T90histogram.eps Acta Polytechnica Vol. 52 No. 1/2012 BOOTES Observation of GRB080603B M. Jeĺınek, J. Gorosabel, A. J. Castro-Tirado, A. de Ugarte Postigo, S. Guziy, R. Cunniffe, P. Kubánek, M. Prouza, S. V́ıtek, R. Hudec, V. Reglero, L. Sabau-Graziati Abstract We report on multicolor photometry of long GRB080603B afterglow from BOOTES-1B and BOOTES-2. The optical afterglow has already been reported to present a break in the optical lightcurve at 0.12 ± 0.2 days after the trigger. We construct the lightcurve and the spectral energy distribution and discuss the nature of the afterglow. Keywords: gamma-ray bursts, individual, GRB080603B. 1 Introduction GRB 080603B was a long gamma-ray burst detected on June 3, 2008, at 19:38:13 UT by Swift-BAT [14]. The burst was also detected by Konus-WIND [5] and INTEGRAL-SPI/ACS [18]. In X-rays, the afterglow was detected by Swift- XRT, providing a rapid and precise localization [13]. The optical afterglow was observed by several telescopes – ROTSE III [19], TAROT [9–11], TLS Tautenburg [8], RTT150 [24], the Liverpool Tele- scope [15], Xinglong EST [23], the 1.0 m telescope at CrAO [21, 20], the 1.5 m telescope of Sayan obser- vatory [12] and from Maidanak [6]. In infrared by PAIRITEL [16], spectroscopy was obtained by the NOT [4] and the Hobby-Eberly Telescope [2], pro- viding a redshift of z = 2.69. An upper limit on radio emission was set by the VLA [1]. 2 Observations At both BOOTES stations, the GRB happened dur- ing twilight, delaying follow-up by ∼ 1 h. Despite the delay, the optical afterglow is well detected in the data from both telescopes. The 60 cm telescope BOOTES-2/TELMA, in La Mayora, Málaga, Spain, started taking data at 20:29:19 UT, i.e. 51 minutes after the GRB trigger. A sequence of r′-band exposures was taken, and later, after confirming the detection of the optical transient, i′, g′ and Y band images were obtained. In the near infrared Y band, despite 600 s of integration, the af- terglow was not detected. The 30 cm telescope BOOTES-1B, located in El Arenosillo, Huelva, Spain, [7] obtained 368 unfiltered images totalling more than 6 hours of integrated light until the end of the night. The images were combined to improve signal-to-noise, to yield 11 data points for the period between 1.2 and 5.2 hours after the GRB. One point has a large error due to clouds crossing the field of view. The best fit astrometric position of the afterglow, obtained from the weighted average of all available images from BOOTES-2 is α = 11 : 46 : 07.73 δ = +68 : 03 : 39.9 (J2000), about 1.6◦ SE from star λ Dra. Photometry was done in the optimal aperture using IRAF/Daophot. Calibration was performed against three SDSS (DR8) [3] stars. The stars are marked on the identification chart (Figure 3) and their brightnesses are in the Table 1. Our unfiltered, “Clear”, best fit magnitude Clear=A1 ∗ g ′ + A2 ∗ r ′ used for BOOTES-1B calibration is also mentioned. For the summary of our observations, see Table 2. Table 1: Calibration stars used ID. g′ r′ i′ Clear 1 18.00 17.50 17.32 17.52 2 18.80 17.35 16.04 17.35 3 19.88 18.42 17.09 18.47 3 Fitting the lightcurve The lightcurve, as already shown by [24] shows a smooth transition between two decay slopes α1 = −0.55 ± 0.16 and α2 = −1.23 ± 0.22. The break oc- curs at tb = 0.129 ± 0.016 days. There is no hint of chromatic evolution within the lightcurve, so all filters were scaled and fitted to- gether with the r′-band. The fitting of the lightcurve was performed in log t/ log f space, where power law functions, typical for gamma-ray bursts, show as straight