arXiv subjects

C. Fransson

Publications and source records attributed to C. Fransson.

At least 91 records · Page 5Linked to original sources

arXiv2012

Inverse Compton X-ray Emission from Supernovae with Compact Progenitors: Application to SN2011fe

We present a generalized analytic formalism for the inverse Compton X-ray emission from hydrogen-poor supernovae and apply this framework to SN2011fe using Swift-XRT, UVOT and Chandra observations. We characterize the optical properties of SN2011fe in the Swift bands and find them to be broadly consistent with a "normal" SN Ia, however, no X-ray source is detected by either XRT or Chandra. We constrain the progenitor system mass loss rate to be lower than 2x10^-9 M_sun/yr (3sigma c.l.) for wind velocity v_w=100 km/s. Our result rules out symbiotic binary progenitors for SN2011fe and argues against Roche-lobe overflowing subgiants and main sequence secondary stars if >1% of the transferred mass is lost at the Lagrangian points. Regardless of the density profile, the X-ray non-detections are suggestive of a clean environment (particle density < 150 cm-3) for (2x10^15<R<5x10^16) cm around the progenitor site. This is either consistent with the bulk of material being confined within the binary system or with a significant delay between mass loss and supernova explosion. We furthermore combine X-ray and radio limits from Chomiuk et al. 2012 to constrain the post shock energy density in magnetic fields. Finally, we searched for the shock breakout pulse using gamma-ray observations from the Interplanetary Network and find no compelling evidence for a supernova-associated burst. Based on the compact radius of the progenitor star we estimate that the shock break out pulse was likely not detectable by current satellites.

astro-ph.HE↗

arXiv2011

The Type II supernovae 2006V and 2006au: two SN 1987A-like events

Supernova 1987A revealed that a blue supergiant (BSG) star can end its life as a core-collapse supernova (SN). SN 1987A and other similar objects exhibit properties that distinguish them from ordinary Type II Plateau (IIP) SNe, whose progenitors are believed to be red supergiants (RSGs). Similarities among 1987A-like events include a long rise to maximum, early luminosity fainter than that of normal Type IIP SNe, and radioactivity acting as the primary source powering the light curves. We present and analyze two SNe monitored by the Carnegie Supernova Project that are reminiscent of SN 1987A. Optical and near-infrared (NIR) light curves, and optical spectroscopy of SNe 2006V and 2006au are presented. These observations are compared to those of SN 1987A, and are used to estimate properties of their progenitors. Both objects exhibit a slow rise to maximum and light curve evolution similar to that of SN 1987A. At the earliest epochs, SN 2006au also displays an initial dip which we interpret as the signature of the adiabatic cooling phase that ensues shock break- out. SNe 2006V and 2006au are both found to be bluer, hotter and brighter than SN 1987A. Spectra of SNe 2006V and 2006au are similar to those of SN 1987A and other normal Type II objects, although both consistently exhibit expansion velocities higher than SN 1987A. Semi-analytic models are fit to the UVOIR light curve of each object from which physical properties of the progenitors are estimated. This yields ejecta mass estimates of about 20 solar masses, explosion energies of 2 - 3 x 10^51 erg, and progenitor radii of 75 - 100 solar radii for both SNe. The progenitors of SNe 2006V and 2006au were most likely BSGs with a larger explosion energy as compared to that of SN 1987A.

astro-ph.CO↗

arXiv2011

X-ray illumination of the ejecta of Supernova 1987A

We present the late-time optical light curve of the ejecta of SN 1987A measured from HST imaging observations spanning the past 17 years. We find that the flux from the ejecta declined up to around year 2001, powered by the radioactive decay of 44Ti. Then the flux started to increase, more than doubling by the end of 2009. We show that the increase is the result of energy deposited by X-rays produced in the interaction with the circumstellar medium. We suggest that the change of the dominant energy input to the ejecta, from internal to external, marks the transition from supernova to supernova remnant. The details of the observations and the modelling are described in the accompanying supplementary information.

