| 1. |
- Chugai, Nikolai N., et al.
(författare)
-
The Type IIn supernova 1994W : evidence for the explosive ejection of a circumstellar envelope
- 2004
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 352, s. 1213-1231
-
Tidskriftsartikel (refereegranskat)abstract
- We present and analyse spectra of the Type IIn supernova (SN) 1994W obtained between 18 and 203d after explosion. During the luminous phase (first 100d) the line profiles are composed of three major components: (i) narrow P-Cygni lines with the absorption minima at -700kms-1 (ii) broad emission lines with blue velocity at zero intensity ~4000km s-1 and (iii) broad, smooth wings extending out to at least ~5000kms-1, most apparent in Hα. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post-shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P-Cygni lines from the SN is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the density (n~ 109cm-3), radial extent [~(4-5) × 1015cm] and Thomson optical depth (τT>~ 2.5) of the CS envelope during the first month. The plateau-like SN light curve is reproduced by a hydrodynamical model and is found to be powered by a combination of internal energy leakage after the explosion of an extended pre-SN (~1015cm) and subsequent luminosity from CS interaction. The pre-explosion kinematics of the CS envelope is recovered, and is close to homologous expansion with outer velocity ~1100kms-1 and a kinematic age of ~1.5yr. The high mass (~0.4Msolar) and kinetic energy (~2 × 1048erg) of the CS envelope, combined with low age, strongly suggest that the CS envelope was explosively ejected ~1.5yr prior to the SN explosion.
|
|
| 2. |
- Serafimovich, Natalia I., 1974-, et al.
(författare)
-
The young pulsar PSR B0540-69.3 and its synchrotron nebula in the optical and X-rays
- 2004
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 425:3, s. 1041-1060
-
Tidskriftsartikel (refereegranskat)abstract
- The young PSR B0540-69.3 in the LMC is the only pulsar (except the Crab pulsar) for which a near-UV spectrum has been obtained. However, the absolute flux and spectral index of the HST/FOS spectrum are significantly higher than suggested by previous broad-band time-resolved groundbased UBVRI photometry. To investigate this difference, observations with ESO/VLT/FORS1 and analysis of HST/WFPC2 archival data were done. We show that the HST and VLT spectral data for the pulsar have ⪆50% nebular contamination and that this is the reason for the above-mentioned difference. The broadband HST spectrum for the range 3300-8000 Å is clearly nonthermal and has a negative spectral index, Fν ∝ ν-α with αν = 1.07+0.20-0.19. This is different from the almost flat spectrum of the Crab pulsar, and also steeper than for the previously published broadband photometry of PSR B0540-69.3. We have also studied the spatial variations of the brightness and spectral index of the Pulsar Wind Nebula (PWN) around the pulsar, and find no significant spectral index variation over the PWN. The HST data show a clear asymmetry of the surface brightness distribution along the major axis of the torus-like structure of the PWN with respect to the pulsar position, also seen in Chandra/HRC X-ray images. This is different from the Crab PWN and likely linked to the asymmetry of the surrounding SN ejecta. The HST/WFPC2 archival data have an epoch separation of 4 years, and this allows us to estimate the proper motion of the pulsar. We find a motion of 4.9±2.3 mas yr-1 (corresponding to a transverse velocity of 1190±560 km s-1) along the southern jet of the PWN. If this is confirmed at a higher significance level by future observations, this makes PSR B0540-69.3 the third pulsar with a proper motion aligned with the jet axis of its PWN, which poses constraints on pulsar kick models. To establish the multiwavelength spectrum of the pulsar and its PWN, we have included recent Chandra X-ray data, and discuss the soft pulsar X-ray spectrum based on spectral fits including absorption by interstellar gas in the Milky Way, LMC as well as the supernova ejecta. We have compared the multiwavelength spectra of PSR B0540-69.3 and the Crab pulsar, and find that both PSR B0540-69.3 and the Crab pulsar have a weaker flux in the optical than suggested by a low-energy power-law extension of the X-ray spectrum. This optical depression is more severe for PSR B0540-69.3 than for the Crab pulsar. The same trend is seen for the PWNe of the two pulsars, and continues for low energies also out in the radio band. We discuss possible interpretations of this behavior. Based on observations performed at the European Southern Observatory, Paranal, Chile (ESO Program 67.D-0519).
|
|
| 3. |
|
|
| 4. |
- Sollerman, Jesper, et al.
(författare)
-
Observations of the Crab Nebula and Its Pulsar in the Far-Ultraviolet and in the Optical
- 2000
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 537, s. 861-874
-
Tidskriftsartikel (refereegranskat)abstract
- We present far-UV observations of the Crab Nebula and its pulsar made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Broad, blueshifted absorption arising in the nebula is seen in C IV λ1550, reaching a blueward velocity of ~2500 km s-1. This can be interpreted as evidence for a fast outer shell surrounding the Crab Nebula, and we adopt a spherically symmetric model to constrain the properties of such a shell. From the line profile we find that the density appears to decrease outward in the shell. A likely lower limit to the shell mass is ~0.3 Msolar with an accompanying kinetic energy of ~1.5×1049 ergs. A fast massive shell with 1051 ergs cannot be excluded but is less likely if the density profile is much steeper than ρ(R)~R-4 and the maximum velocity is <~6000 km s-1. The observations cover the region 1140-1720 Å, which is further into the ultraviolet than has previously been obtained for the pulsar. With the time-tag mode of the spectrograph we obtain the pulse profile in this spectral regime. The profile is similar to that previously obtained by us in the near-UV, although the primary peak is marginally narrower. Together with the near-UV data, and new optical data from the Nordic Optical Telescope, our spectrum of the Crab pulsar covers the entire region from 1140 to 9250 Å. Dereddening the spectrum with a standard extinction curve we achieve a flat spectrum for the reddening parameters E(B-V)=0.52, R=3.1. This dereddened spectrum of the Crab pulsar can be fitted by a power law with spectral index αν=0.11+/-0.04. The main uncertainty in determining the spectral index is the amount and characteristics of the interstellar reddening, and we have investigated the dependence of αν on E(B-V) and R. In the extended emission covered by our 25''×0.5" slit in the far-UV, we detect C IV λ1550 and He II λ1640 emission lines from the Crab Nebula. Several interstellar absorption lines are detected along the line of sight to the pulsar. The Lyα absorption indicates a column density of (3.0+/-0.5)×1021 cm-2 of neutral hydrogen, which agrees well with our estimate of E(B-V)=0.52 mag. Other lines show no evidence of severe depletion of metals in atomic gas. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.
|
|
