Peter Lundqvist - Profile on Academia.edu (original) (raw)

Papers by Peter Lundqvist

Monthly Notices of the Royal Astronomical Society, May 3, 2012

The low kinetic energy and mass of the Crab supernova remnant challenge our understanding of core... more The low kinetic energy and mass of the Crab supernova remnant challenge our understanding of core-collapse supernova explosions. A possibility is that the Crab nebula is surrounded by a shell of fast ejecta containing the 'missing' kinetic energy and mass. The only direct evidence for such a fast shell comes from an absorption feature in the Crab pulsar spectrum as a result of C IVλ1550. The velocities inferred from the C IV line absorption extend to at least ∼2500 km s -1 , which is about twice as fast as the expansion of main shell of the remnant in our direction. We have searched for additional evidence of fast-moving ejecta in the optical spectra obtained with the FORS1 instrument at the European Southern Observatory (ESO) 8.2-m Very Large Telescope (VLT) and with the Andalucia Faint Object Spectrograph and Camera (ALFOSC) at the 2.56-m Nordic Optical Telescope (NOT), with the focus on absorption in Ca II λλ3934,3968, and emission components in [O III] λλ4959,5007. The data are compared with the C IVλ1550 absorption, and with theoretical expectations derived from shell models with ballistic gas motion, and a power-law density profile of the fast ejecta. Along the line of sight to the pulsar, we find that no gas in the nebula moves faster towards us than ≈1400 km s -1 . We identify this gas as part of the known main shell of the remnant. This velocity agrees with previous results showing that the Crab nebula is moving slowly in this direction. It is slower than the velocity of 1680 km s -1 used in the models of Sollerman et al. as a minimum velocity of the presumed fast shell of supernova ejecta to account for the C IV line absorption. We find faster moving gas within 3-10 arcsec north and south of the pulsar, where the fastest gas moving towards us, as traced by [O III], has a velocity of 1650-1700 km s -1 . The fastest [O III] emitting gas along the line of sight to the pulsar, on the rear side of the nebula, has a velocity of ≈+1800 km s -1 , which is higher than the velocity previously recorded for that direction. However, neither the [O III] nor Ca II lines display any signatures of fast shell ejecta at the velocities inferred from the C IV line absorption. To fully rule out the possibility that a chimney-like structure directed towards us could be responsible for the C IV line absorption, we need deep observations taken with 8-10-m class telescopes with good spectral resolution. We show that a spectral resolution better than ∼200 km s -1 is needed to draw any conclusions on emission lines from gas moving towards us, along the line of sight of the pulsar, faster than ≈1700 km s -1 . To probe the fast shell ejecta, new observations from the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) should be substantially more powerful than the previous HST Space Telescope Imaging Spectrograph (STIS) data to fully explore the C IV λ1550 absorption-line profile.

Advances in Space Research, 2005

We have used the ESO NTT/EMMI and VLT/FORS1 instruments to examine the LMC supernova remnant 0540... more 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 , 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 × 10 4 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 αν = 1.07 +0.20 -0.19 . 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 -1 , corresponding to a transverse velocity of 1190 ± 560 km s -1 , projected along the southern jet of the pulsar nebula.

Astronomy and Astrophysics, Aug 1, 2003

We report results from high resolution optical spectroscopy of three non-radiative galactic super... more We report results from high resolution optical spectroscopy of three non-radiative galactic supernova remnants, RCW 86, Kepler's supernova remnant and SN 1006. We have measured the narrow component Hα line widths in Balmerdominated filaments in RCW 86 and SN 1006, as well as the narrow component width in a Balmer-dominated knot in Kepler's SNR. The narrow component line widths measured in RCW 86 and Kepler's SNR show FWHM of 30-40 km s -1 , similar to what has been seen in other Balmer-dominated remnants. Of the remnants in our sample, SN 1006 is the fastest shock (∼3000 km s -1 ). The narrow component Hα and Hβ lines in this remnant have a FWHM of merely 21 km s -1 . Comparing the narrow component widths measured in our sample with those measured in other remnants shows that the width of the narrow component does not correlate in a simple way with the shock velocity. The implications for the pre-heating mechanism responsible for the observed line widths are discussed.