lines. We used a hyperbolic transition be- tween two slopes (smoothly broken power-law): 34 Acta Polytechnica Vol. 52 No. 1/2012 Table 2: Optical photometric observations of the optical afterglow of the GRB080603B UT Date of mid exp. T − T0 [h] tel. filter Texp [s] mag δ mag Jun 3.855805 0.902 B-2 r′ 3 × 120 s 17.46 0.07 Jun 3.859348 0.987 B-2 r′ 2 × 120 s 17.59 0.13 Jun 3.862188 1.056 B-2 r′ 2 × 120 s 17.31 0.05 Jun 3.864311 1.107 B-2 r′ 120 s 17.57 0.08 Jun 3.865747 1.141 B-2 r′ 120 s 17.30 0.07 Jun 3.867151 1.175 B-2 r′ 120 s 17.46 0.06 Jun 3.868946 1.218 B-1B Clear 10 × 60 s 17.53 0.07 Jun 3.870011 1.243 B-2 g′ 3 × 120 s 18.29 0.04 Jun 3.874248 1.345 B-2 g′ 3 × 120 s 18.24 0.04 Jun 3.876758 1.405 B-1B Clear 10 × 60 s 17.54 0.06 Jun 3.879225 1.465 B-2 g′ 4 × 120 s 18.14 0.03 Jun 3.884248 1.585 B-2 r′ 3 × 120 s 17.50 0.09 Jun 3.884664 1.595 B-1B Clear 10 × 60 s 17.70 0.06 Jun 3.889912 1.721 B-2 r′ 3 × 120 s 17.70 0.15 Jun 3.892654 1.787 B-1B Clear 10 × 60 s 17.75 0.06 Jun 3.893455 1.806 B-2 r′ 4 × 120 s 17.74 0.06 Jun 3.899839 1.959 B-2 g′ 5 × 120 s 18.42 0.19 Jun 3.900620 1.978 B-1B Clear 10 × 60 s 17.79 0.06 Jun 3.906961 2.130 B-2 g′ 5 × 120 s 18.42 0.04 Jun 3.908509 2.167 B-1B Clear 10 × 60 s 17.87 0.09 Jun 3.914867 2.320 B-2 r′ 4 × 120 s 18.15 0.13 Jun 3.916482 2.359 B-1B Clear 10 × 60 s 17.91 0.11 Jun 3.922694 2.508 B-2 i′ 5 × 120 s 17.89 0.05 Jun 3.931774 2.726 B-2 r′ 7 × 120 s 18.01 0.06 Jun 3.934988 2.803 B-1B Clear 35 × 60 s 18.30 0.32 Jun 3.940845 2.943 B-2 i′ 5 × 120 s 17.88 0.07 Jun 3.947882 3.112 B-2 r′ 5 × 120 s 18.12 0.08 Jun 3.956941 3.330 B-1B Clear 20 × 60 s 18.45 0.07 Jun 3.971736 3.685 B-1B Clear 21 × 60 s 18.38 0.06 Jun 3.977109 3.814 B-2 r′ 5 × 120 s 18.26 0.18 Jun 4.006997 4.531 B-1B Clear 78 × 60 s 18.79 0.07 h(a, b) = a + b 2 √ 1 + a2 b2 m(t) = m0−2.5α2 log t tb +h(−2.5(α1−α2) log t tb , G) where α1 and α2 are pre-break and post-break de- cay indices, tb is the break time, m0 is an absolute scaling parameter of the brightness and G expresses smoothness of the break. Although the early point by ROTSE [19] was not used, it agrees with the backward extrapolation of the α1 slope and so supports this simple interpretation. We constructed a spectral energy distribution (SED) by fitting the needed magnitude shift of the R-band lightcurve model to the photometric points from BOOTES, UVOT [14] and PAIRI- TEL [16] obtained in other filters. While the points from UVOT are practically contemporane- ous to BOOTES, PAIRITEL observed rather later (0.32 days after the trigger), so the SED is therefore model-dependent in its infrared part. The synthetic AB magnitudes equivalent to t = 0.1 days are in Ta- ble 3. 35 Acta Polytechnica Vol. 52 No. 1/2012 16 16.5 17 17.5 18 18.5 19 19.5 20 40m 1h 2h 4h 8h 50 uJy 0.1 mJy 0.2 mJy 0.5 mJy 1 mJy A B m a g n it u d e fl u x d e n si ty time post trigger r’ gcn r-band g’+1 i’-1 C Fig. 1: Detail of the optical light curve of GRB080603B showing the observations by BOOTES (filled symbols) and from the literature (empty symbols) 14 15 16 17 18 19 20 21 10s 30s 1m 2m 5m 10m 30m 1h 2h 4h 8h 1d 2d 10 uJy 20 uJy 50 uJy 0.1 mJy 0.2 mJy 0.5 mJy 1 mJy 2 mJy 5 mJy 10 mJy A B m a g n it u d e fl u x d e n si ty time post trigger r’ gcn r-band g’ i’ C Fig. 2: Overall view of the light curve of GRB080603B Fig. 3: The finding chart of the afterglow of GRB080603B. Combination of images taken by BOOTES-2 17 18 19 20 21 200 300 500 1000 2000 10 100 1000 A B m a g n it u d e fl u x d e n si ty [ u Jy ] wavelength [nm] Fig. 4: The spectral energy distribution of the afterglow in rest frame. The small