8 research outputs found
Gravitational-wave Electromagnetic Counterpart Korean Observatory (GECKO): GECKO Follow-up Observation of GW190425
One of the keys to the success of multimessenger astronomy is the rapid
identification of the electromagnetic wave counterpart, kilonova (KN), of the
gravitational-wave (GW) event. Despite its importance, it is hard to find a KN
associated with a GW event, due to a poorly constrained GW localization map and
numerous signals that could be confused as a KN. Here, we present the
Gravitational-wave Electromagnetic wave Counterpart Korean Observatory (GECKO)
project, the GECKO observation of GW190425, and prospects of GECKO in the
fourth observing run (O4) of the GW detectors. We outline our follow-up
observation strategies during O3. In particular, we describe our
galaxy-targeted observation criteria that prioritize based on galaxy
properties. Armed with this strategy, we performed an optical and/or
near-infrared follow-up observation of GW190425, the first binary neutron star
merger event during the O3 run. Despite a vast localization area of 7460 deg^2,
we observed 621 host galaxy candidates, corresponding to 29.5% of the scores we
assigned, with most of them observed within the first 3 days of the GW event.
Ten transients were discovered during this search, including a new transient
with a host galaxy. No plausible KN was found, but we were still able to
constrain the properties of potential KNe using upper limits. The GECKO
observation demonstrates that GECKO can possibly uncover a GW170817-like KN at
a distance less than 200 Mpc if the localization area is of the order of
hundreds of square degrees, providing a bright prospect for the identification
of GW electromagnetic wave counterparts during the O4 run.Comment: 35 pages, 19 figures Accepted for publication in Ap
The Early Light Curve of a Type Ia Supernova 2021hpr in NGC 3147: Progenitor Constraints with the Companion Interaction Model
The progenitor system of Type Ia supernovae (SNe Ia) is expected to be a
close binary system of a carbon/oxygen white dwarf (WD) and a non-degenerate
star or another WD. Here, we present results from a high-cadence monitoring
observation of SN 2021hpr in a spiral galaxy, NGC 3147, and constraints on the
progenitor system based on its early multi-color light curve data. First, we
classify SN 2021hpr as a normal SN Ia from its long-term photometric and
spectroscopic data. More interestingly, we found a significant "early excess"
in the light curve over a simple power-law evolution. The early
light curve evolves from blue to red and blue during the first week. To explain
this, we fitted the early part of -band light curves with a two-component
model of the ejecta-companion interaction and a simple power-law model. The
early excess and its color can be explained by shock cooling emission due to a
companion star having a radius of . We also examined
HST pre-explosion images with no detection of a progenitor candidate,
consistent with the above result. However, we could not detect signs of a
significant amount of the stripped mass from a non-degenerate companion star
( for H emission). The early excess light in
the multi-band light curve supports a non-degenerate companion in the
progenitor system of SN 2021hpr. At the same time, the non-detection of
emission lines opens a door for other methods to explain this event.Comment: 26 pages, 13 figures + appendix, Accepted for publication in Ap
Spectral evolution of dark asteroid surfaces induced by space weathering over a decade
The surface of airless bodies like asteroids in the Solar System are known to
be affected by space weathering. Experiments simulating space weathering are
essential for studying the effects of this process on meteorite samples, but
the problem is that the time spent to reproduce space weathering in these
experiments is billions of times shorter than the actual phenomenon. In
December 2010, the T-type asteroid 596 Scheila underwent a collision with a
few-tens-of-meters impactor. A decade later, there is an opportunity to study
how the surface layer of this asteroid is being altered by space weathering
after the impact. To do so, we performed visible spectrophotometric and
near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum
is consistent with those observed shortly after the 2010 impact event within
the observational uncertainty range. This indicates that the surface color of
dark asteroids is not noticeably changed by space weathering over a 10-year
period. This study is the first to investigate color changes due to space
weathering on an actual asteroid surface in the Solar System. Considering that
fresh layers are regularly created on asteroid surfaces by collisions, we
suggest a genetic link between D/T-type and dark (low albedo) X-complex
asteroids and very red objects such as 269 Justitia, 732 Tjilaki (and 203
Pompeja). New observations show that 203 Pompeja has a X-type-like surface,