Monthly Notices of the Royal Astronomical Society, 2020

We present optical photometric and spectroscopic observations of the faint-and-fast evolving Type... more We present optical photometric and spectroscopic observations of the faint-and-fast evolving Type Iax supernova (SN) 2019gsc, extending from the time of g-band maximum until about 50 d post-maximum, when the object faded to an apparent r-band magnitude mr = 22.48 ± 0.11 mag. SN 2019gsc reached a peak luminosity of only Mg = −13.58 ± 0.15 mag, and is characterized with a post-maximum decline rate Δm15(g) = 1.08 ± 0.14 mag. These light curve parameters are comparable to those measured for SN 2008ha of Mg = −13.89 ± 0.14 mag at peak and Δm15(g) =1.80 ± 0.03 mag. The spectral features of SN 2019gsc also resemble those of SN 2008ha at similar phases. This includes both the extremely low ejecta velocity at maximum, ∼3000 km s−1, and at late-time (phase +54 d) strong forbidden iron and cobalt lines as well as both forbidden and permitted calcium features. Furthermore, akin to SN 2008ha, the bolometric light curve of SN 2019gsc is consistent with the production of ≈0.003 ± 0.001 M⊙ of 56Ni....

Astronomy & Astrophysics, 2019

Context. Pulsars are well studied all over the electromagnetic spectrum, and the Crab pulsar may ... more Context. Pulsars are well studied all over the electromagnetic spectrum, and the Crab pulsar may be the most studied object in the sky. Nevertheless, a high-quality optical to near-infrared (NIR) spectrum of the Crab or any other pulsar has not been published to date. Aims. Obtaining a properly flux-calibrated spectrum enables us to measure the spectral index of the pulsar emission, without many of the caveats from previous studies. This was the main aim of this project, but in addition we could also detect absorption and emission features from the pulsar and nebula over an unprecedentedly wide wavelength range. Methods. A spectrum was obtained with the X-shooter spectrograph on the Very Large Telescope. Special care was given to the flux-calibration of these data. Results. A high signal-to-noise spectrum of the Crab pulsar was obtained from 300 nm to 2400 nm. The spectral index fit to this spectrum is flat with αν = 0.16 ± 0.07. For the emission lines we measured a maximum velocity...

Springer Proceedings in Physics, 2005

The high resolution obtained through the use of VLBI gives an unique opportunity to directly obse... more The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd. use, available at .

Astronomy & Astrophysics - ASTRON ASTROPHYS, 1999

We present optical data gathered by the VLT Test Camera in the V-band at the radio (interferometr... more We present optical data gathered by the VLT Test Camera in the V-band at the radio (interferometric) position of PSR1706-44. We find no optical counterpart to the pulsar in the VLT image. At a distance of 2\farcs7 from a nearby bright star, the 3sigma upper limit to the pulsar magnitude above the background is V = 25.5. Within an error circle of 1\farcs0 the upper limit is degraded in the direction towards the star. At a distance ≲ 2arcsec from the star we can with confidence only claim an upper limit of V = 24.5. This is still several magnitudes fainter than previous estimates. The implications of the optical upper limit taken together with the high energy pulsed gamma-ray radiation for theoretical models of pulsar emission are discussed. Based on observations collected at the European Southern Observatory, Paranal, Chile (VLT-UT1 Science Verification Program)

