Ejecta, Dust, and Synchrotron Radiation in SNR B0540−69.3: A More Crab‐Like Remnant than the Crab

Abstract

We present near and mid-infrared observations of the pulsar-wind nebula (PWN) B0540-69.3 and its associated supernova remnant made with the Spitzer Space Telescope. We report detections of the PWN with all four IRAC bands, the 24 µm band of MIPS, and the Infrared Spectrograph (IRS). We find no evidence of IR emission from the X-ray/radio shell surrounding the PWN resulting from the forward shock of the supernova blast wave. The flux of the PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths, with a warm dust component longward of 20 µm. We show that this dust continuum can be explained by a small amount (∼ 1 − 3 × 10 −3 M ⊙ ) of dust at a temperature of ∼ 50 − 65 K, heated by the shock wave generated by the PWN being driven into the inner edge of the ejecta. This is evidently dust synthesized in the supernova. We also report the detection of several lines in the spectrum of the PWN, and present kinematic information about the PWN as determined from these lines. Kinematics are consistent with previous optical studies of this object. Line strengths are also broadly consistent with what one expects from optical line -2strengths. We find that lines arise from slow (∼ 20 km s −1 ) shocks driven into oxygen-rich clumps in the shell swept-up by an iron-nickel bubble, which have a density contrast of ∼ 100 − 200 relative to the bulk of the ejecta, and that faster shocks (∼ 250 km s −1 ) in the hydrogen envelope are required to heat dust grains to observed temperatures. We infer from estimates of heavy-element ejecta abundances that the progenitor star was likely in the range of 20-25 M ⊙ .

The near-infrared detection of PSR B0540–69 and its nebula

“…Moreover, our nIR and the optical fluxes were corrected for the contribution from the pulsar and the background/foreground stars overlapping the PWN, while this is clearly not the case for the Spitzer fluxes, where both the pulsar and the stars are not resolved at the angular scale of the IRAC and MIPS data. For this reason, the true intrinsic nebular fluxes in the mIR are, most likely, lower that those presented in Williams et al (2008). We note that the PWN spectral index has to change once more somewhere between the nIR/mIR and the radio bands from α PWN nIR = 0.56 to α PWN R = 0.25 ± 0.1 (Manchester et al 1993).…”

“…This is probably due to the 336W flux, which is lower than the best-fit optical/nIR PL and, then, produces a steepening of the PL in the optical. The best-fit Chandra PL spectrum of the PWN in 0.6-10 keV energy range Kaaret et al (2001) is also shown in Fig.8, together with the mIR fluxes from the Spitzer IRAC and MIPS observations (Williams et al 2008) and the radio fluxes from Manchester et al (1993). The extrapolation of the PWN X-ray spectrum, with spectral index α PWN X = 1.04, to the nIR-optical domain clearly overestimates the PWN optical and nIR fluxes.…”

“…However, only very few pulsars have been observed to pulsate in the optical (see Mignani 2010Mignani , 2012, for recent reviews), including the Crab and Vela pulsars and PSR B0540−69. Of them, only the Crab (Eikenberry et al 1997) has been observed to pulsate in the nIR, although not Mignani et al (2010), the Spitzer IRAC and MIPS fluxes (triangles) of Williams et al (2008), and the radio fluxes (diamonds) from Manchester et al (1993). The Chandra PL fit to the X-ray spectrum of the PWN (Kaaret et al 2001) is shown as a black bow-tie.…”

The PSR J1124-5916 wind nebula in the near-infrared

“…A sharp, probably double-knee break between the optical and X-rays is visible in the spectrum of the similar age 3C 58 PWN 6 . The spectrum of B0540-69, which is slightly older than the Crab, suggesting a break at a few microns (Mignani et al 2012), and then flattens again at longer wavelengths (Williams et al 2008). A double-knee break between the optical and X-rays is not excluded either (Serafimovich et al 2005).…”

“…A double-knee break between the optical and X-rays is not excluded either (Serafimovich et al 2005). At the same time, the IR part of the G21.5-09 spectrum is probably almost 3 The data are taken for the Crab from Green et al (2004), Temim et al (2006), Grasdalen (1979), Veron-Cetty & Woltjer (1993), and Kirsch et al (2005); for G21.5-0.9 from Zajczyk et al (2012); for B0540-69.3 from Manchester et al (1993), Williams et al (2008), Mignani et al (2012), and Serafimovich et al (2005); for 3C 58 from Shibanov et al (2008), Shearer & Neustroev (2008), and Slane et al (2008). 4 We indicate in the plot the SNR (870 yr, Bietenholz & Bartel 2008) and spindown (4800 yr, Camilo et al 2006) ages for this PWN.…”