We observed supernova 1987A (SN 1987A) with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) in 1999 September, and again with the Advanced Camera for Surveys (ACS) on the HST in 2003 November. No point source is observed in the remnant. We obtain a limiting flux of F_opt < 1.6 x 10^{-14} ergs/s/cm^2 in the wavelength range 2900-9650 Angstroms for any continuum emitter at the center of the supernova remnant (SNR). It is likely that the SNR contains opaque dust that absorbs UV and optical emission, resulting in an attenuation of ~35% due to dust absorption in the SNR. Taking into account dust absorption in the remnant, we find a limit of L_opt < 8 x 10^{33} ergs/s. We compare this upper bound with empirical evidence from point sources in other supernova remnants, and with theoretical models for possible compact sources. Bright young pulsars such as Kes 75 or the Crab pulsar are excluded by optical and X-ray limits on SN 1987A. Of the young pulsars known to be associated with SNRs, those with ages < 5000 years are all too bright in X-rays to be compatible with the limits on SN 1987A. Examining theoretical models for accretion onto a compact object, we find that spherical accretion onto a neutron star is firmly ruled out, and that spherical accretion onto a black hole is possible only if there is a larger amount of dust absorption in the remnant than predicted. In the case of thin-disk accretion, our flux limit requires a small disk, no larger than 10^{10} cm, with an accretion rate no more than 0.3 times the Eddington accretion rate. Possible ways to hide a surviving compact object include the removal of all surrounding material at early times by a photon-driven wind, a small accretion disk, or very high levels of dust absorption in the remnant.
Nebular-phase spectra of SN 2006aj, which was discovered in coincidence with X-ray flash 060218, were obtained with Keck in 2006 July and the Very Large Telescope in 2006 September. At the latter epoch spectropolarimetry was also attempted, yielding an upper limit of ~ 2% for the polarization. The spectra show strong emission lines of [OI] and MgI], as expected from a Type Ic supernova, but weak CaII lines. The [FeII] lines that were strong in the spectra of SN 1998bw are much weaker in SN 2006aj, consistent with the lower luminosity of this SN. The outer velocity of the line-emitting ejecta is ~ 8000 km/s in July and ~ 7400 km/s in September, consistent with the relatively low kinetic energy of expansion of SN 2006aj. All emission lines have similar width, and the profiles are symmetric, indicating that no major asymmetries are present in the ejecta at the velocities sampled by the nebular lines (v < 8000 km/s), except perhaps in the innermost part. The spectra were modelled with a non-LTE code. The mass of 56Ni required to power the emission spectrum is ~ 0.20 Msun, in excellent agreement with the results of early light curve modelling. The oxygen mass is ~ 1.5 Msun, again much less than in SN 1998bw but larger by ~ 0.7 Msun than the value derived from the early-time modelling. The total ejected mass is ~ 2 Msun below 8000 km/s. This confirms that SN 2006aj was only slightly more massive and energetic than the prototypical Type Ic SN 1994I, but also indicates the presence of a dense inner core, containing ~ 1 Msun of mostly oxygen and carbon. The presence of such a core is inferred for all broad-lined SNe Ic. This core may have the form of an equatorial oxygen-dominated region, but it is too deep to affect the early light curve and too small to affect the late polarization spectrum.
The tool of spectropolarimetry applied to supernovae has shown that core collapse supernovae are strongly asymmetric and that Type Ia supernovae are less so, but still systematically asymmetric. These studies will lead to new insight into the explosion mechanisms of both core collapse and thermonuclear supernovae. The latter may give long sought clues to the binary nature of Type Ia and new insight into the origin of the observed scatter in the properties of Type Ia that may help to make them even more precise tools of cosmology.
