Observational Constraints on Superbubble X-Ray Energy Budgets

Abstract

The hot, X-ray-emitting gas in superbubbles imparts energy and enriched material to the interstellar medium (ISM) and generates the hot ionized medium, the ISM's high-temperature component. The evolution of superbubble energy budgets is not well understood, however, and the processes responsible for enhanced X-ray emission in superbubbles remain a matter of debate. We present Chandra ACIS-S observations of two X-ray-bright superbubbles in the Large Magellanic Cloud (LMC), DEM L50 (N186) and DEM L152 (N44), with an emphasis on disentangling the true superbubble X-ray emission from non-related diffuse emission and determining the spatial origin and spectral variation of the X-ray emission. An examination of the superbubble energy budgets shows that on the order of 50% of the X-ray emission comes from regions associated with supernova remnant (SNR) impacts. We find some evidence of mass-loading due to swept-up clouds and metallicity enrichment, but neither mechanism provides a significant contribution to the X-ray luminosities. We also find that one of the superbubbles, DEM L50, is likely not in collisional ionization equilibrium. We compare our observations to the predictions of the standard Weaver et al. model and to 1-D hydrodynamic simulations including cavity supernova impacts on the shell walls. Our observations show that mass-loading due to thermal evaporation from the shell walls and SNR impacts are the dominant source of enhanced X-ray luminosities in superbubbles. These two processes should affect most superbubbles, and their contribution to the X-ray luminosity must be considered when determining the energy available for transport to the ISM.

The soft and hard X-rays thermal emission from star cluster winds with a supernova explosion

“…Moreover, the numerical models that appear in Jaskot et al (2011) produce luminosities that are two orders of magnitude lower than the observations (∼ 10 36 erg s −1 ). Therefore the authors explored the effect of the metallicity and of mass loading by clouds to bridge the luminosity deficit in soft X-rays.…”

“…According to observations DM L152 has a radius of approximately 50 pc (Jaskot et al 2011), and DEM L50 has roughly the same radius (Oey 1996). Jaskot et al (2011) reported an X-ray luminosity in the range 2.0-4.0×10 36 erg s −1 for DEM L50 and an emission of 5.4-5.7×10 35 erg s −1 . These two superbubbles contrast with N70 and N185 in that they contain an off-centre SN explosion, which is clearly distinguishable in the observations.…”

“…For this purpose we have taken a sample of Figure 8. Comparison of the X-ray emissivity in the soft (color maps, with the shown logarithmic scale given in erg s −1 cm −2 sterad −1 ) and hard (contours, logarithmically-spaced levels from 10 −11 to 10 −8 erg s −1 cm −2 sterad −1 ) bands at the three different stages shown in Figure 3. 26 bubbles with luminosities greater than 10 34 erg s −1 from the literature (Oey 1996;Jaskot et al 2011;Reyes-Iturbide et al 2014;Dunne et al 2001). Out of these, 18 have luminosities above 10 35 erg s −1 while only 3 are observed with L soft > 10 36 erg s −1 .…”

“…These models are those discussed in Section 3: two with a centred SN explosion that differ in the presence of thermal conduction, and the third with the SN explosion 10 pc off-centre. Following Jaskot et al (2011), the hardness ratio is defined as:…”

“…Some of these superbubbles (for instance, DEM L50 and DEM L152, see Jaskot et al 2011) show evidence for off-centre supernova events which seem to interact with the external shell pushed by the stellar winds. In the observations made by Jaskot et al (2011) the gas of the supernova remnant is still seen. This remnant is located close to the superbubble edge.…”