Astronomy & Astrophysics, 2009

Aims. We investigate the emission mechanism and evolution of pulsars that are associated with sup... more Aims. We investigate the emission mechanism and evolution of pulsars that are associated with supernova remnants. Methods. We used imaging techniques in both the optical and near infrared, using images with very good seeing (≤0. 6) to study the immediate surroundings of the Crab pulsar. In the case of the infrared, we took two data sets with a time window of 75 days to check for variability in the inner part of the Crab nebula. We also measure the spectral indices of all these wisps, the nearby knot, and the interwisp medium, using our optical and infrared data. We then compared the observational results with the existing theoretical models. Results. We report variability in the three nearby wisps located to the northwest of the pulsar and also in a nearby anvil wisp in terms of their structure, position, and emissivity within the time window of 75 days. All the wisps display red spectra with similar spectral indices (α ν = -0.58 ± 0.08, α ν = -0.63 ± 0.07, α ν = -0.53 ± 0.08) for the northwest triplet. The anvil wisp (anvil wisp 1) has a spectral index of α ν = -0.62 ± 0.10. Similarly, the interwisp medium regions also show red spectra similar to those of the wisps, with the spectral index being α ν = -0.61 ± 0.08, α ν = -0.50 ± 0.10, while the third interwisp region has a flatter spectrum with spectral α ν = -0.49 ± 0.10. The inner knot has a spectral index of α ν = -0.63 ± 0.02. Also, based on archival HST data and our IR data, we find that the inner knot remains stationary for a time period of 13.5 years. The projected average velocity relative to the pulsar for this period is 8 km s -1 . Conclusions. By comparing the spectral indices of the structures in the inner Crab with the current theoretical models, we find that the Del Zanna et al. model for the synchrotron emission fits our observations, although the spectral index is at the flatter end of their modelled spectra.

Advances in Space Research, 2004

We present results of hydrodynamical simulations of young supernova remnants. To model the ejecta... more We present results of hydrodynamical simulations of young supernova remnants. To model the ejecta, we use several models (discussed in literature) of type Ia supernova explosions with different abundances. Our hydro models are one-dimensional and spherically symmetrical, but they take into account ionization kinetics with all important processes. We include detailed calculations for the X-ray emission, allowing for timedependent ionization and recombination. In particular, we compare the computed X-ray spectra with recent XMM-Newton observations of the Tycho SN remnant. Our goal is to find the most viable thermonuclear SN model that gives good fits to both these X-ray observations and typical SN Ia light curves.

Monthly Notices of the Royal Astronomical Society

The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations o... more The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations of SN 2020acat covering ∼250 d after explosion are presented here. Using the fast rising photometric observations, spanning from the UV to NIR wavelengths, a pseudo-bolometric light curve was constructed and compared to several other well-observed Type IIb supernovae (SNe IIb). SN 2020acat displayed a very short rise time reaching a peak luminosity of mathrmrmLog10(L)=42.49pm0.17,mathrmerg,s−1\mathrm{{\rm Log}_{10}}(L) = 42.49 \pm 0.17 \, \mathrm{erg \, s^{-1}}mathrmrmLog10(L)=42.49pm0.17,mathrmerg,s−1 in only ∼14.6 ± 0.3 d. From modelling of the pseudo-bolometric light curve, we estimated a total mass of 56Ni synthesized by SN 2020acat of MNi = 0.13 ± 0.03 M⊙, with an ejecta mass of Mej = 2.3 ± 0.4 M⊙ and a kinetic energy of Ek = 1.2 ± 0.3 × 1051 erg. The optical spectra of SN 2020acat display hydrogen signatures well into the transitional period (≳ 100 d), between the photospheric and the nebular phases. The spectra also display a strong feature around 4900 Å that c...

Spectroscopic classification of Gaia 16bjx (= SN 2016gok) with the Nordic Optical Telescope

The astronomer's telegram, Oct 1, 2016

Spectroscopic observation of Gaia17abx (AT 2017ij) by NUTS (NOT Un-biased Transient Survey)

The astronomer's telegram, 2017

Spectroscopic classification of Gaia16bji with the Nordic Optical Telescope

The astronomer's telegram, Oct 1, 2016

Spectroscopic observations of four transients by NUTS (NOT Un-biased Transient Survey)

ATel, 2017

Spectroscopic observation of the supernova SN2016ios/Gaia16byj by NUTS (NOT Un-biased Transient Survey)

