234 research outputs found
Late-Time Spectral Observations of the Strongly Interacting Type Ia Supernova PTF11kx
PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorption
features, including saturated Ca II H&K lines that weakened and eventually went
into emission. The strength of the emission component of H{\alpha} increased,
implying that the SN was undergoing significant interaction with its
circumstellar medium (CSM). These features were blueshifted slightly and showed
a P-Cygni profile, likely indicating that the CSM was directly related to, and
probably previously ejected by, the progenitor system itself. These and other
observations led Dilday et al. (2012) to conclude that PTF11kx came from a
symbiotic nova progenitor like RS Oph. In this work we extend the spectral
coverage of PTF11kx to 124-680 rest-frame days past maximum brightness. These
spectra of PTF11kx are dominated by H{\alpha} emission (with widths of ~2000
km/s), strong Ca II emission features (~10,000 km/s wide), and a blue
"quasi-continuum" due to many overlapping narrow lines of Fe II. Emission from
oxygen, He I, and Balmer lines higher than H{\alpha} is weak or completely
absent at all epochs, leading to large observed H{\alpha}/H{\beta} intensity
ratios. The broader (~2000 km/s) H{\alpha} emission appears to increase in
strength with time for ~1 yr, but it subsequently decreases significantly along
with the Ca II emission. Our latest spectrum also indicates the possibility of
newly formed dust in the system as evidenced by a slight decrease in the red
wing of H{\alpha}. During the same epochs, multiple narrow emission features
from the CSM temporally vary in strength. The weakening of the H{\alpha} and Ca
II emission at late times is possible evidence that the SN ejecta have
overtaken the majority of the CSM and agrees with models of other strongly
interacting SNe Ia. The varying narrow emission features, on the other hand,
may indicate that the CSM is clumpy or consists of multiple thin shells.Comment: 12 pages, 7 figures, 1 table, re-submitted to Ap
Exploring the spectral diversity of low-redshift Type Ia supernovae using the Palomar Transient Factory
We present an investigation of the optical spectra of 264 low-redshift (z <
0.2) Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory,
an untargeted transient survey. We focus on velocity and pseudo-equivalent
width measurements of the Si II 4130, 5972, and 6355 A lines, as well those of
the Ca II near-infrared (NIR) triplet, up to +5 days relative to the SN B-band
maximum light. We find that a high-velocity component of the Ca II NIR triplet
is needed to explain the spectrum in ~95 per cent of SNe Ia observed before -5
days, decreasing to ~80 per cent at maximum. The average velocity of the Ca II
high-velocity component is ~8500 km/s higher than the photospheric component.
We confirm previous results that SNe Ia around maximum light with a larger
contribution from the high-velocity component relative to the photospheric
component in their Ca II NIR feature have, on average, broader light curves and
lower Ca II NIR photospheric velocities. We find that these relations are
driven by both a stronger high-velocity component and a weaker contribution
from the photospheric Ca II NIR component in broader light curve SNe Ia. We
identify the presence of C II in very-early-time SN Ia spectra (before -10
days), finding that >40 per cent of SNe Ia observed at these phases show signs
of unburnt material in their spectra, and that C II features are more likely to
be found in SNe Ia having narrower light curves.Comment: 18 page, 10 figures, accepted for publication in MNRA
Exploring the Optical Transient Sky with the Palomar Transient Factory
The Palomar Transient Factory (PTF) is a wide-field experiment designed to
investigate the optical transient and variable sky on time scales from minutes
to years. PTF uses the CFH12k mosaic camera, with a field of view of 7.9 deg^2
and a plate scale of 1 asec/pixel, mounted on the the Palomar Observatory
48-inch Samuel Oschin Telescope. The PTF operation strategy is devised to probe
the existing gaps in the transient phase space and to search for theoretically
predicted, but not yet detected, phenomena, such as fallback supernovae,
macronovae, .Ia supernovae and the orphan afterglows of gamma-ray bursts. PTF
will also discover many new members of known source classes, from cataclysmic
variables in their various avatars to supernovae and active galactic nuclei,
and will provide important insights into understanding galactic dynamics
(through RR Lyrae stars) and the Solar system (asteroids and near-Earth
objects). The lessons that can be learned from PTF will be essential for the
preparation of future large synoptic sky surveys like the Large Synoptic Survey
Telescope. In this paper we present the scientific motivation for PTF and
describe in detail the goals and expectations for this experiment.Comment: 15 pages, 6 figures, submitted to PAS
Swift J2058.4+0516: Discovery of a Possible Second Relativistic Tidal Disruption Flare?
