arXiv subjects

P. Milne

Publications and source records attributed to P. Milne.

25 records · Page 2Linked to original sources

arXiv2008

Massive stars exploding in a He-rich circumstellar medium. I. Type Ibn (SN 2006jc-like) events

We present new spectroscopic and photometric data of the type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf-Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf-Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous type Ia event with some resemblance to SN 1991bg.

astro-ph↗

arXiv2008

Swift and Chandra Detections of Supernova 2006jc: Evidence for Interaction of the Supernova Shock with a Circumstellar Shell

The peculiar Type Ib supernova (SN) 2006jc has been observed with the UV/Optical Telescope (UVOT) and X-Ray Telescope (XRT) on board the Swift observatory over a period of 19 to 183 days after the explosion. Signatures of interaction of the outgoing SN shock with dense circumstellar material (CSM) are detected, such as strong X-ray emission (L_{0.2-10} > E39 erg/s) and the presence of MgII 2800A line emission visible in the UV spectra. In combination with a Chandra observation obtained on day 40 after the explosion, the X-ray light curve is constructed, which shows a unique rise of the X-ray emission by a factor of ~5 over a period of ~4 months, followed by a rapid decline. We interpret the unique X-ray and UV properties as a result of the SN shock interacting with a shell of material that was deposited by an outburst of the SN progenitor two years prior to the explosion. Our results are consistent with the explosion of a Wolf-Rayet star that underwent an episodic mass ejection qualitatively similar to those of luminous blue variable stars prior to its explosion. This led to the formation of a dense (>E7 cm**-3) shell at a distance of ~E16 cm from the site of the explosion, which expands with the WR wind at a velocity of (1300+/-300) km/s.

astro-ph↗

arXiv2007

X-Ray, UV, and Optical Observations of Supernova 2006bp with Swift: Detection of Early X-Ray Emission

We present results on the X-ray and optical/UV emission from the type IIP SN 2006bp and the interaction of the SN shock with its environment, obtained with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on-board the Swift observatory. SN 2006bp is detected in X-rays at a 4.5 sigma level of significance in the merged XRT data from days 1 to 12 after the explosion. If the X-ray luminosity of (1.8+/-0.4)E39 ergs/s is caused by interaction of the SN shock with circumstellar material (CSM), deposited by a stellar wind from the progenitor's companion star, a mass-loss rate of ~E-05 M_sun/yr is inferred. The mass-loss rate is consistent with the non-detection in the radio with the VLA on days 2, 9, and 11 after the explosion and characteristic of a red supergiant progenitor with a mass around 12-15 M_sun prior to the explosion. In combination with a follow-up XMM-Newton observation obtained on day 21 after the explosion, an X-ray rate of decline with index 1.2+/-0.6 is inferred. Since no other SN has been detected in X-rays prior to the optical peak and since type IIP SNe have an extended 'plateau' phase in the optical, we discuss the scenario that the X-rays might be due to inverse Compton scattering of photospheric optical photons off relativistic electrons produced in circumstellar shocks. However, due to the high required value of the Lorentz factor (~10-100) we conclude that Inverse Compton scattering is an unlikely explanation for the observed X-ray emission. The fast evolution of the optical/ultraviolet spectral energy distribution and the spectral changes observed with Swift reveal the onset of metal line-blanketing and cooling of the expanding photosphere during the first few weeks after the outburst.

astro-ph↗

arXiv2007

The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?

We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of SN 2005hk. These data reveal that SN 2005hk was nearly identical in its observed properties to SN 2002cx, which has been called ``the most peculiar known type Ia supernova.'' Both supernovae exhibited high ionization SN 1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities that were roughly half those of typical type Ia supernovae. The R and I light curves of both supernovae were also peculiar in not displaying the secondary maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk reveals the same peculiarity in the near-infrared. By combining our optical and near-infrared photometry of SN 2005hk with published ultraviolet light curves obtained with the Swift satellite, we are able to construct a bolometric light curve from ~10 days before to ~60 days after B maximum. The shape and unusually low peak luminosity of this light curve, plus the low expansion velocities and absence of a secondary maximum at red and near-infrared wavelengths, are all in reasonable agreement with model calculations of a 3D deflagration which produces ~0.25 M_sun of 56Ni.

astro-ph↗

arXiv2007

The sky distribution of 511 keV positron annihilation line emission as measured with INTEGRAL/SPI

The imaging spectrometer SPI on board ESA's INTEGRAL observatory provides us with an unprecedented view of positron annihilation in our Galaxy. The first sky maps in the 511 keV annihilation line and in the positronium continuum from SPI showed a puzzling concentration of annihilation radiation in the Galactic bulge region. By now, more than twice as many INTEGRAL observations are available, offering new clues to the origin of Galactic positrons. We present the current status of our analyses of this augmented data set. We now detect significant emission from outside the Galactic bulge region. The 511 keV line is clearly detected from the Galactic disk; in addition, there is a tantalizing hint at possible halo-like emission. The available data do not yet permit to discern whether the emission around the bulge region originates from a halo-like component or from a disk component that is very extended in latitude.

astro-ph↗

arXiv2006

X-Ray Observations of Type Ia Supernovae with Swift: Evidence for Circumstellar Interaction for SN 2005ke

We present a study of the early (days to weeks) X-ray and UV properties of eight Type Ia supernovae (SNe Ia) which have been extensively observed with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) onboard Swift, ranging from 5-132 days after the outburst. SN 2005ke is tentatively detected (at a 3-3.6 sigma level of significance) in X-rays based on deep monitoring with the XRT ranging from 8 to 120 days after the outburst. The inferred X-ray luminosity [(2+/-1) x 10^{38} ergs/s; 0.3-2 keV band] is likely caused by interaction of the SN shock with circumstellar material (CSM), deposited by a stellar wind from the progenitor's companion star with a mass-loss rate of ~ 3 x 10^{-6} M_sun/yr (v_w/10 km/s). Evidence of CSM interaction in X-rays is independently confirmed by an excess of UV emission as observed with the UVOT onboard Swift, starting around 35 days after the explosion. The non-detection of SN 2005ke with Chandra 105 days after the outburst implies a rate of decline steeper than L_x \propto t^{-0.75}, consistent with the decline expected from the interaction of the SN shock with a spherically symmetric CSM (t^{-1}). None of the other seven SNe Ia is detected in X-rays or shows a UV excess, which allows us to put tight constraints on the mass-loss rates of the progenitor systems.

astro-ph↗

arXiv2005

Ultraviolet, Optical, and X-Ray Observations of the Type Ia Supernova 2005am with Swift

We present ultraviolet and optical light curves in six broadband filters and grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia supernova SN2005am. The data were collected beginning about four days before the B-band maximum, with excellent coverage of the rapid decline phase and later observations extending out to 69 days after the peak. The optical and near UV light curve match well those of SN1992A. The other UV observations constitute the first set of light curves shorter than 2500 Angstroms and allow us to compare the light curve evolution in three UV bands. The UV behavior of this and other low redshift supernovae can be used to constrain theories of progenitor evolution or to interpret optical light curves of high redshift supernovae. Using Swift's X-Ray Telescope, we also report the upper limit to SN2005am's X-ray luminosity to be 1.77 x 10^40 erg s^-1 in the 0.3--10 keV range from 58,117 s of exposure time.

astro-ph↗