ATel, Dec 1, 2016

Spectroscopic classification of SN 2017cjb by NUTS (NOT Un-biased Transient Survey)

The astronomer's telegram, Mar 1, 2017

Searching for the presence of a circumstellar medium (CSM) is a direct observational way to discr... more Searching for the presence of a circumstellar medium (CSM) is a direct observational way to discriminate between different types of progenitor systems for Type Ia supernovae (SNe Ia). We have modeled whether such gas may give rise to detectable emission, especially in Hα, and compare the models with observations of SN 1994D. We obtainṀ ∼ < 2.5 × 10 −5 M⊙ yr −1 for a wind speed of 10 km s −1. We find that X-ray observations in the range 5 − 10 keV, e.g., with AXAF, provide the most useful limits on the mass loss, while high-resolution optical spectroscopy offers the only direct way of identifying circumstellar hydrogen.

The Astrophysical Journal, Apr 9, 2019

We perform hydrodynamical simulations of the interaction between supernova (SN) ejecta and circum... more We perform hydrodynamical simulations of the interaction between supernova (SN) ejecta and circumstellar medium (CSM) for SN1993J and SN2011dh, and calculate the radio and X-ray emissions expected from the shocked gas at late epochs (t). Considering the ejecta structure from multi-group radiation hydrodynamics simulation, we find that the observed rapid drop in radio and X-ray light curves of SN1993J at t>3000days may be due to a change in the mass-loss rate (Ṁ) ∼6500 yr prior to the explosion of the SN. The exact epoch scales inversely with the assumed wind velocity of v w =10 km s 1. The progenitor of this SN very likely belonged to a binary system, where, during its evolution, the primary had transferred material to the secondary. It is argued in this paper that the change inṀcan happen because of a change in the mass accretion efficiency (η) of the companion star. It is possible that before ∼6500(v w /10 km s 1) −1 yr prior to the explosion, η was high, and thus the CSM was tenuous, which causes the late-time downturn in fluxes. In the case of SN2011dh, the late-time evolution is found to be consistent with a wind medium withṀ/v w =4×10 −6- M yr 1 /10 km s 1. It is difficult from our analysis to predict whether the progenitor of this SN had a binary companion; however, if future observations show a similar decrease in radio and X-ray fluxes, then this would give strong support to a scenario where both SNe had undergone a similar kind of binary evolution before explosion.

Monthly Notices of the Royal Astronomical Society, Jul 1, 2005

We used the interferometric visibility data to estimate angular diameter sizes for the supernova ... more We used the interferometric visibility data to estimate angular diameter sizes for the supernova by model fitting. Our data nominally suggest a relatively strong deceleration for the expansion of SN 2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 2003 April 8, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of E min = (0.3-14) × 10 47 erg, and a corresponding equipartition average magnetic field of B min = 50-350 mG. We also present multiwavelength Very Large Array (VLA) measurements of SN 2001gd made at our second VLBI epoch at frequencies of 1.4, 4.9, 8.4, 15.0, 22.5 and 43.3 GHz. The VLA data are well fitted by an optically thin, synchrotron spectrum (α = −1.0 ± 0.1; S ν ∝ ν α), partially absorbed by thermal plasma. We obtain a supernova flux density of 1.02 ± 0.05 mJy at the observing frequency of 8.4 GHz for the second epoch, which results in an isotropic radio luminosity of (6.0 ± 0.3) × 10 36 erg s −1 between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we report on an XMM-Newton X-ray detection of SN 2001gd on 2002 December 18. The supernova X-ray spectrum is consistent with optically thin emission from a soft component (associated with emission from the reverse shock) at a temperature of around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of L X = (1.4 ± 0.4) × 10 39 erg s −1 in the 0.3-5 keV band. We suggest that both radio and X-ray observations of SN 2001gd indicate that a circumstellar interaction similar to that displayed by SN 1993J in M 81 is taking place.

