The Lulin GRB program, using the Lulin One-meter Telescope (LOT) in Taiwan
started in July 2003. Its scientific aims are to discover optical counterparts
of XRFs and short and long GRBs, then to quickly observe them in multiple
bands. Thirteen follow-up observations were provided by LOT between July 2003
and Feb. 2005. One host galaxy was found at GRB 031203. Two optical afterglows
were detected for GRB 040924 and GRB 041006. In addition, the optical
observations of GRB 031203 and a discussion of the non-detection of the optical
afterglow of GRB 031203 are also reported in this article.Comment: 5 pages, 2 figure. Accepted for publication into "il nuovo cimento".
  Proceeding of the 4th Rome GRB conference, eds. L. Piro, L. Amati, S. Covino,
  B. Gendr

Huang, K. Y.

Ip, W. H.

Makishima, K.

Onda, K.

Tamagawa, T.

Urata, Y.

English

arXiv

The Lulin GRB program, using the Lulin One-meter Telescope

(LOT) in Taiwan started in July 2003. Its scientific aims are to discover optical counterparts of XRFs and short and long GRBs, then to quickly observe them in multiple bands. Thirteen follow-up observations were provided by LOT between

July 2003 and Feb. 2005. One host galaxy was found at GRB 031203. Two optical afterglows were detected for GRB 040924 and GRB 041006. In addition, the optical observations of GRB 031203 and a discussion of the non-detection of the optical afterglow of GRB 031203 are also reported in this article

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DOI 10.1393/ncc/i2005-10072-xIL NUOVO CIMENTO Vol. 28 C, N. 4-5 Luglio-Ottobre 2005GRBs Optical follow-up observation at Lulin observatory,Taiwan(∗)K. Y. Huang(1), Y. Urata(2)(3), W. H. Ip(1), T. Tamagawa(2), K. Onda(2)and K. Makishima(2)(4)(1) Institute of Astronomy, National Central UniversityChung-Li 32054, Taiwan, Republic of China(2) RIKEN (Institute of Physical and Chemical Research)2-1 Hirosawa, Wako, Saitama 351-0198, Japan(3) Department of Physics, Tokyo Institute of Technology2-12-1 Oookayama, Meguro-ku, Tokyo 152-8551, Japan(4) Department of Physics, University of Tokyo7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan(ricevuto il 23 Maggio 2005; pubblicato online il 20 Ottobre 2005)Summary. — The Lulin GRB program, using the Lulin One-meter Telescope(LOT) in Taiwan started in July 2003. Its scientific aims are to discover opticalcounterparts of XRFs and short and long GRBs, then to quickly observe them inmultiple bands. Thirteen follow-up observations were provided by LOT betweenJuly 2003 and Feb. 2005. One host galaxy was found at GRB 031203. Two opticalafterglows were detected for GRB 040924 and GRB 041006. In addition, the opticalobservations of GRB 031203 and a discussion of the non-detection of the opticalafterglow of GRB 031203 are also reported in this article.PACS 95.55.Cs – Ground-based ultraviolet, optical and infrared telescopes.PACS 98.70.Rz – γ-ray sources; γ-ray bursts.PACS 01.30.Cc – Conference proceedings.1. – IntroductionA parallel effort based on the Kiso GRB optical observation system [1,2], was startedin July 2003 using the Lulin One-meter Telescope (LOT) at Taiwan. The scientificaims of our Lulin GRB program are: 1) to discover optical counterparts of XRFs, andshort- and long-duration GRBs; 2) to perform multi-band observations that will unlockthe temporal and spectral evolution of the corresponding optical afterglows. The Lulinobservatory is located in Nantou County, Taiwan, at 120◦52′25′′E, 23◦28′07′′N , on a2862-m high peak. The sky background levels in the UBV RI bands are: U = 21.8;B = 22.0; V = 21.3; R = 20.9; I = 19.5 mag arcsec−2, respectively. From statistical(∗) Paper presented at the “4th Workshop on Gamma-Ray Burst in the Afterglow Era”, Rome,October 18-22, 2004.c© Societa` Italiana di Fisica 731732 K. Y. HUANG, Y. URATA, W. H. IP, T. TAMAGAWA ETC.Table I. – Basic characteristics of LOT with PI1300B and AP8 CCDFilter PI1300B CCD AP8 CCDZero pointa Color term Extinction Zero point Color term ExtinctionB 22.34±0.02 0.199±0.018 0.19±0.02 21.99±0.03 0.035±0.005 0.28±0.02V 22.68±0.02 −0.058±0.017 0.11±0.01 21.97±0.02 0.069±0.004 0.20±0.02R 22.66±0.01 −0.049±0.021 0.09±0.01 21.87±0.02 0.113±0.007 0.15±0.02I 21.99±0.04 0.040±0.029 0.06±0.01 21.27±0.03 0.043±0.005 0.12±0.02aUnits: Zero point (mag), Color term (mag), Extinction (mag/airmass)measurements at Lulin site, it was found that the typical accumulative observation timeis 1700 hours per year and the typical seeing is 1.5 arcsec. The LOT is a Cassegraintelescope (f/8) with an ACE filter system and a main CCD camera— PI1300B (1340 ×1300, F.O.V.∼ 11.5′ × 11.2′) as well as a spare CCD camera—Ap8 (1k × 1k, F.O.V. ∼10.6′× 10.6′). Table I shows the characteristics of LOT with AP8 and PI1300B CCD [3].Due to the fact that there are only a very few telescopes for GRB follow-up observa-tions in East Asia, and that the observational range can reach up to Dec. −40 degree,Lulin enjoys a unique position for GRB study. The fast PI1300B read out time thatallows small cadence multi-band time series photometry is another distinct advantage.Due to the nature of GRBs detection, the Lulin GRB project is included as a part of theTarget of Opportunity (TOO) program. We have developed two approaches to search forGRB optical afterglows, according to the dimensions of the burst error box provided bysuch satellites as HETE-2, INTEGRAL, and SWIFT. First, if the error range is largerthan the FOV of the LOT, we can dither the field and search for the optical counterpartin the B or R band. Second, if the error range is smaller than the FOV, we can quicklylocate the counterpart and monitor the temporal variation of the brightness of the opticalafterglow in several wavelengths.During the analysis procedure, the positions and coordinates of the detected objects inour images are compared with the USNO stellar coordinates. These physical coordinatesare then transformed to equatorial coordinates using the WCS (World Coordinate Sys-tem). After this, our images compared with DSS2 images, to look for likely candidates.2. – Summary of observed eventsBetween July 2003 and Feb. 2005 (table II), thirteen follow-up observations wereprovided by LOT. We could provide upper limits to the magnitude for ten events. Twooptical afterglows were detected for GRB 040924 and GRB 041006 and the host galaxyof GRB 031203 was identified. We will focus on the GRB 031203 case in the following.GRB 031203 was detected by the