV, the star underwent mass eruptions that were later overrun by the fast winds of the current WR phase. The final result is the round nebula revealed by the optical and IR images, and the molecular clumps detected. We have also computed the peculiar velocity of WR16 using Gaia data and, accordingly, confirm it as a runaway star. We propose that several features observed in different wavelengths can be explained under a bow-shock scenario linked to the high velocity of WR16.