A Linear Relation between the Color Stretch s _BV and the Rising Color Slope s0*(B−V) of Type Ia Supernovae

The Astrophysical Journal, Apr 1, 2023

Monthly Notices of the Royal Astronomical Society, May 3, 2012

The low kinetic energy and mass of the Crab supernova remnant challenge our understanding of core... more The low kinetic energy and mass of the Crab supernova remnant challenge our understanding of core-collapse supernova explosions. A possibility is that the Crab nebula is surrounded by a shell of fast ejecta containing the 'missing' kinetic energy and mass. The only direct evidence for such a fast shell comes from an absorption feature in the Crab pulsar spectrum as a result of C IVλ1550. The velocities inferred from the C IV line absorption extend to at least ∼2500 km s -1 , which is about twice as fast as the expansion of main shell of the remnant in our direction. We have searched for additional evidence of fast-moving ejecta in the optical spectra obtained with the FORS1 instrument at the European Southern Observatory (ESO) 8.2-m Very Large Telescope (VLT) and with the Andalucia Faint Object Spectrograph and Camera (ALFOSC) at the 2.56-m Nordic Optical Telescope (NOT), with the focus on absorption in Ca II λλ3934,3968, and emission components in [O III] λλ4959,5007. The data are compared with the C IVλ1550 absorption, and with theoretical expectations derived from shell models with ballistic gas motion, and a power-law density profile of the fast ejecta. Along the line of sight to the pulsar, we find that no gas in the nebula moves faster towards us than ≈1400 km s -1 . We identify this gas as part of the known main shell of the remnant. This velocity agrees with previous results showing that the Crab nebula is moving slowly in this direction. It is slower than the velocity of 1680 km s -1 used in the models of Sollerman et al. as a minimum velocity of the presumed fast shell of supernova ejecta to account for the C IV line absorption. We find faster moving gas within 3-10 arcsec north and south of the pulsar, where the fastest gas moving towards us, as traced by [O III], has a velocity of 1650-1700 km s -1 . The fastest [O III] emitting gas along the line of sight to the pulsar, on the rear side of the nebula, has a velocity of ≈+1800 km s -1 , which is higher than the velocity previously recorded for that direction. However, neither the [O III] nor Ca II lines display any signatures of fast shell ejecta at the velocities inferred from the C IV line absorption. To fully rule out the possibility that a chimney-like structure directed towards us could be responsible for the C IV line absorption, we need deep observations taken with 8-10-m class telescopes with good spectral resolution. We show that a spectral resolution better than ∼200 km s -1 is needed to draw any conclusions on emission lines from gas moving towards us, along the line of sight of the pulsar, faster than ≈1700 km s -1 . To probe the fast shell ejecta, new observations from the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) should be substantially more powerful than the previous HST Space Telescope Imaging Spectrograph (STIS) data to fully explore the C IV λ1550 absorption-line profile.

Advances in Space Research, 2005

We have used the ESO NTT/EMMI and VLT/FORS1 instruments to examine the LMC supernova remnant 0540... more 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 , 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 × 10 4 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 αν = 1.07 +0.20 -0.19 . 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 -1 , corresponding to a transverse velocity of 1190 ± 560 km s -1 , projected along the southern jet of the pulsar nebula.

Astronomy and Astrophysics, Aug 1, 2003

We report results from high resolution optical spectroscopy of three non-radiative galactic super... more We report results from high resolution optical spectroscopy of three non-radiative galactic supernova remnants, RCW 86, Kepler's supernova remnant and SN 1006. We have measured the narrow component Hα line widths in Balmerdominated filaments in RCW 86 and SN 1006, as well as the narrow component width in a Balmer-dominated knot in Kepler's SNR. The narrow component line widths measured in RCW 86 and Kepler's SNR show FWHM of 30-40 km s -1 , similar to what has been seen in other Balmer-dominated remnants. Of the remnants in our sample, SN 1006 is the fastest shock (∼3000 km s -1 ). The narrow component Hα and Hβ lines in this remnant have a FWHM of merely 21 km s -1 . Comparing the narrow component widths measured in our sample with those measured in other remnants shows that the width of the narrow component does not correlate in a simple way with the shock velocity. The implications for the pre-heating mechanism responsible for the observed line widths are discussed.

