//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3665 SUBJECT: GRB050724: a short-burst detected by Swift DATE: 05/07/24 13:34:04 GMT FROM: Stefano Covino at Brera Astronomical Observatory S. Covino (INAF/OAB), L.A. Antonelli (INAF/OAR), P. Romano (INAF/OAB), D. Palmer (LANL), C. Markwardt(GSFC, UMd), D. Burrows (PSU), N. Gehrels (GSFC), S. Barthelmy (GSFC), M. Chester (PSU), S. Hunsberger (PSU), J. Cummings (GSFC/NRC) on behalf of the Swift team At 12:34:09 UT, Swift-BAT triggered and located GRB050724 (trigger=147478). The spacecraft slewed immediately. The BAT on-board calculated location is RA,Dec 246.214, -27.524 {+16h 24m 51s, -27d 31' 25"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The light curve appears to be short, with full-width half maximum of less than 0.25 sec, and a peak rate of 10,000 ct/s in that interval. The XRT started the observation at 12:35:22.9 UT with XRT in automatic state, 74 sec after the BAT Trigger. A rapidly fading, uncatalogued, X- ray source was detected at the following position RA, Dec 16h 24m 44.9s, -27d 32' 34.0" with an uncertainty of about 6 arcsec (90% containment). This is 1.78 arcmin from the BAT position reported above. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3666 SUBJECT: GRB 050724: possible host galaxy in DSS DATE: 05/07/24 14:25:16 GMT FROM: Angelo Antonelli at Obs. Astro. di Roma L.A. Antonelli (INAF/OAR), S. Covino (INAF/OAB), D. Malesani (SISSA), P. Romano, A. Moretti (INAF/OAB) on behalf of the MISTICI collaboration report: We looked at the DSS image of the field of the short GRB 050724 (Covino et al., GCN 3665). We note the presence of a faint object located at RA: 16h 24m 44.9s DEC -27d 32' 33.3" (J2000) and centered on XRT position (Covino et al., GCN 3665) which is under the threshold of both USNO and 2MASS catalogues. We estimated a R mag for this object of 19.1 calibrating with the nearby USNO star (U600_20428424 RA: 16:24:47.92, DEC: -27:32:21.05 R=16.5 mag). This message can be cited //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3667 SUBJECT: GRB050724: Refined analysis of the Swift-BAT possible short burst DATE: 05/07/24 16:27:35 GMT FROM: Scott Barthelmy at NASA/GSFC H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hinshaw (GSFC-SPSYS), D. Hullinger (GSFC/UMD), C. Markwardt (GSFC/UMD), K. McLean (LANL) D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the full data set from the recent telemetry downlink, we report further analysis of Swift-BAT Trigger #147478 (Covino, et al., GCN 3665). The ground-analysis position is RA,Dec 246.177,-27.525 (J2000) with an uncertainty of 3 arcmin (radius, 90%, stat+sys). T90 is 3 +- 1 sec. The lightcurve has an initial hard FRED peak at T+0.00 sec (FWHM of 0.256 sec) and there is a smaller much softer peak at T+1.00 sec. Fitting a simple power law over the full interval from T-1.0 to T+3.0 seconds, the photon index is 1.71 +/- 0.16 with a fluence of 6.3 +/- 1.0 X 10^-7 erg/cm^2. The peak flux in a 1-sec wide window starting at T+0.04 seconds is 3.9 +/- 0.3 ph/cm^2/sec. All values are in the 15-350 keV band at the 90% confidence level. Given the second emission peak at T+1, the T90 of 3 sec, and the power law index value of 1.71, we can not confirm, nor rule out, that this burst falls into the short-burst category. However, in the energy range above 25 keV, the second, softer peak and subsequent emission is much less prominent, and so it is likely that BATSE would have classified this as a short GRB. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3668 SUBJECT: GRB 050724 : Lulin early R-band monitoring observations DATE: 05/07/24 16:48:46 GMT FROM: Yuji Urata at RIKEN I.C. Yen (NTNU), H.C. Lin, K.Y. Huang, W.H. Ip (NCU), Y. Urata (RIKEN), Y. Qiu (BAO), Y.Q. Lou (THCA) on behalf of EAFON report: " We started to image the GRB 050724 error region (Covino et al GCN 3665) at 14.26 UT (~1.69 hours after the burst) using 1.0-m telescope at Lulin Observatory, Taiwan. The source reported by Antonelli et al. (GCN 3666) was detected in a series of R-band 300 sec exposure. Our preliminary analysis shows the brightness of the source do not have significant variability during our monitoring observations (1.69-3.59 hours after the burst). This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3669 SUBJECT: GRB 050724: early Swift XRT analysis results DATE: 05/07/24 18:30:47 GMT FROM: Pat Romano at OAB-Swift P. Romano, A. Moretti, S. Covino (INAF-OAB), L.A. Antonelli(IANF-OAR), D.N. Burrows, D. Grupe (PSU), M. Chester (PSU), G. Chincarini, G. Tagliaferri (INAF-OAB), P. Boyd (GSFC-UMBC) on behalf of the Swift-XRT Team report. We have analyzed the Swift XRT data from the first orbit observation of GRB 050724 (Covino et al., GCN 3665). The new refined coordinates are: RA(J2000) = 16h 24m 45s Dec(J2000) = -27 32 25.2. This position is 65 arcseconds from the refined BAT position given in GCN 3667 (H. Krimm et al), and 9 arcseconds from the XRT position given in GCN 3665. We estimate an uncertainty of 6.3 arcseconds radius (90% containment). However, we note that there is accumulating evidence of a time-dependent systematic shift in XRT positions derived from ground-processed data towards lower declinations than the optical counterparts. This effect is being investigated but is not yet understood. Extrapolation of earlier positional errors suggests that the correct position could be approximately 7 arcseconds north of the position given above, which would be close to the on-board position given in GCN 3665. A preliminary spectral fit (simple absorbed power-law) to the WT data yields a photon index of 1.93-/+0.05 in the [0.5-10] keV band. The derived NH is (5.7)E21 cm^-2, which is higher than the Galactic value (1.46E+21 cm-2; Dickey & Lockman 1990). The average (79-342 seconds from trigger) estimated unabsorbed 0.5-10 keV flux is 5.3E-9 ergs/s/cm2. The light curves in Windowed Timing (WT) and Photon Counting (PC) mode start 79 and 343 seconds from the BAT trigger (T0), and they show a fading afterglow which can be fitted with a broken power law of slopes -3.2+/-0.1 and -0.8+/-0.2. The unabsorbed 0.5-10.0 keV flux at 24 hours after the burst is then estimated to 9E-14 ergs/s/cm2. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3670 SUBJECT: GRB 050724: Swift/UVOT Upper Limit DATE: 05/07/24 21:10:45 GMT FROM: Margaret Chester at PSU M. Chester (PSU), S. Covino (OAB), P. Schady (MSSL), P. Roming (PSU) N. Gehrels (GSFC), on behalf of the Swift UVOT team. Using summed images from Swift/UVOT of the field of GRB 050724 (Covino et al., GCN 3665), accumulated during the first forty minutes after the BAT trigger, no new source is detected within the XRT error circle in the V filter down to a 3-sigma limit of V=18.84. The magnitudes are based on preliminary zero-points, measured in orbit, and will require refinement with further calibration. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3671 SUBJECT: GRB 050724: RTT150 optical observations DATE: 05/07/24 22:40:13 GMT FROM: Rodion Burenin at IKI, Moscow R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), A. Alpar (SabUni), I. Bikmaev, N. Sakhibullin (KSU/AST) report: We observed the error box of GRB 050724 (Covino et al., GCN 3665) with Russian-Turkish 1.5-m telescope (RTT150, Bakyrlytepe, TUBITAK National Observatory, Turkey). We made a set of 600s exposures in R, starting at 18:11 UT, July 24, i.e. approximately 5.6 hours after the burst. Observations were made at very high zenith distance (65-75 degrees) and in poor seeing conditions (~2 arcsec). We found no variable sources brighter than our limiting magnitude, which is only slightly deeper than DSS. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3672 SUBJECT: GRB 050724: Optical imaging/astrometry DATE: 05/07/25 01:09:43 GMT FROM: Josh Bloom at Harvard/CFA J. S. Bloom (UC Berkeley), A. Dupree (Smithsonian Astrophysical Observatory), H-W. Chen (MIT), & J. X. Prochaska (UC Santa Cruz) report: "Comparison of the 2MASS catalog with a short exposure with the unfiltered MIKE (Magellan II/Clay) guider CCD camera beginning on 2005-07-24 23:25:25 UTC shows faint sources near the XRT localizations (GCNs #3665 & #3669). We find the following positions (systematic error relative to the ICRS is 0.2" in both RA and DEC): A 16:24:44.964 -27:32:23.21 J2000 Source 1 in #3669 error circle B 16:24:44.912 -27:32:32.73 J2000 Source 1 in #3665 error circle, noted by Antonelli et al. #3666 C 16:24:45.303 -27:32:34.67 J2000 Source 2 in #3665 error circle D 16:24:44.398 -27:32:26.85 J2000 Bright galaxy to the West of XRT error circles Source D appears to be an extended galaxy and, while formally excluded by the 90% confidence regions of the various positions reported for the X-ray afterglow, is of interest nonetheless (especially given what appears to be an emerging trend of low-redshift galaxies associated with short bursts)." A finding chart may be found at: http://astro.berkeley.edu/~jbloom/grb050724.png Please email JSB if you would like to make use of the guider FITS image. This message may be cited. [GCN OPS NOTE 924jul05): Per author's request, hanged "astronomy" to "astrometry" in the Subject.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3673 SUBJECT: GRB 050724: optical and near-IR observations DATE: 05/07/25 02:38:16 GMT FROM: Javier Gorosabel at LAEFF-INTA, Madrid A.J. Castro-Tirado, J. Gorosabel, A. de Ugarte Postigo, S. Guziy and M. Jelínek (IAA-CSIC), M. Karrer (Obs. de Geneve), H.-J. Roeser (MPI Heidelberg), N. Elías-Rosa (Obs. Astr. di Padova), O. Bogdanov (Nikolaev State Univ.) and A. Aguirre (CAHA Almería) report: "We have imaged a 6' x 6' region centred on the SWIFT/BAT error box for the short/hard GRB 050724 (Covino et al. GCNC 3665) with the 1.2-m Mercator telescope (+ Merope) at the Observatorio del Roque de los Muchachos on La Palma starting on July 24.890 UT (i.e. 8.8 hours after the GRB) under good meteorological conditions. Within the refined SWIFT/XRT position (Romano et al. GCNC 3669), the co-added R-band image (5400 s exposure time) shows a source close to the center of the 6.3 arcsec radius error box, labelled as A by Bloom et al. (GCN Circ. 3672). Coordinates yield: RA(2000) = 16 24 44.96, Dec(2000) = -27 32 23.6 (+/- 0.5"). We measure R = 22.40 +/- 0.13 using the USNO-A2.0 star at RA(2000) = 16 24 44.55, Dec(2000) = -27 32 59.9. This source is blue, since it is barely detected in contemporaneous J- and K-band images obtained at the 3.5-m telescope (+ Omega2000) at the German-Spanish Calar Alto Observatory and in H-band frames obtained at the 3.5-m Telescope Nazionale Galileo (+ NICS) on La Palma. The colours of objects B and C are also consistent with being blue, in contrast to the redder galaxy labelled D. Further observations are needed to confirm whether any of these objects has any relationship to GRB 050724." This message can be quoted. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3674 SUBJECT: GRB 050724: Optical limit DATE: 05/07/25 03:56:34 GMT FROM: Ken ichi Torii at RIKEN K. Torii (Osaka U.) reports on behalf of the ART collaboration: The error region of the possible short GRB 050724 (Covino et al. 3665, Krimm et al. GCN 3667) was observed by the 14 inch Automated Response Telescope in Osaka. The imaging started at 2005 July 24 12:40:35 UT (75 s after the alert reception; 386 s after the trigger) and RcIcBV frames of 60s integration were obtained. We find no optical counterpart for the X-ray afterglow (GCN 3665, Romano et al. GCN 3669) and derive its 3-sigma upper limit relative to USNO-B1.0 magnitude as follows. ================================ Start(UT) Filter Mag Exposure -------------------------------- 12:41:43 Ic >14.5 60s -------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3675 SUBJECT: GRB 050724: spectroscopy of object in the XRT error circle DATE: 05/07/25 18:05:48 GMT FROM: Silvia Piranomonte at OAR S. Piranomonte (INAF/OAR), D. Fugazza (INAF/OABr), F. Fiore (INAF/OAR), S. Covino (INAF/OABr), P. D'Avanzo (INAF/OABr), D. Malesani (SISSA), G. Tagliaferri (INAF/OABr), G. Chincarini (Univ. Milano-Bicocca) and L. Stella (INAF/OAR), on behalf of the MISTICI collaboration, report: Using the FORS1 instrument at the ESO VLT, we obtained a spectrum of the object indicated by Antonelli et al. (GCN 3666), also named as object B by Bloom et al. (GCN 3672). This object is liying close to the XRT errorbox center (Covino et al., GCN 3665; Romano et al., GCN 3669). Observations were obtained on 2005, July 24, starting at 23:16:00 UT, under good seeing conditions. We used the grism 300V with a slit of 1.0 arcsec. The integration time was 900 s. The object is identified with a star trough Ca, CN, G-band, Hbeta, Na and Halpha faint absorption lines. It has therefore no likely association with GRB 050724. We thank the excellent work by the ESO staff in performing these observations. This message may be cited. [GCN OPS NOTE(28jul05): Per author's request, in the Subject-line the "GRB 050624" was changed to "GRB 050724".] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3676 SUBJECT: GRB050724: Radio Observation DATE: 05/07/25 21:19:00 GMT FROM: Patrick B. Cameron at Caltech P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie collaboration: "We observed the field of GRB050724 (GCN 3665) with the Very Large Array at 8.5 GHz on July 25.09. We identify one radio source that is ~9" west from the center of the XRT error circle (GCN#3669). Its position is (J2000): RA= 16:24:44.35, Dec= -27:32:26.9. We note that, within our current astrometric errors this source is positionally coincident with with the bright galaxy identified as Source D by Bloom et al. (GCN#3672). Based on background source counts, we expect 0.02 sources per square arcminute above this brightness (~170 uJy). Further observations are planned to determine the nature of this radio source. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3677 SUBJECT: RXTE ASM Detection of GRB050724 DATE: 05/07/25 22:55:57 GMT FROM: Ron Remilard at MIT Ron Remillard (MIT), Jean Swank (GSFC), and Alan Levine (MIT) report for the RXTE/ASM team at MIT and NASA/GSFC The RXTE All-Sky Monitor detected GRB050724 in a single camera (SSC 2) with a significance of 9.5 sigma. The event duration is 2.0 (0.5) s, and the burst (integrated) is detected in each of the 3 standard ASM energy bands: 1.5-3, 3-5, and 5-12 keV. When plotted at 32 ms time resolution, the instantaneous maximum is 10.8 (3.0) Crab. Despite weak statistics, the burst profile appears to show two peaks, as reported in GCN Circular 3667, and both peaks are stronger at 5-12 keV, compared to 2-5 keV (see http://xte.mit.edu/~rr/grb050724_32ms.ps). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3678 SUBJECT: GRB 050724: SWIFT XRT refined position DATE: 05/07/25 23:46:41 GMT FROM: Angelo Antonelli at Obs. Astro. di Roma L.A. Antonelli (INAF/OAR), P. Romano, A. Moretti, S. Covino (INAF/OAB), D. Burrows (PSU) on behalf of the SWIFT XRT Team report: We have analyzed the first 20 ksec of the Swift XRT observation of GRB 050724 (GCN 3665, Covino et al.). We derived a refined position of the X-ray afterglow by performing a boresight correction based on the USNO catalog. The new coordinates of the X-ray afterglow are: RA(J2000) = 16h 24m 44.8s, Dec (J2000) = -27d 32' 31.8" with an uncertainty of 5.4 arcseconds radius (3 sigma). This position is 69 arcseconds from the refined BAT position given in GCN 3667 (H. Krimm et al), 2.6 arcseconds from the XRT position given in GCN 3665 and 7.1 arcseconds from the XRT position given in GCN 3669 (Romano et al.). This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3679 SUBJECT: GRB 050724: GMOS Imaging and Spectroscopy DATE: 05/07/26 00:44:54 GMT FROM: Jason Prochaska at UCO/Lick Obs J.X. Prochaska (UCO/Lick), H.