392 research outputs found
Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe
We present photometric and spectroscopic observations of the Type Ia
supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery
announcement at what turned out to be ten days after peak, we detected it at V
~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North
telescope 2 weeks prior to the peak, and then followed it up with telescopes
ranging in aperture from 10-cm to 6.5-m. Using early photometric data available
only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN
1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95
mag. The early post-maximum spectra closely resemble those of SN 1991T, while
the late time spectra are more similar to those of normal Type Ia SNe.
Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale
lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This
indicates that the progenitor of SN 2009nr is not associated with a young
stellar population, calling into question the conventional association of
luminous SNe Ia with the "prompt" component directly correlated with current
star formation. The pre-discovery observation of SN 2009nr using ASAS
demonstrates the science utility of high cadence all sky surveys conducted
using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.Comment: 11 pages, 11 figures, 4 tables. Accepted for publication in ApJ on
11/02/201
Development of a selftriggered high counting rate ASIC for readout of 2D gas microstrip neutron detectors
In the frame of the DETNI project a 32-channel ASIC suitable for readout of a novel 2D thermal neutron detector based on a hybrid low-pressure Micro-Strip Gas Chamber with solid 157Gd converter has been developed. Each channel delivers position information, a fast time stamp of 2 ns resolution and the signal amplitude (called energy below). The time stamp is used for correlating the signals from X and Y strips while the amplitude is used for finding the center of gravity of a cluster of strips. The timing and energy information are stored in derandomizing buffers and read out via token ring architecture
ASASSN-15lh: A Highly Super-Luminous Supernova
We report the discovery of ASASSN-15lh (SN 2015L), which we interpret as the
most luminous supernova yet found. At redshift z = 0.2326, ASASSN-15lh reached
an absolute magnitude of M_{u,AB} = -23.5+/-0.1 and bolometric luminosity L_bol
= (2.2+/-0.2)x 10^45 ergs s^-1, which is more than twice as luminous as any
previously known supernova. It has several major features characteristic of the
hydrogen-poor super-luminous supernovae (SLSNe-I), whose energy sources and
progenitors are currently poorly understood. In contrast to most previously
known SLSNe-I that reside in star-forming dwarf galaxies, ASASSN-15lh appears
to be hosted by a luminous galaxy (M_K ~ -25.5) with little star formation. In
the 4 months since first detection, ASASSN-15lh radiated (1.1+/- 0.2)x10^52
ergs, challenging the magnetar model for its engine.Comment: Published in the January 15, 2016 Issue of Science Magazin
SDWFS-MT-1: A Self-Obscured Luminous Supernova at z~0.2
We report the discovery of a six-month-long mid-infrared transient,
SDWFS-MT-1 (aka SN 2007va), in the Spitzer Deep, Wide-Field Survey of the NOAO
Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low
luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8)
irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2
in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least
10^51 ergs. The optical emission was likely fainter than the mid-infrared,
although our constraints on the optical emission are poor because the transient
peaked when the source was "behind" the Sun. The Spitzer data are consistent
with emission by a modified black body with a temperature of ~1350 K. We rule
out a number of scenarios for the origin of the transient such as a Galactic
star, AGN activity, GRB, tidal disruption of a star by a black hole and
gravitational lensing. The most plausible scenario is a supernova exploding
inside a massive, optically thick circumstellar medium, composed of multiple
shells of previously ejected material. If the proposed scenario is correct,
then a significant fraction (~10%) of the most luminous supernova may be
self-enshrouded by dust not only before but also after the supernova occurs.
The spectral energy distribution of the progenitor of such a supernova would be
a slightly cooler version of eta Carina, peaking at 20-30 microns.Comment: 26 pages, 5 figures, 1 table, accepted for publication in Ap
Six Months of Multi-Wavelength Follow-up of the Tidal Disruption Candidate ASASSN-14li and Implied TDE Rates from ASAS-SN
We present ground-based and Swift photometric and spectroscopic observations
of the candidate tidal disruption event (TDE) ASASSN-14li, found at the center
of PGC 043234 ( Mpc) by the All-Sky Automated Survey for SuperNovae
(ASAS-SN). The source had a peak bolometric luminosity of ergs
s and a total integrated energy of ergs radiated
over the months of observations presented. The UV/optical emission of
the source is well-fit by a blackbody with roughly constant temperature of
K, while the luminosity declines by roughly a factor of 16 over
this time. The optical/UV luminosity decline is broadly consistent with an
exponential decline, , with days.
ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the
optical and UV emission but declining at a slower rate, and the X-ray emission
now dominates. Spectra of the source show broad Balmer and helium lines in
emission as well as strong blue continuum emission at all epochs. We use the
discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by
ASAS-SN, finding an average rate of
per galaxy with a 90% confidence interval of per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia
supernovae in 2014, a rate that is much higher than that of other surveys.Comment: 21 pages, 9 figures, 6 tables. Photometric data presented in this
submission are included as ancillary files. Manuscript updated to reflect
changes made in the published version. For a brief video explaining this
paper, see https://youtu.be/CTbr-d7cWZ
De-Trending Time Series for Astronomical Variability Surveys
We present a de-trending algorithm for the removal of trends in time series.
Trends in time series could be caused by various systematic and random noise
sources such as cloud passages, changes of airmass, telescope vibration or CCD
noise. Those trends undermine the intrinsic signals of stars and should be
removed. We determine the trends from subsets of stars that are highly
correlated among themselves. These subsets are selected based on a hierarchical
tree clustering algorithm. A bottom-up merging algorithm based on the departure
from normal distribution in the correlation is developed to identify subsets,
which we call clusters. After identification of clusters, we determine a trend
per cluster by weighted sum of normalized light-curves. We then use quadratic
programming to de-trend all individual light-curves based on these determined
trends. Experimental results with synthetic light-curves containing artificial
trends and events are presented. Results from other de-trending methods are
also compared. The developed algorithm can be applied to time series for trend
removal in both narrow and wide field astronomy.Comment: Revised version according to the referee's second revie
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