Monthly Notices of the Royal Astronomical Society, 2020

We present optical photometric and spectroscopic observations of the faint-and-fast evolving Type... more We present optical photometric and spectroscopic observations of the faint-and-fast evolving Type Iax supernova (SN) 2019gsc, extending from the time of g-band maximum until about 50 d post-maximum, when the object faded to an apparent r-band magnitude mr = 22.48 ± 0.11 mag. SN 2019gsc reached a peak luminosity of only Mg = −13.58 ± 0.15 mag, and is characterized with a post-maximum decline rate Δm15(g) = 1.08 ± 0.14 mag. These light curve parameters are comparable to those measured for SN 2008ha of Mg = −13.89 ± 0.14 mag at peak and Δm15(g) =1.80 ± 0.03 mag. The spectral features of SN 2019gsc also resemble those of SN 2008ha at similar phases. This includes both the extremely low ejecta velocity at maximum, ∼3000 km s−1, and at late-time (phase +54 d) strong forbidden iron and cobalt lines as well as both forbidden and permitted calcium features. Furthermore, akin to SN 2008ha, the bolometric light curve of SN 2019gsc is consistent with the production of ≈0.003 ± 0.001 M⊙ of 56Ni....

Astronomy & Astrophysics, 2019

Context. Pulsars are well studied all over the electromagnetic spectrum, and the Crab pulsar may ... more Context. Pulsars are well studied all over the electromagnetic spectrum, and the Crab pulsar may be the most studied object in the sky. Nevertheless, a high-quality optical to near-infrared (NIR) spectrum of the Crab or any other pulsar has not been published to date. Aims. Obtaining a properly flux-calibrated spectrum enables us to measure the spectral index of the pulsar emission, without many of the caveats from previous studies. This was the main aim of this project, but in addition we could also detect absorption and emission features from the pulsar and nebula over an unprecedentedly wide wavelength range. Methods. A spectrum was obtained with the X-shooter spectrograph on the Very Large Telescope. Special care was given to the flux-calibration of these data. Results. A high signal-to-noise spectrum of the Crab pulsar was obtained from 300 nm to 2400 nm. The spectral index fit to this spectrum is flat with αν = 0.16 ± 0.07. For the emission lines we measured a maximum velocity...

Springer Proceedings in Physics, 2005

The high resolution obtained through the use of VLBI gives an unique opportunity to directly obse... more The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd. use, available at .

Astronomy & Astrophysics - ASTRON ASTROPHYS, 1999

We present optical data gathered by the VLT Test Camera in the V-band at the radio (interferometr... more We present optical data gathered by the VLT Test Camera in the V-band at the radio (interferometric) position of PSR1706-44. We find no optical counterpart to the pulsar in the VLT image. At a distance of 2\farcs7 from a nearby bright star, the 3sigma upper limit to the pulsar magnitude above the background is V = 25.5. Within an error circle of 1\farcs0 the upper limit is degraded in the direction towards the star. At a distance ≲ 2arcsec from the star we can with confidence only claim an upper limit of V = 24.5. This is still several magnitudes fainter than previous estimates. The implications of the optical upper limit taken together with the high energy pulsed gamma-ray radiation for theoretical models of pulsar emission are discussed. Based on observations collected at the European Southern Observatory, Paranal, Chile (VLT-UT1 Science Verification Program)

