25 research outputs found
Constraining the role of novae as progenitors of Type Ia Supernovae
(Abridged) White dwarfs (WDs) undergoing unstable nuclear burning on their
surfaces, resulting in the nova phenomenon, have been considered as one of the
prospective candidates for the still elusive progenitors of SNeIa. We propose
that statistics of novae in nearby galaxies may be a powerful tool to gauge the
role of such systems in producing SNeIa. Using multicycle nova evolutionary
models, we compute the number and temporal distribution of novae that would be
produced by a typical (unstably burning) SNIa progenitor before reaching the
Chandrasekhar mass limit (M_ch) and exploding. Combined with the observed nova
rates, this can be used to constrain the maximal contribution of the nova
channel to the SNIa rate in nearby galaxies. The M31 nova rate measured by the
POINT-AGAPE survey is 65/yr. Assuming that all these novae will reach M_ch, we
obtain the maximal SNIa rate novae may produce to be (1-5)x10^-4/yr. This
constrains the overall contribution of the nova channel to the SNIa rate in M31
at <2-7%. Furthermore, ~80% of novae generated by a successful SNIa progenitor
have short decay times (t2<10 days), and are produced when the WD mass is close
to M_ch. We point out that statistics of such fast novae can provide a
sensitive diagnostic of the contribution of the nova channel to the final
stages of mass accumulation by the single degenerate (SD) SNIa progenitors. To
explore the prospects of their use, we investigate the efficiency of detecting
fast novae in an M31 nova survey of the PTF class. We find that a survey with
limiting magnitude of m_R~22 observing at least every 2nd night will catch ~90%
of fast novae expected in the SD scenario. Such surveys should be detecting
fast novae in M31 at a rate of the order of >10^3xf per yr, where f is the
fraction of SNeIa which accreted in the unstable nuclear burning regime while
accumulating the final ~0.1M_sun before the SNIa explosion.Comment: 14 pages, A&A, in pres
Prediction of Supernova Rates in Known Galaxy-galaxy Strong-lens Systems
We propose a new strategy of finding strongly-lensed supernovae (SNe) by
monitoring known galaxy-scale strong-lens systems. Strongly lensed SNe are
potentially powerful tools for the study of cosmology, galaxy evolution, and
stellar populations, but they are extremely rare. By targeting known strongly
lensed starforming galaxies, our strategy significantly boosts the detection
efficiency for lensed SNe compared to a blind search. As a reference sample, we
compile the 128 galaxy-galaxy strong-lens systems from the Sloan Lens ACS
Survey (SLACS), the SLACS for the Masses Survey, and the Baryon Oscillation
Spectroscopic Survey Emission-Line Lens Survey. Within this sample, we estimate
the rates of strongly-lensed Type Ia SN (SNIa) and core-collapse SN (CCSN) to
be and events per year, respectively. The lensed
SN images are expected to be widely separated with a median separation of 2
arcsec. Assuming a conservative fiducial lensing magnification factor of 5 for
the most highly magnified SN image, we forecast that a monitoring program with
a single-visit depth of 24.7 mag (5 point source, band) and a
cadence of 5 days can detect 0.49 strongly-lensed SNIa event and 2.1
strongly-lensed CCSN events per year within this sample. Our proposed
targeted-search strategy is particularly useful for prompt and efficient
identifications and follow-up observations of strongly-lensed SN candidates. It
also allows telescopes with small field of views and limited time to
efficiently discover strongly-lensed SNe with a pencil-beam scanning strategy.Comment: 14 pages, 5 figures, ApJ in pres
A novel method for transient detection in high-cadence optical surveys: Its application for a systematic search for novae in M31
[abridged] In large-scale time-domain surveys, the processing of data, from
procurement up to the detection of sources, is generally automated. One of the
main challenges is contamination by artifacts, especially in regions of strong
unresolved emission. We present a novel method for identifying candidates for
variables and transients from the outputs of such surveys' data pipelines. We
use the method to systematically search for novae in iPTF observations of the
bulge of M31. We demonstrate that most artifacts produced by the iPTF pipeline
form a locally uniform background of false detections approximately obeying
Poissonian statistics, whereas genuine variables and transients as well as
