arXiv subjects

S. Immler

Publications and source records attributed to S. Immler.

25 records · Page 2Linked to original sources

arXiv2007

SN 2006gy: An extremely luminous supernova in the galaxy NGC 1260

With an extinction-corrected V-band peak absolute magnitude of about -22, supernova (SN) 2006gy is probably the brightest SN ever observed. We report on multi-wavelength observations of this SN and its environment. Our spectroscopy shows an H alpha emission line as well as absorption features which may be identified as SiII lines at low expansion velocity. The high peak luminosity, the slow rise to maximum, and the narrow H alpha line are similar to those observed in hybrid type-Ia/IIn (also called IIa) SNe. The host galaxy, NGC 1260, is dominated by an old stellar population with solar metallicity. However, our high resolution adaptive optics images reveal a dust lane in this galaxy, and there appears to be an HII region in the vicinity of the SN. The extra-ordinarily large peak luminosity, ~3x10^44 erg/s, demands a dense circum-stellar medium, regardless of the mass of the progenitor star. The inferred mass loss rate of the progenitor is ~0.1 solar mass per year over a period of ~10 yr prior to explosion. Such an high mass-loss rate may be the result of a binary star common envelope ejection. The total radiated energy in the first two months is about 1.1x10^51 erg, which is only a factor of two less than that available from a super-Chandrasekhar Ia explosion. Therefore, given the presence of a star forming region in the vicinity of the SN and the high energy requirements, a plausible scenario is that SN 2006gy is related to the death of a massive star (e.g., pair production SN).

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arXiv2006

Swift observations of GRB050904: the most distant cosmic explosion ever observed

Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). GRB050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 hours after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from -1.2 during the BAT observation to -1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b). We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation.

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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.

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arXiv2006

The shock break-out of GRB 060218/SN 2006aj

Although the link between long Gamma Ray Bursts (GRBs) and supernovae (SNe) has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a GRB. In particular, we do not know however how a GRB jet emerges from the star surface nor how a GRB progenitor explodes. Here we report on observations of the close GRB060218 and its connection to SN2006aj. In addition to the classical non-thermal emission, GRB060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/UV band as time passes. We interpret these features as arising from the break out of a shock driven by a mildly relativistic shell into the dense wind surrounding the progenitor. Our observations allow us for the first time to catch a SN in the act of exploding, to directly observe the shock break-out and to provide strong evidence that the GRB progenitor was a Wolf-Rayet star.

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arXiv2005

A Radio and X-Ray Study of Historical Supernovae in M83

We report the results of 15 years of radio observations of the six historical supernovae (SNe) in M83 using the Very Large Array. We note the near linear decline in radio emission from SN 1957D, a type II SN, which remains a non-thermal radio emitter. The measured flux densities from SNe 1923A and 1950B have flattened as they begin to fade below detectable limits, also type II SNe. The luminosities for these three SNe are comparable with the radio luminosities of other decades-old SNe at similar epochs. SNe 1945B, 1968L, and 1983N were not detected in the most recent observations and these non-detections are consistent with previous studies. We report the X-ray non-detections of all six historical SNe using the Chandra X-ray Observatory, consistent with previous X-ray searches of other decades-old SNe, and low inferred mass loss rates of the progenitors.

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arXiv2003

Probing the Complex and Variable X-ray Absorption of Markarian 6 with XMM-Newton

We report on an X-ray observation of the Seyfert 1.5 galaxy Mrk 6 obtained with the EPIC instruments onboard XMM-Newton. Archival BeppoSAX PDS data from 18-120 keV were also used to constrain the underlying hard power-law continuum. The results from our spectral analyses generally favor a double partial-covering model, although other spectral models such as absorption by a mixture of partially ionized and neutral gas cannot be firmly ruled out. Our best-fitting model consists of a power law with a photon index of 1.81+/-0.20 and partial covering with large column densities up to 10^{23} cm**-2. We also detect a narrow emission line consistent with Fe Kalpha fluorescence at 6.45+/-0.04 keV with an equivalent width of ~93+/-25 eV. Joint analyses of XMM-Newton, ASCA, and BeppoSAX data further provide evidence for both spectral variability (a factor of ~2 change in absorbing column) and absorption-corrected flux variations (by ~60%) during the ~4 year period probed by the observations.

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arXiv2002

X-ray, Optical, and Radio Observations of the Type II Supernovae 1999em and 1998S

Observations of the Type II-P (plateau) Supernova (SN) 1999em and Type IIn (narrow emission line) SN 1998S have enabled estimation of the profile of the SN ejecta, the structure of the circumstellar medium (CSM) established by the pre-SN stellar wind, and the nature of the shock interaction. SN 1999em is the first Type II-P detected at both X-ray and radio wavelengths. The Chandra X-ray data indicate non-radiative interaction of SN ejecta with a power-law density profile (rho \propto r^{-n} with n ~ 7) with a pre-SN wind with a low mass-loss rate of ~2 \times 10^{-6} M_sun/yr for a wind velocity of 10 km/sec, in agreement with radio mass-loss rate estimates. The Chandra data show an unexpected, temporary rise in the 0.4--2.0 keV X-ray flux at ~100 days after explosion. SN 1998S, at an age of >3 years, is still bright in X-rays and is increasing in flux density at cm radio wavelengths. Spectral fits to the Chandra data show that many heavy elements (Ne, Al, Si, S, Ar, and Fe) are overabundant with respect to solar values. We compare the observed elemental abundances and abundance ratios to theoretical calculations and find that our data are consistent with a progenitor mass of approximately 15-20 M_sun if the heavy element ejecta are radially mixed out to a high velocity. If the X-ray emission is from the reverse shock wave region, the supernova density profile must be moderately flat at a velocity ~10^4 km/sec, the shock front is non-radiative at the time of the observations, and the mass-loss rate is 1-2 \times 10^{-4} M_sun/yr for a pre-supernova wind velocity of 10 km/sec. This result is also supported by modeling of the radio emission which implies that SN 1998S is surrounded by a clumpy or filamentary CSM established by a high mass-loss rate, ~2 \times 10^{-4} M_sun/yr, from the pre-supernova star.

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