73 research outputs found
Building the Evryscope: Hardware Design and Performance
The Evryscope is a telescope array designed to open a new parameter space in
optical astronomy, detecting short timescale events across extremely large sky
areas simultaneously. The system consists of a 780 MPix 22-camera array with an
8150 sq. deg. field of view, 13" per pixel sampling, and the ability to detect
objects down to Mg=16 in each 2 minute dark-sky exposure. The Evryscope,
covering 18,400 sq.deg. with hours of high-cadence exposure time each night, is
designed to find the rare events that require all-sky monitoring, including
transiting exoplanets around exotic stars like white dwarfs and hot subdwarfs,
stellar activity of all types within our galaxy, nearby supernovae, and other
transient events such as gamma ray bursts and gravitational-wave
electromagnetic counterparts. The system averages 5000 images per night with
~300,000 sources per image, and to date has taken over 3.0M images, totaling
250TB of raw data. The resulting light curve database has light curves for 9.3M
targets, averaging 32,600 epochs per target through 2018. This paper summarizes
the hardware and performance of the Evryscope, including the lessons learned
during telescope design, electronics design, a procedure for the precision
polar alignment of mounts for Evryscope-like systems, robotic control and
operations, and safety and performance-optimization systems. We measure the
on-sky performance of the Evryscope, discuss its data-analysis pipelines, and
present some example variable star and eclipsing binary discoveries from the
telescope. We also discuss new discoveries of very rare objects including 2 hot
subdwarf eclipsing binaries with late M-dwarf secondaries (HW Vir systems), 2
white dwarf / hot subdwarf short-period binaries, and 4 hot subdwarf reflection
binaries. We conclude with the status of our transit surveys, M-dwarf flare
survey, and transient detection.Comment: 24 pages, 24 figures, accepted PAS
An empirical limit on the kilonova rate from the DLT40 one day cadence Supernova Survey
Binary neutron star mergers are important to understand stellar evolution,
the chemical enrichment of the universe via the r-process, the physics of short
gamma-ray bursts, gravitational waves and pulsars. The rates at which these
coalescences happen is uncertain, but it can be constrained in different ways.
One of those is to search for the optical transients produced at the moment of
the merging, called a kilonova, in ongoing SN searches. However, until now,
only theoretical models for kilonovae light curve were available to estimate
their rates. The recent kilonova discovery AT~2017gfo/DLT17ck gives us the
opportunity to constrain the rate of kilonovae using the light curve of a real
event. We constrain the rate of binary neutron star mergers using the DLT40
Supernova search, and the native AT~2017gfo/DLT17ck light curve obtained with
the same telescope and software system. Excluding AT~2017gfo/DLT17ck due to
visibility issues, which was only discovered thanks to the aLIGO/aVirgo
trigger, no other similar transients detected during 13 months of daily cadence
observations of 2200 nearby (40 Mpc) galaxies. We find that the rate
of BNS mergers is lower than 0.47 - 0.55 kilonovae per 100 years per
(depending on the adopted extinction distribution). In volume,
this translates to <0.99\times
10^{-4}\,_{-0.15}^{+0.19},\rm{Mpc^{-3}}\,\rm{yr^{-1}}(SNe Ia-like extinction
distribution), consistent with previous BNS coalescence rates. Based on our
rate limit, and the sensitivity of aLIGO/aVirgo during O2, it is very unlikely
that kilonova events are lurking in old pointed galaxy SN search datasets.Comment: 3 figures, 2 table
EvryFlare II: Rotation Periods of the Cool Flare Stars in TESS Across Half the Southern Sky
We measure rotation periods and sinusoidal amplitudes in Evryscope light
curves for 122 two-minute K5-M4 TESS targets selected for strong flaring. The
Evryscope array of telescopes has observed all bright nearby stars in the
South, producing two-minute cadence light curves since 2016. Long-term,
high-cadence observations of rotating flare stars probe the complex
relationship between stellar rotation, starspots, and superflares. We detect
periods from 0.3487 to 104 d, and observe amplitudes from 0.008 to 0.216 g'
mag. We find the Evryscope amplitudes are larger than those in TESS with the
effect correlated to stellar mass (p-value=0.01). We compute the Rossby number
(Ro), and find our sample selected for flaring has twice as many intermediate
rotators (0.040.44) rotators; this may
be astrophysical or a result of period-detection sensitivity. We discover 30
fast, 59 intermediate, and 33 slow rotators. We measure a median starspot
coverage of 13% of the stellar hemisphere and constrain the minimum magnetic