IBIS instrument on INTEGRAL on December 3,2003 at 22:01:28 UT as a single peaked burst with a duration of 30s [4]. Newton-XMMdetected two sources named S1 and S2 within the INTEGRAL error circle. The brightestsource S1, which faded throughout the observation period, was interpreted to be theafterglow [5]. Its position coincided with that of a fading radio source [6].A new source was detected by Lulin I-band observations [7]; see fig. 1. Bloom et al. [8]have pointed out that this new source could either be a galaxy in the foreground or theGRBS OPTICAL FOLLOW-UP OBSERVATION AT LULIN OBSERVATORY, TAIWAN 733Table II. – Log of Lulin GRB follow-up observations.GRB Delay time Triggered Limit mag. Results Publications(hr) Spacecraft (3σ)GRB 030823 3.3 HETE-2 R ∼ 19 Upper limit GCN 2360GRB 031026 6.0 HETE-2 R ∼ 21 Upper limit GCN 2436GRB 031203 19.6 INTEGRAL I ∼ 20 Host Galaxy GCN 2470GRB 031220 8.0 HETE-2 R ∼ 20 Upper limit GCN 2494GRB 040422 9.6 INTEGRAL R ∼ 20 Upper limit GCN 2577GRB 040916 16.3 HETE-2 I ∼ 20 Upper limit GCN 2721GRB 040924 2.3 HETE-2 − OT GCN 2744GRB 041006 9.0 HETE-2 − OT GCN 2785GRB 041211 3.4 HETE-2 R ∼ 20 Upper limit GCN 2840GRB 041219 9.6 SWIFT R ∼ 21 Upper limit GCN 2891GRB 050123 5.5 HETE-2 I ∼ 19 Upper limit GCN 2971GRB 050124 4.4 SWIFT R ∼ 20 Upper limit GCN 2976GRB 050215B 13.1 SWIFT V ∼ 19 Upper limit GCN 3030I ∼ 20 Upper limit GCN 3030host of GRB 031203. A radio afterglow was detected at the same position. From spectro-scopic observations, Prochaska et al. [9] found this to be an active star-forming galaxy,with z = 0.105 and that should be the host galaxy of GRB 031203, designated HG 031203.The LOT follow-up observations in combination with other I-band data [10-12], indi-cated that the source did not show variability in terms of its brightness (fig. 2). Thus, theoptical source detected was the host galaxy, HG 031203, and no variable source brighterthan I = 20.0 was found during our observations. The astrometry of the GRB 031203field was corrected by matching with stars in the USNO A2 catalog. This resulted inthe following astrometric position of HG 031203: R.A. = 08h02m30s.177 ± 0.175 arcsec,Dec. = −39◦51′03′′.960 ± 0.164 arcsec (J2000.0). It is important to note that opticaland spectroscopic observations made by several groups have revealed that SN 2003lwwas associated with GRB 031203. It had a brightness peak between 26 and 34 days afterthe gamma-ray burst [10-13].In order to explore the reason behind the absence of optical afterglow, we have an-alyzed the X-ray Newton-XMM afterglow data. Using the power law plus absorptionmodel, we found that the best fit of the photon index is 1.8 ± 0.1 (χ2 = 14.07 with22 dof) with NH = 7.73 ± 0.04 × 1021 cm−2 for the energy between 0.6 keV to 10 keV.Our results are consistent with those found by Watson et al. [14]. Assuming no breakin the lightcurve, the spectral flux distribution follows Fν ∝ ν−β(β = 0.8± 0.1) and theFig. 1. – LOT I-band image of XMM -Source: S1 and S2. By comparing this with the DSSI-band image, we found a source near S1.734 K. Y. HUANG, Y. URATA, W. H. IP, T. TAMAGAWA ETC.Fig. 2. – Lightcurve of HG 031203 at the I-band. The solid line shows the magnitude of thehost galaxy (I = 19.21).extrapolation of the X-ray flux to the optical range yields I = 20.65 and R = 21.13, at0.26 days after the burst.In comparison with the value of NH = 7.73 ± 0.04 × 1021 cm−2, the neutral hydro-gen column density along the line-of-sight to GRB 031203, is on the order of NH =6.21× 1021 cm−2 within the Galaxy [15]. This means that most of the extinction of theoptical emission of this gamma-ray burst should have come from the Galactic interstellarmedium. This effect alone is enough to reduce the optical brightness by 2 magnitudesfrom 20.65 to about 22.65 at the I-band [15]. This might explain why GRB 031203 showsno optical afterglow.∗ ∗ ∗We thank all those of Lulin users for helping with the GRB follow-up observations.This work is supported by NSC 93-2752-M-008-001-PAE and NSC 93-2112-M-008-006.K. Y. Huang acknowledges support from from Foundation For the Advancement ofOutstanding Scholarship.REFERENCES[1] Urata, Y. et al., these proceedings (2005).[2] Urata, Y. et al., A.S.P Con. Ser., Vol. 312 (2004) 243.[3] Kinosuita, D. et al., in press (2005).[4] Sazonov, S. Y. et al., Nature, 430 (2004) 646.[5] Vaughan, S. et al., ApJ, 603 (2004) L5.[6] Soderberg, A. M. et al., Nature, 430 (2004) 648.[7] Hsia, C. H. et al., GCN Circ., (2003) 2470.[8] Bloom, J. S. et al., GCN Circ., (2003) 2481.[9] Prochaska, J. X. et al., ApJ, 611 (2004) 200.[10] Thomsen, B. et al., A&A, 419 (2004) L21.[11] Cobb, B. E. et al., ApJ, 608 (2004) L93.[12] Malesani, D. et al., ApJ, 609 (2004) L5.[13] Gal-Yam, A. et al., ApJ, 609 (2004) L59.[14] Watson, D. et al., ApJ, 605 (2004) L101.[15] Dickey, J. M. and Lockman, F. J. , Annu. Rev. Astron. Astrophys., 28 (1990) 215.

GRBs Optical follow-up observation at Lulin observatory, Taiwan

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