arXiv subjects

Tomoki Morokuma

Publications and source records attributed to Tomoki Morokuma.

At least 91 records · Page 5Linked to original sources

arXiv2015

Hyper-luminous Dust Obscured Galaxies discovered by the Hyper Suprime-Cam on Subaru and WISE

We present the photometric properties of a sample of infrared (IR) bright dust obscured galaxies (DOGs). Combining wide and deep optical images obtained with the Hyper Suprime-Cam (HSC) on the Subaru Telescope and all-sky mid-IR (MIR) images taken with Wide-Field Infrared Survey Explorer (WISE), we discovered 48 DOGs with $i - K_\mathrm{s} > 1.2$ and $i - [22] > 7.0$, where $i$, $K_\mathrm{s}$, and [22] represent AB magnitude in the $i$-band, $K_\mathrm{s}$-band, and 22 $μ$m, respectively, in the GAMA 14hr field ($\sim$ 9 deg$^2$). Among these objects, 31 ($\sim$ 65 %) show power-law spectral energy distributions (SEDs) in the near-IR (NIR) and MIR regime, while the remainder show a NIR bump in their SEDs. Assuming that the redshift distribution for our DOGs sample is Gaussian, with mean and sigma $z$ = 1.99 $\pm$ 0.45, we calculated their total IR luminosity using an empirical relation between 22 $μ$m luminosity and total IR luminosity. The average value of the total IR luminosity is (3.5 $\pm$ 1.1) $\times$ $10^{13}$ L$_{\odot}$, which classifies them as hyper-luminous infrared galaxies (HyLIRGs). We also derived the total IR luminosity function (LF) and IR luminosity density (LD) for a flux-limited subsample of 18 DOGs with 22 $μ$m flux greater than 3.0 mJy and with $i$-band magnitude brighter than 24 AB magnitude. The derived space density for this subsample is log $ϕ$ = -6.59 $\pm$ 0.11 [Mpc$^{-3}$]. The IR LF for DOGs including data obtained from the literature is well fitted by a double-power law. The derived lower limit for the IR LD for our sample is $ρ_{\mathrm{IR}}$ $\sim$ 3.8 $\times$ 10$^7$ [L$_{\odot}$ Mpc$^{-3}$] and its contributions to the total IR LD, IR LD of all ultra-luminous infrared galaxies (ULIRGs), and that of all DOGs are $>$ 3 %, $>$ 9 %, and $>$ 15 %, respectively.

astro-ph.GA↗

arXiv2015

The Subaru-XMM-Newton Deep Survey (SXDS) VIII.: Multi-wavelength Identification, Optical/NIR Spectroscopic Properties, and Photometric Redshifts of X-ray Sources

We report the multi-wavelength identification of the X-ray sources found in the Subaru-XMM-Newton Deep Survey (SXDS) using deep imaging data covering the wavelength range between the far-UV to the mid-IR. We select a primary counterpart of each X-ray source by applying the likelihood ratio method to R-band, 3.6micron, near-UV, and 24micron source catalogs as well as matching catalogs of AGN candidates selected in 1.4GHz radio and i'-band variability surveys. Once candidates of Galactic stars, ultra-luminous X-ray sources in a nearby galaxy, and clusters of galaxies are removed there are 896 AGN candidates in the sample. We conduct spectroscopic observations of the primary counterparts with multi-object spectrographs in the optical and NIR; 65\% of the X-ray AGN candidates are spectroscopically-identified. For the remaining X-ray AGN candidates, we evaluate their photometric redshift with photometric data in 15 bands. Utilising the multi-wavelength photometric data of the large sample of X-ray selected AGNs, we evaluate the stellar masses, M*, of the host galaxies of the narrow-line AGNs. The distribution of the stellar mass is remarkably constant from z=0.1 to 4.0. The relation between M* and 2--10 keV luminosity can be explained with strong cosmological evolution of the relationship between the black hole mass and M*. We also evaluate the scatter of the UV-MIR spectral energy distribution (SED) of the X-ray AGNs as a function of X-ray luminosity and absorption to the nucleus. The scatter is compared with galaxies which have redshift and stellar mass distribution matched with the X-ray AGN. The UV-NIR SEDs of obscured X-ray AGNs are similar to those of the galaxies in the matched sample. In the NIR-MIR range, the median SEDs of X-ray AGNs are redder, but the scatter of the SEDs of the X-ray AGN broadly overlaps that of the galaxies in the matched sample.

