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Urata, Yuji,Huang, Kuiyun,Im, Myungshin,Lee, Induk,Deng, Jinsong,Ip, WingHuen,Krimm, Hans,Liping, Xin,Ohno, Masanori,Qiu, Yulei,Sugita, Satoshi,Tashiro, Makoto,Wei, Jianyan,Yamaoka, Kazutaka,Zheng, We IOP Publishing 2009 ASTROPHYSICAL JOURNAL LETTERS - Vol.706 No.1
<P>We present multi-band results for GRB071010B based on Swift, Suzaku, and ground-based optical observations. This burst is an ideal target to evaluate the robustness of the E-peak(src) - E-iso and E-peak(src) - E-gamma relations, whose studies have been in stagnation due to the lack of the combined estimation of E-peak(src) and long-term optical monitoring. The joint prompt spectral fitting using Swift/Burst Alert Telescope and Suzaku/Wide-band All-sky Monitor data yielded the spectral peak energy as E-peak(src) of 86.5(-6.3)(+6.4) keV and E-iso of 2.25(-0.16)(+0.19) x 10(52) erg with z = 0.947. The optical afterglow light curve is well fitted by a simple power law with temporal index alpha = -0.60 +/- 0.02. The lower limit of temporal break in the optical light curve is 9.8 days. Our multi-wavelength analysis reveals that GRB071010B follows E-peak(src) - E-iso but violates the E-peak(src) - E-gamma and E-iso - E-peak(src) - t(jet)(src) at more than the 3 sigma level.</P>
SYNCHROTRON SELF-INVERSE COMPTON RADIATION FROM REVERSE SHOCK ON GRB 120326A
Urata, Yuji,Huang, Kuiyun,Takahashi, Satoko,Im, Myungshin,Yamaoka, Kazutaka,Tashiro, Makoto,Kim, Jae-Woo,Jang, Minsung,Pak, Soojong IOP Publishing 2014 The Astrophysical journal Vol.789 No.2
<P>We present multi-wavelength observations of a typical long duration GRB 120326A at z = 1.798, including rapid observations using a Submillimeter Array (SMA) and a comprehensive monitoring in the X-ray and optical. The SMA observation provided the fastest detection to date among seven submillimeter afterglows at 230 GHz. The prompt spectral analysis, using Swift and Suzaku, yielded a spectral peak energy of E-peak(src) = 107.8(- 15.3)(+15.3) keV and an equivalent isotropic energy of E-iso as 3.18(-0.32)(+0.40) x 10(52) erg. The temporal evolution and spectral properties in the optical were consistent with the standard forward shock synchrotron with jet collimation (6 degrees.69 +/- 0 degrees.16). The forward shock modeling, using a two-dimensional relativistic hydrodynamic jet simulation, was also determined by the reasonable burst explosion and the synchrotron radiation parameters for the optical afterglow. The X-ray light curve showed no apparent jet break and the temporal decay index relation between the X-ray and optical (alpha o - alpha x = -1.45 +/- 0.10) indicated different radiation processes in each of them. Introducing synchrotron self-inverse Compton radiation from reverse shock is a possible solution, and the detection and slow decay of the afterglow in submillimeter supports that this is a plausible idea. The observed temporal evolution and spectral properties, as well as forward shock modeling parameters, enabled us to determine reasonable functions to describe the afterglow properties. Because half of the events share similar properties in the X- ray and optical as the current event, GRB 120326A will be a benchmark with further rapid follow-ups, using submillimeter instruments such as an SMA and the Atacama Large Millimeter/submillimeter Array.</P>
Constrain the SED Type of Unidentified Fermi Objects
Tsai, An-Li,Urata, Yuji,Takahashi, Satoko,Chuang, Chia-Jung 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.3
2FGL J1823.8+4312 and 2FGL J1304.1-2415 are two unidentified Fermi objects which are associated with cluster of galaxies. In order to exam the possibility of cluster of galaxies as gamma-ray emitters, we search for counterpart of these two unidentified Fermi objects in other wavebands. However, we find other candidate to be more likely the counterpart of the unidentified Fermi object for both sources. We compare their light curves and SEDs in order to identify their source types. However, data at millimeter and sub-millimeter wavebands, which is important for us to constrain the SED at synchrotron peak, is lacking of measurement. Therefore, we proposed to SMA observation for these two sources. We have got data and are doing further analysis.
Constrain the SED Type of Unidentified Fermi Objects
An-Li Tsai,Yuji Urata,Satoko Takahashi,Chia-Jung Chuang 한국우주과학회 2013 Journal of Astronomy and Space Sciences Vol.30 No.3
2FGL J1823.8+4312 and 2FGL J1304.1-2415 are two unidentified Fermi objects which are associated with cluster of galaxies. In order to exam the possibility of cluster of galaxies as gamma-ray emitters, we search for counterpart of these two unidentified Fermi objects in other wavebands. However, we find other candidate to be more likely the counterpart of the unidentified Fermi object for both sources. We compare their light curves and SEDs in order to identify their source types. However, data at millimeter and sub-millimeter wavebands, which is important for us to constrain the SED at synchrotron peak, is lacking of measurement. Therefore, we proposed to SMA observation for these two sources. We have got data and are doing further analysis.
