Improved distance determination to M51 from supernovae 2011dh and 2005cs

The appearance of two recent supernovae, SN 2011dh and 2005cs, both in M51, provides an opportunity to derive an improved distance to their host galaxy by combining the observations of both SNe. We apply the Expanding Photosphere Method to get the distance to M51 by fitting the data of these two SNe simultaneously. In order to correct for the effect of flux dilution, we use correction factors (zeta) appropriate for standard type II-P SNe atmospheres for 2005cs, but find zeta ~ 1 for the type IIb SN 2011dh, which may be due to the reduced H-content of its ejecta. The EPM analysis resulted in D_M51 = 8.4 +/- 0.7 Mpc. Based on this improved distance, we also re-analyze the HST observations of the proposed progenitor of SN 2011dh. We confirm that the object detected on the pre-explosion HST-images is unlikely to be a compact stellar cluster. In addition, its derived radius (~ 277$ R_sun) is too large for being the real (exploded) progenitor of SN 2011dh. The supernova-based distance, D = 8.4 Mpc, is in good agreement with other recent distance estimates to M51.Comment: 6 pages, 5 figures, accepted for publication in A&

SN 2009N: linking normal and subluminous Type II-P SNe

We present ultraviolet, optical, near-infrared photometry and spectroscopy of SN 2009N in NGC 4487. This object is a Type II-P supernova with spectra resembling those of subluminous II-P supernovae, while its bolometric luminosity is similar to that of the intermediate-luminosity SN 2008in. We created synow models of the plateau phase spectra for line identification and to measure the expansion velocity. In the near-infrared spectra we find signs indicating possible weak interaction between the supernova ejecta and the pre-existing circumstellar material. These signs are also present in the previously unpublished near-infrared spectra of SN 2008in. The distance to SN 2009N is determined via the expanding photosphere method and the standard candle method as D = 21.6 ± 1.1 Mpc. The produced nickel-mass is estimated to be ∼0.020 ± 0.004 M_⊙. We infer the physical properties of the progenitor at the explosion through hydrodynamical modelling of the observables. We find the values of the total energy as ∼0.48 × 10^(51) erg, the ejected mass as ∼11.5 M_⊙, and the initial radius as ∼287 R_⊙

Optical photometry and spectroscopy of the 1987A-like supernova 2009mw

We present optical photometric and spectroscopic observations of the 1987A-like supernova (SN) 2009mw. Our $BVRI$ and $g'r'i'z'$ photometry covers 167 days of evolution, including the rise to the light curve maximum, and ends just after the beginning of the linear tail phase. We compare the observational properties of SN 2009mw with those of other SNe belonging to the same subgroup, and find that it shows similarities to several objects. The physical parameters of the progenitor and the SN are estimated via hydrodynamical modelling, yielding an explosion energy of $1$ foe, a pre-SN mass of $19\,{\rm M_{\odot}}$, a progenitor radius as $30\,{\rm R_{\odot}}$ and a $^{56}$Ni mass as $0.062\,{\rm M_{\odot}}$. These values indicate that the progenitor of SN 2009mw was a blue supergiant star, similar to the progenitor of SN 1987A. We examine the host environment of SN 2009mw and find that it emerged from a population with slightly sub-solar metallicty.Comment: 11 pages, 12 figures, accepted for publication in MNRA

Measuring Expansion Velocities in Type II-P Supernovae

We estimate photospheric velocities of Type II-P supernovae using model spectra created with SYNOW, and compare the results with those obtained by more conventional techniques, such as cross-correlation, or measuring the absorption minimum of P Cygni features. Based on a sample of 81 observed spectra of 5 SNe, we show that SYNOW provides velocities that are similar to ones obtained by more sophisticated NLTE modeling codes, but they can be derived in a less computation-intensive way. The estimated photospheric velocities (v_model) are compared to ones measured from Doppler-shifts of the absorption minima of the Hbeta and the FeII \lambda5169 features. Our results confirm that the FeII velocities (v_Fe) have tighter and more homogeneous correlation with the estimated photospheric velocities than the ones measured from Hbeta, but both suffer from phase-dependent systematic deviations from those. The same is true for comparison with the cross-correlation velocities. We verify and improve the relations between v_Fe, v_Hbeta and v_model in order to provide useful formulae for interpolating/extrapolating the velocity curves of Type II-P SNe to phases not covered by observations. We also discuss the implications of our results for the distance measurements of Type II-P SNe, and show that the application of the model velocities is preferred in the Expanding Photosphere Method.Comment: 19 pages, 10 figures, accepted in MNRA

