//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18050 SUBJECT: GRB 150724A: Swift detection of a burst DATE: 15/07/24 06:02:12 GMT FROM: David Palmer at LANL J. L. Racusin (NASA/GSFC), A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 05:46:35 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150724A (trigger=650141). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 97.540, -19.154 which is RA(J2000) = 06h 30m 09s Dec(J2000) = -19d 09' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed multiple peaks structure with a duration of about 40 sec. The peak count rate was ~1412 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 05:48:18.6 UT, 102.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source located at RA, Dec 97.56060, -19.16395 which is equivalent to: RA(J2000) = 06h 30m 14.54s Dec(J2000) = -19d 09' 50.2" with an uncertainty of 3.7 arcseconds (radius, 90% containment). This location is 78 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.94 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.27e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 108 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.27. Burst Advocate for this burst is J. L. Racusin (judith.racusin AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18052 SUBJECT: GRB 150724A: Prompt enhanced Swift-XRT position DATE: 15/07/24 06:23:32 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using promptly downlinked XRT event data for GRB 150724A, we find an enhanced XRT position of the afterglow: RA, Dec: 97.5600, -19.1646 which is equivalent to: RA (J2000) = 06 30 14.41 Dec (J2000) = -19 09 52.5 with an uncertainty of 2.0 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/650141. Position enhancement is is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18054 SUBJECT: GRB 150724A: Enhanced Swift-XRT position DATE: 15/07/24 11:32:50 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 2472 s of XRT Photon Counting mode data and 4 UVOT images for GRB 150724A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 97.56044, -19.16479 which is equivalent to: RA (J2000): 06h 30m 14.51s Dec (J2000): -19d 09' 53.3" with an uncertainty of 1.9 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18055 SUBJECT: GRB 150724A: Swift-BAT refined analysis DATE: 15/07/24 12:10:27 GMT FROM: Scott Barthelmy at NASA/GSFC D. M. Palmer (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), J. L. Racusin (NASA/GSFC), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-240 to T+902 sec from recent telemetry downlinks, we report further analysis of BAT GRB 150724A (trigger #650141) (Racusin, et al., GCN Circ. 18050). The BAT ground-calculated position is RA, Dec = 97.549, -19.147 deg, which is RA(J2000) = 06h 30m 11.7s Dec(J2000) = -19d 08' 48.1" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve has at least 4 peaks starting at ~T-10 sec, with peaks at ~T+1 sec, ~T+24 sec, ~T+160 sec, & ~T+220 sec, and the emission ending at ~T+300 sec. T90 (15-350 keV) is 280 +- 44 sec (estimated error including systematics). The time-averaged spectrum from T-1.07 to T+325.42 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.06 +- 0.15. The fluence in the 15-150 keV band is 2.2 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+24.08 sec in the 15-150 keV band is 0.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/650141/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18057 SUBJECT: GRB 150724A: Swift/UVOT Upper Limits DATE: 15/07/24 14:41:21 GMT FROM: Massimiliano de Pasquale at IASF-Palermo M. De Pasquale (UCL-MSSL) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150724A 108 s after the BAT trigger (Racusin et al., GCN Circ. 18050). No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 18054) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent summed exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u_FC 108 358 246 >19.7 v 415 6930 510 >19.2 b 364 12898 1165 >20.6 u 108 12238 1769 >20.7 w1 464 11324 1387 >20.5 m2 439 7135 502 >19.9 w2 390 6726 529 >20.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.27 in the direction of the burst (Schlegel et al. 1998). -- Dr. Massimiliano De Pasquale Research associate - Swift UVOT scientist Mullard Space Science Laboratory, University College London //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18059 SUBJECT: GRB 150724A: Swift-XRT refined Analysis DATE: 15/07/24 18:02:03 GMT FROM: Phil Evans at U of Leicester T.G.R. Roegiers (PSU), B.P. Gompertz (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), L.M. McCauley (PSU), J.A. Kennea (PSU) and J.L. Racusin report on behalf of the Swift-XRT team: We have analysed 11 ks of XRT data for GRB 150724A (Racusin et al. GCN Circ. 18050), from 91 s to 24.4 ks after the BAT trigger. The data comprise 349 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 18052). The late-time light curve (from T0+4.7 ks) is consistent with a constant source of mean count rate 2.2e+00 ct/sec. A power-law fit gives an index of -0.02 (+0.19, -0.20). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.70 (+/-0.04). The best-fitting absorption column is 3.70 (+0.21, -0.20) x 10^21 cm^-2, in excess of the Galactic value of 2.9 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.13 (+0.18, -0.17) and a best-fitting absorption column of 3.6 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.6 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 2.9 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 2.13 (+0.18, -0.17) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00650141. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18065 SUBJECT: GRB 150724B: Fermi-LAT detection DATE: 15/07/25 13:52:53 GMT FROM: Judith Racusin at GSFC E. Bissaldi (INFN Bari), J. L. Racusin (NASA/GSFC), and E. Moretti (MPP Munich) report on behalf of the Fermi-LAT team: At 18:45:36.71 on 2015-07-24, Fermi-LAT detected high-energy emission from GRB 150724B, which was also detected by Fermi-GBM (trigger 459456340/150724782). The best LAT on-ground location is found to be RA, Dec = 351.92, 3.67 (J2000) with an error radius of 0.3 deg (90% containment, systematic error only). This was 58 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a ~5 sigma increase in the event rate within 7 degrees of the GBM location after the GBM trigger that is spatially and temporally correlated with the GBM emission. More than 11 photons above 100 MeV and 1 photons above 1 GeV were observed within 300 seconds. The highest-energy photon is a 2 GeV event which is observed ~50 seconds after the GBM trigger. A Swift ToO has been requested for this burst. The Fermi-LAT point of contact for this burst is Elisabetta Bissaldi (elisabetta.bissaldi@ba.infn.it). The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18066 SUBJECT: GRB 150724B: Fermi GBM detection DATE: 15/07/25 16:22:15 GMT FROM: Peter Veres at ELTE,Budapest P. Veres (UAH), V. Connaughton (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 18:45:37.714 UT on 24 July 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150724B (trigger 459456341 / 150724782) which was also detected by the Fermi/LAT (Bissaldi et al. 2008, GCN 18065). The GBM on-ground location is consistent with the Fermi/LAT position. The on-ground calculated location, using the GBM trigger data, is RA = 350.92, DEC = +10.160 (J2000 degrees, equivalent to 23h 24m, 10d 10'), with an uncertainty of 1.05 degrees (radius, 1-sigma containment, statistical only). The GBM light curve consists of two emission episodes with a total duration (T90) of about 38 s (50-300 keV). The time-averaged spectrum from T0-6.1 s to T0+46 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -0.75 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 729 +/- 35 keV. The event fluence (10-1000 keV) in this time interval is (3.55 +/- 0.04)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+40 s in the 8-1000 keV band is 8.3 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18068 SUBJECT: GRB 150724B: Swift ToO observations DATE: 15/07/25 19:24:14 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Fermi/LAT GRB 150724B. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/ToO_GRBs/00020543 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/LAT event. 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: 18069 SUBJECT: GRB 150724B: Swift-XRT observations DATE: 15/07/26 05:24:25 GMT FROM: Kim Page at U.of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), A. Maselli (INAF-IASFPA), L.M. McCauley (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 150724B (Bissaldi et al. GCN Circ. 18065), collecting 1.8 ks of Photon Counting (PC) mode data between T0+94.4 ks and T0+96.2 ks. One uncatalogued X-ray source has been detected, it is below the RASS limit and shows no definitive signs of fading. Therefore, at the present time we cannot confirm this as the afterglow. Details of this source are given below: Source 1: RA (J2000.0): 351.8904 = 23:27:33.70 Dec (J2000.0): +3.8186 = +03:49:06.8 Error: 4.3 arcsec (radius, 90% conf.) Count-rate: 0.0143 +/- 0.0033 ct s^-1 Flux: (4.6 +/- 1.1)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at http://www.swift.ac.uk/ToO_GRBs/00020543. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18072 SUBJECT: GRB 150724B: RATIR Optical Observations DATE: 15/07/27 03:33:50 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM 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), Owen Littlejohns (ASU), 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 the LAT GRB 150724B (Bissaldi et al., GCN 18065) 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 2015/07 26.28 to 2015/07 26.48 UTC (36.02 to 40.86 hours after the BAT trigger), obtaining a total of 2.39 hours exposure in the r and i bands. For a source within the Swift XRT error circle (Osborne et al., GCN 18069), in comparison with the SDSS DR9 catalog, we obtain the following detections: r 23.24 +/- 0.34 i 22.39 +/- 0.15 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. At this moment we have no information on fading. Further observations are planned. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18074 SUBJECT: Konus-Wind observation of GRB 150724B DATE: 15/07/27 14:09:55 GMT FROM: Anastasia Tsvetkova 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: The long-duration, hard-spectrum GRB 150724B (Fermi-LAT detection: Bissaldi, Racusin & Moretti, GCN 18065; Fermi GBM detection: Veres, Connaughton & Meegan, GCN 18066) triggered Konus-Wind at T0=67574.792 s UT (18:46:14.792). The burst light curve shows a double-peaked structure which starts ~30 s before the trigger and has a total duration of ~41 s. The emission is seen up to ~5 MeV. As observed by Konus-Wind, the burst had a fluence of 3.63(-0.29,+0.69)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+2.064 s, of 6.01(-1.60,+1.62)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). Only the brightest part of the burst is covered by the KW triggered mode data and, therefore, available for the multi-channel spectral analysis. The time-averaged spectrum measured from T0 to