field strength consistent with our flare energies and spot coverage to be 500
G, with later-type stars exhibiting lower values than earlier-types. We observe
a possible change in superflare rates at intermediate periods. However, we do
not conclusively confirm the increased activity of intermediate rotators seen
in previous studies. We split all rotators at Ro~0.2 into Prot10
d bins to confirm short-period rotators exhibit higher superflare rates, larger
flare energies, and higher starspot coverage than do long-period rotators, at
p-values of 3.2 X 10^-5, 1.0 X 10^-5, and 0.01, respectively.Comment: 16 pages, 8 figures, 3 tables. Ancillary machine-readable files
included. Accepted for publication in ApJ (proofs submitted). Includes
significant new material, including starspot color that depends on stellar
mass, more rotation periods, potential changes in activity during spin-down,
and examples of binary rotator
The discovery of the electromagnetic counterpart of GW170817: kilonova AT 2017gfo/DLT17ck
During the second observing run of the Laser Interferometer gravitational-
wave Observatory (LIGO) and Virgo Interferometer, a gravitational-wave signal
consistent with a binary neutron star coalescence was detected on 2017 August
17th (GW170817), quickly followed by a coincident short gamma-ray burst trigger
by the Fermi satellite. The Distance Less Than 40 (DLT40) Mpc supernova search
performed pointed follow-up observations of a sample of galaxies regularly
monitored by the survey which fell within the combined LIGO+Virgo localization
region, and the larger Fermi gamma ray burst error box. Here we report the
discovery of a new optical transient (DLT17ck, also known as SSS17a; it has
also been registered as AT 2017gfo) spatially and temporally coincident with
GW170817. The photometric and spectroscopic evolution of DLT17ck are unique,
with an absolute peak magnitude of Mr = -15.8 \pm 0.1 and an r-band decline
rate of 1.1mag/d. This fast evolution is generically consistent with kilonova
models, which have been predicted as the optical counterpart to binary neutron
star coalescences. Analysis of archival DLT40 data do not show any sign of
transient activity at the location of DLT17ck down to r~19 mag in the time
period between 8 months and 21 days prior to GW170817. This discovery
represents the beginning of a new era for multi-messenger astronomy opening a
new path to study and understand binary neutron star coalescences, short
gamma-ray bursts and their optical counterparts.Comment: ApJL in press, 4 figure
2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable -ray emission
We present optical photometric and spectroscopic observations of the likely
stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT)
-ray source 2FGL J0846.0+2820, selected for study based on positional
coincidences of optical variables with unassociated LAT sources. Using optical
spectroscopy from the SOAR telescope, we have identified a late-G giant in an
eccentric ( = 0.06) 8.133 day orbit with an invisible primary. Modeling the
spectroscopy and photometry together lead us to infer a heavy neutron star
primary of and a partially stripped giant secondary of . H emission is observed in some of the spectra, perhaps
consistent with the presence of a faint accretion disk. We find the
-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009,
accompanied by an increased variation in the optical brightness, and since then
it has not been detected by \emph{Fermi}. The long period and giant secondary
are reminiscent of the -ray bright binary 1FGL J1417.7--4407, which
hosts a millisecond pulsar apparently in the final stages of the pulsar
recycling process. The discovery of 2FGL J0846.0+2820 suggests the
identification of a new subclass of millisecond pulsar binaries that are the
likely progenitors of typical field millisecond pulsars.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Ap
Supernova 2010ev: A reddened high velocity gradient type Ia supernova
Aims. We present and study the spectroscopic and photometric evolution of the
type Ia supernova (SN Ia) 2010ev. Methods. We obtain and analyze multi-band
optical light curves and optical-near-infrared spectroscopy at low and medium
resolution spanning from -7 days to +300 days from the B-band maximum. Results.
A photometric analysis shows that SN 2010ev is a SN Ia of normal brightness
with a light curve shape of and a stretch s =
suffering significant reddening. From photometric and
spectroscopic analysis, we deduce a color excess of
and a reddening law of . Spectroscopically, SN 2010ev
belongs to the broad-line SN Ia group, showing stronger than average Si II
{\lambda}6355 absorption features. We also find that SN 2010ev is a
high-velocity gradient SN, with a value of km s d.
