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  • 1.
    Gröningsson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leibundgut, Bruno
    Spyromilio, Jason
    Chevalier, Roger
    Gilmozzi, Roberto
    Kjaer, Karina
    Mattila, Seppo
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    High resolution spectroscopy of the inner ring of SN 1987A2008In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 479, no 3, p. 761-777Article in journal (Refereed)
    Abstract [en]

    We discuss high resolution VLT/UVES observations (FWHM similar to 6 kms(-1)) from October 2002 (day similar to 5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A large number of narrow emission lines from the unshocked ring, with ion stages from neutral up to Ne V and Fe VII, have been identified. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (similar to 1.5 - 5.0) x 10(3) cm(-3) and temperatures of similar to 6.5 x 10(3) - 2.4 x 104 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [FeXIV]. From a nebular analysis we find that the density in the low ionization region is 4 x 10(6) - 10(7) cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X - XIV], with the latter extending up to similar to- 390 km s(-1) in the blue wing for [Fe XIV], while the low ionization lines extend to typically similar to- 260 km s(-1). For H alpha a faint extension up to similar to- 450 km s(-1) can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are similar to 510 km s(-1). We expect the maximum width of especially the low ionization lines to increase with time.

  • 2.
    Gröningsson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nymark, Tanja
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Chevalier, R.
    Leibundgut, B.
    Spyromilio, J.
    Coronal emission from the shocked circumstellar ring of SN 1987A2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 456, no 2, p. 581-589Article in journal (Refereed)
    Abstract [en]

    High resolution spectra with UVES/VLT of SN 1987A from December 2000 until November 2005 show a number of high ionization lines from gas with velocities of ± 350 km s-1, emerging from the shocked gas formed by the ejecta-ring collision. These include coronal lines from [Fe X], [Fe XI] and [Fe XIV] which have increased by a factor of 20 during the observed period. The evolution of the lines is similar to that of the soft X-rays, indicating that they arise in the same component. The line ratios are consistent with those expected from radiative shocks with velocity 310{-}390 km s-1, corresponding to a shock temperature of (1.6{-}2.5)× 106 K. A fraction of the coronal emission may, however, originate in higher velocity adiabatic shocks.

  • 3.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Supernova remnants and their pulsar wind nebulae2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Massive stars die in powerful stellar explosions, so-called supernovae. In most cases, a neutron star or a black hole is expected to form in the center. The ejected material in these explosions expands out into the surroundings for tens of thousands of years, forming a supernova remnant. If a rapidly rotating neutron star, i.e. pulsar, has been created in the center, a pulsar wind nebula (PWN) will form around it. This thesis focuses mainly on the composite supernova remnant SNR B0540-69.3, as well as the pulsar\psr. This object has a dynamical PWN for which detailed observations have been done using various ground-based and space-borne telescopes. The thesis also includes a detailed study of the Crab-like supernova remnant 3C 58, which allowed us to detect optical emission from the pulsar+PWN system. This made it become the third PWN, after the Crab nebula and the 0540 PWN, to be seen in the optical.

  • 4.
    Lundqvist, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Björnsson, Claes-Ingvar
    Stockholm University, Faculty of Science, Department of Astronomy.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pires, S.
    Shibanov, Yu. A.
    Zyuzin, D. A.
    Spectral evolution and polarization of variable structures in the pulsar wind nebula of PSR B0540-69.32011In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 413, no 1, p. 611-627Article in journal (Refereed)
    Abstract [en]

    We present high spatial resolution optical imaging and polarization observations of the PSR B0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with Hubble Space Telescope, and compare them with X-ray data obtained with the Chandra X-ray Observatory. In particular, we have studied the bright region south-west of the pulsar where a bright 'blob' is seen in 1999. In a recent paper by De Luca et al. it was argued that the 'blob' moves away from the pulsar at high speed. We show that it may instead be a result of local energy deposition around 1999, and that the emission from this then faded away rather than moved outward. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-'blob' orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the 'blob' position, faster orthogonal to the pulsar-'blob' direction than along this axis of orientation. This could indicate that the pulsar-'blob' orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an [S ii]-to-[O iii]-ratio map, and comparing this to optical continuum and X-ray emission maps. We argue, through modelling, that the high [S ii]/[O iii] ratio is not due to time-dependent photoionization caused by possible rapid X-ray emission variations in the 'blob' region. We have also created a multiwavelength energy spectrum for the 'blob' position showing that one can, to within 2 Sigma, connect the optical and X-ray emission by a single power law. The slope of that power law (defined from <file name=mnr_18159_mu1.gif type=gif/>) would be alpha(nu) = 0.74 +/- 0.03, which is marginally different from the X-ray spectral slope alone with alpha(nu) = 0.65 +/- 0.03. A single power law for most of the PWN is, however, not be possible. We obtain best power-law fits for the X-ray spectrum if we include 'extra' oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20-25 M(circle dot) range, i.e. in the upper mass range for progenitors of Type IIP supernovae.

