| 1. |
- Veres, P., et al.
(författare)
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Observation of inverse Compton emission from a long gamma-ray burst
- 2019
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Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 575:7783, s. 459-
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Tidskriftsartikel (refereegranskat)abstract
- Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectron volt-to-mega electronvoltband, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission(1,2). Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands(1-6). The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock(7-9). Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C(10,11). Here we report multifrequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 x 10(-6) to 10(12) electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.
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| 2. |
- Anderson, P., et al.
(författare)
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The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor
- 2018
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 2:7, s. 574-579
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Tidskriftsartikel (refereegranskat)abstract
- Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae(1). However, while such stars are observed with masses > 25 M-circle dot (ref. (2)), detections of > 18 M-circle dot progenitors remain elusive(1). Red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. Here, we report observations of the type II supernova, SN 2015bs, for which we infer a progenitor metallicity of <= 0.1 Z(circle dot) from comparison to photospheric-phase spectral models(3), and a zero-age main-sequence mass of 17-25 M-circle dot through comparison to nebular-phase spectral models(4,5). SN 2015bs displays a normal 'plateau' light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. This is the first example of such a high-mass progenitor for a 'normal' type II supernova, suggesting a link between high-mass red supergiant explosions and low-metallicity progenitors.
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| 3. |
- Stritzinger, M. D., et al.
(författare)
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The Carnegie Supernova Project II : Observations of the luminous red nova AT 2014ej
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- We present optical and near-infrared broadband photometry and optical spectra of AT 2014ej from the Carnegie Supernova Project-II. These observations are complemented with data from the CHilean Automatic Supernova sEarch, the Public ESO Spectroscopic Survey of Transient Objects, and from the Backyard Observatory Supernova Search. Observational signatures of AT 2014ej reveal that it is similar to other members of the gap-transient subclass known as luminous red novae (LRNe), including the ubiquitous double-hump light curve and spectral properties similar to that of LRN SN 2017jfs. A medium-dispersion visual-wavelength spectrum of AT 2014ej taken with the Magellan Clay telescope exhibits a P Cygni H alpha feature characterized by a blue velocity at zero intensity of approximate to 110 km s(-1) and a P Cygni minimum velocity of approximate to 70 km s(-1). We attribute this to emission from a circumstellar wind. Inspection of pre-outbust Hubble Space Telescope images yields no conclusive progenitor detection. In comparison with a sample of LRNe from the literature, AT 2014ej lies at the brighter end of the luminosity distribution. Comparison of the ultra-violet, optical, infrared light curves of well-observed LRNe to common-envelope evolution models from the literature indicates that the models underpredict the luminosity of the comparison sample at all phases and also produce inconsistent timescales of the secondary peak. Future efforts to model LRNe should expand upon the current parameter space we explore here and therefore may consider more massive systems and a wider range of dynamical timescales.
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| 4. |
- Stritzinger, M. D., et al.
(författare)
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The Carnegie Supernova Project I : Photometry data release of low-redshift stripped-envelope supernovae
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 609
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Tidskriftsartikel (refereegranskat)abstract
- The first phase of the Carnegie Supernova Project (CSP-I) was a dedicated supernova follow-up program based at the Las Campanas Observatory that collected science data of young, low-redshift supernovae between 2004 and 2009. Presented in this paper is the CSP-I photometric data release of low-redshift stripped-envelope core-collapse supernovae. The data consist of optical (uBgVri) photometry of 34 objects, with a subset of 26 having near-infrared (YJH) photometry. Twenty objects have optical pre-maximum coverage with a subset of 12 beginning at least five days prior to the epoch of B-band maximum brightness. In the near-infrared, 17 objects have pre-maximum observations with a subset of 14 beginning at least five days prior to the epoch of J-band maximum brightness. Analysis of this photometric data release is presented in companion papers focusing on techniques to estimate host-galaxy extinction and the light-curve and progenitor star properties of the sample. The analysis of an accompanying visual-wavelength spectroscopy sample of similar to 150 spectra will be the subject of a future paper.
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| 5. |
- Holmbo, S., et al.
(författare)
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Discovery and progenitor constraints on the Type Ia supernova 2013gy
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 627
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Tidskriftsartikel (refereegranskat)abstract
- We present an early-phase g-band light curve and visual-wavelength spectra of the normal Type Ia supernova (SN) 2013gy. The light curve is constructed by determining the appropriate S-corrections to transform KAIT natural-system B- and V-band photometry and Carnegie Supernova Project natural-system g-band photometry to the Pan-STARRS1 g-band natural photometric system. A Markov chain Monte Carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of 2.16(-0.06)(+0.06) and a time of first light of MJD 56629.4(-0.1)(+0.1), which is 1.93(-0.13)(+0.12) days (i.e., <48 h) before the discovery date (2013 December 4.84 UT) and -19.10(-0.13)(+0.12) days before the time of B- band maximum (MJD 56648.5 +/- 0.1). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the Si II lambda 6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to R-c <= 4 R-circle dot. In addition to our early-time constraints, we used a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of <0.018 M-circle dot. Combined, these limits effectively rule out H-rich nondegenerate companions.
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| 6. |
- Phillips, M. M., et al.
