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Register a new userOptical and spectral observations and hydrodynamic modelling of Type IIb Supernova 2017gpn
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In this work we present the photometric and spectroscopic observations of Type IIb Supernova 2017gpn. This supernova was discovered in the error-box of LIGO/Virgo G299232 gravitational-wave event. We obtained the light curves in B and R passbands and modelled them numerically using the one-dimensional radiation hydrocode STELLA. The best-fit model has the following parameters: the pre-SN star mass and the radius are 3.5 Msun and 50 Rsun, respectively; the explosion energy is Eexp = 1.2 * 10^51 erg; the mass of radioactive nickel is M56Ni =0.11 Msun, which is totally mixed through the ejecta, the mass of the hydrogen envelope 0.06 Msun. Moreover, SN 2017gpn is a confirmed SN IIb that is located at the farthest distance from the center of its host galaxy NGC 1343 (i.e. the projected distance is about 21 kpc). This challenges the scenario of the origin of Type IIb Supernovae from massive stars.
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We present Swift UVOT and XRT observations, and visual wavelength spectroscopy of the Type IIb supernova (SN) 2009mg, discovered in the Sb galaxy ESO 121-G26. The observational properties of SN 2009mg are compared to the prototype Type IIb SNe 1993J and 2008ax, with which we find many similarities. However, minor differences are discernible including SN 2009mg not exhibiting an initial fast decline or u-band upturn as observed in the comparison objects, and its rise to maximum is somewhat slower leading to slightly broader light curves. The late-time temporal index of SN 2009mg, determined from 40 days post-explosion, is consistent with the decay rate of SN 1993J, but inconsistent with the decay of 56Co. This suggests leakage of gamma-rays out of the ejecta and a stellar mass on the small side of the mass distribution. Our XRT non-detection provides an upper limit on the mass-loss rate of the progenitor of <1.5x10^-5 Msun per yr. Modelling of the SN light curve indicates a kinetic energy of 0.15 (+0.02,-0.13) x10^51 erg, an ejecta mass of 0.56(+0.10,-0.26) Msun and a 56Ni mass of 0.10pm0.01 Msun.
CCD UBVRI photometry is presented for type IIb SN 2011dh for about 300 days. The main photometric parameters are derived and the comparison with SNe of similar types is reported. The light curves are similar to those for SN IIb 2008ax, but the initial flash is stronger and very short, and there are humps on the light curves in U and B at the onset of linear decline. Preliminary modeling is carried out, and the results are compared to the quasi-bolometric light curve and to the light curves in UBVRI bands.
We present Murchison Widefield Array observations of the supernova remnant (SNR) 1987A between 72 and 230 MHz, representing the lowest frequency observations of the source to date. This large lever arm in frequency space constrains the properties of the circumstellar medium created by the progenitor of SNR 1987A when it was in its red supergiant phase. As of late-2013, the radio spectrum of SNR 1987A between 72 MHz and 8.64 GHz does not show any deviation from a non-thermal power-law with a spectral index of $-0.74 pm 0.02$. This spectral index is consistent with that derived at higher frequencies, beneath 100 GHz, and with a shock in its adiabatic phase. A spectral turnover due to free-free absorption by the circumstellar medium has to occur below 72 MHz, which places upper limits on the optical depth of $leq$ 0.1 at a reference frequency of 72 MHz, emission measure of $lesssim$ 13,000 cm$^{-6}$ pc, and an electron density of $lesssim$ 110 cm$^{-3}$. This upper limit on the electron density is consistent with the detection of prompt radio emission and models of the X-ray emission from the supernova. The electron density upper limit implies that some hydrodynamic simulations derived a red supergiant mass loss rate that is too high, or a wind velocity that is too low. The mass loss rate of $sim 5 times 10^{-6}$ $M_{odot}$ yr$^{-1}$ and wind velocity of 10 km s$^{-1}$ obtained from optical observations are consistent with our upper limits, predicting a current turnover frequency due to free-free absorption between 5 and 60 MHz.
SN 2017ein is a narrow-lined Type Ic SN that was found to share a location with a point-like source in the face on spiral galaxy NGC 3938 in pre-supernova images, making SN 2017ein the first credible detection of a Type Ic progenitor. Results in the literature suggest this point-like source is likely a massive progenitor of 60-80 M$_{odot}$, depending on if the source is a binary, a single star, or a compact cluster. Using new photometric and spectral data collected for 200 days, including several nebular spectra, we generate a consistent model covering the photospheric and nebular phase using a Monte Carlo radiation transport code. Photospheric phase modelling finds an ejected mass 1.2-2.0 M$_{odot}$ with an $E_mathrm{k}$ of $sim(0.9 pm0.2)times 10^{51}$ erg, with approximately 1 M$_{odot}$ of material below 5000 km s$^{-1}$ found from the nebular spectra. Both photospheric and nebular phase modelling suggests a $^{56}$Ni mass of 0.08-0.1 M$_{odot}$. Modelling the [OI] emission feature in the nebular spectra suggests the innermost ejecta is asymmetric. The modelling results favour a low mass progenitor of to 16-20 M$_{odot}$, which is in disagreement with the pre-supernova derived high mass progenitor. This contradiction is likely due to the pre-supernova source not representing the actual progenitor.
We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within 1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on the timescale of one week. High-cadence monitoring of this transition suggests that absorption attributable to a high velocity (> 12,000 km/s) H-rich shell is not rare in Type Ib events. Radio observations imply a shock velocity of v = 0.13c and a progenitor star mass-loss rate of 1.4 x 10^{-5} Msun yr^{-1} (assuming wind velocity v_w=10^3 km/s). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN 2011ei are consistent with the explosion of a lower-mass (3-4 Msun), compact (R* <= 1x10^{11} cm), He core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass-loss. We conclude that SN 2011eis rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of explosion rates for Type IIb and Ib objects, and that important information about a progenitor stars evolutionary state and mass-loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations.
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