astro-ph.SR↗

arXiv2011

The discovery and classification of 16 supernovae at high redshifts in ELAIS-S1 - the Stockholm VIMOS Supernova Survey II

Supernova surveys can be used to study a variety of subjects such as: (i) cosmology through type Ia supernovae (SNe), (ii) star-formation rates through core-collapse SNe, and (iii) supernova properties and their connection to host galaxy characteristics. The Stockholm VIMOS Supernova Survey (SVISS) is a multi-band imaging survey aiming to detect supernovae at redshift ~0.5 and derive thermonuclear and core-collapse supernova rates at high redshift. In this paper we present the supernovae discovered in the survey along with light curves and a photometric classification into thermonuclear and core-collapse types. To detect the supernovae in the VLT/VIMOS multi-epoch images, we used difference imaging and a combination of automatic and manual source detection to minimise the number of spurious detections. Photometry for the found variable sources was obtained and careful simulations were made to estimate correct errors. The light curves were typed using a Bayesian probability method and Monte Carlo simulations were used to study misclassification. We detected 16 supernovae, nine of which had a core-collapse origin and seven had a thermonuclear origin. The estimated misclassification errors are quite small, in the order of 5%, but vary with both redshift and type. The mean redshift of the supernovae is 0.58. Additionally, we found a variable source with a very extended light curve that could possibly be a pair instability supernova.

astro-ph.CO↗

arXiv2011

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate $γ$-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.

astro-ph.HE↗

arXiv2011

The High-Metallicity Explosion Environment of the Relativistic Supernova 2009bb

We investigate the environment of the nearby (d ~ 40Mpc) broad-lined Type Ic supernova SN 2009bb. This event was observed to produce a relativistic outflow likely powered by a central accreting compact object. While such a phenomenon was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB was detected in association with SN 2009bb. Using an optical spectrum of the SN 2009bb explosion site, we determine a variety of ISM properties for the host environment, including metallicity, young stellar population age, and star formation rate. We compare the SN explosion site properties to observations of LGRB and broad-lined SN Ic host environments on optical emission line ratio diagnostic diagrams. Based on these analyses, we find that the SN 2009bb explosion site has a very high metallicity of ~2x solar, in agreement with other broad-lined SN Ic host environments and at odds with the low-redshift LGRB host environments and recently proposed maximum metallicity limits for relativistic explosions. We consider the implications of these findings and the impact that SN 2009bb's unusual explosive properties and environment have on our understanding of the key physical ingredient that enables some SNe to produce a relativistic outflow.

astro-ph.HE↗

arXiv2010

The 3-D Structure of SN 1987A's inner Ejecta

Twenty years after the explosion of SN 1987A, we are now able to observe the three-dimensional spatially resolved inner ejecta. Detailed mapping of newly synthesised material and its radioactive decay daughter products sheds light on the explosion mechanism. This may reveal the geometry of the explosion and its connection to the equatorial ring and the outer rings around SN 1987A. We have used integral field spectroscopy to image the supernova ejecta and the equatorial ring in the emission lines of [Si I]+[Fe II] and He I. The spectral information can be mapped into a radial velocity image revealing the expansion of the ejecta both as projected onto the sky and perpendicular to the sky plane. The inner ejecta are spatially resolved in a North-South direction and are clearly asymmetric. We argue that the bulk of the ejecta is situated in the same plane as defined by the equatorial ring and does not form a bipolar structure as has been suggested. The exact shape of the ejecta is modelled and we find that an elongated triaxial ellipsoid fits the observations best. From our spectral analyses of the ejecta spectrum we find that most of the He I, [Si I] and [Fe I-II] emission originates in the core material which has undergone explosive nucleosynthesis. The He I emission may be the result of alpha-rich freeze-out if the positron energy is deposited locally. Our observations clearly indicate a non-symmetric explosion mechanism for SN 1987A. The elongation and velocity asymmetries point towards a large-scale spatial non-spherical distribution as predicted in recent explosion models. The orientation of the ejecta in the plane of the equatorial ring argues against a jet-induced explosion through the poles due to stellar rotation.

