25 research outputs found
The Progenitor of Supernova 2011dh Has Vanished
We conducted Hubble Space Telescope (HST) Snapshot observations of the Type
IIb Supernova (SN) 2011dh in M51 at an age of ~641 days with the Wide Field
Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN
HST images, has disappeared, implying that this star was almost certainly the
progenitor of the SN. Interpretation of the early-time SN data which led to the
inference of a compact nature for the progenitor, and to the expected survival
of this yellow supergiant, is now clearly incorrect. We also present
ground-based UBVRI light curves obtained with the Katzman Automatic Imaging
Telescope (KAIT) at Lick Observatory up to SN age ~70 days. From the
light-curve shape including the very late-time HST data, and from recent
interacting binary models for SN 2011dh, we estimate that a putative surviving
companion star to the now deceased yellow supergiant could be detectable by
late 2013, especially in the ultraviolet. No obvious light echoes are
detectable yet in the SN environment.Comment: 6 pages, new versions of the 3 figures, improved U-band SN
photometry, to appear in ApJ Letter
Nebular spectroscopy of the nearby Type IIb supernova 2011dh
We present nebular spectra of the nearby Type IIb supernova (SN) 2011dh taken between 201 and 678 d after core collapse. At these late times, SN 2011dh exhibits strong emission lines including a broad and persistent Hα feature. New models of the nebular spectra confirm that the progenitor of SN 2011dh was a low-mass giant (M ≈ 13–15 M_⊙) that ejected ∼ 0.07 M_⊙ of ^(56)Ni and ∼ 0.27 M_⊙ of oxygen at the time of explosion, consistent with the recent disappearance of a candidate yellow supergiant progenitor. We show that light from the SN location is dominated by the fading SN at very late times (∼2 yr) and not, for example, by a binary companion or a background source. We present evidence for interaction between the expanding SN blast wave and a circumstellar medium at late times and show that the SN is likely powered by positron deposition ≳1 yr after explosion. We also examine the geometry of the ejecta and show that the nebular line profiles of SN 2011dh indicate a roughly spherical explosion with aspherical components or clumps
The Berkeley Sample of Stripped-Envelope Supernovae
We present the complete sample of stripped-envelope supernova (SN) spectra
observed by the Lick Observatory Supernova Search (LOSS) collaboration over the
last three decades: 888 spectra of 302 SNe, 652 published here for the first
time, with 384 spectra (of 92 SNe) having photometrically-determined phases.
After correcting for redshift and Milky Way dust reddening and reevaluating the
spectroscopic classifications for each SN, we construct mean spectra of the
three major spectral subtypes (Types IIb, Ib, and Ic) binned by phase. We
compare measures of line strengths and widths made from this sample to the
results of previous efforts, confirming that O I {\lambda}7774 absorption is
stronger and found at higher velocity in Type Ic SNe than in Types Ib or IIb
SNe in the first 30 days after peak brightness, though the widths of nebular
emission lines are consistent across subtypes. We also highlight newly
available observations for a few rare subpopulations of interest.Comment: 13 pages; 14 figures; 3 tables. Accepted for publication in MNRA
SN 2000cx and SN 2013bh: extremely rare, nearly twin Type Ia supernovae
The Type Ia supernova (SN Ia) SN 2000cx was one of the most peculiar transients ever discovered, with a rise to maximum brightness typical of a SN Ia, but a slower decline and a higher photospheric temperature. 13 yr later SN 2013bh (also known as iPTF13abc), a near identical twin, was discovered and we obtained optical and near-infrared photometry and low-resolution optical spectroscopy from discovery until about 1 month past r-band maximum brightness. The spectra of both objects show iron-group elements [Co II, Ni II, Fe II, Fe III and high-velocity features (HVFs) of Ti II], intermediate-mass elements (Si II, Si III and S II) and separate normal velocity features (∼12 000 km s^(−1)) and HVFs (∼24 000 km s^(−1)) of Ca II. Persistent absorption from Fe III and Si III, along with the colour evolution, implies high blackbody temperatures for SNe 2013bh and 2000cx (∼12 000 K). Both objects lack narrow Na I D absorption and exploded in the outskirts of their hosts, indicating that the SN environments were relatively free of interstellar or circumstellar material and may imply that the progenitors came from a relatively old and low-metallicity stellar population. Models of SN 2000cx, seemingly applicable to SN 2013bh, imply the production of up to ∼1 M_⊙ of ^(56)Ni and (4.3–5.5) × 10^(−3) M_⊙ of fast-moving Ca ejecta
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
A REVERSE SHOCK in GRB 160509A
We present the second multi-frequency radio detection of a reverse shock in a γ-ray burst. By combining our extensive radio observations of the Fermi-Large Area Telescope γ-ray burst 160509A at z = 1.17 up to 20 days after the burst with Swift X-ray observations and ground-based optical and near-infrared data, we show that the afterglow emission comprises distinct reverse shock and forward shock contributions: the reverse shock emission dominates in the radio band at ≲10 days, while the forward shock emission dominates in the X-ray, optical, and near-infrared bands. Through multi-wavelength modeling, we determine a circumburst density of , supporting our previous suggestion that a low-density circumburst environment is conducive to the production of long-lasting reverse shock radiation in the radio band. We infer the presence of a large excess X-ray absorption column, N H ≈ 1.5 ×1022 , and a high rest-frame optical extinction, A V ≈ 3.4 mag. We identify a jet break in the X-ray light curve at , and thus derive a jet opening angle of , yielding a beaming-corrected kinetic energy and radiated γ-ray energy of erg and erg (1-104 keV, rest frame), respectively. Consistency arguments connecting the forward shocks and reverse shocks suggest a deceleration time of s ≈ T 90, a Lorentz factor of , and a reverse-shock-to-forward-shock fractional magnetic energy density ratio of . Our study highlights the power of rapid-response radio observations in the study of the properties and dynamics of γ-ray burst ejecta. © 2016. The American Astronomical Society. All rights reserved