arrow marks Ly-α position for z =2.69 Table 3: The spectral energy distribution in AB magni- tudes equivalent to 0.1days after the trigger. († UVOT, ‡ PAIRITEL) Filter mAB ∆mAB W† 20.98 0.56 U† 19.83 0.23 B† 19.22 0.14 g′ 18.57 0.07 r′ 17.88 0.05 i′ 17.81 0.09 J‡ 17.44 0.10 H‡ 17.19 0.10 K‡ 17.22 0.10 The SED shows a clear suppression of radiation above 4 500 Å, i.e. a redshifted Ly-α line. No radia- tion is detected above the Lyman break at 3 365 Å. A rather shallow power law with an index β = −0.53 ± 0.06 was found redwards from r′ band. The fit was performed using the E(B − V ) = 0.013 mag [22]. The strong suppression of light for wavelengths shorter than r′ band is likely due to the Ly-α ab- sorption within the host galaxy and Ly-alpha line blanketing for z = 2.69. 4 Discussion The values of α2 = −1.23±0.22 and β = −0.53±0.06 both point to a common electron distribution pa- rameter p = 2.05 ± 0.20 (α = (3 ∗ p − 1)/4, β = (p− 1)/2) [17]. Such a combination suggests a stellar wind profile expansion and a slow cooling regime. The pre-break decay rate α1 = −0.55 ± 0.16 re- mains unexplained by the standard fireball model. It is unlikely that the break at tb = 0.129 ± 0.016 would be a jet break. It is quite possible that the plateau is not really a straight power law, and that some late 36 Acta Polytechnica Vol. 52 No. 1/2012 activity of the inner engine may be producing bump- ing of hydrodynamic origin. We note that the literature contains a number of observations suggesting a rapid decay by about one day after the GRB. Without having all the images, it is, however, impossible to decide whether this is a real physical effect or a zero-point mismatch. 5 Conclusions The 0.6 m telescope BOOTES-2 in La Mayora ob- served the optical afterglow of GRB 080603B in three filters. The 0.3 m BOOTES-1B in El Arenosillo ob- served the same optical afterglow without a filter. Using the data we obtained at BOOTES and from the literature, we construct the lightcurve and broad- band spectral energy distribution. Our fit of the obained data privides the decay pa- rameters α2 = 1.23 ± 0.22 and β = −0.53 ± 0.06, which suggest a slow cooling expansion into a stellar wind. Acknowledgement We acknowledge the support of the Spanish Min- isterio de Ciencia y Tecnoloǵıa through Projects AYA2008-03467/ESP and AYA2009-14000-C03-01/ ESP, and Junta de Andalućıa through the Excel- lence Reseach Project P06-FQM-219, and the GAČR grants 205/08/1207 and 102/09/0997. We are also in- debted to T. Mateo-Sanguino (UHU), J. A. Adame, J. A. Andreu, B. de la Morena, J. Torres (INTA) and to R. Fernández-Munoz (EELM-CSIC), V. Munoz- Fernández and C. Pérez del Pulgar (UMA) for their support. References [1] Chandra, P., Frail, D. A.: GRB 080603B: PAIRITEL infrared detection. GCN Circular, 7827, 2008. [2] Cucchiara, A., Fox, D.: GRB 080603B: Hobby- Eberly Telescope redshift confirmation. GCN Circular, 7815, 2008. [3] Eisenstein, D. J., Weinberg, D. H., Agol, E., Ai- hara, H., Allende Prieto, C., Anderson, S. F., Arns, J. A., Aubourg, É., Bailey, S., Bal- binot, E., et al.: SDSS-III: Massive Spectro- scopic Surveys of the Distant Universe, the Milky Way, and Extra-Solar Planetary Systems. AJ, 142, 72, Sept. 2011. [4] Fynbo, J., Quirion, P.