Astronomy & Astrophysics, 2009

Aims. We investigate the emission mechanism and evolution of pulsars that are associated with sup... more Aims. We investigate the emission mechanism and evolution of pulsars that are associated with supernova remnants. Methods. We used imaging techniques in both the optical and near infrared, using images with very good seeing (≤0. 6) to study the immediate surroundings of the Crab pulsar. In the case of the infrared, we took two data sets with a time window of 75 days to check for variability in the inner part of the Crab nebula. We also measure the spectral indices of all these wisps, the nearby knot, and the interwisp medium, using our optical and infrared data. We then compared the observational results with the existing theoretical models. Results. We report variability in the three nearby wisps located to the northwest of the pulsar and also in a nearby anvil wisp in terms of their structure, position, and emissivity within the time window of 75 days. All the wisps display red spectra with similar spectral indices (α ν = -0.58 ± 0.08, α ν = -0.63 ± 0.07, α ν = -0.53 ± 0.08) for the northwest triplet. The anvil wisp (anvil wisp 1) has a spectral index of α ν = -0.62 ± 0.10. Similarly, the interwisp medium regions also show red spectra similar to those of the wisps, with the spectral index being α ν = -0.61 ± 0.08, α ν = -0.50 ± 0.10, while the third interwisp region has a flatter spectrum with spectral α ν = -0.49 ± 0.10. The inner knot has a spectral index of α ν = -0.63 ± 0.02. Also, based on archival HST data and our IR data, we find that the inner knot remains stationary for a time period of 13.5 years. The projected average velocity relative to the pulsar for this period is 8 km s -1 . Conclusions. By comparing the spectral indices of the structures in the inner Crab with the current theoretical models, we find that the Del Zanna et al. model for the synchrotron emission fits our observations, although the spectral index is at the flatter end of their modelled spectra.

Advances in Space Research, 2004

We present results of hydrodynamical simulations of young supernova remnants. To model the ejecta... more We present results of hydrodynamical simulations of young supernova remnants. To model the ejecta, we use several models (discussed in literature) of type Ia supernova explosions with different abundances. Our hydro models are one-dimensional and spherically symmetrical, but they take into account ionization kinetics with all important processes. We include detailed calculations for the X-ray emission, allowing for timedependent ionization and recombination. In particular, we compare the computed X-ray spectra with recent XMM-Newton observations of the Tycho SN remnant. Our goal is to find the most viable thermonuclear SN model that gives good fits to both these X-ray observations and typical SN Ia light curves.

Monthly Notices of the Royal Astronomical Society

The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations o... more The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations of SN 2020acat covering ∼250 d after explosion are presented here. Using the fast rising photometric observations, spanning from the UV to NIR wavelengths, a pseudo-bolometric light curve was constructed and compared to several other well-observed Type IIb supernovae (SNe IIb). SN 2020acat displayed a very short rise time reaching a peak luminosity of mathrmrmLog10(L)=42.49pm0.17,mathrmerg,s−1\mathrm{{\rm Log}_{10}}(L) = 42.49 \pm 0.17 \, \mathrm{erg \, s^{-1}}mathrmrmLog10(L)=42.49pm0.17,mathrmerg,s−1 in only ∼14.6 ± 0.3 d. From modelling of the pseudo-bolometric light curve, we estimated a total mass of 56Ni synthesized by SN 2020acat of MNi = 0.13 ± 0.03 M⊙, with an ejecta mass of Mej = 2.3 ± 0.4 M⊙ and a kinetic energy of Ek = 1.2 ± 0.3 × 1051 erg. The optical spectra of SN 2020acat display hydrogen signatures well into the transitional period (≳ 100 d), between the photospheric and the nebular phases. The spectra also display a strong feature around 4900 Å that c...

Spectroscopic classification of Gaia 16bjx (= SN 2016gok) with the Nordic Optical Telescope

The astronomer's telegram, Oct 1, 2016

Spectroscopic observation of Gaia17abx (AT 2017ij) by NUTS (NOT Un-biased Transient Survey)

The astronomer's telegram, 2017

Spectroscopic classification of Gaia16bji with the Nordic Optical Telescope

The astronomer's telegram, Oct 1, 2016

Spectroscopic observations of four transients by NUTS (NOT Un-biased Transient Survey)

ATel, 2017

Spectroscopic observation of the supernova SN2016ios/Gaia16byj by NUTS (NOT Un-biased Transient Survey)

ATel, Dec 1, 2016

Spectroscopic classification of SN 2017cjb by NUTS (NOT Un-biased Transient Survey)

