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Register a new userOptical observations of the young supernova remnant SNR 0540-69.3 and its pulsar
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Added by
Natalia Serafimovich I.
Publication date
2005
fields
Physics
and research's language is
English
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We have used the ESO NTT/EMMI and VLT/FORS1 instruments to examine the LMC supernova remnant 0540-69.3 as well as its pulsar (PSR B0540-69) and pulsar-powered nebula in the optical range.Spectroscopic observations of the remnant covering the range of 3600-7350 A centered on the pulsar produced results consistent with those of Kirshner et al. (1989), but also revealed many new emission lines. The most important are [Ne III] 3869, 3967 and Balmer lines of hydrogen. In both the central part of the remnant, as well as in nearby H II regions, the [O III] temperature is higher than about 20 000 K, but lower than previously estimated. For PSR B0540-69, previous optical data are mutually inconsistent: HST/FOS spectra indicate a significantly higher absolute flux and steeper spectral index than suggested by early time-resolved groundbased UBVRI photometry. We show that the HST and VLT spectroscopic data for the pulsar have more then about 50% nebular contamination, and that this is the reason for the previous difference. Using HST/WFPC2 archival images obtained in various bands from the red part of the optical to the NUV range we have performed an accurate photometric study of the pulsar, and find that the spectral energy distribution of the pulsar emission has a negative slope with 1.07 +/- 0.2. This is steeper than derived from previous UBVRI photometry, and also different from the almost flat spectrum of the Crab pulsar. We also estimate that the proper motion of the pulsar is 4.9 +/- 2.3 mas/yr, corresponding to a transverse velocity of 1190 +/- 560 km/s, projected along the southern jet of the pulsar nebula.
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We present a study of the plerionic supernova remnant 0540-69.3 in the LMC in X-ray, radio, optical, and infrared. We find that the shell of 0540-69.3 is characterized in the X-ray by thermal nonequilibrium plasma with depleted Mg and Si abundances and a temperature of kT ~ 0.7 keV. This thermal emission is superimposed with synchrotron emission in several regions. Based on X-ray spectra and on morphological considerations in all surveyed wavebands, we conclude that the shell is expanding into a clumpy and highly inhomogeneous medium. In one region of the shell we find an overabundance of Ne, suggesting the presence of ejecta near the edge of the remnant. We also see evidence for reheating of material via a reverse shock originating from the interaction of the supernova blast wave with a particularly dense cloud in the surrounding medium. Finally, we perform the first detailed study of the halo region extending 1.2-2.2 pc from the central pulsar. We detect the presence of thermal and nonthermal spectral components but do not find evidence for mixing or ejecta. We conclude that the thermal component is not a counterpart to similar optical and infrared halos and that it is most likely due to the projection of shell material along the line of sight.
We present observations of the pulsar-wind nebula (PWN) region ofSNR 0540-69.3. The observations were made with the Atacama Compact Array (ACA) in Bands 4 and 6. We also add radio observations from the Australia Compact Array (ATCA) at 3 cm. For 1.449 - 233.50 GHz we obtain a synchrotron spectrum $F_{ u} propto u^{-alpha_{ u}}$, with the spectral index $alpha_{ u} = 0.17pm{0.02}$. To conclude how this joins the synchrotron spectrum at higher frequencies we include hitherto unpublished AKARI mid-infrared data, and evaluate published data in the ultraviolet (UV), optical and infrared (IR). In particular, some broad-band filter data in the optical must be discarded from our analysis due to contamination by spectral line emission. For the UV/IR part of the synchrotron spectrum, we arrive at $alpha_{ u} = 0.87^{+0.08}_{-0.10}$. There is room for $2.5times10^{-3}$ solar masses of dust with temperature $sim 55$ K if there are dual breaks in the synchrotron spectrum, one around $sim 9times10^{10}$ Hz, and another at $sim 2times10^{13}$ Hz. The spectral index then changes at $sim 9times10^{10}$ Hz from $alpha_{ u} = 0.14pm0.07$ in the radio, to $alpha_{ u} = 0.35^{-0.07}_{+0.05}$ in the millimetre to far-IR range. The ACA Band 6 data marginally resolves the PWN. In particular, the strong emission 1.5 south-west of the pulsar, seen at other wavelengths, and resolved in the 3-cm data with its 0.8 spatial resolution, is also strong in the millimeter range. The ACA data clearly reveal the supernova remnant shell 20-35 arcsec west of the pulsar, and for the shell we derive $alpha_{ u} = 0.64pm{0.05}$ for the range $8.6-145$~GHz.
