//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17825 SUBJECT: GRB 150518A: MAXI/GSC detection DATE: 15/05/18 23:27:34 GMT FROM: H. Negoro at Nihon U. T. Kawamuro (Kyoto U.), S. Nakahira, S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, R.Imatani (Osaka U.), H. Negoro, M. Nakajima, K. Tanaka, T. Masumitsu (Nihon U.), Y. Ueda, T. Hori (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 21:42:14 UT. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (234.342 deg, 16.307 deg) = (15 37 22, +16 18 25) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.20 deg and 0.20 deg, respectively. The roll angle of long axis from the north direction is 75.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 327 +- 49 mCrab (4-10keV, 1 sigma error). Without assumptions on the source constancy,we obtain a rectangular error box for the transient source with the following corners: (R.A., Dec) = (233.970 deg, 15.521 deg) = (15 35 52, +15 31 15) (J2000) (R.A., Dec) = (233.627 deg, 15.744 deg) = (15 34 30, +15 44 38) (J2000) (R.A., Dec) = (234.594 deg, 16.941 deg) = (15 38 22, +16 56 26) (J2000) (R.A., Dec) = (234.939 deg, 16.717 deg) = (15 39 45, +16 43 01) (J2000) There was no significant excess flux in the previous transit at 5/18 21:39 UT. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17826 SUBJECT: GRB 150518A: Tiled Swift observations DATE: 15/05/19 00:43:18 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a series of observations, tiled on the sky, of the MAXI GRB 150518A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00044 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the MAXI event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17827 SUBJECT: GRB 150518A: Swift-XRT afterglow detection DATE: 15/05/19 10:18:56 GMT FROM: Claudio Pagani at U of Leicester B. Sbarufatti (INAF-OAB/PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows (PSU), J.A. Kennea (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the MAXI-detected burst GRB 150518A (Kawamuro et al. GCN Circ. 17825) in a series of observations tiled on the sky. The total exposure time is 2.4 ks, distributed over 7 tiles; the maximum exposure at a single sky location was 742 s. The data were collected between T0+10.4 ks and T0+20.2 ks, and are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected and is above the RASS limit, and is therefore likely the GRB afterglow. The position of this source is RA, Dec=234.2006, +16.3291 which is equivalent to: RA (J2000): 15:36:48.14 Dec(J2000): +16:19:44.9 with an uncertainty of 3.8 arcsec (radius, 90% confidence). This position is 8.2 arcmin from the MAXI position. The light curve is consistent with a constant source of mean count rate 4.0e-01 ct/sec. A power-law fit gives an index of 0.4 (+0.7, -0.9). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 3.6 (+1.0, -0.8). The best-fitting absorption column is 8.2 (+4.0, -3.2) x 10^21 cm^-2, in excess of the Galactic value of 3.4 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 2.2 x 10^-11 (2.1 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.2 (+4.0, -3.2) x 10^21 cm^-2 Galactic foreground: 3.4 x 10^20 cm^-2 Excess significance: 4.1 sigma Photon index: 3.6 (+1.0, -0.8) The results of the XRT-team automatic analysis of the likely afterglow are at http://www.swift.ac.uk/xrt_products/TILED_GRB00044/index_1.php. The results of the full analysis of the tiled XRT observations are available at http://www.swift.ac.uk/xrt_products/TILED_GRB00044. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17828 SUBJECT: Swift/UVOT observations of GRB150518A DATE: 15/05/19 14:27:38 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (MSSL-UCL) and B.Cenko (NASA-GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150518A 10383 s after the MAXI-GSC trigger (Kawamuro et al, GCN Circ. 17825). No UVOT source is detected at the XRT position or within the XRT error circle (Sbarufatti et al., GCN Circ. 17827) in the initial UVOT exposures. Preliminary 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) is Filter T_start(s) T_stop(s) Exp(s) Mag U.L. u 10383 20164 364 >20.3 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.05 in the direction of the burst (Schlegel et al. 1998). I.A.S.F. INAF Mailing System Outgoing mail is certified Virus Free. Checked by Kaspersky anti-virus system //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17829 SUBJECT: GRB 150518A: Xinglong2.16m optical afterglow detection DATE: 15/05/19 23:26:00 GMT FROM: Dong Xu at NAOC/CAS Dong Xu (NAOC/CAS), Xue-Bing Wu, Qian Yang (PKU) report We observed the field of the XRT transient (Sbarufatti et al., GCN 17827), which is very likely the X-ray counterpart of GRB 150518A (Kawamuro et al., GCN 17825) , using the 2.16m telescope located at Xinglong, Hebei, China. Observations started at 14:23:06 UT (i.e., 16.68 hr after the burst) in a rather poor seeing of 3", and 4x300s R-band frames were obtained. At the XRT-UVOT enhanced position (R.A. = 15:36:48.25, Dec. = +16:19:47.3 , Err. Rad: = 2.2′′), an optical source is well detected at m(R) = 20.3 +/- 0.2 mag, calibrated with nearby SDSS stars. The source largely looks round in our stacked image. We note that there exists a source at the XRT-UVOT position that is already detected and classified as a galaxy by SDSS (u=22.88, g=22.14, r=21.43, i=21.24, z=20.74), with a photometric redshift of z_ph=0.35 +/- 0.11. The Xinglong detection is brighter than the SDSS detection by about 1 magnitude in the R/r filters, and we thus think that it is the optical afterglow of the GRB. If the afterglow is indeed associated with the galaxy at such a redshift, it would be doable to search for a GRB-associated supernova. We thank Junjun Jia for carrying out these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17830 SUBJECT: GRB 150518A: GMG observation DATE: 15/05/20 01:16:47 GMT FROM: Jirong Mao at Yunnan Obs J. Mao, X. Zhang and J. Bai (YNAO) report: We observed the Swift-XRT field of GRB 150518A (Sbarufatti et al., GCN 17827) with the 2.4-meter optical telescope at Gao-Mei-Gu (GMG) station of Yunnan Observatory. Observations began from 16:02:40 UT, May 19, 2015, about 18.3 hours after the trigger. At the position of RA=15:36:48.27 DEC=16:19:47.1, we clearly detect one source with roughly estimated magnitude r'~21.2+/- 0.1. We could not distinguish the SDSS galaxy noticed by Xu et al. (GCN 17829) and the afterglow at this position. Detailed analysis is ongoing. We thank D. Xu for his kind information. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17831 SUBJECT: GRB 150518A: RATIR optical observations DATE: 15/05/20 06:28:43 GMT FROM: Owen Littlejohns at Az State U Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report: We observed the field of GRB 150518A (Kawamuro, et al., GCN 17825) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2015/05 20.15 to 2015/05 20.24 UTC (29.94 to 32.08 hours after the BAT trigger), obtaining a total of 1.78 hours exposure in the r, i and z bands. For a source within the Swift-XRT error circle (Sbarufattim et al., GCN 17827), in comparison with the SDSS DR9, we obtain the following detections and upper limit (3-sigma): r 21.26 +/- 0.04 i 21.04 +/- 0.04 z > 20.08 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. This source is spatially consistent with the catalogued galaxy SDSS J153648.25+161946.9, as previously reported by Xinglong Station (Xu, et al., GCN 17829). We note that the RATIR detections in the r and i bands are brighter than the SDSS catalogue values, indicating that the GRB may indeed be within the galaxy, providing an excess flux. We also note that our detections are consistent with those from Xinglong Station. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17832 SUBJECT: GRB 150518A: VLT/X-shooter redshift of the likely host galaxy DATE: 15/05/20 07:44:28 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Xu (NAOC/CAS), A. J. Levan (Univ. Warwick), A. de Ugarte Postigo (IAA/CSIC), N. R. Tanvir (Univ. Leicester), D. Malesani (DARK/NBI), J. P. U. Fynbo (DARK/NBI), report on behalf of the X-shooter GRB collaboration. We observed the optical counterpart (Xu et al., GCN 17829; Mao et al., GCN 17830; Littlejohns et al., GCN 17831) of the MAXI GRB 150518A (Kawamuro et al., GCN 17825; Sbarufatti et al., GCN 17827) using the X-shooter spectrograph at the ESO Very Large Telescope (VLT). A total of 40 min integration was secured starting on 2015 May 20.184 UT (1.28 days after the GRB) covering the wavelength range 3000-18000 AA. The counterpart, which may include light from both host galaxy and afterglow, is clearly detected, and a number of prominent emission lines are visible. Among others, we identify the Balmer lines, [O II] 3727, [O III] 4957,5007, [N II], [S II], all at a common redshift of z = 0.256. At this redshift, any supernova similar to other associated with GRBs would peak at R ~ 21. Although extinction along the line of the sight to the burst is unknown at present, the low redshift makes GRB 150518A an ideal opportunity for supernova characterisation. We acknowledge excellent support from the observing staff in Paranal, in particular Dimitri Gadotti, Marcelo Lopez, and John Pritchard. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17833 SUBJECT: GRB 150518A: Correction DATE: 15/05/20 09:24:40 GMT FROM: H. Negoro at Nihon U. H. Negoro (Nihon U.), T. Kawamuro (Kyoto U.), S. Nakahira (JAXA), M. Serino (RIKEN) on hehalf of the MAXI team: The previous scan transit time reported in GCN 17825 (GRB 150518A) was incorrect. The correct time was 20:09 UT on May 18, and not 21:39. We apologize fo the mistake. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17834 SUBJECT: GRB 150518A: SAO RAS optical observations DATE: 15/05/20 18:42:42 GMT FROM: Moskvitin Alexander at SAO RAS A. S. Moskvitin (SAO RAS) report on behalf of larger GRB follow-up collaboration: The field of GRB 150518A (Kawamuro et al., GCNC 17825; Sbarufatti et al., GCNC 17827) was observed with the Zeiss-1000, 1-m telescope of SAO RAS. The observations were carried out on the May, 19, 20:10:25 -- 21:26:30 UT (T - T0 ~ 23 hours). 12 x 300 sec frames in Rc filter were obtained. We clearly detect the source mentioned by the other teams (Xu et al., GCNC 17829, 17832; Mao et al., GCNC 17830; Littlejohns et al., GCNC 17831). The magnitude of the object is R = 21.2 +/- 0.1 is almost equal to the magnitude of SDSS J153648.25+161946.9 (within the errors), probable host galaxy of GRB, so we can not find a significant excess from the possible OT. Photometry is based on the nearby stars, whose SDSS magnitudes were transformed to UBVRI system. The magnitude of object is not corrected for the Galactic extinction. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17835 SUBJECT: GRB 150518A : Xinglong TNT upper limit DATE: 15/05/21 04:01:03 GMT FROM: L.P. Xin at NAOC L. P. Xin, X. F. Wang, J. Y. Wei, Y. L. Qiu, J. S. Deng, J. Wang, X. H. Han and C. Wu on behalf of EAFON report: We observed GRB 150518A (Kawamuro, et al., GCN 17825) with Xinglong 0.8-m TNT telescope during 2015-05-20, 16:51:46 and 18:16:34 (UT), bout 43.2-44.7 hour after the trigger time. No any source was detected in our 17*300sec R-band coadded image within the Swift-XRT error circle (Sbarufattim et al., GCN 17827) and at the location of the reported source (Xu et al., GCN 17829; Mao et al., GCN 17830) down to the 3 sigma limit of 20.7 mag, calibrated by USNO B1.0 R2 mag. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17836 SUBJECT: GRB 150518A: Swift-XRT follow-up observations DATE: 15/05/21 08:07:23 GMT FROM: Claudio Pagani at U of Leicester C. Pagani (U. Leicester) reports on behalf of the Swift team: A second epoch of XRT data was collected on the field of the MAXI-detected burst: GRB 150518A (Kawamuro et al., GCN Circ. 17825) on 2015 May 20. The observations consist of 5 ks of PC mode data, from T0+146 ks to T0+154 ks. The X-ray source reported in GCN Circ. 17827, Sbarufatti et al., measured at a mean count rate of 3.4 x 10^-1 count s^-1 (0.3-10 keV) in the first epoch of XRT observations has faded with a power law decay index of alpha=1.04 +/- 0.11 to a mean count rate of 3.1 x 10^-2 count s^-1 (0.3-10 keV) in the second epoch. We therefore confirm that this is the X-ray afterglow of GRB 150518A. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17837 SUBJECT: Konus-Wind observation of GRB 150518A DATE: 15/05/21 11:15:33 GMT FROM: Dmitry Svinkin at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, and T. Cline on behalf of the Konus-Wind team, report: At about 15 minutes before the MAXI/GSC trigger on GRB 150518A (Kawamuro, et al., GCN Circ. 17825; T0(MAXI)=21:42:14 UT) Konus-Wind detected in the waiting mode a burst of high X-ray/soft gamma-ray emission which had a duration of ~250 s. Taking in account the proximity of this burst to the MAXI/GSC trigger and consistency of the KW ecliptic latitude response with the position of GRB 150518A we suggest this burst is the main part of GRB 150518A. There is a hint of emission in the KW softest energy band (20-80 keV) around T0(MAXI). Due to a gap in the data during the main episode we cannot accurately estimate the burst energetics. The K-W light curve of this burst is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB150518A/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17838 SUBJECT: GRB 150518A: MASTER-net before, early and after optical stereoscopic observations with possible MP discovery inside MAXI error box DATE: 15/05/21 13:09:21 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs E. Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov, P.Balanutsa, A.Kuznetsov,D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute D.Buckley, S. Potter, A.Kniazev, M.Kotze South African Astronomical Observatory A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory K.Ivanov, O.Gres, N.M.Budnev, S.Yazev, O.Chuvalaev, V.A.Poleshchuk Irkutsk State University V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk V.Krushinski, I.Zalozhnih, A. Popov Ural Federal University, Kourovka Hugo Levato and Carlos Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) Claudio Mallamaci, Carlos Lopez and Federico Podest Observatorio Astronomico Felix Aguilar (OAFA) MASTER-Kislovodsk robotic telescope (MASTER-Net: http://observ.pereplet.ru, FOV = 2x2 square degrees in paralel mode ( Lipunov et al., 2010, MASTER Robotic Net, Advances in Astronomy, vol. 2010, pp. 1-7)) located in Kislovodsk was pointed to the MAXI/GSC GRB150518A (Kawamuro et al., GCN 17825) 21 sec after notice time and 3189 sec after trigger time at 2015-05-18 22:35:43 UT. On our first (180s exposure) image we do not found OTs within Swift/XRT erro-box (Sbarufatti et al., GCN 17827) brighter then 18.5 . But we see bright object at positon: 15h 36m 53.67s , +16d 19m 36s.5 with 17.5 unfiltered mag outside XRT and inside MAXI. MASTER-SAAO robotic telescope (MASTER-Net: http://observ.pereplet.ru, FOV = 2x2 square degrees in paralel mode ( Lipunov et al., 2010, MASTER Robotic Net, Advances in Astronomy, vol. 2010, pp. 1-7)) located in Souht Africa Astronomical Observatory was pointed to the MAXI/GSC GRB150518A (Kawamuro et al., GCN 17825) 13 sec after notice time and 3189 sec after trigger time at 2015-05-18 22:35:35 UT. On our first (180s exposure) image we not found OTs within Swift/XRT error-box (Sbarufatti et al., GCN 17827) brighter then 17.1 . But we see bright object at positon: 15h 36m 51.70s , +16d 19m 13s.6 with ~ 17.0 unfiltered mag outside Swift/XRT and inside MAXI. There is one asteroid MPC 2010 KL61 with poorly astrometrical efemerids (Leave for survey recovery) at MPC Data Base. The offset both Russian and South Africa OT positiion 36 arc sec. This corresponds to parallax