artifacts associated with bright stars result in clusters of detections, whose
spread is determined by the source localization accuracy. This makes the
problem analogous to source detection on images produced by X-ray telescopes,
enabling one to utilize tools developed in X-ray astronomy. In particular, we
use a wavelet-based source detection algorithm from the Chandra data analysis
package CIAO. Starting from ~2.5x10^5 raw detections made by the iPTF data
pipeline, we obtain ~4000 unique source candidates. Cross-matching these
candidates with the source-catalog of a deep reference image, we find
counterparts for ~90% of them. These are either artifacts due to imperfect PSF
matching or genuine variable sources. The remaining ~400 detections are
transient sources. We identify novae among these candidates by applying
selection cuts based on the expected properties of nova lightcurves. Thus, we
recovered all 12 known novae registered during the time span of the survey and
discovered three nova candidates. Our method is generic and can be applied for
mining any target out of the artifacts in optical time-domain data. As it is
fully automated, its incompleteness can be accurately computed and corrected
for.Comment: 16 pages, 8 figures, accepted to A&
Variability of Red Supergiants in M31 from the Palomar Transient Factory
Most massive stars end their lives as Red Supergiants (RSGs), a short-lived
evolution phase when they are known to pulsate with varying amplitudes. The RSG
period-luminosity (PL) relation has been measured in the Milky Way, the
Magellanic Clouds and M33 for about 120 stars in total. Using over 1500 epochs
of R-band monitoring from the Palomar Transient Factory (PTF) survey over a
five-year period, we study the variability of 255 spectroscopically cataloged
RSGs in M31. We find that all RGSs brighter than M_K~ -10 mag
(log(L/L_sun)>4.8) are variable at dm_R>0.05 mag. Our period analysis finds 63
with significant pulsation periods. Using the periods found and the known
values of M_K for these stars, we derive the RSG PL relation in M31 and show
that it is consistent with those derived earlier in other galaxies of different
metallicities. We also detect, for the first time, a sequence of likely
first-overtone pulsations. Comparison to stellar evolution models from MESA
confirms the first overtone hypothesis and indicates that the variable stars in
this sample have 12 M_sun<M<24 M_sun. As these RSGs are the immediate
progenitors to Type II-P core-collapse supernovae (SNe), we also explore the
implication of their variability in the initial-mass estimates for SN
progenitors based on archival images of the progenitors. We find that this
effect is small compared to the present measurement errors.Comment: 17 pages, 10 figure
AT 2020iko: a WZ Sge-type DN candidate with an anomalous precursor event
The ongoing Zwicky Transient Facility (ZTF) survey is generating a massive
alert rate from a variety of optical transients and variable stars, which are
being filtered down to subsets meeting user-specified criteria by broker
systems such as ANTARES. In a beta implementation of the algorithm of Soraisam
et al. (2020) on ANTARES, we flagged AT 2020iko from the ZTF real-time alert
stream as an anomalous source. This source is located close to a red extended
SDSS source. In the first few epochs of detection, it exhibited a V-shaped
brightness profile, preceded by non-detections both in ZTF and in ASASSN
extending to 2014. Its full light curve shows a precursor event, followed by a
main superoutburst and at least two rebrightenings. A low-resolution spectrum
of this source points to a dwarf nova (DN) nature. Although some of the
features of AT 2020iko indicate an SU UMa-type DN, its large amplitude,
presence of rebrightenings, and inferred supercycle period of > 6 yr are in
favor of AT 2020iko being a new WZ Sge-type dwarf nova candidate, a subset of
rare DNe consisting of extreme mass-ratio (< 0.1) binaries with orbital period
around the period minimum. AT 2020iko's precursor event brightened by 6.5 mag,
while its decay spanned 3-5 mag. We speculate this superoutburst is associated
with a less expanded accretion disk than in typical superoutbursts in WZ Sge
systems, with the large depth of the precursor decay implying an extremely
small mass-ratio. To the best of our knowledge, such a precursor event has not
been recorded for any DN. This result serves to demonstrate the efficacy of our
real-time anomaly search algorithm.Comment: 11 pages, 4 figures; accepted to A