442 research outputs found
Dust masses for SN 1980K, SN1993J and Cassiopeia A from red-blue emission line asymmetries
We present Monte Carlo line transfer models that investigate the effects of dust on the very late time emission line spectra of the core collapse supernovae SN 1980K and SN 1993J and the young core collapse supernova remnant Cassiopeia A. Their blue-shifted emission peaks, resulting from the removal by dust of redshifted photons emitted from the far sides of the remnants, and the presence of extended red emission wings are used to constrain dust compositions and radii and to determine the masses of dust in the remnants. We estimate dust masses of between 0.08 β 0.15 Mβ for SN 1993J at year 16, 0.12 β 0.30 Mβ for SN 1980K at year 30 and βΌ1.1 Mβ for Cas A at year βΌ330. Our models for the strong oxygen forbidden lines of Cas A require the overall modelled profiles to be shifted to the red by between 700 β 1000 km sβ1, consistent with previous estimates for the shift of the dynamical centroid of this remnant
An ultraviolet excess in the superluminous supernova Gaia16apd reveals a powerful central engine
Since the discovery of superluminous supernovae (SLSNe) in the last decade,
it has been known that these events exhibit bluer spectral energy distributions
than other supernova subtypes, with significant output in the ultraviolet.
However, the event Gaia16apd seems to outshine even the other SLSNe at
rest-frame wavelengths below \AA. Yan et al (2016) have recently
presented HST UV spectra and attributed the UV flux to low metallicity and
hence reduced line blanketing. Here we present UV and optical light curves over
a longer baseline in time, revealing a rapid decline at UV wavelengths despite
a typical optical evolution. Combining the published UV spectra with our own
optical data, we demonstrate that Gaia16apd has a much hotter continuum than
virtually any SLSN at maximum light, but it cools rapidly thereafter and is
indistinguishable from the others by -15 days after peak. Comparing
the equivalent widths of UV absorption lines with those of other events, we
show that the excess UV continuum is a result of a more powerful central power
source, rather than a lack of UV absorption relative to other SLSNe or an
additional component from interaction with the surrounding medium. These
findings strongly support the central-engine hypothesis for hydrogen-poor
SLSNe. An explosion ejecting M, where
is the opacity in cmg, and forming a magnetar with spin
period ms, and G (lower than other SLSNe with
comparable rise-times) can consistently explain the light curve evolution and
high temperature at peak. The host metallicity, Z, is
comparable to other SLSNe.Comment: Updated to match accepted version (ApJL
A Hydrogen-Poor Superluminous Supernova with Enhanced Iron-Group Absorption: A New Link Between SLSNe and Broad-Lined Type Ic SNe
We present optical observations of the Type I superluminous supernova
(SLSN-I) SN2017dwh at , which reached
mag at peak. Spectra taken a few days after peak show an unusual and strong
absorption line centered near 3200\AA\ that we identify with Co II, suggesting
a high fraction of synthesized Ni in the ejecta. By month
after peak, SN2017dwh became much redder than other SLSNe-I, instead strongly
resembling broad-lined Type Ic supernovae (Ic-BL SNe) with clear suppression of
the flux redward of \AA, providing further evidence for a large
mass of Fe-group elements. Late-time upper limits indicate a Ni mass of
M, leaving open the possibility that SN2017dwh produced
a Ni mass comparable to SN1998bw ( M). Fitting the
light curve with a combined magnetar and Ni model using ,
we find that the light curve can easily accommodate such masses without
affecting the inferred magnetar parameters. We also find that SN2017dwh
occurred in the least-luminous detected host galaxy to date for a SLSN-I, with
mag and an implied metallicity of .
The spectral properties of SN2017dwh provide new evidence linking SLSNe-I with
Type Ic-BL SNe, and in particular the high Fe-group abundance may be due to
enhanced Ni production or mixing due to asphericity. Finally, we find
that SN2017dwh represents the most extreme end of a correlation between
continuum shape and Co II absorption strength in the near-peak spectra of
SLSNe-I, indicating that Fe-group abundance likely accounts for some of the
variation in their spectral shapes.Comment: 16 pages, 7 figures, Submitted to Ap
Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
We recently started a systematic search of low-energy counterparts of the
unidentified gamma-ray sources (UGSs) listed in the Fermi-Large Area Telescope
(LAT) First Source Catalog (1FGL) and the Fermi-LAT 2-Year Source Catalog
(2FGL).} The main goal of our investigation is to find active galaxies
belonging to the blazar class that lie within the positional uncertainty region
of the UGSs and thus could be their potential low-energy counterparts. To
achieve our aims, we first adopted several procedures based on the peculiar
observational properties of blazars in the radio and in the IR. Then we carried
out a follow-up spectroscopic campaign in the optical band to verify the nature
of the candidates selected as potential counterparts of the UGSs. Here we
present the results of the observations carried out in 2013 in the Northern
Hemisphere at Kitt Peak National Observatory (KPNO). Optical spectroscopy is
crucial to confirm the nature of the sources and can be used to estimate their
redshifts; it will also allow us to test the robustness of our methods when the
whole campaign is completed. Here we present the optical spectroscopic
observations of 39 sources. Within our sample we found that 6 sources are
blazars, candidates to be low-energy counterparts of the UGSs listed in the
2FGL. We confirm that an additional 8 sources, previously classified as active
galaxies of uncertain type and associated in the 2FGL, are also all BL Lac
objects. Moreover, we also present 20 new spectra for known blazars listed in
the Multi-frequency Catalogue of Blazars as having an uncertain redshift and/or
being classified as BL Lac candidates. We conclude that our methods for
selecting gamma-ray blazar candidates allows us to discover new blazars and
increase the list of potential low-energy counterparts for the Fermi UGSs.Comment: 27 pages, 39 figures, 1 table, A&A accepted for publication
(pre-proof version
The Evolution of Late-time Optical Emission from SN 1986J
We present late-time optical images and spectra of the Type IIn supernova SN
1986J. HST ACS/WFC images obtained in February 2003 show it to be still
relatively bright with m(F606W) = 21.4 and m(F814W) = 20.0 mag. Compared
against December 1994 HST WFPC2 images, SN 1986J shows a decline of only <1 mag
in brightness over eight years. Ground-based spectra taken in 1989, 1991 and
2007 show a 50% decline in Halpha emission between 1989-1991 and an order of
magnitude drop between 1991-2007, along with the disappearance of He I line
emissions during the period 1991-2007. The object's [O I] 6300, 6364, [O II]
7319, 7330 and [O III] 4959, 5007 emission lines show two prominent peaks near
-1000 km/s and -3500 km/s, with the more blueshifted component declining
significantly in strength between 1991 and 2007. The observed spectral
evolution suggests two different origins for SN 1986J's late-time optical
emission: dense, shock-heated circumstellar material which gave rise to the
initially bright Halpha, He I, and [N II] 5755 lines, and reverse-shock heated
O-rich ejecta on the facing expanding hemisphere dominated by two large clumps
generating two blueshifted emission peaks of [O I], [O II], and [O III] lines.Comment: 4 pages, 3 figures. Submitted to the Astrophysical Journal (Letters
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