VLBI observations of SN2011dh: imaging of the youngest radio supernova

We report on the VLBI detection of supernova SN2011dh at 22GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor 2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations.Comment: Letter. Accepted in A&

Testing SNe Ia distance measurement methods with SN 2011fe

The nearby, bright, almost completely unreddened Type Ia supernova 2011fe in M101 provides a unique opportunity to test both the precision and the accuracy of the extragalactic distances derived from SNe Ia light curve fitters. We apply the current, public versions of the independent light curve fitting codes MLCS2k2 and SALT2 to compute the distance modulus of SN 2011fe from high-precision, multi-color (BVRI) light curves. The results from the two fitting codes confirm that 2011fe is a "normal" (not peculiar) and only slightly reddened SN Ia. New unreddened distance moduli are derived as 29.21 +/- 0.07 mag (D ~ 6.95 +/- 0.23$ Mpc, MLCS2k2), and 29.05 +/- 0.07 mag (6.46 +/- 0.21 Mpc, SALT2). Despite the very good fitting quality achieved with both light curve fitters, the resulting distance moduli are inconsistent by 2 sigma. Both are marginally consistent (at ~1 sigma) with the HST Key Project distance modulus for M101. The SALT2 distance is in good agreement with the recently revised Cepheid- and TRGB-distance to M101. Averaging all SN- and Cepheid-based estimates, the absolute distance to M101 is ~6.6 +/- 0.5 Mpc.Comment: 8 pages, 7 figures, accepted for publication in A&

Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej

We present extensive optical ($UBVRI$, $g'r'i'z'$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9\pm0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2\% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $\lambda6355$ as early as +8 days. The photospheric velocity ($v_{\rm ph}$) is determined by modeling the spectra in the vicinity of Fe II $\lambda5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{\rm ph} = 4500\pm500$ km s$^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94\pm7$ days long, yields an explosion energy of $0.9\pm0.3\times10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2\pm4.2$~M$_\odot$ and a radius of $250\pm70$~R$_\odot$. We observe a broken exponential profile beyond +120 days, with a break point at +$183\pm16$ days. Measurements beyond this break time yield a $^{56}$Ni mass of $0.013\pm0.001$~M$_\odot$.Comment: 29 pages, 23 figures, 15 tables, Published in The Astrophisical Journa

Optical photometry and spectroscopy of the 1987A-like supernova 2009mw

We present optical photometric and spectroscopic observations of the 1987A-like supernova (SN) 2009mw. Our BVRI and g′r′i′z′ photometry covers 167 d of evolution, including the rise to the light-curve maximum, and ends just after the beginning of the linear tail phase. We compare the observational properties of SN 2009mw with those of other SNe belonging to the same subgroup and find that it shows similarities to several objects. The physical parameters of the progenitor and the SN are estimated through hydrodynamical modelling, and yield an explosion energy of 1 foe, a pre-SN mass of 19 M⊙, a progenitor radius of 30 R⊙ and a 56Ni mass of 0.062 M⊙. These values indicate that the progenitor of SN 2009mw was a blue supergiant star, similar to the progenitor of SN 1987A. We examine the host environment of SN 2009mw and find that it emerged from a population with a slightly subsolar metallicty.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Optical photometry and spectroscopy of the 1987A-like supernova 2009mw

We present optical photometric and spectroscopic observations of the 1987A-like supernova (SN) 2009mw. Our BVRI and g′r′i′z′ photometry covers 167 d of evolution, including the rise to the light-curve maximum, and ends just after the beginning of the linear tail phase. We compare the observational properties of SN 2009mw with those of other SNe belonging to the same subgroup and find that it shows similarities to several objects. The physical parameters of the progenitor and the SN are estimated through hydrodynamical modelling, and yield an explosion energy of 1 foe, a pre-SN mass of 19 M⊙, a progenitor radius of 30 R⊙ and a 56Ni mass of 0.062 M⊙. These values indicate that the progenitor of SN 2009mw was a blue supergiant star, similar to the progenitor of SN 1987A. We examine the host environment of SN 2009mw and find that it emerged from a population with a slightly subsolar metallicty.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat