arXiv subjects

F. Patat

Publications and source records attributed to F. Patat.

119 records · Page 7Linked to original sources

arXiv2000

The template type Ia supernova 1996X

UBVRIJ photometry and optical spectra of the Type Ia SN 1996X obtained at ESO during a one-year-long observational campaign are presented, and supplemented by late time HST photometry. Spectroscopically, SN 1996X appears to be a `normal' SN Ia. The apparent magnitude at maximum was B=13.24 +/- 0.02, and the colour B-V=0.00 +/- 0.03. The luminosity decline rate, Delta m_B(15) = 1.31 +/- 0.08, is close to average for a SN Ia. The best estimate of the galactic extinction is A_B=0.30 +/- 0.05, and there is evidence that reddening within the parent galaxy is negligible. Detailed comparison of the light and colour curves of various `normal' SNe Ia shows that the assumption that multicolour light curves can be described simply as a one-parameter family is not perfect. Together with problems in the calibration of the templates, this may explain the discrepancies in the distance modulus derived adopting different calibrations of the absolute magnitude vs. light curve shape relations. Indeed we found that M_B ranges from -19.08 to -19.48 and M-m range from 32.02 to 32.48 depending on the method used (Hamuy et al. 1996a,Phillips et al. 1999, Riess et al. 1998a). Computations of model light curve and synthetic spectra for both early- and late-times, confirm that 1996X is a normal Type Ia SN and that a satisfactory fit can be obtained using a W7 progenitor structure only if we adopt the short distance. A larger distance would imply a too large Ni mass for this fainter than average SNIa.

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arXiv2000

The Properties of Hypernovae: SNe Ic 1998bw, 1997ef, and SN IIn 1997cy

We discuss the properties of the hyper-energetic Type Ic supernovae (SNe Ic) 1998bw and 1997ef and Type IIn supernova (SN IIn) 1997cy. SNe Ic 1998bw and 1997ef are characterized by their large luminosity and the very broad spectral features. Their observed properties can be explained if they are very energetic SN explosions with the kinetic energy of $E_{\rm K} \gsim 1\times10^{52}$ erg, originating probably from the core collapse of the bare C+O cores of massive stars ($\sim 30-40$M$_\odot$). At late times, both the light curves and the spectra suggest that the explosions may have been asymmetric; this may help us understand the claimed connection with GRB's. The Type IIn SN 1997cy is even more luminous than SN 1998bw and the light curve declines more slowly than $^{56}$Co decay. We model such a light curve with circumstellar interaction, which requires the explosion energy of $\sim 5 \times 10^{52}$ erg. Because these kinetic energies of explosion are much larger than in normal core-collapse SNe, we call objects like these SNe "hypernovae". The mass of $^{56}$Ni in SN 1998bw is estimated to be as large as 0.5 - 0.7 $M_\odot$ from both the maximum brightness and late time emission spectra, which suggests that the asymmetry may not be extreme.

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arXiv2000

The properties of Supernova 1997cy associated to GRB970514

The extraordinary SN 1997cy associated with GRB 970514 has been observed photometrically and spectroscopically for nearly 2 yr. At the time of discovery SN 1997cy was the brightest SN ever observed (Mv=<-20.1, v(hel)=19140 km/s, H_0=65 km/s/Mpc). Up to the last available observations (600 days after the GRB) the total time-integrated flux was equal to or larger than that expected from the complete thermalization of the gamma-rays produced by 2.3 Mo of 56Co. However, starting already on day 60 the luminosity decline is slower than the 56Co decay rate, indicating that the SN ejecta was interacting with circumstellar material (CSM). The interaction appeared to weaken around day 550. The spectra of SN 1997cy are dominated at all epochs by Halpha emission, which shows at least 3 components of different widths, as in SN 1988Z. Several other lines with different widths are also visible, especially at early epochs. The entire light curve of SN 1997cy is reproduced by a model of the interaction of the very energetic (E=5 x 10^(52) ergs) ejecta of a massive star (25 Mo) with the CSM, with some contribution from radioactive decays. The CSM could have been ejected with a mass-loss rate of Mdot ~ 4x10^(-4) Mo yr^(-1) as the progenitor star evolved from a BSG to a RSG about 10^4 yr before the explosion. The lack of oxygen and magnesium lines in the spectra at nebular phases poses a problem for models requiring high mass progenitors. The possibility that most of the core material of the progenitor has fallen onto a massive black hole so that the reverse shock dies at the inner edge of the H/He envelope is discussed.

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arXiv1999

Magnitude, color and spectral type of Aql X-1 in quiescence

Direct I and V-band imaging of Aql X-1 in quiescence and during outburst maximum shows that the true optical counterpart is the interloper located 0.48" West of the previously known star. We find for the new counterpart V = 21.6 and V-I = 2.2 in quiescence, when its contribution to the total light was 12% in V and 22% in I. Analysis of this photometry and of low-resolution spectra of the sum of both stars, also taken during quiescence, shows that the likely spectral types for the previously known star and the optical counterpart are late G and late K, respectively, reddened by E(B-V) = 0.5 $\pm$0.1.

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arXiv1998

A `Hypernova' model for SN 1998bw associated with gamma-ray burst of 25 April 1998

The discovery of the peculiar supernova (SN) 1998bw and its possible association with the gamma-ray burst (GRB) 980425$^{1,2,3}$ provide new clues to the understanding of the explosion mechanism of very massive stars and to the origin of some classes of gamma-ray bursts. Its spectra indicate that SN~1998bw is a type Ic supernova$^{3,4}$, but its peak luminosity is unusually high compared with typical type Ic supernovae$^3$. Here we report our findings that the optical spectra and the light curve of SN 1998bw can be well reproduced by an extremely energetic explosion of a massive carbon+oxygen (C+O) star. The kinetic energy is as large as $\sim 2-5 \times 10^{52}$ ergs, more than ten times the previously known energy of supernovae. For this reason, the explosion may be called a `hypernova'. Such a C+O star is the stripped core of a very massive star that has lost its H and He envelopes. The extremely large energy, suggesting the existence of a new mechanism of massive star explosion, can cause a relativistic shock that may be linked to the gamma-ray burst.

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arXiv1998

A new faint Type Ia Supernova: SN 1997cn in NGC 5490

Observations of the recent SN 1991bg in the elliptical galaxy NGC 5490 show that this objects closely resembles, both photometrically and spectroscopically, the faint SNIa 1991bg. The two objects have similar light curves, which do not show secondary maxima in the near IR as normal type Ia supernovae. The host galaxy, NGC5490, lies in the Hubble flow. Adopting for SN1997cn a reddening E(B-V)=0, the absolute magnitude is faint: MV = -17.98 using Ho=65 and MV = -17.40 using Ho=85 km/(s Mpc). The latter value is in close agreement with the absolute magnitude of SN 1991bg on the SBF--PNLF--TF distance scale. The photospheric spectra of the two SNe show the same peculiarities, the deep TiII trough between 4000 and 4500A, the strong CaII IR triplet, the narrow absorption at about 5700A and the slow expansion velocity. In analogy to SN 1991bg the observed spectrum of SN1997cn has been successfully modeled by scaling down the W7 model by a factor of 2, assuming a rise time to B maximum of 18 days, a photospheric velocity and an effective temperature low compared to normal SNIa. The influence of the distance scale adopted on the input parameters of the best fit model is also discussed. These data demonstrate that peculiar SNIa like SN 1991bg are not once--in--a--lifetime events and that deep SN searches can be contaminated by underluminous SN Ia in a fairly large volume.

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arXiv1998

Discovery of the peculiar supernova 1998bw in the error box of GRB980425

The discovery of X-ray, optical and radio afterglows of gamma-ray bursts (GRBs) and the measurements of the distances to some of them have established that these events come from Gpc distances and are the most powerful photon emitters known in the Universe, with peak luminosities up to 10^52 erg/s. We here report the discovery of an optical transient, in the BeppoSAX Wide Field Camera error box of GRB980425, which occurred within about a day of the gamma-ray burst. Its optical light curve, spectrum and location in a spiral arm of the galaxy ESO 184-G82, at a redshift z = 0.0085, show that the transient is a very luminous type Ic supernova, SN1998bw. The peculiar nature of SN1998bw is emphasized by its extraordinary radio properties which require that the radio emitter expand at relativistical speed. Since SN1998bw is very different from all previously observed afterglows of GRBs, our discovery raises the possibility that very different mechanisms may give rise to GRBs, which differ little in their gamma-ray properties.

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arXiv1997

SNIa light curves and radioactive decay

The absolute V light curves of 5 SNe Ia, selected to represent the known range of absolute luminosities at maximum for this class of objects, are presented. Comparison of the long term luminosity evolution shows that the differences seen at maximum persist, and actually increase with time, einforcing the notion that intrinsic differences do exist among SNe Ia. Since such differences are not accounted for in the standard progenitor scenario, it becomes important to derive constraints for the models directly from the observations. In order to investigate the influence of the two most important parameters, that is the masses of the synthesized radioactive material and of the ejecta, a simple MC light curve model was used to simulate the luminosity evolution from the explosion to very late epochs (~1000 days). It was found that the observations require a range of a factor 10 in the masses of the radioactive material synthesized in the explosion (Mni= 0.1-1.1 Msun,) and a factor 2 in the total mass of the ejecta (Mej = 0.7-1.4 Msun). Differences of a factor 2 in Mni seem to be present even among `normal' SNe Ia. Some evidence was also found that the deposition of the positrons from Co decay varies from object to object, and with time. In particular, the latest HST observations of SN 1992A seem to imply complete trapping of the positrons.

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arXiv1997

Supernova 1994aj: a probe for pre-supernova evolution and mass loss from the progenitor

Extensive photometric and spectroscopic observations of SN1994aj until 540d after maximum light have been obtained. The photometry around maximum suggests that the SN belongs to the Type II Linear class, with a peak absolute magnitude of Mv ~ -17.8 (assuming Ho=75 km/s/Mpc). The spectra of SN1994aj were unusual with the presence of a narrow line with a P-Cygni profile on the top of the broad Balmer line emission. This narrow feature is attributed to the presence of a dense superwind surrounding the SN. At 100-120 days after maximum light the SN ejecta starts to interact with this CSM. The SN luminosity decline rates slowed down (gamma_R=0.46 mag/100d), becoming less steep than the average late luminosity decline of normal SNII (~1 mag/100d). This dense (Mdot/u_w ~ 10^15 g/cm) wind was confined to a short distance from the progenitor (R_out ~ 5x10^16 cm), and results from a very strong mass loss episode (Mdot = 10^-3 Msun/yr), which terminated shortly before explosion (~5-10 yr).

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arXiv1996

Revised photometry and color distribution of Type Ia supernovae observed at Asiago in the seventies

Following recent claims regarding possible errors in the photometry of SNe carried out at Asiago observatory during the 70's, which produced very blue $(B-V)$ color at maximum for some objects, we present the result of new CCD photometry of the sequences around 16 type Ia supernovae. Except for a few cases, e.g. SN1970J and SN1972J for which a large zero point error has been found, the new data show that the old Asiago observations have been carried out properly and that their accuracy was comparable to that expected for a photometry based on photographic transfers. This result is also substantiated by comparison with the re-calibration of some Asiago sequences made photo-electrically by Tsvetkov. New light curves of the SNe have been determined and B magnitudes and (B-V) colors at light peak derived. With the new data the color distribution of the SNe studied here becomes narrower and moves to the red by only 0.06 mag, showing no more very blue objects except for one, still uncertain, case. As far as the use of SNIa as standard candles is concerned, we show that the utilization of all SNe in the M$_B$ vs. (B-V)$^{max}_0$ plane reduces the uncertainties due to the photometry.

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arXiv1996

The properties of the peculiar Type Ia SN~1991bg. Analysis and discussion of two years of observations

Observations of the peculiar type Ia SN~1991bg in NGC~4374 collected at ESO--La Silla and Asiago are presented and discussed. The broad--band light curves in the early months have a narrower peak and a luminosity decline faster than other SNIa while the R and I light curves do not show the secondary peak. The SN is intrinsically very red (\bv$_{max}=0.74$) and faint ($B_{max}=-16.54$). The $uvoir$ bolometric light curve of SN~1991bg is fainter with a steeper decline than that of the normal SNIa (e.g. 1992A). This object enhances the correlation which exists between the peak luminosity of SNIa, the decline rate and the kinetic energy. Although a number of spectral peculiarities are present the spectral evolution retains a general resemblance to that of other SNIa until the latest available observation (day 203). This work suggests that the explosion energy was probably a factor 3 to 5 lower than in normal SNIa.

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