Abstract
The Galactic global magnetic field is thought to play a vital role in shaping Galactic structures such as spiral arms and giant molecular clouds. However, our knowledge of magnetic field ...structures in the Galactic plane at different distances is limited, as measurements used to map the magnetic field are the integrated effect along the line of sight. In this study, we present the first ever tomographic imaging of magnetic field structures in a Galactic spiral arm. Using optical stellar polarimetry over a
17
′
×
10
′
field of view, we probe the Sagittarius spiral arm. Combining these data with stellar distances from the Gaia mission, we can isolate the contributions of five individual clouds along the line of sight by analyzing the polarimetry data as a function of distance. The observed clouds include a foreground cloud (
d
< 200 pc) and four clouds in the Sagittarius arm at 1.23, 1.47, 1.63, and 2.23 kpc. The column densities of these clouds range from 0.5 to 2.8 × 10
21
cm
−2
. The magnetic fields associated with each cloud show smooth spatial distributions within their observed regions on scales smaller than 10 pc and display distinct orientations. The position angles projected on the plane of the sky, measured from the Galactic north to the east, for the clouds in increasing order of distance are 135°, 46°, 58°, 150°, and 40°, with uncertainties of a few degrees. Notably, these position angles deviate significantly from the direction parallel to the Galactic plane.
Abstract
We present optical and near-infrared observations of SN 2019ehk, which was initially reported as a Type Ib supernova (SN). We show that it evolved to a Ca-rich transient according to its ...spectral properties and evolution in late phases. However, it shows a few properties distinct from those of the canonical Ca-rich transients: a short-duration first peak in the light curve, high peak luminosity, and association with a star-forming environment. Indeed, some of these features are shared with iPTF14gqr and iPTF16hgs, which are candidates for a special class of core-collapse SNe: the so-called ultra-stripped envelope SNe, i.e., a relatively low-mass He (or C+O) star explosion in a binary as a precursor of short-period double neutron star (NS) binaries. The estimated ejecta mass (0.4
M
⊙
) and explosion energy (1.7 × 10
50
erg) are consistent with this scenario. The analysis of the first peak suggests the existence of dense circumstellar material in the vicinity of the progenitor, implying a CCSN origin. Based on this analysis, we suggest SN 2019ehk is another candidate for a low-mass He star explosion. It might create a double NS binary, but with a wide separation. These candidates for low-mass stripped envelope SNe, including ultra-stripped envelope SN candidates, seem to form a subpopulation among Ca-rich transients, associated with young population. We propose that the key to distinguishing this population is the early first peak in their light curves.
We report X-ray, optical, and near-infrared monitoring of the new X-ray transient MAXI J1820+070 discovered with MAXI on 2018 March 11. Its X-ray intensity reached ∼2 crab at 2-20 keV at the end of ...March, and then gradually decreased until the middle of June. In this period, the X-ray spectrum was described by Comptonization of the disk emission, with a photon index of ∼1.5 and an electron temperature of ∼50 keV, which is consistent with a black hole X-ray binary in the low/hard state. The electron temperature was slightly decreased, and the photon index increased, with increasing flux. The source showed significant X-ray flux variation on a timescale of seconds. This short-term variation was found to be associated with changes in the spectral shape, and the photon index became slightly harder at higher fluxes. This suggests that the variation was produced by a change in the properties of the hot electron cloud responsible for the strong Comptonization. Modeling a multi-wavelength spectral energy distribution around the X-ray flux peak at the end of March, covering the near-infrared to X-ray bands, we found that the optical and near-infrared fluxes were likely contributed substantially by the jet emission. Before this outburst, the source was never detected in the X-ray band with MAXI (with a 3 upper limit of ∼0.2 mcrab at 4-10 keV, obtained from seven years of data from 2009 to 2016), whereas weak optical and infrared activity was found at flux levels ∼3 orders of magnitude lower than the peak fluxes in the outburst.