The structure, elemental abundances, physical conditions of the LMC supernova remnant (SNR) 0540-69.3 and its surroundings were investigated using [O III] imaging and spectroscopy. Several new spectral lines are identified, both in central filaments and in interstellar clouds shocked by the supernova blast wave. The central lines are redshifted by $440pm80$ km s$^{-1}$ with respect to the LMC, and the [O III] emission displays a symmetry axis of ring-like structures which could indicate that the pulsar shares the same general redshift as the central supernova ejecta. [O II], [S II], [Ar III] and H$beta$ have more compact structures than [O III], and possibly [Ne III]. The average [O III] temperature is $23,500 pm 1,800$ K, and the electron density from [S II] is typically $10^3$ cm$^{-3}$. By mass, the relative elemental abundances of the central shocked ejecta are ${rm O:Ne:S:Ar} approx 1:0.07:0.10:0.02$, consistent with explosion models of $13-20$ solar mass progenitors, and similar to that of SN 1987A, as is also the mixing of hydrogen and helium into the center. [O III] is also seen in freely coasting ejecta outside the pulsar-wind nebula out to well above $2,000$ km s$^{-1}$. From this a pulsar age of $approx 1,200$ years is estimated. Four filaments of shocked interstellar medium with a wide range in degree of ionization of iron are identified. One was observed in X-rays, and another has a redshift of $85pm30$ km~s$^{-1}$ relative to LMC. From this the electron density of the [O III]-emitting gas is estimated to be $10^3$ cm$^{-3}$. The line of the most highly ionized ion, [Fe XIV] $lambda$5303, likely comes from an evaporation zone in connection with the radiatively cooled gas emitting, e.g., [O III].
We present and discuss new visual wavelength-range observations of the inner regions of the supernova remnant SNR 0540-69.3 that is located in the Large Magellanic Cloud (LMC). These observations provide us with more spatial and spectral information than were previously available for this object. We use these data to create a detailed three-dimensional model of the remnant, assuming linear expansion of the ejecta. With the observations and the model we study the general three-dimensional structure of the remnant, and the influence of an active region in the remnant - a blob - that we address in previous papers. We used the fibre-fed integral-field spectrograph VIMOS at the Very Large Telescope of the European Southern Observatory. The observations provide us with three-dimensional data in [OIII]5007 and [SII]6717,6731 at an 0.33x0.33 spatial sampling and a velocity resolution of about 35 km/s. We decomposed the two, partially overlapping, sulphur lines and used them to calculate electron densities across the remnant at high signal-to-noise ratio. Our analysis reveals a structure that stretches from the position of the blob, and into the plane of the sky at a position angle of about 60 degrees. We speculate that the pulsar is positioned along this activity axis, where it has a velocity along the line of sight of a few hundred km/s. The blob is most likely a region of shock activity, as it is mainly bright in [SII]; future observations of [OII]3729 would be useful to test whether the S/O abundance ratio is higher than average for that location in the remnant. The striking resemblance in X-rays between the pulsar wind nebula (PWN) of SNR 0540-69.3 and the Crab, in combination with our findings in this paper, suggests that the symmetry axis is part of a torus in the PWN. (abridged)
The distribution of ejecta in young supernova remnants offers a powerful observational probe of their explosions and progenitors. Here we present a 3D reconstruction of the ejecta in SNR 0540-69.3, which is an O-rich remnant with a pulsar wind nebula located in the LMC. We use observations from VLT/MUSE to study Hbeta, [O III] lambda lambda 4959, 5007, Halpha, [S II] lambda lambda 6717, 6731, [Ar III] lambda 7136 and [S III] lambda 9069 emission lines. This is complemented by 2D spectra from VLT/X-shooter, which also cover [O II] lambda lambda 3726, 3729 and [Fe II] lambda 12567. We identify three main emission components: (i) Clumpy rings in the inner nebula (<1000 km/s) with similar morphologies in all lines; (ii) Faint extended [O III] emission dominated by an irregular ring-like structure with radius ~1600 km/s and inclination ~40 dg, but with maximal velocities reaching ~3000 km/s; and (iii) A blob of Halpha and Hbeta located southeast of the pulsar at velocities ~1500-3500 km/s. We analyze the geometry using a clump-finding algorithm and use the clumps in the [O III] ring to estimate an age of 1146 pm 116 years. The observations favor an interpretation of the [O III] ring as ejecta, while the origin of the H-blob is more uncertain. An alternative explanation is that it is the blown-off envelope of a binary companion. From the detection of Balmer lines in the innermost ejecta we confirm that SNR 0540 was a Type II supernova and that hydrogen was mixed down to low velocities in the explosion.
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