astro-ph.GA↗

arXiv2015

OISTER Optical and Near-Infrared Observations of Type Iax Supernova 2012Z

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared wavelengths from immediately after the explosion until $\sim$ $260$ days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) Target-of-Opportunity (ToO) program and the Subaru telescope. We found that the near-infrared (NIR) light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes ($M_{J}\sim-18.1$ mag and $M_{H}\sim-18.3$ mag) and the rate of decline of the light curve ($Δ$ $m_{15}$($B$)$=1.6 \pm 0.1$ mag) are very similar to those of SN 2005hk ($M_{J}\sim-17.7$ mag, $M_{H}\sim$$-18.0$ mag, and $Δ$ $m_{15}$($B$)$\sim1.6$ mag), yet differ significantly from SNe 2008ha and 2010ae ($M_{J}\sim-14 - -15$ mag and $Δ$ $m_{15}$($B$)$\sim2.4-2.7$ mag). The estimated rise time is $12.0 \pm 3.0$ days, which is significantly shorter than that of SN 2005hk or any other Ia SNe. The rapid rise indicates that the $^{56}$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 6--8. 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.

astro-ph.SR↗

arXiv2015

ANIR : Atacama Near-Infrared Camera for the 1.0-m miniTAO Telescope

We have developed a near-infrared camera called ANIR (Atacama Near-InfraRed camera) for the University of Tokyo Atacama Observatory 1.0m telescope (miniTAO) installed at the summit of Cerro Chajnantor (5640 m above sea level) in northern Chile. The camera provides a field of view of 5'.1 $\times$ 5'.1 with a spatial resolution of 0".298 /pixel in the wavelength range of 0.95 to 2.4 $μ$m. Taking advantage of the dry site, the camera is capable of hydrogen Paschen-$α$ (Pa$α$, $λ=$1.8751 $μ$m in air) narrow-band imaging observations, at which wavelength ground-based observations have been quite difficult due to deep atmospheric absorption mainly from water vapor. We have been successfully obtaining Pa$α$ images of Galactic objects and nearby galaxies since the first-light observation in 2009 with ANIR. The throughputs at the narrow-band filters ($N1875$, $N191$) including the atmospheric absorption show larger dispersion (~10%) than those at broad-band filters (a few %), indicating that they are affected by temporal fluctuations in Precipitable Water Vapor (PWV) above the site. We evaluate the PWV content via the atmospheric transmittance at the narrow-band filters, and derive that the median and the dispersion of the distribution of the PWV are 0.40+/-0.30 mm for $N1875$ and 0.37+/-0.21 mm for $N191$, which are remarkably smaller (49+/-38% for $N1875$ and 59+/-26% for $N191$) than radiometry measurements at the base of Cerro Chajnantor (5100 m alt.). The decrease in PWV can be explained by the altitude of the site when we assume that the vertical distribution of the water vapor is approximated at an exponential profile with scale heights within 0.3-1.9 km (previously observed values at night). We thus conclude that miniTAO/ANIR at the summit of Cerro Chajnantor indeed provides us an excellent capability for a "ground-based" Pa$α$ observation.

astro-ph.IM↗

arXiv2015

Multi-wavelength observations of the black widow pulsar 2FGL J2339.6-0532 with OISTER and Suzaku

Multi-wavelength observations of the black-widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which a recycled millisecond pulsar (MSP) is evaporating up the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to 52$^{\circ}$ < i < 59$^{\circ}$, which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 10$^{11}$ cm from the pulsar, the pulsar wind is already in particle dominant-stage, with a magnetization parameter of $σ$ < 0.1. In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of orbital modulation. The observed phenomenon may be related to an unstable pulsar-wind activity or a weak mass accretion, both of which can result in the temporal extinction of radio-pulse.