view Abstract Citations (28) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Spectroscopic Observations of the Ejecta of SN 1987A at 2000 Days Wang, Lifan ; Wheeler, J. Craig ; Kirshner, Robert P. ; Challis, Peter M. ; Filippenko, Alexei V. ; Fransson, Claes ; Panagia, Nino ; Phillips, Mark M. ; Suntzeff, Nicholas Abstract We have used the Faint Object Spectrograph on the Hubble Space Telescope (HST) to observe the spectra of SN 1987A over the wavelength range 2000-8000 A on dates 1862 and 2210 days after the supernova outburst. Even these preCOSTAR observations avoid much of the contamination from the bright stars nearby and provide a very useful set of line strengths and shapes for analysis. The spectrum is formed in an unusual physical setting: cold gas that is excited and ionized by energetic electrons from the radioactive debris of the supernova explosion. The spectra of SN 1987A at this phase are surprisingly similar to those of the nova shells of CP Puppis and T Pyxidis decades after . SN 1987A and the novae are characterized by emission from material with electron temperatures of only a few hundred kelvins and show narrow Balmer continuum emission and strong emission lines from O^+^. The Balmer continuum shape requires the electron temperature in the supernova ejecta to be as low as 500 K on day 1862 and 400 K on day 2210 after outburst. The [O II] 位位3726, 3728 doublet is surprisingly strong and is plausibly powered by collisional ionization of neutral oxygen to excited states of O^+^. The line intensity ratio of the [O I] 位位6300, 6364 doublet obtained from Gaussian fits of the line profiles is 1.8 +/- 0.2, contrary to the optically thin limit of 3. This ratio is not due to an optical depth effect but, rather, is an artifact of assuming a Gaussian profile to fit the [O I] 位位6300, 6364 doublet profile. Specifying the line ratio R = F([O I] 位6300)/F([O I] 位6364) = 3 is consistent with the data and allows a calculation of the decomposed line profile. All the observed strong lines are found to be blueshifted by a similar amount of 400 km s^-1^. The line profiles are quite similar for lines arising from dIfferent chemical elements. The profiles are all asymmetric, showing redshifted extended tails with velocities up to 10,000 km s^-1^ in some strong lines. The blueshift of the line peaks is attributed to dust that condensed from the SN 1987A ejecta that is still distributed in dense opaque clumps. The strongest ultraviolet lines are those of Mg I 位2852 and Mg II 位位2795,2802. The Mg I 位2852 line is significantly broader than most lines in the optical, which provides a natural explanation for the size differences in the optical and ultraviolet of the SN 1987A ejecta derived from HST direct images. Publication: The Astrophysical Journal Pub Date: August 1996 DOI: 10.1086/177570 arXiv: arXiv:astro-ph/9602157 Bibcode: 1996ApJ...466..998W Keywords: STARS: INDIVIDUAL ALPHANUMERIC: SN 1987A; ISM: SUPERNOVA REMNANTS; ULTRAVIOLET: STARS; Astrophysics E-Print: 26 pages, 8 Postcript figures availlable at ftp://tycho.as.utexas.edu/pub/users/lwang/SN87ASIN/ full text sources arXiv | ADS | data products NED (2) SIMBAD (1) MAST (1) ESA (1)
We present a comparative study of two nearby type Ia supernovae (SNe Ia), 2018xx and 2019gbx, that exploded in NGC 4767 and MCG-02-33-017 at a distance of 48 Mpc and 60 Mpc, respectively. The B -band light curve decline rate for SN 2018xx is estimated to be 1.48 ± 0.07 mag and for SN 2019gbx it is 1.37 ± 0.07 mag. Despite the similarities in photometric evolution, quasi-bolometric luminosity, and spectroscopy between these two SNe Ia, SN 2018xx has been found to be fainter by about ∼0.38 mag in the B -band and has a lower 56 Ni yield. Their host galaxies have similar metallicities at the SN location, indicating that the differences between these two SNe Ia may be associated with the higher progenitor metallicity of SN 2018xx. Further inspection of the near-maximum-light spectra has revealed that SN 2018xx has relatively strong absorption features near 4300 Å relative to SN 2019gbx. The application of the code TARDIS fitting to the above features indicates that the absorption features near 4300 Å appear to be related to not only Fe II /Mg II abundance but possibly to the other element abundances as well. Moreover, SN 2018xx shows a weaker carbon absorption at earlier times, which is also consistent with higher ejecta metallicity.
