//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7988 SUBJECT: GRB 080721: Swift detection of a burst with a bright optical counterpart. DATE: 08/07/21 10:42:45 GMT FROM: David Palmer at LANL F. E. Marshall (NASA/GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC), V. Mangano (INAF-IASFPA), P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), D. Perez (U Leicester), M. Perri (ASDC), B. Preger (ASDC), P. Romano (INAF-IASFPA), M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester), T. N. Ukwatta (GSFC/GWU), P. A. Ward (MSSL-UCL) and H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team: At 10:25:16 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 080721 (trigger=317508). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 224.471, -11.712 which is RA(J2000) = 14h 57m 53s Dec(J2000) = -11d 42' 43" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed at least 4 peaks structure with a duration of about 35 sec. The peak count rate was ~19k counts/sec (15-350 keV), at ~0 sec after the trigger, during the second peak. The XRT began observing the field at 10:27:04.1 UT, 107.2 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 224.4899, -11.7242 which is equivalent to: RA(J2000) = 14h 57m 55.9s Dec(J2000) = -11d 43' 27.3" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 79 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. UVOT took a finding chart exposure of nominal 100 seconds with the White (160-650 nm) filter starting 180 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 14:57:55.8 = 224.48268 DEC(J2000) = -11:43:25 = -11.72361 with a 1-sigma error radius of about 1.0 arc sec. The estimated white magnitude is 14.6 with a 1-sigma error of about 0.01 mag. No correction has been made for Galactic extinction. Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.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: 7989 SUBJECT: GRB 080721: Swift-XRT correct position DATE: 08/07/21 12:34:14 GMT FROM: Cristiano Guidorzi at INAF-OAB C. Guidorzi (INAF-OAB), P. A. Evans and K. L. Page (U Leicester) report on behalf of the Swift-XRT team: We note that the correct XRT position of GRB 080721 (Marshall et al., GCN Circ. 7988) is that given in sexagesimal coordinates, which corresponds to RA, Dec 224.48292, -11.72425 degrees (J2000; 4.7 arcsec radius, 90%) and is also consistent with the UVOT position. The XRT position given in degrees in the same circular, which has also been distributed in the XRT position notice, is not correct. We apologise for any inconvenient this may have caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7990 SUBJECT: GRB 080721 : Lulin Optical follow-ups DATE: 08/07/21 13:04:35 GMT FROM: Yuji Urata at Saitama U T-W Chen, L-C Huang, Y-T Chen (NCU) K.Y Huang (ASIAA) and Y. Urata (Saitama U./ASIAA) on behalf of the EAFON report; "We have been monitoring the optical afterglow of GRB080721 (Marshall et al. GCN Circ 7988) using the Lulin 1 m telescope after the twilight (~ 96 min after the burst). Based on Lulin R-band data, the optical afterglow is located at RA=14:57:55.835, Dec=-11:43:24.76 with less than 1" position error. The brightness of the optical afterglow at 98 min after the burst is R~18.1. Further optical observation is in progress." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7991 SUBJECT: GRB 080721: Swift/UVOT Photometric Redshift DATE: 08/07/21 15:05:46 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland, P. A. Ward (MSSL-UCL), and F. E. Marshall (NASA/GSFC) report on behalf of the Swift/UVOT Team: Preliminary UVOT photometry of the afterglow of GRB 080721 (Marshall, et al. 2008, GCN Circ. 7988) shows that the afterglow is strongly detected in the U band, but not in the UVW1, UVM2, or UVW2 bands at approximately 825 s after the BAT trigger. This suggests that the redshift of GRB 080721 may be greater than approximately 2.3. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7992 SUBJECT: GRB 080721, Swift-BAT refined analysis DATE: 08/07/21 15:19:27 GMT FROM: Scott Barthelmy at NASA/GSFC J. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC), K. McLean (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+750 sec from the recent telemetry downlink, we report further analysis of BAT GRB 080721 (trigger #317508) (Marshall, et al., GCN Circ. 7988). The BAT ground-calculated position is RA, Dec = 224.481, -11.709 deg, which is RA(J2000) = 14h 57m 55.4s Dec(J2000) = -11d 42' 33.3" with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). The partial coding was 4%. The mask-weighted light curve shows approximately six peaks. The first starts at ~T-11 sec and peaks at ~T-7 sec. The second and third peaks are much brighter. They peak at ~T+1 and ~T+7 sec. The remaining peaks are much smaller and stretch out to ~T+370 sec. T90 (15-350 keV) is 16.2 +- 4.5 sec (estimated error including systematics). The time-averaged spectrum from T-2.6 to T+25.8 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.11 +- 0.08. The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band is 20.9 +- 1.8 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/317508/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7993 SUBJECT: GRB 080721: Enhanced Swift-XRT position DATE: 08/07/21 16:20:26 GMT FROM: Phil Evans at U of Leicester J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) report on behalf of the Swift-XRT team. Using 2722 s of XRT Photon Counting mode data and 6 UVOT images for GRB 080721, 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 = 224.48231, -11.72363 which is equivalent to: RA (J2000): 14h 57m 55.75s Dec (J2000): -11d 43' 25.1" 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 http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an extension of this method. This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7994 SUBJECT: GRB 080721: Swift-XRT refined analysis DATE: 08/07/21 17:16:43 GMT FROM: Cristiano Guidorzi at INAF-OAB C. Guidorzi, F. Pasotti (INAF-OAB), F. E. Marshall (NASA/GSFC) report on behalf of the Swift-XRT team: We have analysed the first three orbits of Swift-XRT data obtained for GRB 080721 (Marshall et al., GCN Circ. 7988), covering 1.3 ks and 2.8 ks of Windowed Timing (WT) and Photon Counting (PC) modes data, respectively, between 113 s and 10.6 ks after the trigger. Notably, the whole first orbit data are taken in WT mode. The UVOT-enhanced XRT position was given by Osborne et al. in GCN Circ. 7993. The light-curve can be modelled by an initial power law with index 0.75 +/- 0.04 followed by a constant rate step from ~260 to 330 s, after which the curve resumes a power-law decay with an index of 1.06 +/- 0.01 up to 10.6 ks (chisq/dof = 1292/1207). A spectrum extracted from the first orbit of data can be modelled with an absorbed power-law, with Gamma = 1.90 +/- 0.02 and NH = (1.10 +/- 0.05)x1e21 cm^-2, in excess of the Galactic column in this direction of 6.9e20 cm^-2. We found no evidence for spectral evolution during this time interval. The observed (unabsorbed) flux over this time interval (113-1370 s post-trigger) is 2.2e-9 (2.7e-9) erg cm^-2 s^-1. If the light-curve continues to decay with alpha ~1.06, the count rate 24 hours after the burst is estimated to be 0.23 count s^-1, which corresponds to an observed flux of 9.6e-12 erg cm^-2 s^-1. This is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7995 SUBJECT: Konus-Wind observation of GRB 080721 DATE: 08/07/21 18:44:21 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team report: The bright GRB 080721 (Swift-BAT trigger #317508: Marshall et al., GCN 7988, Cummings et al., GCN 7992) triggered Konus-Wind at T0=37510.927 s UT (10:25:10.927). The burst light shows multipeaked structure with a duration of ~30 s. As observed by Konus-Wind the burst had a fluence of 8.38(-0.60, +0.62)x10^-5 erg/cm2, and a 64-ms peak flux measured from T0+9.648 s of (1.96 +/- 0.31)x10^-5 erg/cm2/s (both in the 20 keV - 5 MeV energy range). The time-integrated spectrum of the burst (from T0 to T0+23.808 s) is well fitted (in the 20 keV - 5 MeV range) by GRBM (Band) model for which: the low-energy photon index is alpha = -0.933(-0.084, +0.106), the high energy photon index beta = -2.43(-0.42, +0.24), the peak energy Ep = 485(-59, +67) keV (chi2 = 60.6/76 dof). All the quoted errors are at the 90% confidence level. The Konus-Wind light curve of this GRB is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB080721_T37510/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7996 SUBJECT: GRB 080721: UVOT Follow-Up Observations DATE: 08/07/21 20:55:10 GMT FROM: Paul Ward at MSSL P. Ward (MSSL-UCL), S. T. Holland (CRESST/USRA/GSFC) and F. E. Marshall (NASA/GSFC) report on behalf of the Swift/UVOT team: The Swift Ultra-Violet/Optical Telescope (UVOT) started observing GRB 080721 (Marshall et al., GCN 7988) ~118 seconds after the trigger. A fading afterglow is found in the UVOT White, V, B and U filters. The refined Swift/UVOT position of the optical afterglow candidate is: RA(J2000) = 14:57:55.855 = 224.48273 DEC(J2000) = -11:43:24.54 = -11.723483 with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence). The