We report the discovery by the Swift hard X-ray monitor of the transient
source Swift J2058.4+0516 (Sw J2058+05). Our multi-wavelength follow-up
campaign uncovered a long-lived (duration >~ months), luminous X-ray (L_X,iso ~
3 x 10^47 erg s^-1) and radio (nu L_nu,iso ~ 10^42 erg s^-1) counterpart. The
associated optical emission, however, from which we measure a redshift of
1.1853, is relatively faint, and this is not due to a large amount of dust
extinction in the host galaxy. Based on numerous similarities with the recently
discovered GRB 110328A / Swift J164449.3+573451 (Sw J1644+57), we suggest that
Sw J2058+05 may be the second member of a new class of relativistic outbursts
resulting from the tidal disruption of a star by a supermassive black hole. If
so, the relative rarity of these sources (compared with the expected rate of
tidal disruptions) implies that either these outflows are extremely narrowly
collimated (theta < 1 degree), or only a small fraction of tidal disruptions
generate relativistic ejecta. Analogous to the case of long-duration gamma-ray
bursts and core-collapse supernovae, we speculate that rapid spin of the black
hole may be a necessary condition to generate the relativistic component.
Alternatively, if powered by gas accretion (i.e., an active galactic nucleus
[AGN]), Sw J2058+05 would seem to represent a new mode of variability in these
sources, as the observed properties appear largely inconsistent with known
classes of AGNs capable of generating relativistic jets (blazars, narrow-line
Seyfert 1 galaxies).Comment: Minor typos correcte
Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels
Since the discovery of the unusual prototype SN 2002cx, the eponymous class
of low-velocity, hydrogen-poor supernovae has grown to include at most another
two dozen members identified from several heterogeneous surveys, in some cases
ambiguously. Here we present the results of a systematic study of 1077
hydrogen-poor supernovae discovered by the Palomar Transient Factory, leading
to nine new members of this peculiar class. Moreover we find there are two
distinct subclasses based on their spectroscopic, photometric, and host galaxy
properties: The "SN 2002cx-like" supernovae tend to be in later-type or more
irregular hosts, have more varied and generally dimmer luminosities, have
longer rise times, and lack a Ti II trough when compared to the "SN
2002es-like" supernovae. None of our objects show helium, and we counter a
previous claim of two such events. We also find that these transients comprise
5.6+17-3.7% (90% confidence) of all SNe Ia, lower compared to earlier
estimates. Combining our objects with the literature sample, we propose that
these subclasses have two distinct physical origins.Comment: 49 pages, 36 figures, submitted to Ap
Early Radio and X-Ray Observations of the Youngest Nearby Type Ia Supernova PTF 11kly (SN 2011fe)
On 2011 August 24 (UT) the Palomar Transient Factory (PTF) discovered PTF11kly (SN 2011fe), the youngest
and most nearby Type Ia supernova (SN Ia) in decades. We followed this event up in the radio (centimeter and
millimeter bands) and X-ray bands, starting about a day after the estimated explosion time.We present our analysis
of the radio and X-ray observations, yielding the tightest constraints yet placed on the pre-explosion mass-loss rate
from the progenitor system of this supernova. We find a robust limit of Ṁ ≾ 10^(−8)(w/100 km s^(−1))M_☉ yr^(−1) from
sensitive X-ray non-detections, as well as a similar limit from radio data, which depends, however, on assumptions
about microphysical parameters. We discuss our results in the context of single-degenerate models for SNe Ia and
find that our observations modestly disfavor symbiotic progenitor models involving a red giant donor, but cannot
constrain systems accreting from main-sequence or sub-giant stars, including the popular supersoft channel. In
view of the proximity of PTF11kly and the sensitivity of our prompt observations, we would have to wait for a long
time (a decade or longer) in order to more meaningfully probe the circumstellar matter of SNe Ia
Real-Time Detection and Rapid Multiwavelength Follow-up Observations of a Highly Subluminous Type II-P Supernova from the Palomar Transient Factory Survey
The Palomar Transient Factory (PTF) is an optical wide-field variability
survey carried out using a camera with a 7.8 square degree field of view
mounted on the 48-in Oschin Schmidt telescope at Palomar Observatory. One of
the key goals of this survey is to conduct high-cadence monitoring of the sky
in order to detect optical transient sources shortly after they occur. Here, we
describe the real-time capabilities of the PTF and our related rapid
multiwavelength follow-up programs, extending from the radio to the gamma-ray
bands. We present as a case study observations of the optical transient
PTF10vdl (SN 2010id), revealed to be a very young core-collapse (Type II-P)
supernova having a remarkably low luminosity. Our results demonstrate that the
PTF now provides for optical transients the real-time discovery and
rapid-response follow-up capabilities previously reserved only for high-energy
transients like gamma-ray bursts.Comment: ApJ, in press; all spectroscopic data available from the Weizmann
Institute of Science Experimental Astrophysics Spectroscopy System (WISEASS;
http://www.weizmann.ac.il/astrophysics/wiseass/
Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor
We present the discovery of an optical transient (OT) in Messier 51,
designated M51 OT2019-1 (also ZTF19aadyppr, AT 2019abn, ATLAS19bzl), by the
Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed
luminosity of (), in the
luminosity gap between novae and typical supernovae (SNe). Spectra during the
outburst show a red continuum, Balmer emission with a velocity width of
km s, Ca II and [Ca II] emission, and absorption features
characteristic of an F-type supergiant. The spectra and multiband light curves
are similar to the so-called "SN impostors" and intermediate-luminosity red
transients (ILRTs). We directly identify the likely progenitor in archival
Spitzer Space Telescope imaging with a m luminosity of
and a color redder than 0.74 mag, similar
to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive
monitoring of M51 with Spitzer further reveals evidence for variability of the
progenitor candidate at [4.5] in the years before the OT. The progenitor is not
detected in pre-outburst Hubble Space Telescope optical and near-IR images. The
optical colors during outburst combined with spectroscopic temperature
constraints imply a higher reddening of mag and higher
intrinsic luminosity of
() near peak than seen in previous ILRT
candidates. Moreover, the extinction estimate is higher on the rise than on the
plateau, suggestive of an extended phase of circumstellar dust destruction.
