//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22832 SUBJECT: GRB 180624A: Swift detection of a burst DATE: 18/06/24 14:02:45 GMT FROM: Scott Barthelmy at NASA/GSFC S. L. Gibson (U Leicester), S. D. Barthelmy (GSFC), A. Deich (PSU), S. W. K Emery (UCL-MSSL), J.D. Gropp (PSU), K. L. Page (U Leicester), T. Sakamoto (AGU) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 13:49:40 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180624A (trigger=844192). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 318.071, -2.332, which is RA(J2000) = 21h 12m 17s Dec(J2000) = -02d 19' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to missing downlinked realtime data in the light curve, we cannot give the BAT light curve description. The XRT began observing the field at 13:51:32.6 UT, 112.2 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 318.0951, -2.3397 which is equivalent to: RA(J2000) = +21h 12m 22.82s Dec(J2000) = -02d 20' 22.9" with an uncertainty of 5.2 arcseconds (radius, 90% containment). This location is 91 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.93e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 118 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 19.6 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 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.05. Burst Advocate for this burst is S. L. Gibson (slg44 AT le.ac.uk). 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: 22835 SUBJECT: GRB 180624A: Enhanced Swift-XRT position DATE: 18/06/24 21:20:42 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 6 UVOT images for GRB 180624A, 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 = 318.09749, -2.33826 which is equivalent to: RA (J2000): 21h 12m 23.40s Dec (J2000): -02d 20' 17.7" with an uncertainty of 1.5 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: 22836 SUBJECT: GRB 180624A: Swift/UVOT Upper Limits DATE: 18/06/24 22:33:42 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL) and S. L. Gibson (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180624A 118 s after the BAT trigger (Gibson et al., GCN Circ. 22832). No optical afterglow consistent with the XRT position (Gibson et al. GCN Circ. 22832) 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 exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 118 268 147 >20.7 u_FC 276 526 246 >19.4 white 118 6151 541 >21.3 v 4927 6395 229 >20.0 b 4312 5947 393 >21.2 u 276 5742 639 >20.6 w1 3902 5537 393 >20.2 m2 5132 5332 197 >19.7 w2 4723 6357 393 >20.8 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). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22837 SUBJECT: GRB 180624A: Swift-XRT refined Analysis DATE: 18/06/25 00:10:26 GMT FROM: Phil Evans at U of Leicester B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), A. Tohuvavohu (PSU) and S.L. Gibson report on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 180624A (Gibson et al. GCN Circ. 22832), from 118 s to 23.6 ks after the BAT trigger. The data comprise 538 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 22835). The late-time light curve (from T0+3.9 ks) can be modelled with a power-law decay with a decay index of alpha=0.84 (+0.12, -0.11). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.472 (+/-0.025). The best-fitting absorption column is 1.53 (+/-0.11) x 10^21 cm^-2, in excess of the Galactic value of 4.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.08 (+0.19, -0.18) and a best-fitting absorption column of 1.3 (+/-0.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.3 (+/-0.5) x 10^21 cm^-2 Galactic foreground: 4.6 x 10^20 cm^-2 Excess significance: 3.0 sigma Photon index: 2.08 (+0.19, -0.18) If the light curve continues to decay with a power-law decay index of 0.84, the count rate at T+24 hours will be 0.013 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x 10^-13 (5.5 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00844192. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22838 SUBJECT: GRB 180624A: MITSuME Okayama optical upper limits DATE: 18/06/25 04:46:32 GMT FROM: Ryosuke Itoh at Tokyo Institute of Tech. R. Itoh, K. L. Murata, Y. Tachibana, K. Morita, K. Shiraishi, M. Oeda, R. Adachi, K. Iida, S. Niwano, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 180624A (S. L. Gibson et al., GCN Circular #22832) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory. The observation started on 2018-06-24 13:51:38.54 UT (~118 sec after the burst). We did not find any new point source within the enhanced XRT error circle in all the three bands. We obtained following limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- ~118 ~13:52:08 60 >15.5 >16.1 >16.2 ~1537 ~14:15:47 2100 >17.2 >17.7 >17.6 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used UCAC-4 catalog for flux calibration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22839 SUBJECT: GRB 180624A: LCO Siding Springs afterglow candidate DATE: 18/06/25 06:43:03 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), A. Cucchiara (U. of Virgin Islands) on behalf of a large collaboration report: One LCO 1-m unit at Siding Springs Observatory began observing Swift GRB 180624A (Gibson et al. GCN 22832) on June 24, 14:18 UT (28.5 min since the GRB trigger time) with the SDSS r filter. Within the enhanced Swift-XRT error circle (Goad et al. GCN 22835) we find an uncatalogued object with a magnitude of r'=19.92 +- 0.10 (AB) at a mid time of 0.54 hours since the GRB trigger time at the following position: RA(J2000) = 21:12:23.38 DEC(J2000)= -02:20:16.7 with an error radius of ~1". //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22840 SUBJECT: GRB 180624A: GROND observations DATE: 18/06/25 08:09:51 GMT FROM: Patricia Schady at MPE/Swift Patricia Schady (MPE Garching) reports: We observed the field of GRB 180624A (Swift trigger 844192; Gibson et al., GCN #22832) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 04:42 UT on 2018-06-25, 14.9 hrs after the GRB trigger. They were performed under poor seeing conditions and at an average airmass of 1.5. A source is visible within the 1.5" enhanced Swift-XRT error circle reported by GOAD et al. (GCN #22835), and consistent with the position of the optical afterglow candidate reported by Guidorzi et al. (GCN #22839). The source appears extended and most of the flux in the JHK bands is to the NW of the afterglow error circle. Based on a total of 22 min exposure time in g'r'i'z', we estimate preliminary AB magnitudes of g' = 21.5 +/- 0.1 mag r' = 20.2 +/- 0.1 mag i' = 19.9 +/- 0.1 mag z' = 19.6 +/- 0.1 mag A fit to the GROND optical SED implies a photometric redshift of z_phot=3.75+/-0.10. Given magnitudes are calibrated against SDSS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)=0.04 in the direction of the burst (Schlafly & Finkbeiner 2011). We thank Markus Rabus for the excellent support from La Silla. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22845 SUBJECT: GRB 180624A: LBT/MODS redshift measurement DATE: 18/06/25 18:25:52 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst A. Rossi (INAF-OAS), A. Gargiulo (INAF/IASF Milano), D. B. Malesani (DAWN/NBI and DARK/NBI), S. D. Vergani (GEPI/Obs. Paris), V. D'Elia (ASDC), S. Campana (INAF-OAB), report on behalf of the CIBO collaboration: We observed the field of GRB 180624A (Swift trigger 844192; Gibson et al., GCN 22832) with the Multi-Object Double Spectrographs (MODS) instrument mounted on the 2x8.4-m LBT telescope (Mt Graham, AZ, USA). Images were obtained starting at 10:15 UT on 2018-06-25, 20.5 hr after the GRB trigger. Inspection of the 60 s acquisition image reveals a point source within the Swift/XRT enhanced error circle (Evans et al., GCN 22835), at coordinates: RA(J2000) = 21:12:23.378 Dec(J2000)= -02:20:17.30 with an uncertainty of 0.2" in each coordinate, which is consistent with the source reported by Guidorzi et al. (GCN 22839). The source has magnitude r' = 20.6 +- 0.1 (AB), calibrated against r'-band SDSS field stars, and it is not visible in Pan-STARRS images, thus clearly singling it out as the afterglow. Spectroscopy of the source was obtained for a total of 2x600 s, covering the wavelength range 3200-10000 AA. A broad trough is well visible centered around 4700 AA, which we identify as a DLA feature at z ~ 2.86. Detection of several absorption features, which we interpret as due to, among others, Si II, C IV, Al II, Al III, Fe II, allows to precisely measure the redshift to be z = 2.855, which we consider to be the redshift of GRB 180624A. We also note the presence of a close-by and fainter galaxy, which is also visible in the Pan-STARRS images, 2.5" NW of the afterglow, at position: RA(J2000) = 21:12:23.244 Dec(J2000)= -02:20:15.76 possibly consistent with the extended source reported by Schady (GCN 22840). Given the measured redshift, we do not consider this object as related to the GRB, as it would have an unreasonable brightness and large separation at z = 2.8. No correction for the expected Galactic foreground extinction, corresponding to a reddening of E_(B-V) = 0.05 mag in the direction of the burst (Schlafly & Finkbeiner 2011), has been applied. We acknowledge the excellent support from the LBT-INAF staff, particularly Olga Kuhn and Steve Allanson in obtaining these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22846 SUBJECT: GRB 180624A: RATIR Optical Observations DATE: 18/06/25 22:16:14 GMT FROM: Alan M. Watson at Instituto de Astronomia UNAM Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat Butler (ASU), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report: We observed the field of GRB 180624A (Gibson et al., GCN Circ. 22832) 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 2018/06 25.26 to 2018/06 25.47 UTC (16.42 to 21.45 hours after the BAT trigger), obtaining a total of 3.91 hours exposure in the r and i bands. We detect a source in the enhanced Swift-XRT error circle (Goad et al., GCN Circ. 22835) with the following magnitudes: r = 21.03 +/- 0.02 i = 20.45 +/- 0.01 These magnitudes are calibrated against the SDSS DR9 catalog, are in the AB system, and are not corrected for Galactic extinction in the direction of the GRB. We note that the source has faded significantly from the earlier observations of Guidorzi et al. (GCN Circ. 22839) of r = 19.9 +/- 0.1 at 0.54 hours and Schady (GCN Circ. 22840) of r = 20.2 +/- 0.1 at 15.07 hours. We also see the source fade by about 0.5 mag in each our bands during the course of our observations. We confirm the observation of Rossi et al. (GCN Circ. 22845) that the source is a couple of arcsec to the SE of the SDSS galaxy J211223.25-022015.9. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22848 SUBJECT: GRB 180624A: Swift-BAT refined analysis DATE: 18/06/26 02:19:59 GMT FROM: Amy Lien at GSFC J. R. Cummings (CPI), S. D. Barthelmy (GSFC), S. L. Gibson (U Leicester), H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), 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+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 180624A (trigger #844192) (Gibson et al., GCN Circ. 22832). The BAT ground-calculated position is RA, Dec = 318.096, -2.356 deg which is RA(J2000) = 21h 12m 22.9s Dec(J2000) = -02d 21' 21.0" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 47%. The mask-weighted light curve shows a multi-peaked light curve that starts at ~T-60 s and ends at ~T+540 s. The largest peak occurs at ~T+7 s. The burst went out of the BAT FOV at ~T+720 s. T90 (15-350 keV) is 486.4 +- 38.5 sec (estimated error including systematics). The time-averaged spectrum from T-60.61 to T+541.80 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.91 +- 0.10. The fluence in the 15-150 keV band is 5.8 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+6.02 sec in the 15-150 keV band is 1.4 +- 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/844192/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22858 SUBJECT: GRB 180624A: LCO Haleakala observations DATE: 18/06/26 15:32:43 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), A. Cucchiara, D. Morris (U. of Virgin Islands) on behalf of a large collaboration report: The LCO 2-m unit at Haleakala Observatory (Hawaii) observed the optical afterglow of Swift GRB 180624A (Gibson et al. GCN 22832) on June 25, from 13:02 to 13:14 UT (0.97 days after the GRB trigger time) with the SDSS r filter. The source is detected with a magnitude of 21.44 +- 0.10 (AB). Compared with previous reports (Guidorzi et al. GCN 22839; Schady GCN 22840; Rossi et al. GCN 22845; Watson et al. GCN 22846) we confirm that the source's decay has significantly steepened from ~0.6 to ~1.0 days, as first noted by Watson et al. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22867 SUBJECT: GRB 180624A: NOT optical counterpart DATE: 18/06/27 19:06:20 GMT FROM: Jonatan Selsing at DARK/NBI Jonatan Selsing (DAWN/NBI), Kasper E. Heintz (Univ. Iceland and DAWN/NBI), Johan P. U. Fynbo (DAWN/NBI), Daniele B. Malesani (DAWN/NBI and DARK/NBI), Jyri J. Lehtinen (MPS), Teemu Willamo (Univ. of Helsinki), report on behalf of a larger collaboration: We observed the optical afterglow (Guidorzi, GCN #22839; Schady, GCN #22840; Rossi et al., GCN #22845; Watson et al., GCN #22846; Guidorzi et al., GCN #22858) of GRB 180624A (Gibson et al., GCN #22832) with the 2.5-m Nordic Optical Telescope (NOT) equipped with StanCam. Observations were carried out in the Bessel R filter, but calibrated against Pan-STARRS r-band local photometry, using the transformations of Lupton (2005). An optical afterglow is detected at a position consistent with previous reports. At a mid time 11.0 hr after the BAT trigger, we measure for the counterpart R = 20.10 +- 0.04 (Vega). This measurement has not been corrected for Milky Way extinction (A_V = 0.13). Due to the vicinity of the nearby galaxy noted by Schady (GCN #22840), Guidorzi et al. (GCN #22858), and Rossi et al. (GCN 22845), we cannot exclude some minor contamination from this object to the afterglow photometry.