The photometric and spectral comparison with other supernovae shows that SN
2010ev has similar colors and velocities to SN 2002bo and SN 2002dj. The
analysis of the nebular spectra indicates that the [Fe II] {\lambda}7155 and
[Ni II] {\lambda}7378 lines are redshifted, as expected for a high velocity
gradient supernova. All these common intrinsic and extrinsic properties of the
high velocity gradient (HVG) group are different from the low velocity gradient
(LVG) normal SN Ia population and suggest significant variety in SN Ia
explosions.Comment: 16 pages, 13 figures, 7 tables. Accepted to A&
1FGL J1417.7-4407: A likely gamma-ray bright binary with a massive neutron star and a giant secondary
We present multiwavelength observations of the persistent Fermi-LAT
unidentified gamma-ray source 1FGL J1417.7-4407, showing it is likely to be
associated with a newly discovered X-ray binary containing a massive neutron
star (nearly 2 M_sun) and a ~ 0.35 M_sun giant secondary with a 5.4 day period.
SOAR optical spectroscopy at a range of orbital phases reveals variable
double-peaked H-alpha emission, consistent with the presence of an accretion
disk. The lack of radio emission and evidence for a disk suggests the gamma-ray
emission is unlikely to originate in a pulsar magnetosphere, but could instead
be associated with a pulsar wind, relativistic jet, or could be due to
synchrotron self-Compton at the disk--magnetosphere boundary. Assuming a wind
or jet, the high ratio of gamma-ray to X-ray luminosity (~ 20) suggests
efficient production of gamma-rays, perhaps due to the giant companion. The
system appears to be a low-mass X-ray binary that has not yet completed the
pulsar recycling process. This system is a good candidate to monitor for a
future transition between accretion-powered and rotational-powered states, but
in the context of a giant secondary.Comment: ApJL in pres
Signatures of an eruptive phase before the explosion of the peculiar core-collapse SN 2013gc
We present photometric and spectroscopic analysis of the peculiar
core-collapse SN 2013gc, spanning seven years of observations. The light curve
shows an early maximum followed by a fast decline and a phase of almost
constant luminosity. At +200 days from maximum, a brightening of 1 mag is
observed in all bands, followed by a steep linear luminosity decline after +300
d. In archival images taken between 1.5 and 2.5 years before the explosion, a
weak source is visible at the supernova location, with mag20. The
early supernova spectra show Balmer lines, with a narrow (560 km
s) P-Cygni absorption superimposed on a broad (3400 km s)
component, typical of type IIn events. Through a comparison of colour curves,
absolute light curves and spectra of SN 2013gc with a sample of supernovae IIn,
we conclude that SN 2013gc is a member of the so-called type IId subgroup. The
complex profile of the H line suggests a composite circumstellar medium
geometry, with a combination of lower velocity, spherically symmetric gas and a
more rapidly expanding bilobed feature. This circumstellar medium distribution
has been likely formed through major mass-loss events, that we directly
observed from 3 years before the explosion. The modest luminosity
( near maximum) of SN 2013gc at all phases, the very small amount
of ejected Ni (of the order of M), the major
pre-supernova stellar activity and the lack of prominent [O I] lines in
late-time spectra support a fall-back core-collapse scenario for the massive
progenitor of SN~2013gc.Comment: 20 pages, 11 figures, 8 tables, accepted by MNRA
Building the Evryscope: Hardware Design and Performance
The Evryscope is a telescope array designed to open a new parameter space in optical astronomy, detecting short-timescale events across extremely large sky areas simultaneously. The system consists of a 780 MPix 22-camera array with an 8150 sq. deg. field of view, 13″ per pixel sampling, and the ability to detect objects down to {m}g\prime ≃ 16 in each 2-minute dark-sky exposure. The Evryscope, covering 18,400 sq. deg. with hours of high-cadence exposure time each night, is designed to find the rare events that require all-sky monitoring, including transiting exoplanets around exotic stars like white dwarfs and hot subdwarfs, stellar activity of all types within our galaxy, nearby supernovae, and other transient events such as gamma-ray bursts and gravitational-wave electromagnetic counterparts. The system averages 5000 images per night with ∼300,000 sources per image, and to date has taken over 3.0M images, totaling 250 TB of raw data. The resulting light curve database has light curves for 9.3M targets, averaging 32,600 epochs per target through 2018. This paper summarizes the hardware and performance of the Evryscope, including the lessons learned during telescope design, electronics design, a procedure for the precision polar alignment of mounts for Evryscope-like systems, robotic control and operations, and safety and performance-optimization systems. We measure the on-sky performance of the Evryscope, discuss its data analysis pipelines, and present some example variable star and eclipsing binary discoveries from the telescope. We also discuss new discoveries of very rare objects including two hot subdwarf eclipsing binaries with late M-dwarf secondaries (HW Vir systems), two white dwarf/hot subdwarf short-period binaries, and four hot subdwarf reflection binaries. We conclude with the status of our transit surveys, M-dwarf flare survey, and transient detection
- …