These results, enabled by the early discovery of M51 OT2019-1 and extensive
pre-outburst archival coverage, offer new clues about the debated origins of
ILRTs and may challenge the hypothesis that they arise from the
electron-capture induced collapse of extreme asymptotic giant branch stars.Comment: 21 pages, 5 figures, published in ApJ
PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy
We present the discovery and characterisation of PTF10iya, a short-lived (dt
~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21
mag) transient source found by the Palomar Transient Factory. The
ultraviolet/optical spectral energy distribution is reasonably well fit by a
blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x
10^44 erg per s (depending on the details of the extinction correction). A
comparable amount of energy is radiated in the X-ray band that appears to
result from a distinct physical process. The location of PTF10iya is consistent
with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within
350 mas (99.7 per cent confidence radius), or a projected distance of less than
1.2 kpc. At first glance, these properties appear reminiscent of the
characteristic "big blue bump" seen in the near-ultraviolet spectra of many
active galactic nuclei (AGNs). However, emission-line diagnostics of the host
galaxy, along with a historical light curve extending back to 2007, show no
evidence for AGN-like activity. We therefore consider whether the tidal
disruption of a star by an otherwise quiescent supermassive black hole may
account for our observations. Though with limited temporal information,
PTF10iya appears broadly consistent with the predictions for the early
"super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black
hole. Regardless of the precise physical origin of the accreting material, the
large luminosity and short duration suggest that otherwise quiescent galaxies
can transition extremely rapidly to radiate near the Eddington limit; many such
outbursts may have been missed by previous surveys lacking sufficient cadence.Comment: 18 pages, 8 figures; revised following referee's comment
SN 2009bb: a Peculiar Broad-Lined Type Ic Supernova
Ultraviolet, optical, and near-infrared photometry and optical spectroscopy
of the broad-lined Type Ic supernova (SN) 2009bb are presented, following the
flux evolution from -10 to +285 days past B-band maximum. Thanks to the very
early discovery, it is possible to place tight constraints on the SN explosion
epoch. The expansion velocities measured from near maximum spectra are found to
be only slightly smaller than those measured from spectra of the prototype
broad-lined SN 1998bw associated with GRB 980425. Fitting an analytical model
to the pseudo-bolometric light curve of SN 2009bb suggests that 4.1+-1.9 Msun
of material was ejected with 0.22 +-0.06 Msun of it being 56Ni. The resulting
kinetic energy is 1.8+-0.7x10^52 erg. This, together with an absolute peak
magnitude of MB=-18.36+-0.44, places SN 2009bb on the energetic and luminous
end of the broad-lined Type Ic (SN Ic) sequence. Detection of helium in the
early time optical spectra accompanied with strong radio emission, and high
metallicity of its environment makes SN 2009bb a peculiar object. Similar to
the case for GRBs, we find that the bulk explosion parameters of SN 2009bb
cannot account for the copious energy coupled to relativistic ejecta, and
conclude that another energy reservoir (a central engine) is required to power
the radio emission. Nevertheless, the analysis of the SN 2009bb nebular
spectrum suggests that the failed GRB detection is not imputable to a large
angle between the line-of-sight and the GRB beamed radiation. Therefore, if a
GRB was produced during the SN 2009bb explosion, it was below the threshold of
the current generation of gamma-ray instruments.Comment: Accepted for publication in Ap
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