following table gives the measured magnitudes: Filter T_start T_stop Exp Mag white 118 217 99.8 14.58 +/- 0.00 white 858 957 99.8 16.94 +/- 0.03 white 5173 5372 199.8 19.12 +/- 0.08 white 6609 6808 199.8 19.43 +/- 0.11 v 225 624 399.7 14.98 +/- 0.01 v 964 1363 399.8 16.47 +/- 0.03 v 5583 5782 199.8 18.27 +/- 0.17 v 7020 7157 137.7 18.40 +/- 0.23 b 704 6603 409.4 16.56 +/- 0.12 u 680 6398 439.3 16.58 +/- 0.12 uvw1 655 6192 439.2 > 18.01 uvm2 631 5987 245.3 > 17.58 uvw2 734 7014 419.4 > 18.03 Using the measured magnitudes we find a power law decay index of -1.2 and -1.01 in the white and V filters respectively. The strong detection in the U band, but not in the UVW1, UVM2, or UVW2 bands gives an estimated photometric redshift in the range of 2.3 < z < 2.8. The values quoted above are in the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627). No correction has been made for the expected extinction corresponding to E(B-V) of 0.100 mag in the direction of the burst (Schlegel et al. 1998). [GCN OPS NOTE(12aug08): Per author's request, the "080703" was changed to "080721" in the first sentence.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7997 SUBJECT: TNG/DOLORES redshift for GRB080721 DATE: 08/07/21 23:16:34 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo (INAF-OAB), V. D'Elia (INAF-OAR), G. Adreuzzi, G. Tessicini (INAF-TNG), L. A. Antonelli, F. Fiore (INAF-OAR), D. Fugazza, C. Guidorzi (INAF-OAB) and G. Chincarini (Univ. Bicocca) report, on behalf of the CIBO collaboration: Following the Swift detection of GRB080721 (Marshall et al., GCN 7988), we triggered observations with the DOLORES low resolution spectrograph, mounted at the Italian TNG telescope located in the Canary Islands (Spain). The observations were performed using the LR-B grism. We took a 1800 s spectrum starting around Jul 21 at 21:30 UT (about 11.0 hours after the burst) and covering the range 300-780 nm with a resolution of R ~ 600. A preliminary analysis of the spectra shows a broad absorption feature at lambda_obs ~ 440 nm (based on a preliminary wavelength calibration). Interpreting this feature as Ly-alpha we infer a redshift z = 2.602, in agreement with the UVOT photometric redshift estimate (Holland et al., GCN 7991; Ward et al. GCN 7996). At this redshift we can detect also (rest frame) other absorption features like: CII (133.4 nm), SiIV doublet (139.3-140.2 nm), SiII (152.6 nm), CIV doublet (154.8-155.0 nm). We are very grateful for the excellent support of the TNG staff. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7998 SUBJECT: GRB 080721: OA fading and redshift DATE: 08/07/22 08:45:39 GMT FROM: Pall Jakobsson at U Hertfordshire P. Jakobsson (U. Hertfordshire), D. Malesani, P. M. Vreeswijk, J. P. U. Fynbo, B. Milvang-Jensen (DARK/NBI), A. de Ugarte Postigo (ESO), B. Nordstrom (NBI), E. Stonkute (ITPA, Vilnius) and P. Sorensen (NOT) report on behalf of a larger collaboration: We observed the optical afterglow of GRB 080721 (Marshall et al., GCN 7988; Chen et al., GCN 7990) with ALFOSC on the Nordic Optical Telescope at La Palma. The afterglow is well detected in a single 300 s exposure starting on 21.875 July 2008 (10.6 hr after the GRB). Comparison with several USNO-B1 stars (R1 magnitudes) yields R = 20.0 +/- 0.2, where most of the error comes from the calibration. Using the R-band magnitude provided by Chen et al., the inferred decay index is alpha ~ 0.9. Low resolution spectra (3 x 30 min) were also obtained. The combined spectrum displays a strong absorption feature around 4350 A, with the flux dropping substantially blueward of this feature. Associating it with Ly-alpha gives a redshift of z ~ 2.6 for the burst. We find several other absorption features, including O I, Si II, C II, Si IV, C IV, Fe II and Al II, corresponding to a redshift of z = 2.591 +/- 0.001, consistent with the redshift reported by D'Avanzo et al. (GCN 7997) and the UVOT photometric redshift (Ward et al., GCN 7996). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 8011 SUBJECT: VLA radio upper limit on GRB 080721 DATE: 08/07/24 14:13:47 GMT FROM: Poonam Chandra at U Virginia/NRAO Poonam Chandra (NRAO/UVA) and Dale A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We used the Very Large Array to observe the field of view toward optically bright GRB 080721 (GCN 7988) at a frequency of 8.46 GHz on 2008 July 24.15 UT. The GRB radio afterglow is undetected and the peak radio flux at the UVOT afterglow position (GCN 7988) is 93 ± 48 uJy. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."