astro-ph.SR↗

arXiv2010

The normal Type Ia SN 2003hv out to very late phases

An extensive dataset for SN 2003hv that covers the flux evolution from maximum light to day +786 is presented. The data are combined with published nebular-phase infrared spectra, and the observations are compared to model light curves and synthetic nebular spectra. SN 2003hv is a normal Type Ia supernova (SN Ia) with photometric and spectroscopic properties consistent with its rarely observed B-band decline-rate parameter, Delta m_15 = 1.61 +- 0.02. The blueshift of the most isolated [Fe II] lines in the nebular-phase optical spectrum appears consistent with those observed in the infrared at similar epochs. At late times there is a prevalent color evolution from the optical toward the near-infrared bands. We present the latest-ever detection of a SN Ia in the near-infrared in Hubble Space Telescope images. The study of the ultraviolet/optical/infrared (UVOIR) light curve reveals that a substantial fraction of the flux is "missing" at late times. Between 300-700 days past maximum brightness, the UVOIR light curve declines linearly following the decay of radioactive Co56, assuming full and instantaneous positron trapping. At 700 days we detect a possible slowdown of the decline in optical bands, mainly in the V band. The data are incompatible with a dramatic infrared catastrophe. However, the idea that an infrared catastrophe occurred in the densest regions before 350 days can explain the missing flux from the UVOIR wavelengths and the flat-topped profiles in the near-infrared. We argue that such a scenario is possible if the ejecta are clumpy. The observations suggest that positrons are most likely trapped in the ejecta.

astro-ph.SR↗

arXiv2010

A Relativistic Type Ibc Supernova Without a Detected Gamma-ray Burst

Long duration gamma-ray bursts (GRBs) mark the explosive death of some massive stars and are a rare sub-class of Type Ibc supernovae (SNe Ibc). They are distinguished by the production of an energetic and collimated relativistic outflow powered by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested in the pulse of gamma-rays and a long-lived radio afterglow. To date, central engine-driven SNe have been discovered exclusively through their gamma-ray emission, yet it is expected that a larger population goes undetected due to limited satellite sensitivity or beaming of the collimated emission away from our line-of-sight. In this framework, the recovery of undetected GRBs may be possible through radio searches for SNe Ibc with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary Type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. The lack of a coincident GRB makes SN 2009bb the first engine-driven SN discovered without a detected gamma-ray signal. A comparison with our extensive radio survey of SNe Ibc reveals that the fraction harboring central engines is low, ~1 percent, measured independently from, but consistent with, the inferred rate of nearby GRBs. Our study demonstrates that upcoming optical and radio surveys will soon rival gamma-ray satellites in pinpointing the nearest engine-driven SNe. A similar result for a different supernova is reported independently.

astro-ph.HE↗

arXiv2009

An Intermediate Luminosity Transient in NGC300: The Eruption of a Dust-Enshrouded Massive Star

[abridged] We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC300. We find that the transient (NGC300 OT2008-1) has a peak absolute magnitude of M_bol~-11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km/s) hydrogen Balmer lines and CaII emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect broad CaII H&K absorption with an asymmetric red wing extending to ~1000 km/s, indicative of gas infall onto a massive and relatively compact star (blue supergiant or Wolf-Rayet star); an extended red supergiant progenitor is unlikely. The origin of the inflowing gas may be a previous ejection from the progenitor or the wind of a massive binary companion. The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6x10^4 L_sun, indicative of a ~10-20 M_sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst.

astro-ph.HE↗

arXiv2008

Detection efficiency and photometry in supernova surveys - the Stockholm VIMOS Supernova Survey I

