//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6431 SUBJECT: GRB 070521: Swift detection of a burst DATE: 07/05/21 07:04:35 GMT FROM: Scott Barthelmy at NASA/GSFC C. Guidorzi (Univ Bicocca&INAF-OAB), S. D. Barthelmy (GSFC), P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. B. Markwardt (GSFC/UMD), A. Moretti (INAF-OAB), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB) and G. Tagliaferri (INAF-OAB) report on behalf of the Swift Team: At 06:51:10 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070521 (trigger=279935). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 242.669, +30.241 which is RA(J2000) = 16h 10m 41s Dec(J2000) = +30d 14' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows multiple peaks with a duration of about 40 sec. The peak count rate was ~7000 counts/sec (15-350 keV), at ~20 sec after the trigger. The XRT began taking data at 06:52:27 UT, 77 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image and no prompt position is available. However, the downlinked X-ray spectrum and lightcurve show that there is an X-ray object in the field that appears to be fading. Using prompt downlinked data, we find a position RA, Dec 242.6606, 30.2579 which is RA(J2000) = 16h10m 38.5s Dec(J2000) = +30d 15' 28.3'' with an uncertainty of 4.0 arcsec (radius, 90% containment). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 81 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of the BAT error circle. The typical 3-sigma upper limit has been about 18.5 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT 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 0.03. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6432 SUBJECT: GRB070521 - SDSS Pre-Burst Observations DATE: 07/05/21 07:12:54 GMT FROM: Richard J. Cool at U.of AZ/Steward Obs Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL), J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report: The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB070521 prior to the burst. As these data should be useful as a pre-burst comparison and for calibrating photometry, we are supplying the images and photometry measurements for this GRB field to the community. Data from the SDSS, including 5 FITS images, 3 JPGS, and 3 files of photometry and astrometry, are being placed at http://mizar.as.arizona.edu/~grb/public/GRB070521 We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=242.669 (16:10:40.6), dec=30.2410 (30:14:27.6); Swift-BAT TRIGGER 279935), as well as 3 gri color-composite JPGs (with different stretches). The units in the FITS images are nanomaggies per pixel. A pixel is 0.396 arcsec on a side. A nanomaggie is a flux-density unit equal to 10^-9 of a magnitude 0 source or, to the extent that SDSS is an AB system, 3.631e-6 Jy. The FITS images have WCS astrometric information. In the file GRB070521_sdss.calstar.dat, we report photometry and astrometry of 558 bright stars (r<20.5) within 15' of the burst location. The magnitudes presented in this file are asinh magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118, 1406). Beware that some of these stars are not well-detected in the u-band; use the errors and object flags to monitor data quality. In the files GRB070521_sdss.objects_flux.dat and GRB070521_sdss.objects_magnitudes.dat, we report photometry of 1833 objects detected within 6' of the GRB position. We have removed saturated objects and objects with model magnitudes fainter than 23.0 in the r-band. The fluxes listed in GRB070521_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB070521_sdss.objects_magnitudes.dat are asinh magnitudes. All quantities reported are standard SDSS photometry, meaning that they are very close to AB zeropoints and magnitudes are quoted in asinh magnitudes. Photometric zeropoints are known to about 2% rms. None of the photometry