astro-ph.HE↗

arXiv2014

Ground-based Pa$α$ Narrow-band Imaging of Local Luminous Infrared Galaxies I: Star Formation Rates and Surface Densities

Luminous infrared galaxies (LIRGs) are enshrouded by a large amount of dust, produced by their active star formation, and it is difficult to measure their activity in the optical wavelength. We have carried out Pa$α$ narrow-band imaging observations of 38 nearby star-forming galaxies including 33 LIRGs listed in $IRAS$ RBGS catalog with the Atacama Near InfraRed camera (ANIR) on the University of Tokyo Atacama Observatory (TAO) 1.0 m telescope (miniTAO). Star formation rates (SFRs) estimated from the Pa$α$ fluxes, corrected for dust extinction using the Balmer Decrement Method (typically $A_V$ $\sim$ 4.3 mag), show a good correlation with those from the bolometric infrared luminosity of $IRAS$ data within a scatter of 0.27 dex. This suggests that the correction of dust extinction for Pa$α$ flux is sufficient in our sample. We measure the physical sizes and the surface density of infrared luminosities ($Σ_{L(\mathrm{IR})}$) and $SFR$ ($Σ_{SFR}$) of star-forming region for individual galaxies, and find that most of the galaxies follow a sequence of local ultra luminous or luminous infrared galaxies (U/LIRGs) on the $L(\mathrm{IR})$-$Σ_{L(\mathrm{IR})}$ and $SFR$-$Σ_{SFR}$ plane. We confirm that a transition of the sequence from normal galaxies to U/LIRGs is seen at $L(\mathrm{IR})=8\times10^{10}$ $L_{\odot}$. Also, we find that there is a large scatter in physical size, different from those of normal galaxies or ULIRGs. Considering the fact that most of U/LIRGs are merging or interacting galaxies, this scatter may be caused by strong external factors or differences of their merging stage.

astro-ph.GA↗

arXiv2014

Dust from Comet 209P/LINEAR during its 2014 Return: Parent Body of a New Meteor Shower, the May Camelopardalids

We report a new observation of the Jupiter-family comet 209P/LINEAR during its 2014 return. The comet is recognized as a dust source of a new meteor shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a heliocentric distance rh = 1.6 au and showed weak activity at rh < 1.4 au. We found an active region of <0.001% of the entire nuclear surface during the comet's dormant phase. An edge-on image suggests that particles up to 1 cm in size (with an uncertainty of factor 3-5) were ejected following a differential power-law size distribution with index q=-3.25+-0.10. We derived a mass loss rate of 2-10 kg/s during the active phase and a total mass of ~5x10^7 kg during the 2014 return. The ejection terminal velocity of millimeter- to centimeter-sized particles was 1-4 m/s, which is comparable to the escape velocity from the nucleus (1.4 m/s). These results imply that such large meteoric particles marginally escaped from the highly dormant comet nucleus via the gas drag force only within a few months of the perihelion passage.

astro-ph.EP↗

arXiv2014

Discovery of Dramatic Optical Variability in SDSS J1100+4421: A Peculiar Radio-Loud Narrow-Line Seyfert 1 Galaxy?

We present our discovery of dramatic variability in SDSS J1100+4421 by the high-cadence transient survey Kiso Supernova Survey (KISS). The source brightened in the optical by at least a factor of three within about half a day. Spectroscopic observations suggest that this object is likely a narrow-line Seyfert 1 galaxy (NLS1) at z=0.840, however with unusually strong narrow emission lines. The estimated black hole mass of ~ 10^7 Msun implies bolometric nuclear luminosity close to the Eddington limit. SDSS J1100+4421 is also extremely radio-loud, with a radio loudness parameter of R ~ 4 x 10^2 - 3 x 10^3, which implies the presence of relativistic jets. Rapid and large-amplitude optical variability of the target, reminiscent of that found in a few radio- and gamma-ray loud NLS1s, is therefore produced most likely in a blazar-like core. The 1.4 GHz radio image of the source shows an extended structure with a linear size of about 100 kpc. If SDSS J1100+4421 is a genuine NLS1, as suggested here, this radio structure would then be the largest ever discovered in this type of active galaxies.