effect for Solar System Body. We do not see any OT at the aftergow canditate position (Xu et al., GCNC 17829, 17832; Mao et al., GCNC 17830; Littlejohns et al., GCNC 17831; Moskvitin GCN 17834) with same limit (3 sigma). We have only one alert image in each telescope because MASTER telescope recieved new MAXI correction of the error box and X-ray Transient leave the MASTER FOV during alert observations. But we have observation this X-ray aftergrow position before last trigger activated by previouse Fermi (trigger number 451674501, 25 apr 2015) and during regular synoptic survey (MASTER-Tunka, ~ 2 days after trigger). Preliminary results: Id Pro.type Date time Exp.time Limit Filt. Site Starting (3sigma) 759597 SumSurvey 2015-05-20 17:02:11 480 20.1 W Tunka 1458076 MaxiAlert 2015-05-18 22:35:35 180 17.1 P/ SAAO 1458345 MaxiAlert 2015-05-18 22:35:43 180 18.5 P| Kislovodsk 823020 FermiInsp 2015-04-25 20:11:41 180 19.9 W Kislovodsk Where W - unfiltered, P - polarization unfiltered. All magnitude calculated with respect to hundrends USNO B stars with calibration: m = 0.2B + 0.8R . At the Tunka Survey we see marginaly faint (~2 sigma) object on the X-ray position (Sbarufatti et al., GCN 17827). But this is may be noice. We have a lot of images in MASTER NET Data Base imaging last several years with Swift XRT error box. No object we see on this place with 20.5 mag limit on first overview (since 2010). The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17839 SUBJECT: GRB 150518A: AMI 15 GHz detection of possible radio counterpart DATE: 15/05/21 14:46:27 GMT FROM: Gemma Anderson at U of Oxford G. E. Anderson, K. Mooley, R. P. Fender, T. D. Staley (University of Oxford), A. J. van der Horst (George Washington University), A. Rowlinson (CASS) We observed the XRT position of GRB 150518A discovered by MAXI (Sbarufatti et al., GCN 17827, Kawamuro et al., GCN 17825) at 15 GHz with the Arcminute Microkelvin Imager (AMI-LA) starting on 2015 May 20.962 to 21.128 UT, corresponding to 2.1 days post-burst (Golenetskii et al., GCN 17837). On this date we detected a radio source coincident with the position of the optical counterpart (Xu et al., GCN 17829) with a preliminary flux of 0.19 +/- 0.04 mJy. There are no catalogued radio sources at this position. An earlier observation was conducted on 2015 May 19.975 to 20.142 UT, corresponding to 1.1 days post-burst, yielding a 3 sigma flux upper limit of 0.13 mJy. Further AMI monitoring is planned. We thank the AMI staff for scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17840 SUBJECT: GRB 150518A: Mondy optical observations DATE: 15/05/21 16:49:28 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), E. Klunko (ISTP), A. Volnova (IKI), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the MAXI/GSC GRB 150518A (Kawamuro, et al., GCN 17825) with AZT-33IK telescope of Sayan observatory (Mondy) starting on May, 20 (UT) 16:50:47. We obtained several images in R-filter of 120 s exposure. The optical afterglow candidate (Xu et al., GCN 17829) which coincides with SDSS J153648.25+161946.9 galaxy is clearly detected. Photometry of the galaxy is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2015-05-20 16:50:47 1.81150 R 20*120 21.22 0.1 Photometry is based on SDSS DR9 stars: SDSS9_id R(Lupton) J153646.11+161904.1 17.65 J153638.21+162002.8 18.41 J153637.55+162040.3 17.10 J153645.59+162055.5 16.35 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17841 SUBJECT: GRB 150518A: MITSuME Akeno Optical observation DATE: 15/05/21 17:36:01 GMT FROM: Taketoshi Yoshii at Tokyo Tech S.Harita, T.Fujiwara, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, Y. Yano, S. Kurita, Y.Ono, Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the XRT-UVOT enhanced position of GRB150518A (T.Kawamuro et al., GCN Circular #17825) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2015-05-19 11:08:33 UT (~13.5 h after the burst). We detected the previously