is corrected for dust extinction. The Schlegel, Finkbeiner, and Davis (1998) predictions for this region are A_U=0.145 mag, A_g=0.107 mag, A_r = 0.078 mag, A_i=0.059 mag, and A_z=0.042 mag. The file GRB070521_sdss.spectro.dat contains a list of the 5 objects with SDSS spectroscopy within 6 arcminutes of the GRB position. In addition to the redshift and 1-sigma error for each object, this file also lists the object spectroscopic classification. SDSS astrometry is generally better than 0.1 arcsecond per coordinate. Users requiring high precision astrometry should take note that the SDSS astrometric system can differ from other systems such as those used in other notices; we have not checked the offsets in this region. More detailed information pertaining to our SDSS GRB releases can be found in our initial data release paper (Cool et al. 2006, PASP 118, 733). See the SDSS DR4 documentation for more details: http://www.sdss.org/dr5. These data have been reduced using a slightly different pipeline than that used for SDSS public data releases. We cannot guarantee that the values here will exactly match those in the data release in which these data are included. In particular, we expect the photometric calibrations to differ by of order 0.01 mag. This note may be cited, but please also cite the SDSS data release paper, Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using the data or referring to the technical documentation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6433 SUBJECT: GRB070521: Bright SDSS Galaxy Near XRT Error Circle DATE: 07/05/21 07:44:44 GMT FROM: S. Bradley Cenko at Caltech E. O. Ofek, S. B. Cenko, and A. Rau (Caltech) report on behalf of a larger collaboration: The XRT error circle of GRB 070521 (Guidorzi et al. 2007; GCN 6431), coincides with the outskirts of a nearby (z=0.0307) bright (i=14.6) galaxy. The XRT position is 30.7" from the galaxy center (19 kpc projected). The SDSS coordinates of the galaxy are: RA = 16:10:40.75 DEC= +30:15:18.5 (J2000.0) For availbility of SDSS pre burst observations see Cool et al. (GCN 6432). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6434 SUBJECT: GRB 070521: TAROT La Silla observatory optical observations DATE: 07/05/21 07:47:14 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report: We imaged the field of GRB 070521 detected by SWIFT (trigger 279935) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 23.8s after the GRB trigger (8.5s after the notice). The elevation of the field decreased from from 24 degrees above horizon and weather conditions were highly variable (cloudy). The date of trigger : t0 = 2007-05-21T06:51:10.656 The first image is trailed with a duration of 60.0s from t0+23.8s to t0+83.8s (see the description in Klotz et al., 2006, A&A 451, L39). The limiting magnitude is R ~ 17.1. We do not detect any OT at the XRT position mentioned by Guidorzi et al. (GCNC 6431) but we have a faint patch at coordinates 16h10m37.5s (+/-0.5s) +30d14'58" (+/-5") J2000.0 near the limiting magnitude. The second image is 30.0s exposure in tracking mode, no OT is detected: t0+89.4s to t0+119.4s : R > 17.5 We co-added a series of exposures: t0+89.4s to t0+570.3s : R > 19.0 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6435 SUBJECT: GRB070521 : Faulkes Telescope North Observations DATE: 07/05/21 07:55:27 GMT FROM: Andrea Melandri at Liverpool John Moores U A. Melandri, I. A. Steele, C. G. Mundell, C. Guidorzi, D. Carter, R. J. Smith, C. J. Mottram, D. F. Bersier, S. Kobayashi, M. F. Bode (Liverpool JMU), A. Gomboc (Ljubljana), P. O'Brien, E. Rol, N. Bannister (Leicester) report The 2-m Faulkes Telescope North robotically followed up GRB070521 (Guidorzi et al., GCN 6431, trigger=279935) beginning ~2.5 minutes after the GRB trigger time (UT:06:51:10). No new object has been detected inside