astro-ph.GA↗

arXiv2014

Kiso Supernova Survey (KISS): Survey Strategy

The Kiso Supernova Survey (KISS) is a high-cadence optical wide-field supernova (SN) survey. The primary goal of the survey is to catch the very early light of a SN, during the shock breakout phase. Detection of SN shock breakouts combined with multi-band photometry obtained with other facilities would provide detailed physical information on the progenitor stars of SNe. The survey is performed using a 2.2x2.2 deg field-of-view instrument on the 1.05-m Kiso Schmidt telescope, the Kiso Wide Field Camera (KWFC). We take a three-minute exposure in g-band once every hour in our survey, reaching magnitude g~20-21. About 100 nights of telescope time per year have been spent on the survey since April 2012. The number of the shock breakout detections is estimated to be of order of 1 during our 3-year project. This paper summarizes the KISS project including the KWFC observing setup, the survey strategy, the data reduction system, and CBET-reported SNe discovered so far by KISS.

astro-ph.SR↗

arXiv2014

Variable optical polarization during high state in gamma-ray loud narrow line Seyfert 1 galaxy 1H 0323+342

We present results of optical polarimetric and multi-band photometric observations for gamma-ray loud narrow-line Seyfert 1 galaxy 1H 0323+342. This object has been monitored by 1.5 m Kanata telescope since 2012 September but following a gamma-ray flux enhancement detected by Fermi-LAT on MJD 56483 (2013 July 10) dense follow-up was performed by ten 0.5-2.0 m telescopes in Japan over one week. The 2-year R_C-band light curve showed clear brightening corresponding to the gamma-ray flux increase and then decayed gradually. The high state as a whole lasted for ~20 days, during which we clearly detected optical polarization from this object. The polarization degree (PD) of the source increased from 0-1% in quiescence to ~3% at maximum and then declined to the quiescent level, with the duration of the enhancement of less than 10 days. The moderate PD around the peak allowed us to precisely measure the daily polarization angle (PA). As a result, we found that the daily PAs were almost constant and aligned to the jet axis, suggesting that the magnetic field direction at the emission region is transverse to the jet. This implies either a presence of helical/toroidal magnetic field or transverse magnetic field compressed by shock(s). We also found small-amplitude intra-night variability during the 2-hour continuous exposure on a single night. We discuss these findings based on the turbulent multi-zone model recently advocated by Marscher (2014). Optical to ultraviolet (UV) spectrum showed a rising shape in the higher frequency and the UV magnitude measured by Swift/UVOT was steady even during the flaring state, suggesting that thermal emission from accretion disk is dominant in that band.

astro-ph.GA↗

arXiv2014

Statistical Properties of Multi-epoch Spectral Variability of SDSS Stripe82 Quasars

We investigate the UV-optical (longward of Ly$α$ 1216Å) spectral variability of nearly 9000 quasars ($0<z<4$) using multi-epoch photometric data within the SDSS Stripe 82 region. The regression slope in the flux-flux space of a quasar light curve directly measures the color of the flux difference spectrum, then the spectral shape of the flux difference spectra can be derived by taking a careful look at the redshift dependence of the regression slopes. First, we confirm that the observed quasar spectrum becomes bluer when the quasar becomes brighter. We infer the spectral index of the composite difference spectrum as $α_ν^{\text{dif}}\sim +1/3$ (in the form of $f_ν\propto ν^{α_ν}$), which is significantly bluer than that of the composite spectrum $α_ν^{\text{com}}\sim -0.5$. We also show that the continuum variability cannot be explained by the accretion disk models with varying mass accretion rate. Second, we examine the effects of broad emission line variability on the color-redshift space. The variability of the "Small Blue Bump" is extensively discussed. We show that the low-ionization lines of MgII and FeII are less variable compared to Balmer emission lines and high-ionization lines, and the Balmer continuum is the dominant variable source around $\sim 3000$Å. These results are compared with previous studies, and the physical mechanisms of the variability of the continuum and emission lines are discussed.