Abstract
A gravitational wave event, S190510g, which was classified as a binary-neutron-star coalescence at the time of preliminary alert, was detected by LIGO/Virgo collaboration on 2019 May 10. At ...1.7 hours after the issue of its preliminary alert, we started a target-of-opportunity imaging observation in the Y band to search for its optical counterpart using the Hyper Suprime-Cam (HSC) on the Subaru Telescope. The observation covers a 118.8 deg2 sky area corresponding to $11.6\%$ confidence in the localization skymap released in the preliminary alert and $1.2\%$ in the updated skymap. We divided the observed area into two fields based on the availability of HSC reference images. For the fields with the HSC reference images, we applied an image subtraction technique; for the fields without the HSC reference images, we sought individual HSC images by matching a catalog of observed objects with the PS1 catalog. The search depth is 22.28 mag in the former method and the limit of search depth is 21.3 mag in the latter method. Subsequently, we performed visual inspection and obtained 83 candidates using the former method and 50 candidates using the latter method. Since we only have the one-day photometric data, we evaluated the probability of candidates being located inside the 3D skymap by estimating their distances with photometry of associated extended objects. We found three candidates are likely located inside the 3D skymap and concluded they could be a counterpart of S190510g, while most of the 133 candidates were likely to be supernovae because the number density of candidates was consistent with the expected number of supernova detections. By comparing our observational depth with a light-curve model of such a kilonova reproducing AT2017gfo, we show that early deep observations with the Subaru/HSC can capture the rising phase of the blue component of a kilonova at the estimated distance of S190510g (∼230 Mpc).
ABSTRACT
We report on the first polarimetric study of (3200) Phaethon, the target of JAXA’s DESTINY+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric ...albedo. We conducted observations at low phase angles (Sun-target-observer angle, α = 8.8–32.4°) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree Pmin = −1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg−1, and an inversion angle α0 = 19.9 ± 0.3°. The derived geometric albedo is pV = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.
Abstract
We followed up the massive young stellar object S255-NIRS3 (= S255-IRS1b) during its recent accretion outburst event in the $K_{\rm s}$ band with Kanata/HONIR for four years after its burst ...and obtained a long-term light curve. This is the most complete near-infrared light curve of the S255-NIRS3 burst event that has ever been presented. The light curve showed a steep increase reaching a peak flux that was 3.4 mag brighter than the quiescent phase and then a relatively moderate year-scale fading until the last observation, similar to that of the accretion burst events such as EXors found in lower-mass young stellar objects. The behavior of the $K_{\rm s}$-band light curve is similar to that observed in 6.7 GHz class II methanol maser emission, with a sudden increase followed by moderate year-scale fading. However, the maser emission peaks appear 30–50 d earlier than that of the $K_{\rm s}$ band emission. The similarities confirmed that the origins of the maser emission and the $K_{\rm s}$-band continuum emission are common, as previously shown from other infrared and radio observations by Stecklum et al. (2016, Astronomer’s Telegram, 8732), Caratti o Garatti et al. (2017b, Nature Phys., 13, 276), and Moscadelli et al. (2017, A&A, 600, L8). However, the differences in energy transfer paths, such as the exciting/emitting/scattering structures, may cause the delay in the flux-peak dates.
Abstract
The LIGO/Virgo detected a gravitational wave (GW) event, named GW200224_222234 (also known as S200224ca) and classified as a binary-black hole coalescence, on 2020 February 24. Given its ...relatively small localization skymap (71 deg
2
for a 90% credible region; revised to 50 deg
2
in GWTC-3), we performed target-of-opportunity observations using the Subaru/Hyper Suprime-Cam (HSC) in the
r
2 and
z
bands. Observations were conducted on 2020 February 25 and 28 and March 23, with the first epoch beginning 12.3 hr after the GW detection. The survey covered the highest-probability sky area of 56.6 deg
2
, corresponding to a 91% probability. This was the first deep follow-up (
m
r
≳ 24,
m
z
≳ 23) for a binary-black hole merger covering >90% of the localization. By performing image subtraction and candidate screening including light-curve fitting with transient templates and examples, we found 22 off-nucleus transients that were not ruled out as the counterparts of GW200224_222234 with our Subaru/HSC data alone. We also performed GTC/OSIRIS spectroscopy of the probable host galaxies for five candidates; two are likely to be located within the 3D skymap, whereas the others are not. In conclusion, 19 transients remain as possible optical counterparts of GW200224_222234; but we could not identify a unique promising counterpart. If there are no counterparts in the remaining candidates, the upper limits of the optical luminosity are
ν
L
ν
<
5.2
−
1.9
+
2.4
×
10
41
erg s
−1
and
ν
L
ν
<
1.8
−
0.6
+
0.8
×
10
42
erg s
−1
in the
r
2 and
z
bands, respectively, at ∼12 hr after GW detection. We also discuss improvements in the strategies of optical follow-ups for future GW events.