Abstract We construct the average spectra of host galaxies of slower, faster, bluer, and redder Type Ia supernovae (SNe Ia) from the SDSS-II supernova survey. The average spectrum of slower declining (broader light curve width or higher stretch) SN Ia hosts shows stronger emission lines compared to the average spectrum of faster declining (narrower light curve width or lower stretch) SN Ia hosts. Using pPXF, we find that hosts of slower declining SNe Ia have metallicities that are, on average, 0.24 dex lower than average metallicities of faster declining SN Ia hosts. Similarly, redder SN Ia hosts have slightly higher metallicities than bluer SN Ia hosts. Lick index analysis of metallic lines and Balmer lines shows that faster declining SN Ia hosts have relatively higher metal content and have relatively older stellar populations compared with slower declining SN Ia hosts. We calculate average star formation rate (SFR), stellar mass, and the specific SFR (sSFR) of host galaxies in these subgroups of SNe Ia. We find that slower declining SN Ia hosts have significantly higher ( ) sSFR than faster declining SN Ia hosts. A Kolmogorov–Smirnov test shows that these two types of hosts originate from different parent distributions. Our results, when compared with the models of Childress et al., indicate that slower declining SNe Ia, being hosted in actively star-forming galaxies, are young (prompt) SNe Ia, originating from similar progenitor age groups.
ABSTRACT Detailed spectropolarimetric studies may hold the key to probing the explosion mechanisms and the progenitor scenarios of Type Ia supernovae (SNe Ia). We present multi-epoch spectropolarimetry and imaging polarimetry of SN 2019ein, an SN Ia showing high expansion velocities at early phases. The spectropolarimetry sequence spans from ∼−11 to +10 d relative to peak brightness in the B band. We find that the level of the continuum polarization of SN 2019ein, after subtracting estimated interstellar polarization, is in the range 0.0–0.3 per cent, typical for SNe Ia. The polarization position angle remains roughly constant before and after the SN light-curve peak, implying that the inner regions share the same axisymmetry as the outer layers. We observe high polarization (∼1 per cent) across both the Si ii λ6355 and Ca ii near-infrared triplet features. These two lines also display complex polarization modulations. The spectropolarimetric properties of SN 2019ein rule out a significant departure from spherical symmetry of the ejecta for up to a month after the explosion. These observations disfavour merger-induced and double-detonation models for SN 2019ein. The imaging polarimetry shows weak evidence for a modest increase in polarization after ∼20 d since the B-band maximum. If this rise is real and is observed in other SNe Ia at similar phases, we may have seen, for the first time, an aspherical interior similar to what has been previously observed for SNe IIP. Future polarization observations of SNe Ia extending to post-peak epochs will help to examine the inner structure of the explosion.
The three Antarctic Survey Telescopes (AST3) aim to carry out time domain imaging survey at Dome A, Antarctica. The first of the three telescopes (AST3-1) was successfully deployed on January 2012. AST3-1 is a 500\,mm aperture modified Schmidt telescope with a 680\,mm diameter primary mirror. AST3-1 is equipped with a SDSS $i$ filter and a 10k $\times$ 10k frame transfer CCD camera, reduced to 5k $\times$ 10k by electronic shuttering, resulting in a 4.3 deg$^2$ field-of-view. To verify the capability of AST3-1 for a variety of science goals, extensive commissioning was carried out between March and May 2012. The commissioning included a survey covering 2000 deg$^2$ as well as the entire Large and Small Magellanic Clouds. Frequent repeated images were made of the center of the Large Magellanic Cloud, a selected exoplanet transit field, and fields including some Wolf-Rayet stars. Here we present the data reduction and photometric measurements of the point sources observed by AST3-1. We have achieved a survey depth of 19.3\,mag in 60 s exposures with 5\,mmag precision in the light curves of bright stars. The facility achieves sub-mmag photometric precision under stable survey conditions, approaching its photon noise limit. These results demonstrate that AST3-1 at Dome A is extraordinarily competitive in time-domain astronomy, including both quick searches for faint transients and the detection of tiny transit signals.
We present spectra of high-redshift supernovae (SNe) that were taken with the Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN surveys with Suprime-Cam on Subaru, the CFH12k camera on the Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These SN surveys specifically targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we obtain redshifts for 32 candidates and spectroscopically identify 7 active candidates as probable SNe Ia, including one at z=1.35, which is the most distant SN Ia to be spectroscopically confirmed with a ground-based telescope. An additional 4 candidates are identified as likely SNe Ia from the spectrophotometric properties of their host galaxies. Seven candidates are not SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia are observed within a week of maximum light, we find that we can spectroscopically identify most of them up to z=1.1. Beyond this redshift, very few candidates were spectroscopically identified as SNe Ia. The current generation of super red-sensitive, fringe-free CCDs will push this redshift limit higher.
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