astro-ph.CO↗

arXiv2014

The Type Ia supernovae rate with Subaru/XMM-Newton Deep Survey

We present measurements of the rates of high-redshift Type Ia supernovae derived from the Subaru/XMM-Newton Deep Survey (SXDS). We carried out repeat deep imaging observations with Suprime-Cam on the Subaru Telescope, and detected 1040 variable objects over 0.918 deg$^2$ in the Subaru/XMM-Newton Deep Field. From the imaging observations, light curves in the observed $i'$-band are constructed for all objects, and we fit the observed light curves with template light curves. Out of the 1040 variable objects detected by the SXDS, 39 objects over the redshift range $0.2 < z < 1.4$ are classified as Type Ia supernovae using the light curves. These are among the most distant SN Ia rate measurements to date. We find that the Type Ia supernova rate increase up to $z \sim 0.8$ and may then flatten at higher redshift. The rates can be fitted by a simple power law, $r_V(z)=r_0(1+z)^α$ with $r_0=0.20^{+0.52}_{-0.16}$(stat.)$^{+0.26}_{-0.07}$(syst.)$\times 10^{-4} {\rm yr}^{-1}{\rm Mpc}^{-3}$, and $α=2.04^{+1.84}_{-1.96}$(stat.)$^{+2.11}_{-0.86}$(syst.).

astro-ph.CO↗

arXiv2014

The Data Release of the Sloan Digital Sky Survey-II Supernova Survey

This paper describes the data release of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey conducted between 2005 and 2007. Light curves, spectra, classifications, and ancillary data are presented for 10,258 variable and transient sources discovered through repeat ugriz imaging of SDSS Stripe 82, a 300 deg2 area along the celestial equator. This data release is comprised of all transient sources brighter than r~22.5 mag with no history of variability prior to 2004. Dedicated spectroscopic observations were performed on a subset of 889 transients, as well as spectra for thousands of transient host galaxies using the SDSS-III BOSS spectrographs. Photometric classifications are provided for the candidates with good multi-color light curves that were not observed spectroscopically. From these observations, 4607 transients are either spectroscopically confirmed, or likely to be, supernovae, making this the largest sample of supernova candidates ever compiled. We present a new method for SN host-galaxy identification and derive host-galaxy properties including stellar masses, star-formation rates, and the average stellar population ages from our SDSS multi-band photometry. We derive SALT2 distance moduli for a total of 1443 SN Ia with spectroscopic redshifts as well as photometric redshifts for a further 677 purely-photometric SN Ia candidates. Using the spectroscopically confirmed subset of the three-year SDSS-II SN Ia sample and assuming a flat Lambda-CDM cosmology, we determine Omega_M = 0.315 +/- 0.093 (statistical error only) and detect a non-zero cosmological constant at 5.7 sigmas.

astro-ph.CO↗

arXiv2014

Discovery of Four Doubly Imaged Quasar Lenses from the Sloan Digital Sky Survey

We report the discovery of four doubly imaged quasar lenses. All the four systems are selected as lensed quasar candidates from the Sloan Digital Sky Survey data. We confirm their lensing hypothesis with additional imaging and spectroscopic follow-up observations. The discovered lenses are SDSS J0743+2457 with the source redshift z_s=2.165, the lens redshift z_l=0.381, and the image separation theta=1.034", SDSS J1128+2402 with z_s=1.608 and theta=0.844", SDSS J1405+0959 with z_s=1.810, z_l~0.66, and theta=1.978", and SDSS J1515+1511 with z_s=2.054, z_l=0.742, and theta=1.989". It is difficult to estimate the lens redshift of SDSS J1128+2402 from the current data. Two of the four systems (SDSS J1405+0959 and SDSS J1515+1511) are included in our final statistical lens sample to derive constraints on dark energy and the evolution of massive galaxies.

astro-ph.CO↗

arXiv2013

Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors -- II. Type II-P and II-L supernovae