(författare)
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Carnegie Supernova Project-II : Extending the Near-infrared Hubble Diagram for Type Ia Supernovae to z ∼ 0.1
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
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Tidskriftsartikel (refereegranskat)abstract
- The Carnegie Supernova Project-II (CSP-II) was an NSF-funded, four-year program to obtain optical and near-infrared observations of a Cosmology sample of similar to 100 Type. Ia supernovae located in the smooth Hubble flow (0.03 less than or similar to z less than or similar to 0.10). Light curves were also obtained of a Physics sample composed of 90 nearby Type. Ia supernovae at z <= 0.04 selected for near-infrared spectroscopic timeseries observations. The primary emphasis of the CSP-II is to use the combination of optical and near-infrared photometry to achieve a distance precision of better than 5%. In this paper, details of the supernova sample, the observational strategy, and the characteristics of the photometric data are provided. In a companion paper, the near-infrared spectroscopy component of the project is presented.
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| 7. |
- Taddia, Francesco, et al.
(författare)
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Supernova 2008J : early time observations of a heavily reddened SN 2002ic-like transient
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 545, s. L7-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: We provide additional observational evidence that some Type Ia supernovae (SNe Ia) show signatures of circumstellar interaction (CSI) with hydrogen-rich material. Methods: Early phase optical and near-infrared (NIR) light curves and spectroscopy of SN 2008J obtained by the Carnegie Supernova Project are studied and compared to those of SNe 2002ic and 2005gj. Our NIR spectrum is the first obtained for a 2002ic-like object extending up to 2.2 μm. A published high-resolution spectrum is used to provide insight on the circumstellar material (CSM). Results: SN 2008J is found to be affected by AV ~ 1.9 mag of extinction and to closely resemble SN 2002ic. Spectral and color comparison to SNe 2002ic and 2005gj suggests RV < 3.1. Spectral decomposition reveals the underlying SN emission matches a 1991T-like event and, since SN 2008J is as luminous as SN 2005gj (Vmax = -20.3 mag), we conclude that their CSI emissions are similarly robust. The high-resolution spectrum reveals narrow emission lines produced from un-shocked gas characterized by a wind velocity of ~50 km s-1. We conclude that SN 2008J best matches an explosion of a SN Ia that interacts with its CSM. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (ESO Programme 080.A-0516).Figure 4 and Tables 1-6 are available in electronic form at http://www.aanda.org
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| 8. |
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| 9. |
- Abbasi, A, et al.
(författare)
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Progress on Partial Discharge Detectionunder DC Voltage Stress
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Detection and evaluation of partial discharges (PD) is important for quality assurance and diagnosis ofelectrical insulation systems. With increasing use of DC voltages in electrical transmission and distributionsystems, the field of PD under DC voltage stress needs to be further investigated.CIGRE Working Group D1.63 was approved for start in May 2015, where available knowledge and experiencein particular concerning the field distribution in insulation systems used in DC voltage systems, and thephysical processes of the PD phenomena under DC voltage stress should be reviewed. In order of guidingto meaningful procedures for DC PD measurements of HV equipment thorough understanding of i) thedifferences of PD behaviour between AC and DC with respect to the physical process and ii) influencingfactors of operating conditions (as e.g. polarization, temperature etc.) of different insulation systems underDC stress and respective effects on PD phenomena had to be examined.
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| 10. |
- Stritzinger, M. D., et al.
(författare)
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The Carnegie Supernova Project II Early observations and progenitor constraints of the Type Ib supernova LSQ13abf
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 634
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Tidskriftsartikel (refereegranskat)abstract
- Supernova LSQ13abf was discovered soon after explosion by the La Silla-QUEST Survey and then followed by the Carnegie Supernova Project II at its optical and near-IR wavelengths. Our analysis indicates that LSQ13abf was discovered within two days of explosion and its first approximate to 10 days of evolution reveal a B-band light curve with an abrupt drop in luminosity. Contemporaneously, the V-band light curve exhibits a rise towards a first peak and the r- and i-band light curves show no early peak.The early light-curve evolution of LSQ13abf is reminiscent of the post-explosion cooling phase observed in the Type Ib SN 2008D, and the similarity between the two objects extends over weeks. Spectroscopically, LSQ13abf also resembles SN 2008D, with P Cygni Hei features that strengthen over several weeks. Spectral energy distributions are constructed from the broad-bandphotometry, a UVOIR light curve is constructed by fitting black-body (BB) functions, and the underlying BB-temperature and BB-radius profiles are estimated. Explosion parameters are estimated by simultaneously fitting an Arnett model to the UVOIR light curve and the velocity evolution derived from spectral features, and an in addition to a post-shock breakout cooling model to the first two epochs of the bolometric evolution. This combined model suggests an explosion energy of 1.27 +/- 0.23 x 10(51) ergs, in addition to a relatively high ejecta mass of 5.94 +/- 1.10 M-circle dot, a Ni-56 mass of 0.16 +/- 0.02 M-circle dot, and a progenitor-star radius of 28.0 +/- 7.5 R-circle dot. The ejecta mass suggests the origins of LSQ13abf lie with a >25 M-circle dot zero-age-main-sequence mass progenitor and its estimated radius is three times larger compared to the result obtained from the same analysis applied to observations of SN 2008D, and nine times larger compared to SN 1999ex. Alternatively, a comparison of hydrodynamical simulations of greater than or similar to 20-25 M-circle dot zero-age-main-sequence progenitors that evolve to pre-supernova envelope masses of less than or similar to 10 M-circle dot and extended (similar to 100 R-circle dot) envelopes also broadly match the observations of LSQ13abf.
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