the XRT error circle (Guidorzi et al., GCN 6431) down to a limiting magnitude of R~19.3 (texp = 30 sec) and I~18.5 (texp = 10 sec), at a mean epoch of ~3 and ~6 minutes after the burst, respectively (comparison with respect to the USNO B1 catalog). Further observations are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6436 SUBJECT: GRB070521: P200 Observations DATE: 07/05/21 08:54:12 GMT FROM: S. Bradley Cenko at Caltech A. Rau, M. M. Kasliwal, and S. B. Cenko (Caltech) report on behalf of a larger collabortation: We obtained R-band photometry of GRB070521 with the Large Format Camera mounted on the Palomar 200-inch telescope. Observations started 29 min post-burst and lasted 3x300s. Calibration was performed relative to the SDSS (Cool et al.; GCN 6432). We find no source in the XRT error circle (Guidorzi et al. 2007; GCN 6431) to a limiting magnitude of R>23.3. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6437 SUBJECT: GRB 070521: optical limit by Pi of the Sky DATE: 07/05/21 09:15:54 GMT FROM: Grzegorz Wrochna at Soltan Inst.for Nuclear Studies M.Biskup, M.Cwiok, W.Dominik, G.Kasprowicz, A.Majcher, A.Majczyna, K.Malek, L.Mankiewicz, M.Molak, K.Nawrocki, L.W.Piotrowski, M.Sokolowski, J.Uzycki, G.Wrochna, F.Zarnecki on behalf of "Pi of the Sky" collaboration http://grb.fuw.edu.pl "Pi of the Sky" apparatus located at Las Campanas Observatory imaged the region of GRB 070521 from 6:13 UT, i.e. 38 minutes before the GRB, with 10s exposures (IR-cut filter only). The most interesting exposure started at 6:51:10.9, i.e. exactly in coincidence with the GRB trigger. Variable thin clouds seriously disturbed the observations. No OT was detected within the XRT error box. Limits for 10s exposures: 6:50:44-6:50:54 >11.7 6:50:57-6:51:07 >11.9 6:51:10-6:51:20 >12.0 --- GRB trigger 6:51:24-6:51:34 >12.0 6:51:38-6:51:48 >12.2 Limits for 20 coadded images 6:42:51-6:47:17 >12.2 6:47:21-6:51:48 >12.6 6:51:52-6:56:18 >12.5 6:56:22-7:00:53 >12.7 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6440 SUBJECT: GRB 070521, Swift-BAT refined analysis DATE: 07/05/21 13:29:22 GMT FROM: Scott Barthelmy at NASA/GSFC D. Palmer (LANL), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-240 to T+377 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070521 (trigger #279935) (Guidorzi, et al., GCN Circ. 6431). The BAT ground-calculated position is RA, Dec = 242.659, 30.261 deg which is RA(J2000) = 16h 10m 38.1s Dec(J2000) = 30d 15' 37.9" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 47%. The mask-weighted light curve shows five main peaks the first of which starts at ~T-10 sec and the last ends at ~T+50 sec. T90 (15-350 keV) is 37.9 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T-14.5 to T+49.7 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.10 +- 0.17, and Epeak of 195 +- 123 keV (chi squared 50 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 8.0 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+30.48 sec in the 15-150 keV band is 6.7 +- 0.3 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.38 +- 0.04 (chi squared 58 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6444 SUBJECT: GRB 070521: Subaru observations and possible host detection DATE: 07/05/21 23:46:59 GMT FROM: Nobuyuki Kawai at Tokyo Tech T. Hattori, K. Aoki (Subaru Telescope, NAOJ), and N. Kawai (Tokyo Tech) report on behalf of the Subaru GRB team: "We observed the field of GRB 070521 (Guidorzi et al., GCN 6431) with FOCAS on the Subaru Telescope starting at 07:31(UT) (40 min after the trigger) with total exposures of 1920 sec (120s x 16) in z'-band and 360 sec (120s x 3) in i'-band. We detected a faint source inside the XRT error circle at RA=16:10:38.55, DEC=30:15:27.7 with a positional uncertainty of 0.5" and an approximate magnitude of z' ~ 23.5. We obtained 3600 sec long-slit