Thirteen explosion sites of type II-P and II-L supernovae in nearby galaxies have been observed using integral field spectroscopy, enabling both spatial and spectral study of the explosion sites. We used the properties of the parent stellar population of the coeval supernova progenitor star to derive its metallicity and initial mass (c.f. Paper I). The spectrum of the parent stellar population yields the estimates of metallicity via strong-line method, and age via comparison with simple stellar population (SSP) models. These metallicity and age parameters are adopted for the progenitor star. Age, or lifetime of the star, was used to derive initial (ZAMS) mass of the star by comparing with stellar evolution models. With this technique, we were able to determine metallicity and initial mass of the SN progenitors in our sample. Our result indicates that some type-II supernova progenitors may have been stars with mass comparable to SN Ib/c progenitors.

astro-ph.CO↗

arXiv2013

Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors - I. Type Ib and Ic supernovae

Integral field spectroscopy of 11 type-Ib/c supernova explosion sites in nearby galaxies has been obtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us to obtain both spatial and spectral information of the explosion site, allowing the identification of the parent stellar population of the supernova progenitor star. The spectrum of the parent population provides metallicity determination via strong-line method and age estimation obtained via comparison with simple stellar population (SSP) models. We adopt this information as the metallicity and age of the supernova progenitor, under the assumption that it was coeval with the parent stellar population. The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass. With this method we were able to determine both the metallicity and initial (ZAMS) mass of the progenitor stars of the type Ib and Ic supernovae. We found that on average SN Ic explosion sites are more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent stellar population age suggests that SN Ic have more massive progenitors than SN Ib. In addition, we also found indication that some of our SN progenitors are less massive than ~25 Msun, indicating that they may have been stars in a close binary system that have lost their outer envelope via binary interactions to produce Ib/c supernovae, instead of single Wolf-Rayet stars. These findings support the current suggestions that both binary and single progenitor channels are in effect in producing type Ib/c supernovae. This work also demonstrates the power of integral field spectroscopy in investigating supernova environments and active star forming regions.

astro-ph.CO↗

arXiv2013

Dense optical and near-infrared monitoring of CTA 102 during high state in 2012 with OISTER: Detection of intra-night "orphan polarized flux flare"

CTA 102, classified as a flat spectrum radio quasar at z=1.037, produced exceptionally bright optical flare in 2012 September. Following Fermi-LAT detection of enhanced gamma-ray activity, we densely monitored this source in the optical and near-infrared bands for the subsequent ten nights using twelve telescopes in Japan and South-Africa. On MJD 56197 (2012 September 27, 4-5 days after the peak of bright gamma-ray flare), polarized flux showed a transient increase, while total flux and polarization angle remained almost constant during the "orphan polarized-flux flare". We also detected an intra-night and prominent flare on MJD 56202. The total and polarized fluxes showed quite similar temporal variations, but PA again remained constant during the flare. Interestingly, the polarization angles during the two flares were significantly different from the jet direction. Emergence of a new emission component with high polarization degree (PD) up to 40% would be responsible for the observed two flares, and such a high PD indicates a presence of highly ordered magnetic field at the emission site. We discuss that the well-ordered magnetic field and even the observed directions of polarization angle which is grossly perpendicular to the jet are reasonably accounted for by transverse shock(s) propagating down the jet.

astro-ph.HE↗

arXiv2012

Unusual Long and Luminous Optical Transient in the Subaru Deep Field

We present observations of SDF-05M05, an unusual optical transient discovered in the Subaru Deep Field (SDF). The duration of the transient is > ~800 d in the observer frame, and the maximum brightness during observation reached approximately 23 mag in the i' and z' bands. The faint host galaxy is clearly identified in all 5 optical bands of the deep SDF images. The photometric redshift of the host yields z~0.6 and the corresponding absolute magnitude at maximum is ~-20. This implies that this event shone with an absolute magnitude brighter than -19 mag for approximately 300 d in the rest frame, which is significantly longer than a typical supernova and ultra-luminous supernova. The total radiated energy during our observation was 1x10^51 erg. The light curves and color evolution are marginally consistent with some of luminous IIn supernova. We suggest that the transient may be a unique and peculiar supernova at intermediate redshift.

astro-ph.CO↗