with some local surface areas exhibiting a very red spectrum.Comment: 16 pages, 9 figures, 2 tables, Accepted for publication in ApJ
Letter
Gravitational-wave Electromagnetic Counterpart Korean Observatory (GECKO): GECKO Follow-up Observation of GW190425
One of the keys to the success of multimessenger astronomy is the rapid identification of the electromagnetic wave counterpart, kilonova (KN), of the gravitational-wave (GW) event. Despite its importance, it is hard to find a KN associated with a GW event, due to a poorly constrained GW localization map and numerous signals that could be confused as a KN. Here, we present the Gravitational-wave Electromagnetic wave Counterpart Korean Observatory (GECKO) project, the GECKO observation of GW190425, and prospects of GECKO in the fourth observing run (O4) of the GW detectors. We outline our follow-up observation strategies during O3. In particular, we describe our galaxy-targeted observation criteria that prioritize based on galaxy properties. Armed with this strategy, we performed an optical and/or near-infrared follow-up observation of GW190425, the first binary neutron star merger event during the O3 run. Despite a vast localization area of 7460 deg ^2 , we observed 621 host galaxy candidates, corresponding to 29.5% of the scores we assigned, with most of them observed within the first 3 days of the GW event. Ten transients were discovered during this search, including a new transient with a host galaxy. No plausible KN was found, but we were still able to constrain the properties of potential KNe using upper limits. The GECKO observation demonstrates that GECKO can possibly uncover a GW170817-like KN at a distance <200 Mpc if the localization area is of the order of hundreds of square degrees, providing a bright prospect for the identification of GW electromagnetic wave counterparts during the O4 run
Spectral Evolution of Dark Asteroid Surfaces Induced by Space Weathering over a Decade
International audienceAbstract The surfaces of airless bodies like asteroids in the solar system are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In 2010 December, the T-type asteroid 596 Scheila underwent a collision with an impactor a few tens of meters in size. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10 yr period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the solar system. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki, and 203 Pompeja. New observations show that 203 Pompeja has an X-type-like surface, with some local surface areas exhibiting a very red spectrum
Spectral Evolution of Dark Asteroid Surfaces Induced by Space Weathering over a Decade
The surfaces of airless bodies like asteroids in the solar system are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In 2010 December, the T-type asteroid 596 Scheila underwent a collision with an impactor a few tens of meters in size. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10 yr period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the solar system. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki, and 203 Pompeja. New observations show that 203 Pompeja has an X-type-like surface, with some local surface areas exhibiting a very red spectrum.Y
Polarimetric properties of the near-Sun asteroid (155140) 2005 UD in comparison with other asteroids and meteoritic samples
The investigation of asteroids near the Sun is important for understanding
the final evolutionary stage of primitive solar system objects. A near-Sun
asteroid, (155140) 2005 UD, has orbital elements similar to those of (3200)
Phaethon (the target asteroid for the JAXA's mission). We conducted
photometric and polarimetric observations of 2005 UD and found that this
asteroid exhibits a polarization phase curve similar to that of Phaethon over a
wide range of observed solar phase angles () but
different from those of (101955) Bennu and (162173) Ryugu (asteroids composed
of hydrated carbonaceous materials). At a low phase angle (), the polarimetric properties of these near-Sun asteroids (2005 UD
and Phaethon) are consistent with anhydrous carbonaceous chondrites, while the
properties of Bennu are consistent with hydrous carbonaceous chondrites. We
derived the geometric albedo, (in the range of
0.088-0.109); mean -band absolute magnitude, ; synodic rotational period, hours
(the two-peaked solution is assumed); and effective mean diameter, km. At large phase angles (), the polarization phase curve are likely explained by the dominance
of large grains and the paucity of small micron-sized grains. We conclude that
the polarimetric similarity of these near-Sun asteroids can be attributed to
the intense solar heating of carbonaceous materials around their perihelia,
where large anhydrous particles with small porosity could be produced by
sintering.Comment: 15 pages, 9 figures, accepted for publication in Monthly Notices of
Royal Astronomical Society (MNRAS