Abstract
Since 2018 July, the black hole X-ray binary GRS 1915+105 has been in an X-ray low luminous state (XLLS), which is the faintest period ever observed in a soft X-ray band. We present here the ...results of near-infrared (NIR) observations from 2019 April–December in the XLLS using HONIR attached to the Kanata telescope, together with radio data obtained by the Yamaguchi Interferometer and archival X-ray data. We found the historical NIR brightening in the XLLS. For several tens of days in the XLLS, NIR flux showed a positive correlation with radio flux and negative correlation with X-ray flux. This result suggests that at least a jet contributes to the NIR bands in the NIR-bright XLLS period. An accretion disk is not likely a candidate for the NIR emission because of the decrease of X-ray flux. In contrast to the NIR band, there was no historical radio brightening in the XLLS. This implies that the NIR emission in the NIR-bright period cannot be explained by the jet alone. The X-ray obscuration suggested by X-ray data is another possible candidate for the nonjet emission component in the NIR band.
In this paper we describe the Kottamia Faint Imaging Spectro-Polarimeter (KFISP) that has been recently developed and designed to be mounted at the Cassegrain focus of the 1.88 m telescope at ...Kottamia Astronomical Observatory (KAO), Egypt. The optical design of KFISP is developed such that it can be used in various modes of operation. These are: direct imaging, spectroscopic, polarimetric imaging, and spectro-polarimetric. The KFISP is an all-refractive design to meet the polarimetric requirements and includes a focal reducer with a corrector section, collimator section, parallel beam section (containing various imaging components), and camera section. The corrector section gives an unvignetted Field-of-View of 8ʹ × 8ʹ and the collimator section has a focal length of 305 mm and matches the focal ratio of the input beam. The parallel beam section is 200 mm long and near the middle of it there is an image of the telescope pupil. The camera section includes 5 elements and has a focal length of 154.51 mm which gives an instrument effective final focal ratio of f/6.14 (acting as a telescope focal reducer of 1:2 ratio). The KFISP contains an internal calibration system which hosts the calibration light injection system, an integrating sphere equipped with the required calibration light sources. The opto-mechanical parts of KFISP contain a double-layered carbon fiber strut structure and comprises its subsystems of slit and guider assemblies, filter wheel drawer, grism wheel drawer, polarimetric components cubical box, and CCD camera which is integrated with camera optics. The CCD camera has 2048
×
2048 pixels with 13.5-micron square pixel size. The camera is cooled by liquid Nitrogen and is fixed to the KFISP through the integrated camera lens. The KFISP has been fully commissioned, mounted and is being tested in all modes of operation. In this paper we introduce the ambitious scientific goals, the optical setups of KFISP, its opto-mechanical implementation and the performance analysis of the instrument. In addition, we describe the camera system, its performance, and its software control. Finally, we present a sample of the first light observations obtained from the instrument.
We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared (NIR) wavelengths from immediately after the explosion until ~260 days after the maximum luminosity using ...the Optical and Infrared Synergetic Telescopes for Education and Research Target-of-Opportunity program and the Subaru Telescope. We found that the NIR light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes (M sub(J) ~ -18.1 mag and M sub(H) ~ -18.3 mag) and the rate of decline of the light curve ( Delta m sub(15)(B) = 1.6 + or - 0.1 mag) are very similar to those of SN 2005hk (M sub(J) ~ -17.7 mag, M sub(H) ~ -18.0 mag, and Delta m sub(15)(B) ~ 1.6 mag), yet differ significantly from SNe 2008ha and 2010ae (M sub(J) ~ -14 to -15 mag and Delta m sub(15)(B) ~ 2.4-2.7 mag). The estimated rise time is 12.0 + or - 3.0 days, which is significantly shorter than that of SN 2005hk or any other SNe Ia. The rapid rise indicates that the super(56)Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of six to eight. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a "failed deflagration" model, although the pulsational delayed detonations is not excluded.
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