spectra of this faint source covering a wavelength range from 6000 to 10000 Ang. We detected [O III] 5007, 4959 emission lines at z=0.553. If this object is the host galaxy of GRB 070521, its location at a relatively low redshift makes it a good candidate for searching the supernova component. Note, however, that the absence of a bright afterglow may indicate that the GRB source is embedded in a region with high extinction, or the host identification is spurious. The image may be viewed at http://www.hp.phys.titech.ac.jp/nkawai/grb/070521/. We thank the Subaru Observatory for the support of this observation." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6445 SUBJECT: GRB 070521: SARA upper limit DATE: 07/05/22 00:21:31 GMT FROM: Adria C. Updike at Clemson U A. C. Updike, J. R. Puls, and D. H. Hartmann (Clemson University) report on behalf of the Clemson GRB Follow-Up Team: We imaged the field of GRB 070521 (GCN 6431, Guidorzi et al.) beginning 14 minutes after the trigger (279935) with the SARA 0.9m at Kitt Peak under decent weather conditions. In 50 minutes of stacked exposures in the R band, we detect no new sources in the XRT error circle down to a limiting magnitude of 20 +/- 0.4. We do not detect the source noted by Hattori et al. (GCN 6444). This magnitude is based on calibration to 5 USNO B1.0 stars. The SARA Homepage can be found at: http://saraobservatory.org This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6448 SUBJECT: GRB 070521 Milagro GeV/TeV Observations DATE: 07/05/22 01:49:29 GMT FROM: Pablo Saz Parkinson at UCSC/Milagro Pablo Saz Parkinson (UC Santa Cruz) on behalf of the Milagro collaboration reports: We have searched Milagro data for emission at GeV/TeV energies from GRB 070521 detected by Swift (GCN Circ 6431, C. Guidorzi et al.), during the main period of emission lasting 60s (GCN Circ 6440, D. Palmer et al.). No evidence for prompt GeV/TeV emission was found. TeV photons are attenuated by pair production with infrared photons in intergalactic space. We calculate an upper limit assuming two possible values for the redshift: z=0.03 (GCN Circ 6433, E. O. Ofek et al.), and z=0.55 (GCN Circ 6444, T. Hattori et al.) using the extragalactic infrared background light (EBL) absorption model of Primack et al. 2005 (AIP Conf. Proc. 745, p. 23). A preliminary analysis, assuming a differential photon spectral index of -2.4, gives upper limits on E^2dN/dE at 99% confidence of: E^2 dN/dE at 250 GeV < 3.5 * 10^(-7) erg cm^(-2) (Assuming z=0.03) and E^2 dN/dE at 200 GeV < 5.5 * 10^(-6) erg cm^(-2) (Assuming z=0.55) The energies quoted represent the approximate median energy of the events that would be detected assuming a power law spectrum with differential index -2.4 convolved with the absorption model. These upper limits are preliminary and will be refined with further analysis. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6449 SUBJECT: GROND upper limits of GRB 070521 DATE: 07/05/22 03:05:20 GMT FROM: Jochen Greiner at MPI J. Greiner, C. Clemens, T. Kruehler, A. Kuepcue-Yoldas, N. Primak, G. Szokoly, A. Yoldas (all MPE Garching), S. Klose, U. Laux (Tautenburg Obs), and C.C. Thoene (DARK/NBI Copenhagen) report: We have observed GRB 070521 (trigger 279935, Guidorzi et al. 2007, GCN #6431) with the 7-channel imager GROND, mounted at the 2.2m Max-Planck Institute telescope at La Silla (ESO/Chile). Observations started at 06:59 UT, about 8 min. after the GRB trigger, and continued for 25 min until the telescope's elevation limit of 20 deg above horizon was reached. The observation consisted of a series of 60-second exposures each in g', r', i, and z', and 10-second exposures in J, H, and Ks, respectively. The GRB field was observed through changing, thick cloud coverage, therefore, only 50% of the images are useful and the flux in the