-O., Xu, D., Malesani, D., Thoene, C., Hjorth, J., Milvang-Jensen, B., Jakobson, P.: GRB 080603B: NOT redshift. GCN Circular, 7797, 2008. [5] Golenetskii, S., Aptekar, R., Mazets, E., Pal’shin, V., Frederiks, D., Cline, T.: Konus- Wind observation of GRB 080603B. GCN Cir- cular, 7812, 2008. [6] Ibrahimov, M., Karimov, P., Rumyantsev, A., Pozanenko, A.: GRB 080603B: optical observa- tions in MAO. GCN Circular, 7975, 2008. [7] Jeĺınek, M., Castro-Tirado, A. J., de Ugarte Postigo, A., Kubánek, P., Guziy, S., Goros- abel, J., Cunniffe, R. Vı́tek, S., Hudec, R., Reglero, V., Sabau-Graziati, L.: Four Years of Real-Time GRB Followup by BOOTES-1B (2005–2008). Advances in Astronomy, 2010, 432 172, 2010. [8] Kann, D., Laux, U., Ertel, S.: GRB 080603B: TLS Afterglow Observation. GCN Circular, 7823, 2008. [9] Klotz, A., Boer, M., Atteia, J.: GRB 080603B: TAROT Calern observatory detection of a plateau in the light curve. GCN Circular, 7795, 2008. [10] Klotz, A., Boer, M., Atteia, J.: GRB 080603B: TAROT Calern observatory confirmation of slow optical decay. GCN Circular, 7799, 2008. [11] Klotz, A., Boër, M., Atteia, J., Gendre, B.: Early Optical Observations of Gamma-Ray Bursts by the TAROT Telescopes: Period 2001–2008. The Astronomical Journal, 2009. [12] Klunko, E., Pozanenko, A.: GRB 080603B: op- tical observation. GCN Circular, 7890, 2008. [13] Mangano, V., La Parola, B., Sbarufatti, B.: GRB 080603B: Swift-XRT refined analysis. GCN Circular, 7806, 2008. [14] Mangano, V., Parsons, A., Sakamoto, T., La Parola, V., Kuin, N., Barthelmy, S., Bur- rows, D., Roming, P., Gehrels, N.: Swift Ob- servation of GRB 080603B. GCN Report, 144, 2008. [15] Melandri, A., Gomboc, A., Guidorzi, C., Smith, R., Steele, I., Bersier, D., Mundell, C., Carter, D., Kobayashi, S., Burgdorf, M., Bode, M., Rol, E., O’Brien, P., Bannister, N., Tanvir, N.: GRB 080603B: Liverpool Telescope Observations. GCN Circular, 7813, 2008. [16] Miller, A., Bloom, J., Perley, D.: GRB 080603B: PAIRITEL infrared detection. GCN Circular, 7827, 2008. [17] Piran, T.: The physics of gamma-ray bursts. Re- views of Modern Physics, 76, 1 143–1 210, Oct. 2004. 37 Acta Polytechnica Vol. 52 No. 1/2012 [18] Rau, A.: Catalogue of SPI-ACS Gamma-Ray Burst. http://www.mpe.mpg.de/gamma/science/ grb/1ACSburst.html, 2012. [19] Rujopakarn, W., Guver, T., Smith, D.: GRB 080603B: ROTSE-III Detection of Optical Counterpart. GCN Circular, 7792, 2008. [20] Rumyantsev, A., Antoniuk, K., Pozanenko, A.: GRB 080603B: optical observations in CrAO. GCN Circular, 7974, 2008. [21] Rumyantsev, V., Pozanenko, A.: GRB 080603B: optical observation. GCN Circular, 7869, 2008. [22] Schlegel, D., Finkbeiner, D., Davis, M.: Maps of Dust Infrared Emission for Use in Estima- tion of Reddening and Cosmic Microwave Back- ground Radiation Foregrounds. AJP, 500, 525, June 1998. [23] Xin, L., Feng, Q., Zhai, M., Qiu, Y., Wei, J., Hu, J., Deng, J., Wang, J., Urata, Y., Zheng, W.: GRB 080603B: Xinglong EST ob- servations. GCN Circular, 7814, 2008. [24] Zhuchkov, R., Bikmaev, I., Sakhibullin, N., Khamitov, I., Eker, Z., Kiziloglu, U., Gogus, E., Burenin, R., Pavlinsky, M., Sunyaev, R.: GRB 080603B: RTT150 optical observations, break in light curves. GCN Circular, 7803, 2008. Martin Jeĺınek E-mail: mates@iaa.es Instituto de Astrof́ısica de Andalućıa CSIC Granada, Spain Javier Gorosabel Alberto J. Castro-Tirado Antonio de Ugarte Postigo Sergei Guziy Ronan Cunniffe Instituto de Astrof́ısica de Andalućıa CSIC Granada, Spain Petr Kubánek Michael Prouza Fyzikálńı ústav (FzÚ AV ČR) Praha, Czech Republic Stanislav Vı́tek Fakulta Elektrotechnická, ČVUT v Praze, Czech Re- public René Hudec Astronomický ústav Akademie věd (ASÚ AV ČR) Ondřejov, Czech Republic Fakulta Elektrotechnická, ČVUT v Praze, Czech Re- public Victor Reglero Image Processing Laboratory Universitat de Valencia, Spain Lola Sabau-Graziati Instituto Nacional de Técnica Aeroespacial Torrejón de Ardoz, Madrid, Spain 38