IR Shell Surrounding the Pulsar Wind Nebula G54.1+0.3

SNRs and PWNe in the Chandra Era Boston, July 8, 2009

Tea Temim(CfA, Univ. of MN)

Collaborators: P. Slane, S. Reynolds, J. Raymond, K. Borkowski

Outline

1. Structure of PWNe Evolving Inside SNRs

1. IR Observations of G54.1+0.3: Evidence for Interaction with SN Ejecta• IRAC and MIPS Imaging• IRS Spectroscopy• Dust emission – evidence for freshly formed dust• New interpretation for the origin of IR emission

2. Summary & Conclusions

Evolution of PWNe inside SNRs

Gaensler & Slane 2006

Examples of PWNe interacting with SN ejecta include: Crab (Hester et al. 2008 for review), 3C58 (Bocchino et al. 2001, Slane et al. 2004), 0540-69.3 (e.g., Reynolds 1985)

• Pulsar wind is shocked at the termination shock• PWN drives a shock into the freely expanding, cold SN ejecta

• SNR blast wave sweeps up ISM material and reverse shock heats the inner ejecta• Reverse shock encounters the PWN surface and crushes the nebula

• G54.1+0.3 PWN sweeping up inner ejecta

G54.1+0.3Pulsar: J1930+1852P = 138 ms (Camilo et al. 2002)Edot = 1.2 x 1037 ergs/sCharacteristic age = 2900 yr Actual age = 1500 – 6000 yr Distance = 6 kpc (5 – 8 kpc) (Lu et al. 2002, Camilo et al. 2002, Leahy et al. 2008)PWN radius = 1 arcmin (1.8 pc)NH = 1.95 (0.04) x 1022 cm-2

• X-ray spectra well described by a power-law model with the spectral index steepening with distance from the pulsar (Lu et al. 2002)

• There has been no evidence for emission from a thermal component in X-rays - new Spitzer IR observations provide evidence for an interaction of the PWN with SN ejecta

Chandra

Spitzer Imaging

Radio, MIPS 70 m, MIPS 24 m, X-ray

5.8 m 8.0 m

24 m 70 m

Infrared images reveal a shell with a radius of 1.5 arcmin - X-ray nebula fills the cavity of the shell

Total IR Fluxes:5.8 m ~ 0.3 Jy8.0 m ~ 1 Jy24 m 40 (4) Jy70 m 76 (15) Jy

MIPS 24 m image shows a dozen point sources embedded in the IR shell – suggested to be young stellar objects (Koo et al. 2008)

Spitzer Spectroscopy

IR spectrum shows various emission lines (strongest from Si, S, Ne, and Ar) and a rising continuum with broad dust features around 13 and 21 m

IRS slits overlaid on the MIPS 24 m image

Spectral Line Profiles

Some emission lines are significantly broadened, up to a FWHM = 1000 km/s (expected resolution of IRS = 500 km/s)

Shock Diagnostics• Models with cosmic abundances and depleted refractory elements run for several shock speeds and pre-shock densities (Hartigan et al. 1987)• A pre-shock density of 10 cm-3 matches the SIII line ratio.• A shock speed of at least 100 km/s needed to produce SIV, but a shock faster than 110 km/s would produce too much OIV.• A factor of 3 depletion in refractory elements needed at position 1, and a larger factor at position 2

Spitzer Spectroscopy

Chevalier 2005 – Models for young PWNe expanding into SN ejecta:

Vsh = 0.25Rp/t t = 4500 yrVexp = 400 km/sVobs = 500 km/s observed line broadeningMsw = EdotRp

-2t3 Msw = 0.5 M

Figures: Rho et al. 2008, 2009

Dust EmissionCas A

G54.1+0.3

• Continuum emission in G54.1+0.3 closely resembles the IR spectrum of Cas A – same broad 21 m feature

• Distribution of 21 m dust in Cas A similar to that of SN ejecta -> freshly formed SN dust (Rho et al. 2008)

Rough dust temperature and mass estimates made by fitting the IR spectrum and the total 24 and 70 m fluxes with forsterite (Mg2SiO4) grain compositions:

Mdust = 0.015 – 0.05 M (T = 60 – 70 K)•Spitzer imaging and spectral maps of SNRs have allowed estimates of masses of freshly formed - dust emission coincides with lines from SN ejecta dust (Rho et al. 2009)

Cas A 0.02 - 0.05 M

E0102 0.007 - 0.015 M

N132D 0.008 M (lower limit)

Dust Mass Estimate Combined Silicon

Argon 21 m Dust Feature

Dust Emission: Heating by Stellar SourcesKoo et al. 2008

• Colors of the point sources in the IR shell resemble colors of young stellar objects• In this case the IR shell would have to be a pre-existing shell, but we see no evidence for outer blast wave MIPS 24 m

Alternative Explanation for IR Point Sources• Dust model (Borkowski 1994) for forsterite with power law distribution of grain sizes, and a grain mass density of 0.007 M/pc3, heated by a main sequence B0 star with T=30,000 K dozen stars and 0.1 M of dust needed to reproduce 24/70 m ratio• Model shows that ejecta dust heated by main sequence stars can produce IR emission resembling point sources at 24 m SN exploding in a stellar cluster could explain IR observations

RADIUS (arcsec)

SURF

ACE

BRIG

HTN

ESS

---- PSF Profiles

24 m

70 m

ConclusionsIR observations of the shell surrounding G54.1+0.3 provide first evidence of the PWN interacting with SN ejecta:• Morphological association between the shell and the PWN

• Spectral lines broadened to 1000 km/s (FWHM)

• Shock velocities on the order of 100 km/s leads to an age of 4500 yr and a shell velocity of 500 km/s, consistent with line broadening

• Dust emission features resemble freshly formed dust in Cas A

• Estimated dust mass is in the same range as for ejecta dust in other SNRs

• IR point sources at 24 m may be explained by radiative heating of ejecta dust by main sequence stars in a cluster

• We may be probing SN dust that is usually destroyed by shocks!

Unidentified 21 m Feature• Similar feature observed in carbon-rich protoplanetary nebulae (Posch et al. 2004 for review) – most likely candidates are FeO (Zhang et al. 2009) and SiC grains (Speck & Hofmeister 2004)• SiO2 used to fit the 21 m feature in Cas A (Rho et al. 2009)• More detailed spectral fitting required to determine dust composition in the shell of G54.1+0.3

Spatial Variation in Line Intensities

• 21 m feature most pronounced at the bright IR knot• [SIII] 18.7 m enhanced at the IR knot -> higher density in this region• Silicon enhanced at the interface between the PWNe and the IR shell• [ArII] also peaks at the position of the shell cavity

Rough dust temperature and mass estimates made by fitting the IR spectrum and the total 24 and 70 micron fluxes with astronomical silicates and forsterite (Mg2SiO4) grain compositions

Total Dust Mass in the IR Shell:

Mdust = 0.015 – 0.05 M (T = 60 – 70 K)

Dust Emission

• Spitzer imaging and spectral maps of SNRs have allowed estimates of masses of freshly formed dust• Dust emission coincides with lines from SN ejecta (Rho et al. 2009)

Cas A 0.02 - 0.05 M

E0102 0.007 - 0.015 M

N132D 0.008 M (lower limit)G11.2-0.3same order of magnitude