The astronomer's telegram, Mar 1, 2017

Searching for the presence of a circumstellar medium (CSM) is a direct observational way to discr... more Searching for the presence of a circumstellar medium (CSM) is a direct observational way to discriminate between different types of progenitor systems for Type Ia supernovae (SNe Ia). We have modeled whether such gas may give rise to detectable emission, especially in Hα, and compare the models with observations of SN 1994D. We obtainṀ ∼ < 2.5 × 10 −5 M⊙ yr −1 for a wind speed of 10 km s −1. We find that X-ray observations in the range 5 − 10 keV, e.g., with AXAF, provide the most useful limits on the mass loss, while high-resolution optical spectroscopy offers the only direct way of identifying circumstellar hydrogen.

The Astrophysical Journal, Apr 9, 2019

We perform hydrodynamical simulations of the interaction between supernova (SN) ejecta and circum... more We perform hydrodynamical simulations of the interaction between supernova (SN) ejecta and circumstellar medium (CSM) for SN1993J and SN2011dh, and calculate the radio and X-ray emissions expected from the shocked gas at late epochs (t). Considering the ejecta structure from multi-group radiation hydrodynamics simulation, we find that the observed rapid drop in radio and X-ray light curves of SN1993J at t>3000days may be due to a change in the mass-loss rate (Ṁ) ∼6500 yr prior to the explosion of the SN. The exact epoch scales inversely with the assumed wind velocity of v w =10 km s 1. The progenitor of this SN very likely belonged to a binary system, where, during its evolution, the primary had transferred material to the secondary. It is argued in this paper that the change inṀcan happen because of a change in the mass accretion efficiency (η) of the companion star. It is possible that before ∼6500(v w /10 km s 1) −1 yr prior to the explosion, η was high, and thus the CSM was tenuous, which causes the late-time downturn in fluxes. In the case of SN2011dh, the late-time evolution is found to be consistent with a wind medium withṀ/v w =4×10 −6- M yr 1 /10 km s 1. It is difficult from our analysis to predict whether the progenitor of this SN had a binary companion; however, if future observations show a similar decrease in radio and X-ray fluxes, then this would give strong support to a scenario where both SNe had undergone a similar kind of binary evolution before explosion.

Monthly Notices of the Royal Astronomical Society, Jul 1, 2005

We used the interferometric visibility data to estimate angular diameter sizes for the supernova ... more We used the interferometric visibility data to estimate angular diameter sizes for the supernova by model fitting. Our data nominally suggest a relatively strong deceleration for the expansion of SN 2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 2003 April 8, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of E min = (0.3-14) × 10 47 erg, and a corresponding equipartition average magnetic field of B min = 50-350 mG. We also present multiwavelength Very Large Array (VLA) measurements of SN 2001gd made at our second VLBI epoch at frequencies of 1.4, 4.9, 8.4, 15.0, 22.5 and 43.3 GHz. The VLA data are well fitted by an optically thin, synchrotron spectrum (α = −1.0 ± 0.1; S ν ∝ ν α), partially absorbed by thermal plasma. We obtain a supernova flux density of 1.02 ± 0.05 mJy at the observing frequency of 8.4 GHz for the second epoch, which results in an isotropic radio luminosity of (6.0 ± 0.3) × 10 36 erg s −1 between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we report on an XMM-Newton X-ray detection of SN 2001gd on 2002 December 18. The supernova X-ray spectrum is consistent with optically thin emission from a soft component (associated with emission from the reverse shock) at a temperature of around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of L X = (1.4 ± 0.4) × 10 39 erg s −1 in the 0.3-5 keV band. We suggest that both radio and X-ray observations of SN 2001gd indicate that a circumstellar interaction similar to that displayed by SN 1993J in M 81 is taking place.

A Linear Relation between the Color Stretch s _BV and the Rising Color Slope s0*(B−V) of Type Ia Supernovae

The Astrophysical Journal, Apr 1, 2023