T0+8.448 s is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.65(-0.11,+0.12), and Ep = 663(-69,+82) keV (chi2 = 77/73 dof). Fitting by the GRB (Band) function yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 77/72 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150724_T67574/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18075 SUBJECT: GRB 150724B: Swift/UVOT Detection DATE: 15/07/27 17:25:04 GMT FROM: Paul Kuin at MSSL N.P.M. Kuin(MSSL/UCL) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150724B 88.6ks after the LAT trigger (Bissaldi et al., GCN Circ. 18065), which was also observed at high energy by Fermi-GBM (Veres et al., GCN Circ 18066) and Konus-Wind (Golenetskii et al. GCN Circ. 18074). Five UVOT exposures were obtained of which the first two show a weak detection at the XRT position (Osborne et al., GCN Circ. 18069). Preliminary magnitudes and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag white 88619 88799 178 19.64+-0.12 white 88802 90608 1765 20.99+-0.14 white 90614 90748 60 >19.53 white 94379 94558 176 >20.82 white 94562 96236 1648 >22.01 The brightness is consistent with the RATIR observation at 147ks in r and i (Butler et al, GCN 18072). The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18077 SUBJECT: GRB 150724B: MASTER upper limit DATE: 15/07/27 20:06:01 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs K.Ivanov, O.Gres, N.M.Budnev, S.Yazev, Irkutsk State University V. Lipunov, E. Gorbovskoy, N.Tyurina, V.Kornilov, P.Balanutsa,A.Kuznetsov,D.Kuvshinov, Lomonosov Moscow State University, Sternberg Astronomical Institute R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias 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 V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk V.Krushinski, I.Zalozhnih 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 II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in Tunka was pointed to the GRB150724B (Bissaldi et al. GCN 18065) 9244 sec after notice time and 78080 sec after trigger time at 2015-07-25 16:26:57 UT. We do not see any OT brighter than 20.3 inside Fermi LAT error box and at Swift XRT transient position (Osborne et al., GCN 18069). All magnitudes are unfiltered (0.2B+0.8R) with respect to number USNO B stars). The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18078 SUBJECT: GRB 150724B: Continued RATIR Optical Observations DATE: 15/07/27 21:00:53 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Nat Butler (ASU), 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), Owen Littlejohns (ASU), 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 reobserved the field of the LAT GRB 150724B (Bissaldi et al., GCN 18065) 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 2015/07 27.24 to 2015/07 27.47 UTC (8819.11 to 8824.45 hours after the Fermi trigger), obtaining a total of 4.01 hours exposure in the r and i bands. We detect the source we previously reported (Butler et al. GCN 18072) at 23:27:33.82 +3:49:06.8 (J2000, ±0.5"). In comparison with the SDSS DR9, we obtain the following detections: r 23.50 ± 0.19 i 23.99 ± 0.27 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. A naive comparison to our observations from the previous night would suggest that the source has not faded in r but has faded in i. However, examining the images in detail, we suspect that our photometry in i from the first night might be influenced by a spuriously bright pixel. We therefore discount the apparent fading in i. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. [GCN OPS NOTE(27jul15): Per author's request, "140724A" was changed to "150724B" in the Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18099 SUBJECT: GRB150724B: Retraction of the uvot detection DATE: 15/07/31 21:00:42 GMT FROM: Paul Kuin at MSSL Paul Kuin (MSSL/UCL) reports on behalf of the Swift/UVOT team: In GCN Circ.18075 we reported a detection in the first two white band images with the Swift UVOT. Further examination of the UVOT data showed that in the initial analysis the background region included part off the detector and gave a false reading. Correcting for that it is found that for the first two images there is just an upper limit of white > 22.00 mag at 88.7ks after the trigger. We apologise for the confusion this error may have caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 18101 SUBJECT: GRB 150724B: Swift-XRT afterglow detection DATE: 15/08/01 05:05:00 GMT FROM: Kim Page at U.of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), A. Maselli (INAF-IASFPA), L.M. McCauley (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has conducted further observations of the field of the Fermi/LAT-detected burst GRB 150724B (Bissaldi et al. GCN Circ. 18065). The observations now extend from T0+88.6 ks to T0+607.8 ks. The source previously reported by Osborne et al. (GCN Circ. 18069), "Source 1", is fading with 3-sigma significance, and is therefore likely the GRB afterglow. The position of this source is RA, Dec=351.8905, +3.8181 which is equivalent to: RA (J2000): 23:27:33.71 Dec(J2000): +03:49:05.2 with an uncertainty of 4.1 arcsec (radius, 90% confidence). This position is 9.1 arcmin from the Fermi/LAT position. The source is fading with alpha >0.3. The results of the XRT-team automatic analysis of the likely afterglow are at http://www.swift.ac.uk/ToO_GRBs/00020543/index_1.php. The results of the full analysis of the XRT observations are available at http://www.swift.ac.uk/ToO_GRBs/00020543. This circular is an official product of the Swift-XRT team.