remaining images is reduced. No source is detected within the Swift XRT error circle (GCN #6431). We derive the following, preliminary 2 sigma upper limits using SDSS (Cool et al 2007, GCN #6432) and 2MASS photometry of stars within the field: g' > 22.0 r' > 21.7 i > 20.7 z' > 20.3 J > 20.0 H > 17.9 K > 17.2 The object see by Subaru (Hattori et al, GCN #6444) is not seen in any of our stacked images. GROND is presently being commissioned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6450 SUBJECT: GRB070521: Gemini Observations DATE: 07/05/22 03:13:53 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko (Caltech), P. A. Price (IfA/Hawaii), and E. Berger (OCIW) report on behalf of a larger collaboration: We have imaged the field of GRB070521 (Guidorzi et al.; GCN 6431) with the Gemini Multi-Object Spectrograph (GMOS) and the Near-Infrared Imager (NIRI) mounted on the Gemini North Telescope. Observations were taken in the g', i', z' (GMOS) and J, H, Ks (NIRI) filters, beginning at 7:36:54 UT on 21 May 2007. We weakly detect the host candidate proposed by Hattori, Aoki, and Kawai (GCN 6444) only in our i'- and Ks-band images. In the table below we report a summary of our observations. Photometric calibration was performed relative to SDSS (Cool et al.; GCN 6432) for the GMOS images and the 2MASS point source catalog for our NIRI imaging. Filter t - t_b (hr) Exposure (s) Magnitude ------------------------------------------------------------------------- g' 1.08 2 x 180 > 25.0 i' 1.21 2 x 180 ~ 24.1 z' 1.33 4 x 180 > 23.0 J 1.92 15 x 30 > 21.5 H 2.20 15 x 30 > 21.0 Ks 2.50 15 x 30 ~ 22.3 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6451 SUBJECT: GRB 070521: Keck imaging DATE: 07/05/22 07:49:54 GMT FROM: Daniel Perley at U.C. Berkeley D. A. Perley, J. S. Bloom (UC Berkeley), J. X. Prochaska (UC Santa Cruz), S. Stanford (LLNL), M. Brodwin (JPL), and N. R. Butler (UCB) report: Starting at 13:21:22 UT (2007-05-21), we imaged the field of GRB 070521 (GCN 6431) in V and R band with the Keck I telescope (+ LRIS), in a series of five exposures of 300 seconds each. The host galaxy candidate of Hattori et al. (GCN 6444, "S1") is clearly detected, as is a second source ("S2") at the edge of the XRT error circle (Guidorzi et al., GCN 6431). We also detect a third, extended source ("S3") further to the south, not consistent with the preliminary XRT position reported by Guidorzi et al. but consistent with our preliminary re-analysis of the XRT data. The positions of these sources (J2000) are: S1: 16:10:38.562 +30:15:27.50 S2: 16:10:38.734 +30:15:31.38 S3: 16:10:38.754 +30:15:21.57 The astrometric uncertainty is about 0.3" in each coordinate. Preliminary aperture magnitudes of these sources, calibrated with respect to the SDSS magnitudes from Cool et al. (GCN 6432) using the Lupton transform [1], are: S1: V = 25.46 +/- 0.12 , I = 23.88 +/- 0.12 S2: V = 25.98 +/- 0.20 , I = 24.26 +/- 0.16 S3: V = 26.63 +/- 0.39 , I = 24.39 +/- 0.17 These magnitudes are not corrected for Galactic extinction, which the NED extinction calculator [2] estimates to be E(B-V) = 0.027, or A_V = 0.09, A_I = 0.05, in this direction. An image of the field is located at: http://lyra.berkeley.edu/~dperley/070521/070521keckI.png http://lyra.berkeley.edu/~dperley/070521/070521keckI_clean.png --- [1] http://www.sdss.org/dr5/algorithms/sdssUBVRITransform.html#Lupton2005 [2] http://nedwww.ipac.caltech.edu/forms/calculator.html //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6452 SUBJECT: GRB 070521: Swift-XRT refined analysis DATE: 07/05/22 09:07:39 GMT FROM: Cristiano Guidorzi at INAF-OAB C. Guidorzi, P. Romano (Univ Bicocca&INAF-OAB), J. Hill (GSFC), A. Beardmore, P.A. Evans (U. Leicester), A. Moretti (INAF-OAB), report on behalf of the Swift team: We have analysed the first five orbits of GRB 070521 (Guidorzi et al., GCN Circ. 6431) with total observing times of 10.2 ks in Photon Counting mode in the Swift XRT. The XRT position, using the UVOT to astrometrically correct the XRT field, assuming a fixed mapping between the XRT and UVOT instruments, is RA(J2000)=242.6608 deg, Dec(J2000)=+30.2561 deg, corresponding to: RA(J2000) = 16h 10m 38.60s Dec(J2000) = +30d 15' 21.8" with an uncertainty of 1.7 arcsec (radius, 90% containment). This was based on 3 intervals of overlapping XRT/UVOT V-band data totalling 866 s. The UVOT astrometry is performed relative to USNOB1. This is 6.6 arcsec from the initial X-ray position, 4.0 arcsec from the XRT position notice, and 17 arcsec from the BAT refined position (Palmer et al., GCN Circ. 6440). The XRT light curve exhibits an initial flaring behaviour superposed to a power-law decay (index of 0.5 +/- 0.1) up to ~T+600 s. A break in the power-law decay is observed at T+(6.8 +/- 0.9) ks, after which it steepens with a power-law index of 1.7 +/- 0.1 up to T+34 ks (90% confidence intervals). We extracted a spectrum of the PC data from T+4.7 ks to T+13 ks. This can be fit with an absorbed power law with a photon index of 2.11 +/- 0.16 and column density of (7+/-1)E21 cm^-2 significantly in excess of the Galactic value (2.8E20 cm^-2; Dickey & Lockman, 1990). The absorbed (unabsorbed) 0.3-10.0keV flux for that spectrum is 1.6E-11 (3.2E-11) ergs cm^-2 s^-1. Assuming the source continues to decay at the same rate, we predict an XRT count rate of 7.9E-3 counts/s at T+24 hours, which corresponds to an observed (unabsorbed) flux of 4.6E-13 (9.3E-13) ergs cm^-2 s^-1. This circular is an official product of the Swift XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6453 SUBJECT: GRB 070521, optical observation DATE: 07/05/22 10:20:04 GMT FROM: Shouta Maeno at U.of Miyazaki S.Maeno, R.Hara, H.Tanaka, E.Sonoda, M.Yamauchi (University of Miyazaki) We have observed the field of GRB 070521 (GCN 6431) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started from 11:47:35 UT on May 21(4.9 h after the trigger). After co-adding a set of 32 images (11:47:35 - 12:46:04 UT) of 30 sec exposures, we have compared with the USNO A2.0 catalog. Preliminary analysis shows there is no new source brighter than 17.8mag. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6454 SUBJECT: GRB 070521: Swift/UVOT Upper Limits DATE: 07/05/22 16:16:15 GMT FROM: Frank Marshall at GSFC F.E. Marshall (NASA/GSFC) and C. Guidorzi (U. Bicocca & INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT observed the field of GRB 070521 starting 82 s after the BAT trigger (Guidorzi et al., GCN Circ. 6431). We do not find any source in any of the UVOT observations inside the refined XRT error circle (Guidorzi et al., GCN Circ. 6452). The 3-sigma upper limits for detecting a source in the first finding chart (FC) exposure and co-added frames are: Filter T_start(s) T_stop(s) Exp(s) Mag (3-sigma UL) White (FC) 82 182 98 >20.6 White 82 24605 1884 >22.3 V 187 17181 1451 >20.4 B 5304 23879 1967 >22.0 U 5099 22968 1278 >21.7 UVW1 4894 18810 1111 >21.1 UWM2 4869 18085 1279 >20.8 UVW2 5713 12897 792 >21.1 The values quoted above are not corrected for the expected Galactic extinction corresponding to a reddening of E(B-V) = 0.03 mag towards the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6456 SUBJECT: GRB070521: NIR observations DATE: 07/05/22 20:25:19 GMT FROM: Paul Price at IfA,UH T. Minezaki (IoA, Tokyo) and P.A. Price (IfA, Hawaii) report on behalf of a larger collaboration: We observed the localisation of GRB070521 with the MAGNUM telescope + MIPS dual-beam imager. While our observations consist of both optical and NIR images, we report here only the NIR imaging. We do not find any afterglow within the XRT error circle (GCN ##6431,6452) to the following limits (based on