The aim of the work presented in this paper is to test and optimise supernova detection methods based on the optimal image subtraction technique. The main focus is on applying the detection methods to wide field supernova imaging surveys and in particular to the Stockholm VIMOS Supernova Survey (SVISS). We have constructed a supernova detection pipeline for imaging surveys. The core of the pipeline is image subtraction using the ISIS 2.2 package. Using real data from the SVISS we simulate supernovae in the images, both inside and outside galaxies. The detection pipeline is then run on the simulated frames and the effects of image quality and subtraction parameters on the detection efficiency and photometric accuracy are studied. The pipeline allows efficient detection of faint supernovae in the deep imaging data. It also allows controlling and correcting for possible systematic effects in the SN detection and photometry. We find such a systematic effect in the form of a small systematic flux offset remaining at the positions of galaxies in the subtracted frames. This offset will not only affect the photometric accuracy of the survey, but also the detection efficiencies. Our study has shown that ISIS 2.2 works well for the SVISS data. We have found that the detection efficiency and photometric accuracy of the survey are affected by the stamp selection for the image subtraction and by host galaxy brightness. With our tools the subtraction results can be further optimised, any systematic effects can be controlled and photometric errors estimated, which is very important for the SVISS, as well as for future SN searches based on large imaging surveys such as Pan-STARRS and LSST.

astro-ph↗

arXiv2007

Adaptive Optics Discovery of Supernova 2004ip in the Nuclear Regions of the Luminous Infrared Galaxy IRAS 18293-3413

We report a supernova discovery in Ks-band images from the NAOS CONICA adaptive optics (AO) system on the ESO Very Large Telescope (VLT). The images were obtained as part of a near-infrared search for highly-obscured supernovae in the nuclear regions of luminous and ultraluminous infrared galaxies. SN 2004ip is located within a circumnuclear starburst at 1.4 arcsec (or 500 pc) projected distance from the K-band nucleus of the luminous infrared galaxy IRAS 18293-3413. The supernova luminosity and light curve are consistent with a core-collapse event suffering from a host galaxy extinction of up to about 40 magnitudes in V-band which is as expected for a circumnuclear starburst environment. This is the first supernova to be discovered making use of AO correction and demonstrates the potential of the current 8-meter class telescopes equipped with AO in discovering supernovae from the innermost nuclear regions of luminous and ultraluminous infrared galaxies.

astro-ph↗

arXiv2006

A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova

We present late-time (590-994 d) mid-IR photometry of the normal, but highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star-formation region or molecular cloud along the line-of-sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly-condensed dust and/or an ejecta/CSM impact but their contributions are likely to be small. For the case of a CSM-IR echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio. Such a CSM would have resulted from episodic mass loss whose rate declined significantly about 28,000 years ago. Alternatively, an IR echo from a surrounding, dense, dusty molecular cloud might also have been responsible for the fading component. Either way, this is the first time that an IR echo has been clearly identified in a Type IIP supernova. We find no evidence for or against the proposal that Type IIP supernovae produce large amounts of dust via grain condensation in the ejecta. However, within the CSM-IR echo scenario, the mass of dust derived implies that the progenitors of the most common of core-collapse supernovae may make an important contribution to the universal dust content.

astro-ph↗

arXiv2005

Early and late time VLT spectroscopy of SN 2001el - progenitor constraints for a type Ia supernova

We present early time high-resolution (VLT/UVES) and late time low-resolution (VLT/FORS) optical spectra of the normal type Ia supernova, SN 2001el. The high-resolution spectra were obtained at -9 and -2 days to allow the detection of narrow hydrogen and/or helium emission lines from the circumstellar medium of the SN. No such lines were detected, and we therefore use photoionisation models to derive upper limits of 9x10^-6 Msun/yr and 5x10^-5 Msun/yr for the mass loss rate from the progenitor system assuming velocities of 10 km/s and 50 km/s, respectively, for a wind extending to outside at least a few x 10^15 cm away from the SN explosion site. These limits exclude a symbiotic star in the upper mass loss rate regime from being the progenitor of SN 2001el. The low resolution spectrum was obtained in the nebular phase of the SN, 400 days after the maximum light, to search for any hydrogen rich gas originating from the SN progenitor system. However, we see no signs of Balmer lines in our spectrum. Therefore, we model the late time spectra to derive an upper limit of ~0.03 Msun for solar abundance material present at velocities lower than 1000 km/s within the SN explosion site. According to simulations of Marietta et al. (2000) this is less than the expected mass lost by a subgiant, red giant or main sequence secondary star at a small binary separation as a result of the SN explosion. Finally, we discuss the origin of high velocity Ca II lines. We see both the CaII IR triplet and the H&K lines in the -9 days spectrum at a very high velocity of up to 34000 km/s. The spectrum also shows a flat-bottomed Si II `6150 A' feature similar to the one previously observed in SN 1990N at -14 days. We compare these spectral features to those observed in SNe 1984A and 1990N at even higher velocities.