Lee, In-Duk,Im, Myung-Shin,Urata, Yuji The Korean Astronomical Society 2010 Journal of The Korean Astronomical Society Vol.43 No.3
We outline our GRB afterglow observation program using the 1-m telescope at Mt. Lemmon Optical Astronomy Observatory (LOAO), and report the first observations of the GRB afterglows. During the 2007B semester, we performed follow-up imaging obsrevations of 6 GRBs, and succeeded in detecting four GRB afterglows (GRB 071010B, GRB 071018, GRB 071020, and GRB 071025) while placing useful upper limits on the light curves of the other GRBs. Among the observed events, we find that three events are special and interesting. GRB 071010B has a light curve which has an unusually long jet break time of 11.8 days. For GRB 071025, its red R-I(~2) color suggests that it is likely to be at z~5. GRB 071020 has a light curve which shows a clear brightening at 0.3-1 days after the burst, where our LOAO data play a crucial role by providing an unambiguous evidence for the brightening. These are the first successful detections of GRB afterglows by a facility owned and operated by a Korean institution, demonstrating the usefulness of the 1-m telescope for transient phenomena such as GRBs up to very high redshift.
Yoon, Yongmin,Im, Myungshin,Jeon, Yiseul,Lee, Seong-Kook,Choi, Philip,Gehrels, Neil,Pak, Soojong,Sakamoto, Takanori,Urata, Yuji IOP Publishing 2015 The Astrophysical journal Vol.808 No.1
<P>We study the host galaxy properties of the tidal disruption object Swift J164449.3+573451 using long-term optical to near-infrared (NIR) data. First, we decompose the galaxy surface brightness distribution and analyze the morphology of the host galaxy using high-resolution Hubble Space Telescope WFC3 images. We conclude that the host galaxy is bulge-dominant and well described by a single Sersic model with Sersic index n = 3.43 +/- 0.05. Adding a disk component, the bulge to total host galaxy flux ratio (B/T) is 0.83 +/- 0.03, which still indicates a bulge-dominant galaxy. Second, we estimate multi-band fluxes of the host galaxy through long-term light curves. Our long-term NIR light curves reveal the pure host galaxy fluxes similar to 500 days after the burst. We fit spectral energy distribution models to the multi-band fluxes from the optical to NIR of the host galaxy and determine its properties. The stellar mass, the star formation rate, and the age of the stellar population are log(M-*/M-circle dot) 9.14(-0.10)(+0.13) , 0.03(-0.03)(+0.28) M-circle dot yr(-1),and 0.63(-0.43)(+0.95) Gyr. Finally, we estimate the mass of the central super massive black hole which is responsible for the tidal disruption event. The black hole mass is estimated to be 10(6.7 +/- 0.4) M-circle dot from M-BH-M-*,M-bul and M-BH-L-bul relations for the K band, although a smaller value of similar to 10(5) M-circle dot cannot be excluded convincingly if the host galaxy harbors a pseudobulge.</P>
Probing the nature of high‐<i>z</i> short GRB 090426 with its early optical and X‐ray afterglows
Xin, Li‐,Ping,Liang, En‐,Wei,Wei, Jian‐,Yan,Zhang, Bing,Lv, Hou‐,Jun,Zheng, Wei‐,Kang,Urata, Yuji,Im, Myungshin,Wang, Jing,Qiu, Yu‐,Lei,Deng, Jin‐,Song,Huang, Blackwell Publishing Ltd 2011 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.410 No.1
<P><B>ABSTRACT</B></P><P>GRB 090426 is a short‐duration burst detected by <I>Swift</I> (<IMG src='/wiley-blackwell_img/equation/MNR_17419_mu1.gif' alt ='inline image'/> s in the observer frame and <IMG src='/wiley-blackwell_img/equation/MNR_17419_mu2.gif' alt ='inline image'/> s in the burst frame at <I>z</I>= 2.609). Its host galaxy properties and some gamma‐ray‐related correlations are analogous to those seen in long‐duration gamma‐ray bursts (GRBs), which are believed to be of a massive star origin (so‐called Type II GRBs). We present the results of its early optical observations with the 0.8‐m Tsinghua University–National Astronomical Observatory of China Telescope (TNT) at Xinglong Observatory and the 1‐m LOAO telescope at Mt Lemmon Optical Astronomy Observatory in Arizona. Our well‐sampled optical afterglow light curve covers from <IMG src='/wiley-blackwell_img/equation/MNR_17419_mu3.gif' alt ='inline image'/> to 10<SUP>4</SUP> s after the GRB trigger. It shows two shallow decay episodes that are likely due to energy injection, which end at <IMG src='/wiley-blackwell_img/equation/MNR_17419_mu4.gif' alt ='inline image'/> and 7100 s, respectively. The decay slopes after the injection phases are consistent with each other (<IMG src='/wiley-blackwell_img/equation/MNR_17419_mu5.gif' alt ='inline image'/>). The X‐ray afterglow light curve appears to trace the optical, although the second energy‐injection phase was missed due to visibility constraints introduced by the <I>Swift</I> orbit. The X‐ray spectral index is <IMG src='/wiley-blackwell_img/equation/MNR_17419_mu6.gif' alt ='inline image'/> without temporal evolution. Its decay slope is consistent with the prediction of the forward shock model. Both X‐ray and optical emission are consistent with being in the same spectral regime above the cooling frequency (<IMG src='/wiley-blackwell_img/equation/MNR_17419_mu7.gif' alt ='inline image'/>). The fact that <IMG src='/wiley-blackwell_img/equation/MNR_17419_mu8.gif' alt ='inline image'/> is below the optical band from the very early epoch of the observation provides a constraint on the burst environment, which is similar to that seen in classical long‐duration GRBs. We therefore suggest that death of a massive star is the possible progenitor of this short burst.</P>