40 research outputs found
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
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
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
Optical follow-up of gravitational wave events during the second advanced LIGO/VIRGO observing run with the DLT40 Survey
We describe the GW follow-up strategy and subsequent results of the DLT40
during the second science run (O2) of the LVC. Depending on the information
provided in the GW alert together with the localization map sent by the LVC,
DLT40 would respond promptly to image the corresponding galaxies selected by
our ranking algorithm in order to search for possible EM counterparts in real
time. During the LVC O2 run, DLT40 followed ten GW triggers, observing between
20-100 galaxies within the GW localization area of each event. From this
campaign, we identified two real transient sources within the GW localizations
with an appropriate on-source time -- one was an unrelated type Ia supernova
(SN~2017cbv), and the other was the optical kilonova, AT
2017fgo/SSS17a/DLT17ck, associated with the binary neutron star coalescence
GW170817 (a.k.a gamma-ray burst GRB170817A). We conclude with a discussion of
the DLT40 survey's plans for the upcoming LVC O3 run, which include expanding
our galaxy search fields out to 65 Mpc to match the LVC's planned
three-detector sensitivity for binary neutron star mergers.Comment: 38 pages, 8 figures and 14 tables, Submitted to Ap
Optical variability of eight FRII-type quasars with 13 yr photometric light curves
We characterize the optical variability properties of eight lobe-dominated radio quasars (QSOs): B2 0709+37, FBQS J095206.3+235245, PG 1004+130, [HB89] 1156+631, [HB89] 1425+267, [HB89] 1503+691, [HB89] 1721+343, and 4C +74.26, systematically monitored for a duration of 13 yr since 2009. The quasars are radio-loud objects with extended radio lobes that indicate their orientation close to the sky plane. Five of the eight QSOs are classified as giant radio quasars. All quasars showed variability during our monitoring, with magnitude variations between 0.3 and 1 mag for the least variable and the most variable QSOs, respectively. We performed both structure function (SF) analysis and power spectral density (PSD) analysis for the variability characterization and search for characteristic timescales and periodicities. As a result of our analysis, we obtained relatively steep SF slopes (α ranging from 0.49 to 0.75) that are consistent with the derived PSD slopes (∼2–3). All the PSDs show a good fit to single power-law forms, indicating a red-noise character of variability between timescales of ∼13 yr and weeks. We did not measure reliable characteristic timescales of variability from the SF analysis, which indicates that the duration of the gathered data is too short to reveal them. The absence of bends in the PSDs (change of slope from ≥1 to ∼0) on longer timescales indicates that optical variations are most likely caused by thermal instabilities in the accretion disk
Optical variability of eight FRII-type quasars with 13-yr photometric light curves
We characterize the optical variability properties of eight lobe-dominated
radio quasars (QSOs): B2 070937, FBQS J095206.3235245, PG 1004130,
[HB89] 1156631, [HB89] 1425267, [HB89] 1503691, [HB89] 1721343, 4C
74.26, systematically monitored for a duration of 13 years since 2009. The
quasars are radio-loud objects with extended radio lobes that indicate their
orientation close to the sky plane. Five of the eight QSOs are classified as
giant radio quasars. All quasars showed variability during our monitoring, with
magnitude variations between 0.3 and 1 mag for the least variable and the most
variable QSO, respectively. We performed both structure function (SF) analysis
and power spectrum density (PSD) analysis for the variability characterization
and search for characteristic timescales and periodicities. As a result of our
analysis, we obtained relatively steep SF slopes ( ranging from 0.49 to
0.75) that are consistent with the derived PSD slopes (2--3). All the
PSDs show a good fit to single power law forms, indicating a red-noise
character of variability between 13 years and weeks timescales. We did
not measure reliable characteristic timescales of variability from the SF
analysis which indicates that the duration of the gathered data is too short to
reveal them. The absence of bends in the PSDs (change of slope from 1 to
0) on longer timescales indicates that optical variations are most likely
caused by thermal instabilities in the accretion disk.Comment: Accepted for publication in ApJS; 17 pages, 5 figures, 5 table
Profound optical flares from the relativistic jets of active galactic nuclei
Intense outbursts in blazars are among the most extreme phenomena seen in
extragalactic objects. Studying these events can offer important information
about the energetic physical processes taking place within the innermost
regions of blazars, which are beyond the resolution of current instruments.
This work presents some of the largest and most rapid flares detected in the
optical band from the sources 3C 279, OJ 49, S4 0954+658, Ton 599, and PG
1553+113, which are mostly TeV blazars. The source flux increased by nearly ten
times within a few weeks, indicating the violent nature of these events. Such
energetic events might originate from magnetohydrodynamical instabilities near
the base of the jets, triggered by processes modulated by the magnetic field of
the accretion disc. We explain the emergence of flares owing to the injection
of high-energy particles by the shock wave passing along the relativistic jets.
Alternatively, the flares may have also arisen due to geometrical effects
related to the jets. We discuss both source-intrinsic and source-extrinsic
scenarios as possible explanations for the observed large amplitude flux
changes.Comment: 8 pages, 2 figures, 38th International Cosmic Ray Conference
(ICRC2023) proceeding
Optical Time-Series Photometry of the Symbiotic Nova V1835 Aquilae
We present time-series CCD photometry in the passbands of the recently
identified symbiotic nova V1835 Aquilae (NSV 11749) over an interval of 5.1
years with 7-14 day cadence, observed during its quiescence. We find slow light
variations with a range of 0.9 mag in and 0.3 mag in .
Analysis of these data show strong periodicity at days, which we
interpret to be the system's orbital period. A dip in the otherwise-sinusoidal
phased light curve suggests a weak ellipsoidal effect due to tidal distortion
of the giant star, which in turn opens the possibility that V1835 Aql transfers
some of its mass to the hot component via Roche lobe overflow rather than via a
stellar wind. We also find evidence that V1835 Aql is an S-type symbiotic star,
relatively free of circumstellar dust, and include it among the nuclear burning
group of symbiotics. Finally, we provide photometry, periods, and light curve
classifications for 22 variable stars in the field around V1835 Aql, about half
of which are newly identified.Comment: Main Paper: 28 pages, 5 figures, 5 tables. Supplement: 15 pages, 4
figures, 1 table. To be published in Publications of the Astronomical Society
of the Pacifi
Catching profound optical flares in blazars
Flaring episodes in blazars represent one of the most violent processes
observed in extra-galactic objects. Studies of such events shed light on the
energetics of the physical processes occurring in the innermost regions of
blazars, which cannot otherwise be resolved by any current instruments. In this
work, we present some of the largest and most rapid flares captured in the
optical band in the blazars 3C 279, OJ 49, S4 0954+658, TXS 1156+295 and PG
1553+113. The source flux was observed to increase by nearly ten times within a
timescale of a few weeks. We applied several methods of time series analysis
and symmetry analysis. Moreover, we also performed searches for periodicity in
the light curves of 3C 279, OJ 49 and PG 1553+113 using the Lomb-Scargle method
and found plausible indications of quasi-periodic oscillations (QPOs). In
particular, the 33- and 22-day periods found in 3C 279, i.e. a 3:2 ratio, are
intriguing. These violent events might originate from magnetohydrodynamical
instabilities near the base of the jets, triggered by processes modulated by
the magnetic field of the accretion disc. We present a qualitative treatment as
the possible explanation for the observed large amplitude flux changes in both
the source-intrinsic and source-extrinsic scenarios.Comment: 11 pages, 6 figures, MNRAS accepte