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Register a new userA flattening in the Optical Light Curve of SN 2002ap
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We present the $UBVR_cI_c$ broad band optical photometry of the Type Ic supernova SN 2002ap obtained during 2002 February 06 -- March 23 in the early decline phases and also later on 2002 15 August. Combining these data with the published ones, the general light curve development is studied. The time and luminosity of the peak brightness and the peak width are estimated. There is a flattening in the optical light curve about 30 days after the $B$ maximum. The flux decline rates before flattening are 0.127$pm$0.005, 0.082$pm$0.001, 0.074$pm$0.001, 0.062$pm$0.001 and 0.040$pm$0.001 mag day$^{-1}$ in $U$, $B$, $V$, $R_c$ and $I_c$ passbands respectively, while the corresponding values after flattening are about 0.02 mag day$^{-1}$ in all the passbands. The maximum brightness of SN 2002ap $M_V = - 17.2$ mag, is comparable to that of the type Ic 1997ef, but fainter than that of the type Ic hypernova SN 1998bw. The peak luminosity indicates an ejection of $sim$ 0.06 M$_{odot}$ ${}^{56}$Ni mass. We also present low-resolution optical spectra obtained during the early phases. The SiII absorption minimum indicates that the photospheric velocity decreased from $sim$ 21,360 km s$^{-1}$ to $sim$ 10,740 km s$^{-1}$ during a period of $sim$ 6 days.
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We present the first observations of a Type I superluminous supernova (SLSN) at $gtrsim 1000$ days after maximum light. We observed SN 2015bn using the Hubble Space Telescope Advanced Camera for Surveys in the F475W, F625W and F775W filters at 721 days and 1068 days. SN 2015bn is clearly detected and resolved from its compact host, allowing reliable photometry. A galaxy template constructed from these data further enables us to isolate the SLSN flux in deep ground-based imaging. We measure a light curve decline rate at $>700$ days of $0.19 pm 0.03$ mag (100 d)$^{-1}$, much shallower than the earlier evolution, and slower than previous SLSNe (at any phase) or the decay rate of $^{56}$Co. Neither additional radioactive isotopes nor a light echo can consistently account for the slow decline. A spectrum at 1083 days shows the same [O I] and [Ca II] lines as seen at $sim300-400$ days, with no new features to indicate strong circumstellar interaction. Radio limits with the Very Large Array rule out an extended wind for mass-loss rates $10^{-2.7} lesssim dot{M}/v_{10} lesssim 10^{-1.1}$ M$_odot$ yr$^{-1}$ (where $v_{10}$ is the wind velocity in units of 10 km s$^{-1}$). The optical light curve is consistent with $L propto t^{-4}$, which we show is expected for magnetar spin-down with inefficient trapping; furthermore, the evolution matches predictions from earlier magnetar model fits. The opacity to magnetar radiation is constrained at $sim 0.01$ cm$^2$ g$^{-1}$, consistent with photon-matter pair-production over a broad $sim$GeV-TeV range. This suggests the magnetar spectral energy distribution, and hence the missing energy leaking from the ejecta, may peak in this range.
We present spectropolarimetry of the Type Ic supernova SN 2002ap and give a preliminary analysis: the data were taken at two epochs, close to and one month later than the visual maximum (2002 February 8). In addition we present June 9 spectropolarimetry without analysis. The data show the development of linear polarization. Distinct polarization profiles were seen only in the O I lambda 7773 multiplet/Ca II IR triplet absorption trough at maximum light and in the Ca II IR triplet absorption trough a month later, with the latter showing a peak polarization as high as ~2 %. The intrinsic polarization shows three clear position angles: 80 degs for the February continuum, 120 degs for the February line feature, and 150 degs for the March data. We conclude that there are multiple asymmetric components in the ejecta. We suggest that the supernova has a bulk asymmetry with an axial ratio projected on the sky that is different from 1 by of order 10 %. Furthermore, we suggest very speculatively that a high velocity ejecta component moving faster than ~0.115c (e.g., a jet) contributes to polarization in the February epoch.
Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the hypernova SN 1997ef. However, its kinetic energy [$sim (4-10) times 10^{51}$ erg] and the mass ejected (2.5-5 $M_{odot}$) are smaller, resulting in a faster-evolving light curve. The SN synthesized $sim 0.07 M_{odot}$ of $^{56}$Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of a high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 $M_{odot}$, which is also lower than that of both hypernovae SNe 1997ef and 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by summer 2002, are necessary to confirm these values.
The supernova SN 2002ap was discovered in the outer regions of the nearby spiral M74 on January 29.4 UT. Early photometric and spectroscopic observations indicate the supernova belongs to the class of Ic hypernova. Late time (After JD 2452500) light curve decay slopes are similar to that of the hypernovae SN 1997ef and SN 1998bw. We present here the $BVRI$ photometric light curves and colour evolutions of SN 2002ap to investigate the late time nature of the light curve.
SN 2003dh, one of the most luminous supernovae ever recorded, and the one with the highest measured velocities, accompanied gamma-ray burst 030329. Its rapid rise to maximum and equally rapid decline pose problems for any spherically symmetric model. We model the supernova here as a very energetic, polar explosion that left the equatorial portions of the star almost intact. The total progenitor mass was much greater than the mass of high-velocity ejecta, and the total mass of 56-Ni synthesized was about 0.5 solar masses. Such asymmetries and nickel masses are expected in the collapsar model. A ``composite two-dimensional model is calculated that agrees well with the characteristics of the observed light curve. The mass of 56-Ni required for this light curve is 0.55 solar masses and the total explosion energy, 26 x 10**51 erg.
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