SerendipitousChandraX-Ray Detection of a Hot Bubble within the Planetary Nebula NGC 5315

Abstract

We report the serendipitous detection of the planetary nebula NGC 5315 by the Chandra X-ray Observatory. The Chandra imaging spectroscopy results indicate that the X-rays from this PN, which harbors a Wolf-Rayet (WR) central star, emanate from a T X ∼ 2.5 × 10 6 K plasma generated via the same windwind collisions that have cleared a compact (∼ 8000 AU radius) central cavity within the nebula. The inferred X-ray luminosity of NGC 5315 is ∼ 2.5 × 10 32 erg s −1 (0.3-2.0 keV), placing this object among the most luminous such "hot bubble" X-ray sources yet detected within PNe. With the X-ray detection of NGC 5315, objects with WR-type central stars now constitute a clear majority -2of known examples of diffuse X-ray sources among PNe; all such "hot bubble" PN X-ray sources display well-defined, quasi-continuous optical rims. We therefore assert that X-ray-luminous hot bubbles are characteristic of young PNe with large central star wind kinetic energies and closed bubble morphologies. However, the evidence at hand also suggests that processes such as wind and bubble temporal evolution, as well as heat conduction and/or mixing of hot bubble and nebular gas, ultimately govern the luminosity and temperature of superheated plasma within PNe.

Formation and X-ray emission from hot bubbles in planetary nebulae – II. Hot bubble X-ray emission

“…Thus, fossil magnetic fields could be present in the nebular gas surrounding the CSPN at the onset of the fast wind. The high incidence of diffuse X-ray detections in PNe (∼ 30%; Kastner et al 2012;Freeman et al 2014) therefore requires explanations that do not necessarily require thermal conduction.…”

“…on spectra convolved with the Chandra ACIS-S response matrices, in order to facilitate direct comparison with current and future results of the Chandra Planetary Nebula Survey (ChanPlaNS; Kastner et al 2012, Freeman et al 2014, Montez et al 2015. Figure 18 shows examples of the final absorbed and convolved spectra for cases with and without thermal conduction for the 1.5-0.597 models at a selection of different times in the post-AGB evolution.…”

“…Hence the physical properties of hot bubbles in PNe derived from such low count-rate spectra will not be very reliable. Unfortunately, there are several PNe that have not been observed with more than 50 counts due to their reduced exposure times (see Kastner et al 2012;Ruiz et al 2013;Freeman et al 2014). On the other hand, 200-count spectra give a reasonable description of the spectral shape.…”

“…The detected objects are generally compact (RHB < 0.2 pc in radius) with closed structures, suggesting that they are young objects (< 5×10 3 yrs), with high nebular electron densities ne > 10 3 cm −3 (as determined via their Hα line luminosities). Detailed spectral analysis of some of the detected objects indicates that the temperature of the X-ray-emitting gas lies in the narrow range (1-3) × 10 6 K with electronic densities of the order of 1-10 2 cm −3 (e.g., Ruiz et al 2013; Kastner et al 2012, and references therein). Some of the objects detected in diffuse emission can be described using the abundances of that of c 0000 RAS the nebular material, while others require stellar abundances (e.g., Yu et al 2009).…”

Analysis of far-UV data of central stars of planetary nebulae: Occurrence and variability of stellar winds

“…This may also be the case for A 43 and Lo 4 although the large number of narrow absorptions over-imposed on the profile makes it hard to determine; the remaining objects show unsaturated P Cygni profiles. All the CSPNe with P Cygni profile in the Ne vii line have T eff > 100 000 K ( NGC 2371-2, NGC 7094, and RX J2117.4+3412 is detected in soft X-rays (Motch et al 1993;Hoare et al 1995;Kastner et al 2012), whereas A 30's central star's soft X-ray emission may have a different origin (Guerrero et al 2012 Despite this difficulty, the P Cygni profiles of the two components can be used to lend weight to the determination of the line profile. Owing very likely to the sulfur abundance in the stellar wind being lower than that of oxygen, the S vi lines are saturated just in three CSPNe (IC 2501, NGC 5882, and NGC 6572) out of the 15 displaying it.…”