reported optical afterglow of GRB150518A (B.Sbarufatti et al., GCN Circular #17827) in the Rc and Ic band. Although estimated magnitude of Ic band has large error, we could find a faint point source. We obtained following limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------ 48379 13:43:24 4380 >20.7 20.4+/-0.3 19.7+/-0.43 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17859 SUBJECT: GRB 150518A: 6.0 GHz VLA detection DATE: 15/05/21 22:21:08 GMT FROM: Atish Kamble at CfA/Harvard Atish Kamble, Alicia Soderberg and Raffaella Margutti (Harvard University) report: We observed the position of the soft-long GRB 150518A (Kawamuro et al., GCN 17825) with the Karl G. Jansky Very Large Array (VLA) beginning on 2015 May 21.12 UT (2.23 days after the burst) at the mean frequency of 6.0 GHz. In this hour long observation, we detect a faint radio source at the position: RA: 15 36 48.25 DEC: 16 19 46.82 with an average positional uncertainty of 0.01 arcsec. The VLA is currently operating in BnA configuration. The radio afterglow position is consistent with that reported by the Swift-XRT (Sbarufatti et al. GCN 17827). We measure a 6.0 GHz flux density of the afterglow to be ~222 +/- 7 microJy. This flux density is comparable to that reported by the Arcminute Microkelvin Imager (Anderson et al. GCN 17839). Further multiband observations are planned. We thank the VLA staff for quickly executing these observations. [GCN OPS NOTE(21may15): Per author's request, the author list was added.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17860 SUBJECT: GRB 150518A: MAXI-GSC further analysis DATE: 15/05/22 16:18:17 GMT FROM: Takanori Sakamoto at AGU T. Sakamoto (AGU), M. Serino (RIKEN), S. Nakahira (JAXA), H. Negoro (Nihon U.), S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Sugizaki, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, R.Imatani (Osaka U.), M. Nakajima, K. Tanaka, T. Masumitsu (Nihon U.), Y. Ueda, T. Hori, T. Kawamuro (Kyoto U.), Y. Tsuboi, S. Kanetou (Chuo U.), M. Yamauchi, D. Itoh (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Morii (ISM) We report further analysis using the MAXI/GSC data of MAXI GRB 150518A (Kawamuro et al. GCN Circ. 17825). The MAXI GSC light curve shows a constant flux during the scan. Due to a poor statistics, it is hard to claim a variability in the light curve. The MAXI light curve plot is available from the following URL. http://maxi.riken.jp/grbs/150518a/ The GSC spectrum (2-20 keV) using the data from 21:42:00 UT to 21:42:49 UT is best fit by a simple power-law model. The best fit power-law photon index is 1.3 +- 0.4. The column density is not well constrained from the GSC spectrum. The unabsorbed flux in the 2-20 keV band is (1.0 +- 0.3) x 10^-8 erg/cm2/s. From this best fit model, the unabsorbed X-ray flux in the 0.3-10 keV band (Swift/XRT energy band) is (7.9 +- 2.4) x 10^-9 erg/cm2/s. No emission was detected from the GRB position during the next scan starting from 23:11 UT at the 1 sigma upper limit of ~9 mCrab. Using the possible host galaxy redshift of 0.256 (Xu et al. GCN Circ. 17832), the X-ray luminosity at the time of the MAXI detection is 1.7 x 10^48 erg/s (2-20 keV) and 1.3 x 10^48 erg/s (0.3-10 keV). Assuming the onset of this GRB is the detection by Konus-Wind (Golenetskii et al. GCN Circ. 17837), we found that the MAXI luminosity around ~1000 sec after this onset is consistent with a typical early afterglow emission seen by Swift/XRT (e.g., Racusin et al. 2011, ApJ, 738, 138). On the other hand, if the possible emission seen by the Konus-Wind data around the MAXI detection is real, the duration of GRB 150518A can be >1000 s. As we reported above, the MAXI GSC spectrum is rather hard for an afterglow. In this case, this GRB can be classified as an ultra-long GRB. All the quoted errors are at the 90% confidence level. The assumed cosmological parameters are H0 = 71 km s^-1 Mpc^-1, Omega_m = 0.27 and Omega_lamda = 0.73. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17861 SUBJECT: GRB 150518A: Continued RATIR optical observations DATE: 15/05/22 20:44:31 GMT FROM: Owen Littlejohns at Az State U Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report: We continued to observe the field of GRB 150518A (Kawamuro, et al., GCN 17825) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir for two further epochs. Our first full epoch now extends from 2015/05 20.15 to 2015/05 20.47 UTC (29.94 to 37.69 hours after the BAT trigger), obtaining a total of 6.04 hours exposure in the r, i and z bands. For the previously reported SDSS galaxy (Xu, et al., GCN 17829; Mao, et al., GCN 17830; Littlejohns, et al., GCN 17831), in comparison with the SDSS DR9, we obtain the following detections: r 21.27 +/- 0.04 i 21.02 +/- 0.04 z 20.53 +/- 0.24 The second epoch of RATIR observations ranged from 2015/05 21.21 to 2015/05 21.45 UTC (55.33 to 61.20 hours after the BAT trigger), obtaining a total of 3.59 hours exposure in the r and i bands, and 1.07 hours in the z band. For the same SDSS galaxy, again in comparison with the SDSS DR9, we obtain the following detections and upper limit (3-sigma): r 21.40 +/- 0.08 i 21.08 +/- 0.08 z > 17.70 The third epoch of RATIR observations was from 2015/05 22.15 to 2015/05 22.47 UTC (77.99 to 85.61 hours after the BAT trigger), obtaining a total of 6.04 hours exposure in the r, i and z bands. In this epoch, we obtain the following detections of the SDSS galaxy: r 21.34 +/- 0.04 i 21.08 +/- 0.04 z 20.80 +/- 0.35 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Combining the r and i band observations from the second and third epochs, we find marginal evidence that the source has faded, changing by 0.07 +/-0.04 magnitudes when compared to the first epoch of RATIR observations (Littlejohns, et al., GCN 17831). During the full first epoch of observations, we also observed marginal (1-sigma) evidence for fading by 0.05 magnitudes in the r and i bands. Finally, we note that image subtraction between the third and first epochs, in both r and i band, yield positive residuals in the Swift-XRT error circle at the 1-sigma level. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17903 SUBJECT: GRB 150518A: possible SN observations DATE: 15/06/06 15:19:15 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Pozanenko (IKI), E. Mazaeva (IKI), A. Sergeev (IRA NASU, IAKhNU), I. Reva (Fesenkov Astrophysical Institute), A. Volnova (IKI), E. Klunko (ISTP), I. Korobtsev (ISTP), report on behalf of larger GRB follow-up collaboration: We observed the field of the MAXI/GSC GRB 150518A (Kawamuro, et al., GCN 17825) with AZT-33IK telescope of Sayan observatory (Mondy), Zeiss-1000 (East) 1-m telescope of Tien Shan Astronomical Observatory and AZT-22 telescope of Maidanak observatory. Observations are continuing in R-filter. The SDSS J153648.25+161946.9 galaxy which coincides with the optical afterglow (Xu et al., GCN 17829) is detected in all observations. The light curve of the host galaxy+afterglow are suggesting re-brightening with a possible maximum brightness on June 2-5. We suggest that this re-brightening can be attributed to Supernova associated with GRB 150518A. Preliminary light curve of the possible SN+host can be found in http://grb.rssi.ru/GRB150518A/GRB150518A_lc.png Photometry of the host galaxy+SN at the possible maximum brightness are following Date UT start t-T0 Filter OT Err. Observatory (mid, days) 2015-06-02 17:43:30 14.8605 R 20.89 0.13 TSHAO 2015-06-03 20:33:20 15.8862 R 20.82 0.10 Maidanak 2015-06-05 18:11:19 17.8535 R 20.90 0.07 Maidanak Photometry is based on SDSS DR9 stars: SDSS9_id R(Lupton) J153646.11+161904.1 17.65 J153638.21+162002.8 18.41 J153637.55+162040.3 17.10 J153645.59+162055.5 16.35 The maximum brightness of a the possible Supernova is an agreement with the brightness predicted for the SN at redshift z = 0.256 (Xu et al., GCN 17832).