astro-ph↗

arXiv2005

Limits from the Hubble Space Telescope on a Point Source in SN 1987A

We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September, and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. No point source is observed in the remnant. We obtain a limiting flux of F_opt < 1.6 x 10^{-14} ergs/s/cm^2 in the wavelength range 2900-9650 Angstroms for any continuum emitter at the center of the supernova remnant (SNR). It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of ~35% due to dust absorption in the SNR. Taking into account dust absorption in the remnant, we find a limit of L_opt < 8 x 10^{33} ergs/s. We compare this upper bound with empirical evidence from point sources in other supernova remnants, and with theoretical models for possible compact sources. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Of the young pulsars known to be associated with SNRs, those with ages < 5000 years are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out, and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 10^{10} cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant.

astro-ph↗

arXiv2004

Optical and near infrared observations of SN 1998bu

Infrared and optical spectra of SN 1998bu at an age of one year after explosion are presented. The data show evidence for the radioactive decay of 56Co to 56Fe, long assumed to be the powering source for the supernova light curve past maximum light. The spectra provide direct evidence for at least 0.4 solar masses of iron being present in the ejecta of the supernova. The fits to the data also show that the widths of the emission lines increase with time. Photometric measurements in the H-band show that the supernova is not fading during the observation period. This is consistent with theoretical expectations.

astro-ph↗

arXiv2004

On the Afterglow of the X-Ray Flash of July 23 2003: Photometric evidence for an off-axis Gamma-Ray Burst with an associated Supernova?

We present optical and near-infrared follow-up observations of the X-Ray Flash (XRF) of July 23 2003. Our observations in the R-band cover the temporal range from 4.2 h to 64 days after the high energy event. We also present the results of multicolor imaging extending to the K-band on three epochs. The lightcurve of the R-band afterglow the first week after the burst is similar to the lightcurve for long duration Gamma-Ray Bursts (GRBs), i.e., a broken power-law with a late time slope of alpha=-2.0 (F_nu propto t^alpha). Furthermore, the spectral energy distribution (SED) has a power-law (F_nu propto nu^beta) shape with slope beta=-1.0. However, the decay slope at t<1 day is shallow, consistent with zero. This is in qualitative agreement with the prediction that XRFs are off-axis classical GRBs. After the first week there is a strong bump in the lightcurve, which peaks at around 16 days. The SED after the peak becomes significantly redder. We discuss the possible interpretations of this bump, and conclude that an underlying supernova is the most likely explanation since no other model appears consistent with the evolution of the SED. Finally, we present deep spectroscopy of the burst both in the afterglow and in the bump phase. A firm upper limit of z=2.3 is placed on the redshift of XRF030723 from the lack of Ly-alpha forest lines in the spectrum of the afterglow. The lack of significant absorption and emission lines in either of the two spectra excludes a spectroscopic redshift determination.

astro-ph↗

arXiv2004

The X-ray and radio emission from SN 2002ap: The importance of Compton scattering

The radio and X-ray observations of the Type Ic supernova SN 2002ap are modeled. We find that inverse Compton cooling by photospheric photons explains the observed steep radio spectrum, and also the X-ray flux observed by XMM. Thermal emission from the shock is insufficient to explain the X-ray flux. The radio emitting region expands with a velocity of, roughly, 70,000 km/s. From the ratio of X-ray to radio emission we find that the energy densities of magnetic fields and relativistic electrons are close to equipartion.

astro-ph↗