  • 5. Sandin, Christer
    et al.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lundqvist, Natallia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Björnsson, Claes-Ingvar
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Shibanov, Yuri A.
    Properties of the three-dimensional structure in the central region of the supernova remnant SNR 0540−69.32013In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 432, no 4, p. 2854-2868Article in journal (Refereed)
    Abstract [en]

    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 Visual Multi-Object Spectrograph at the Very Large Telescope of the European Southern Observatory. The observations provide us with three-dimensional data in [O iii] λ5007 and [S ii] λλ6717, 6731 at a 0.33 arcsec × 0.33 arcsec spatial sampling and a velocity resolution of about 35 km s− 1. We decomposed the two, partially overlapping, sulphur lines and used them to calculate electron densities across the remnant at a high signal-to-noise ratio. In our study, we recover results of previous studies, but we are more importantly able to obtain more detailed information than before. 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 PA ≃ 60°. Assuming a remnant age of 1000 yr and the usual LMC distance, the structure has an inclination angle of about 65° to the line of sight. The position angle is close to the symmetry axis with present and past activity in the visual and the X-ray wavelength ranges. 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− 1. The ‘blob’ is most likely a region of shock activity, as it is mainly bright in [S ii]; future observations of [O ii] λλ3726, 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. This is in agreement with the original suggestion by Gotthelf & Wang.

  • 6.
    Serafimovich, Natalia I.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Shibanov, Yu. A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Optical observations of the young supernova remnant SNR 0540-69.3 and its pulsar2005In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 35, no 6, p. 1106-1111Article in journal (Refereed)
    Abstract [en]

    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 Å centered on the pulsar produced results consistent with those of [Kirshner, R.P., Morse, J.A., Winkler, P.F., et al. The penultimate supernova in the Large Magellanic Cloud - SNR 0540-69.3. Astrophys.J. 342, 260 271, 1989.] but also revealed many new emission lines. The most important are [Ne III] λλ3869, 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 ˜2 × 104 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 ≳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 α=1.07-0.19+0.20. 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 year‑1, corresponding to a transverse velocity of 1190 ± 560 km s‑1, projected along the southern jet of the pulsar nebula.

  • 7.
    Serafimovich, Natalia I.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Shibanov, Yu. A.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    The young pulsar PSR B0540-69.3 and its synchrotron nebula in the optical and X-rays2004In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 425, no 3, p. 1041-1060Article in journal (Refereed)
    Abstract [en]

    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).

  • 8. Shibanov, Yu. A.
    et al.
    Lundqvist, Natalia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy.
    Zyuzin, D.
    Optical identification of the 3C 58 pulsar wind nebula2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 486, no 1, p. 273-282Article in journal (Refereed)
    Abstract [en]

    Context: The Crab-like supernova remnant 3C 58 contains the young pulsar PSR J0295+6449, which powers a radio plerion and a compact torus-like pulsar wind nebula visible in X-rays. Aims: We have performed deep optical imaging of the 3C 58 field to detect the optical counterpart of the pulsar and its wind nebula. Methods: The imaging was carried out with the Nordic Optical Telescope. We also analyzed the archival images of the field obtained with the Chandra/ACIS-S and HRC-S in X-rays and with the Spitzer/IRAC in the mid-infrared. Results: We detect a faint extended elliptical optical object with B=24.06 m ± 0.08 and V=23.11 m ± 0.04, whose center and peak brightness position are consistent at the sub-arcsecond level with the position of the pulsar. The morphology of the object and the orientation of its major axis are in excellent agreement with the torus region of the pulsar wind nebula seen almost edge on in the X-rays, although its extension is only about a half of what is in X-rays. This suggests that in the optical we see only the brightest central part of the torus nebula with the pulsar. The position and morphology of the object are also practically identical to the counterpart of the torus region recently detected in the mid-infrared bands. We do not resolve any point-like source within the nebula that could be identified with the pulsar and estimate that the contribution of the pulsar to the observed optical flux is ⪉10%. Using the archival Chandra/ACIS-S data we analyzed the spectrum of the pulsar+nebula X-ray emission extracted from the spatial region constrained by the optical/infrared source position and extent and find that a single absorbed power law provides an acceptable spectral fit. Combining this fit with the optical and infrared fluxes of the detected candidate torus nebula counterpart, we compile a tentative multi-wavelength spectrum of the central part of the pulsar nebula. Within the uncertainties of the interstellar extinction towards 3C 58, it is reminiscent of either the Crab or PSR B0540-69 pulsar wind nebula spectra. Conclusions: The position, morphology, and spectral properties of the detected source strongly suggest that it is the optical/mid-infrared counterpart of the 3C 58 pulsar + its wind nebula system. This makes 3C 58 the third member, together with the Crab and PSR B0540-69, of such a system as identified in the optical and mid-infrared.

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