flux calibration with a nearby 2MASS star): Filter t - t_GRB (min) Limit (mag) J 49.2 20.7 H 106.6 20.3 K 87.1 19.2 This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6457 SUBJECT: GRB070521: Second Epoch Gemini Imaging DATE: 07/05/23 07:21:00 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko, E. O. Ofek (Caltech) and P. A. Price (IfA) report on behalf of a larger collaboration: We have re-imaged the field of GRB070521 (Guidorzi et al., GCN 6431) with the Gemini Multi-Imaging Spectrograph mounted on the Gemini North telescope. We obtained 5 x 180 s in the Sloan i' filter at a mean epoch of 10:23:38 UT 22 May. The host candidate (S1) identified by Hattori et al. (GCN 6444; see also Perley et al., GCN 6451) is well detected in our second epoch. In comparison with our first epoch of i' imaging (GCN 6450), we find marginal evidence for fading of this source. Specifically, we measure the following magnitudes, with calibration performed relative to SDSS field stars (Cool et al., GCN 6432): t-tb (hr) Magnitude ---------------------------------------------------------------- 1.21 24.07 +\- 0.17 27.54 24.30 +\- 0.09 However, PSF-matched image subtraction using the ISIS software package (Alard & Lupton, ApJ, 503, 1998) reveals no variability at the location of this source. We do not find any new sources inside the revised XRT error circle (Guidorzi et al., GCN 6452) in either epoch of imaging, to limits of i' > 24.0 (epoch 1) and i' > 25.0 (epoch 2). The source S3 is marginally detected in our second epoch near the detection limit. This would represent a decline from measurements reported previously (I = 24.39; Perley et al., GCN 6451). However, we caution our photometry at this location is affected by a variable background from the nearby bright galaxy and is therefore quite uncertain. We encourage further observations to establish the nature of this object. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6459 SUBJECT: Konus-Wind observation of GRB 070521 DATE: 07/05/23 16:45:59 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and T. Cline on behalf of the Konus-Wind team report: The long GRB 070521 (Swift-BAT trigger #279935: Guidorzi et al., GCN 6431; Palmer et al., GCN 6440) triggered Konus-Wind at T0=24691.587 s UT (06:51:31.587). The burst started at T-T0 ~-33 s and had a duration of ~55 s. As observed by Konus-Wind the burst had a fluence of 1.81(-0.31, +0.06)x10^-5 erg/cm2, and a 64-ms peak flux measured from T0+5.312 s 4.12(-1.07, +0.78)x10^-6 erg/cm2/s (both in the 20 keV - 1 MeV energy range). The burst shows strong spectral evolution. The time-integrated spectrum of the burst (from T0 to T0+23.808 s: this interval comprises ~80% of the burst total counts) can be fitted (in the 20 keV - 1 MeV range) by a power law with exponential cutoff model: dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep) with alpha = 0.93 +/- 0.12 and Ep = 222(-21, +27) keV (chi2 = 43/56 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/GRB070521_T24691/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6482 SUBJECT: GRB070521: optical observation DATE: 07/06/02 16:32:24 GMT FROM: Vasilij Rumjantsev at CrAO V. Rumyantsev (CrAO), V. Biryukov (CrAO, SAI MSU), A. Pozanenko (IKI) on behalf of larger GRB follow up collaboration report: We observed error box of GRB070521 (Guidorzi et al., GCN 6431) with 1-m Zeiss (Simeiz) telescope of CrAO in R-band on May 21 between (UT) 20:38 and 21:00. No object is found in a refined XRT error box (Guidorzi et al., GCN 6452). Limiting magnitude of combined a image is based on USNO A2.0: Mid time (UT), Exposure, R_Lim (3sigma), Telescope, Seeing May 21.868 20x60 22.4 1-m Ziess 2.3" This message may be cited. [GCN OPS NOTE(02jun07): The binary attachment was removed as well as the diagnostics from MIMEDefang reacting to that binary.]