-W. Chen (MIT), J.S. Bloom (UCB), and A. Stephens (Gemini) report on behalf of the GRAASP collaboration: We have obtained GMOS/R400 spectroscopy (2400s) of the Sources identified as A, B and D in GCN #3672. We confirm the identification of Source B as a Galactic star (GCN #3675). We tentatively identify Source A as a Galactic star based on its PSF and featureless spectrum. Our acquisition image of the field clearly demonstrates that Source D is extended and therefore a galaxy. Our spectrum of the galaxy is nearly featureless (lambda=5000-9000A), indicating the galaxy is an early type consistent with its red color (GCN #3673). We assign a possible redshift of z=0.257 based on absorption features at ~6510A and ~7415A which we associate with MgI and NaI. The galaxy is located 7.2" from the refined XRT position (GCN #3678) which would correspond to 27kpc at z=0.257. Further observations are encouraged. We thank the Gemini staff for their help in acquiring this dataset. Plots of the data can be found here: http://www.graasp.org/Data/050724 ---------------------------------------------- Jason X. Prochaska UCO/Lick Observatory UC Santa Cruz Santa Cruz, CA 95064 xavier@ucolick.org http://www.ucolick.org/~xavier/ 831-459-2135 (Direct) 831-459-2991 (UCO/Lick Main) 831-459-5244 (Fax) //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3680 SUBJECT: GRB 050724: J-band observations DATE: 05/07/26 01:21:06 GMT FROM: Javier Gorosabel at LAEFF-INTA, Madrid A. de Ugarte Postigo, J. Gorosabel, A.J. Castro-Tirado, M. Jelinek, S. Guziy (IAA-CSIC), H.-J. Roeser (MPI Heidelberg), A. Aguirre, S. Pedraz (CAHA), O. Bogdanov (Nikolaev State Univ.), report: "We have observed the field of GRB 050724 (GCN Circ. 3665) in the J-band with the 3.5m Calar Alto telescope (mean observing epoch July 25.86 UT, Texp=45 min). A comparison with the images taken yesterday with the same telescope (mean observing epoch July 24.87 UT, Texp=15 min) did not reveal any variable source in the reported XRT error boxes (GCN Circ. 3678, 3665, 3669) down to J~20. At first epoch we note the presence of a possible object on our detection limit (J~20.5) located at RA(J2000)=16:24:45.02, DEC(J2000)=-27:32:29.1. However, the worse seeing on July 25.86 UT prevented us from confirming its potential variability." This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3681 SUBJECT: GRB 050724: Optical Variability in Nearby Galaxy DATE: 05/07/26 07:50:06 GMT FROM: S. Bradley Cenko at Caltech A. Gal-Yam, S. B. Cenko (Caltech), E. Berger (Carnegie), W. Krzeminski (LCO) and B. Lee (Toronto) report on behalf of the Caltech-NRAO-Carnegie collaboration: We have obtained three epochs of optical imaging of the field of GRB 050724 (Covino et al., GCN 3665) with the RetroCam CCD Camera on the 1.0-m Swope telescope at Las Campanas Observatory. Each epoch consisted of 2 x 15 min exposures in I-band, with the last epoch also containing one additional ten minute exposure. We subtracted the coadded sum image obtained during the second night of observations (epoch 3; July 26.05 UT) from the coadded sum images taken during the first night (epoch 1, July 25.02 UT; epoch 2, July 25.11 UT ) using the CPM (Gal-Yam et al. 2004) and ISIS (Alard et al. 1999) codes. We clearly detect a variable point source superposed on galaxy "D" of Bloom et al. (GCN 3672). The variable source is offset from the galaxy core (see figure at http://www.its.caltech.edu/~cenko/grb050724/grb050724.jpg; the green circle is centered on the galaxy core from epoch 3, the red is centered on the OT). Furthermore, the light distribution in epoch 1 is markedly different from that in epoch 3, due to the effect of the OT light, disfavoring the possibility that the optical variability results from Galaxy D being an AGN. Calibrating the OT magnitudes against "I2" magnitudes of four nearby stars from the USNO B1 catalog, we find that the OT brightened by 0.6 magnitudes between epochs 1 and 2 (I=21.25 at epoch 1, 12 hours after the burst; I=20.65 at epoch 2, 14.3 hours after the GRB). We note that such behavior is rare among optical afterglows. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3684 SUBJECT: GRB050724: Further Radio Observations DATE: 05/07/26 20:48:52 GMT FROM: Alicia Soderberg at Caltech A. M. Soderberg, P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie collaboration: "We have undertaken additional VLA observations of GRB050724 (GCN 3665) on 2005 July 26.21 UT. The flux density of the radio source, identified in GCN 3676, has varied significantly between these two epochs. This radio variability, together with the close proximity of the radio source with the XRT position (GCN 3676; chance coincidence<0.15%), and the optical variations noted in GCN 3681, argue that this is the afterglow of GRB050724. Further observations are planned. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3685 SUBJECT: GRB 050724: dust-scattered X-ray halo detected in SWIFT/XRT observation DATE: 05/07/26 22:11:58 GMT FROM: Pat Romano at OAB-Swift P. Romano, A. Moretti (OAB), S. Vaughan (U. Leicester), L. A. Antonelli (OAR), S. Campana, G. Chincarini, S. Covino,D. Malesani, G. Tagliaferri (OAB), J. Osborne, R. Willingale, P.T. O'Brien, A. Levan, K. L. Page, M. R. Goad (U. Leicester), D. N. Burrows (PSU), report: Analysis of the SWIFT XRT observation of GRB050724 in Photon Counting (PC) mode has revealed in the first orbit a diffuse X-ray halo centered around the afterglow location. The halo has the form of complete ring which increases in radius through the observation and reached the distance of ~100 arcsec during the first ~2000 sec after the trigger (T0). We can exclude it is due to instrumental effects. During the observation, which started ~343 seconds after the burst trigger time (PC mode), the observed halo follows the expected behaviour of a "light-echo" as X-rays are scattered by dust in our Galaxy. From the radial expansion of the halo we estimate a distance of 175 -/+ 50 pc to the dust (from the observer, 90% confidence interval). GRB 050724 is in the direction (Galactic) l = 350.37, b = 15.10 degrees, in which the density of interstellar medium is quite high as testified by both the neutral Hydrogen column density nH=1.5E21 cm-2 and the optical extiction E(B-V)=0.61 (A_V=2.029, A_K=0.225). This line of sight includes the Scorpius Centaurus OB association at ~150-200 pc, consistent with the derived distance to the scattering medium. The X-ray WT spectrum of GRB050724 is represented by a powerlaw with Photon index 1.93-/+0.05 in the [0.5-10] keV band (as reported in GCN 3669; Romano et al.). The scattered X-ray light has, as expected, a softer spectrum with Photon index 3.2-0.8+1.0 (first orbit). More information is posted at: http://www.merate.mi.astro.it/~romano/grb050724/index.html //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3690 SUBJECT: GRB050724: VLT observations of the variable source DATE: 05/07/27 09:01:59 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo, S. Covino (INAF/OABr), L.A. Antonelli, A. Melandri (INAF/OAR), D. Malesani (SISSA), A. Moretti, P. Romano, G. Tagliaferri (INAF/OAB), S. Piranomonte (INAF/OAR), G. Chincarini (Univ. Milano- Bicocca), and L. Stella (INAF/OAR) report on behalf of the MISTICI collaboration We observed the afterglow of GRB050724 (Covino et al., GCN 3665) with the ESO-VLT equipped with the FORS1 camera, starting on 2005 Jul 25.01 and Jul 25.98 (12 and 35 hours after the burst respectively). The seeing was 1.0" and 0.8" in the two epochs respectively. Observations were carried out in the R and I filters. We clearly detect all the sources listed by Bloom et al. (GCN 3672) and Castro-Tirado et al. (GCN 3673). PSF-matched image subtraction was performed with the ISIS package (Alard & Lupton, 1998). A highly significant variable source is detected superimposed to the galaxy named as source "D" in GCN 3672 (for a figure see http://www.merate.mi.astro.it/~covino/GRB050724). The source is slightly offset with respect to the galaxy center. We give below the 0.2" uncertainty position of the galaxy and the OT: Galaxy centroid: 16:24:44.405 -27:32:26.95 OT centroid: 16:24:44.400 -27:32:27.90 Assuming the object has completely disappeared in our second epoch, the magnitude of the variable source was I = 20.85 +/- 0.05 at our first epoch. This value was derived by adding artificial stars of known brightness to the reference frame, calibrated with Landolt standard stars. This source faded between the two epochs in both the R and I bands. Therefore, we confirm the variability reported by Gal-Yam et al. (GCN 3681). However, our source appears (in both the R and I bands) 1" South with respect to the core of the host galaxy. This is at variance with the picture posted by Gal-Yam et al. (GCN 3681), where the variable object appears North of the host galaxy centroid. After the rebrightening episode reported by them, the source has therefore clearly faded. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3694 SUBJECT: GRB 050724, SMARTS optical/IR afterglow observations DATE: 05/07/28 18:24:13 GMT FROM: Bethany Cobb at Yale U B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS consortium, report: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 050724 (GCN 3665, Covino et al.) at two separate epochs. The two epochs had mid-exposure times of 2005-07-25 01:58 UT (13.4 hours post-burst) and 2005-07-27 03:21 UT (62.8 hours post-burst). Total summed exposure times at each epoch amounted to 36 minutes in I and 30 minutes in J, resulting in approximate limiting magnitudes of I>22 and J>20. In order to search for variability in the host galaxy of GRB 050724 ("source D" from Bloom et al. GCN 3672), the ISIS image subtraction routine was used (Alard et al. 1999). When the second epoch images are subtracted from the first epoch images, the residual light of the afterglow is clearly detected in both the I and J subtracted frames (in agreement with both GCN 3681, Gal-Yam et al. GCN 3690, D'Avanzo et al.). The centroid of this residual is ~0.2" west and ~0.5" south of the centroid of the host galaxy. Preliminary differential photometry of the host galaxy yields a decay of 0.19 +/- 0.03 magnitudes in I and 0.17 +/- 0.05 magnitudes in J between the two imaging epochs. Assuming the afterglow no longer contributes significantly to the brightness of the host galaxy at the second epoch, then the magnitude of the host galaxy is I = 18.78 +/- 0.27 and J = 16.94 +/- 0.09. Unfortunately, imaging was done under non-photometric conditions so no Landolt or Persson standard stars are available with which to determine the offset between instrumental and apparent magnitude. Therefore, the above values are determined using "on-chip" standards (USNO-B1 stars in the optical and 2MASS stars in the IR) and the error is strongly dominated by the uncertainty in the offset derived from these stars. Given the above values for the magnitude of the host and its dimming, the afterglow of GRB 050724 is determined to have a magnitude of I = 20.58 +/- 0.32 and J = 18.87 +/- 0.32 at 13.4 hours post-burst. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3696 SUBJECT: GRB050724: Refined Radio Position DATE: 05/07/28 20:07:36 GMT FROM: Alicia Soderberg at Caltech A. M. Soderberg (Caltech) reports on behalf of the Caltech-NRAO-Carnegie collaboration: "Further observations of the radio afterglow (GCN 3676, 3684) of GRB050724 (GCN 3665) have allowed for a position to be derived with increased astrometric accuracy: RA (J2000) 16 24 44.369 ± 0.007s DEC (J2000) -27 32 27.5 ± 0.2" which is consistent with the position of the optical transient (GCN 3681, 3690)." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3697 SUBJECT: GRB 050724: Chandra Observations of the X-ray Afterglow DATE: 05/07/28 21:14:02 GMT FROM: David Burrows at PSU/Swift D. N. Burrows, D. Grupe (PSU), C. Kouveliotou, S. Patel (MSFC), P. Meszaros (PSU), B. Zhang (UNLV), and R. A. M. J. Wijers (U. Amsterdam) report: We observed the X-ray afterglow of the short GRB 050724 (Covino et al., GCN 3665) with the Chandra X-ray observatory from 20:09 UT on 26 July 2005 to 10:45 UT on 27 July 2005. The total exposure time was 50 ks. We find an uncataloged X-ray source coincident with the VLT source reported by D'Avanzo et al. (GCN 3690) and the VLA source reported by Cameron and Frail (GRB 3676) as updated by Soderberg (GCN 3696). The Chandra position is: RA (J2000) = 16 24 44.36 Dec (J2000) = -27 32 27.5. The astrometry has been verified by comparisons with one 2MASS star with an X-ray counterpart on the ACIS S-3 chip. We estimate an uncertainty of 0.2 arcseconds radius. The X-ray source flux appears to decrease during the Chandra observation, although with marginal statistical significance. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3699 SUBJECT: GRB 050724: WHT optical observations DATE: 05/07/29 17:58:10 GMT FROM: Klaas Wiersema at GRACE/U of Amsterdam K. Wiersema (U. of Amsterdam), E. Rol (U. of Leicester), R. Starling (U. of Amsterdam), N. Tanvir (U. of Hertfordshire), D. S. Bloomfield, H. Thompson (Queen's University Belfast) report: We have observed the position of the short burst GRB 050724 (Covino et al. GCN 3665) with the William Herschel Telescope at the Observatorio del Roque de los Muchachos on La Palma, using the Aux port Imager. We observed two epochs, with midpoints 0.424 days and 3.405 after burst. The epoch 1 observations consisted of 4 x 15 + 5 minutes exposure time in R band. Epoch 2 consisted of 4 x 15 minutes in R band. At the first epoch the weather conditions were good with an average seeing of 0.8 arcsec. During the second epoch the seeing was considerably worse, with an average seeing ~1.3 arcsec. PSF-matched image subtraction of the two epochs using the ISIS code (Alard et al. 1999) reveals a clearly fading source. This behaviour is confirmed in a subtraction of the first and last image from the first epoch. The position of the fading source matches that described in e.g. GCNs 3690 and 3694, as well as the radio (GCN 3684) and X-ray afterglow position (GCN 3683, 3697). We performed aperture photometry of the host galaxy plus the OT with respect to two unsaturated USNO stars: 0624-0502999 and 0624-0503050, whose values we take from the USNO-B catalogue. We find a magnitude difference of approximately 0.2 magnitudes between the two epochs. Assuming the contribution of the afterglow to the total flux at the second epoch to be negligible, we estimate the afterglow to be approximately R ~22.1 at our first epoch. A jpg image showing the position of the afterglow and the host can be found on: http://remote.science.uva.nl/~kwrsema/grb050724/ We thank the staff of the WHT for outstanding support for these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3700 SUBJECT: GRB 050724: Secure Host Redshift from Keck DATE: 05/07/29 18:13:53 GMT FROM: Jason Prochaska at UCO/Lick Obs J. X. Prochaska (UCO/Lick), J. S. Bloom (UCB), H.-W. Chen (MIT), B. Hansen (UCLA), J. Kalirai (UCSC), M. Rich (UCLA) and H. Richer (UBC) report on behalf of the GRAASP collaboration: "We have obtained LRISb spectroscopy (900s; 2005-07-29 06:31 UT) of the putative host galaxy of GRB 050724 (Object D in GCN #3672). We confirm our previously reported redshift (GCN #3679) based on the identification of Ca H+K, G-band absorption features, and the 4000Ang break. We report a redshift z=0.258 +/- 0.002. The velocity dispersion based on CaK appears to exceed 200km/s. The galaxy shows no [OII] emission in our spectrum suggesting minimal current star formation. PAIRITEL imaging of the galaxy from July 29 UT yields a K-band magnitude of 15.3 +/- 0.2 in a 3" radius aperture. At this redshift, and including the effects of Galactic extinction, the galaxy is 1.7 L* based off the 2MASS luminosity function. The properties of this galaxy -- a massive early-type at moderate redshift -- are strikingly similar to the probable host galaxy of GRB 050509b (GCN #3399). Based on this redshift and the reported fluence in GCN #3667, the isotropic -equivalent energy release is E_gamma(iso) = 9.9e49 erg [19-440 keV, comoving], more than 1 order of magnitude brighter than 050509b (Bloom et al. astro-ph/0505480)." Figures and imaging can be found at this following site: http://www.graasp.org/Data/050724 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3892 SUBJECT: Subaru Observations of GRB050724 DATE: 05/08/27 14:49:11 GMT FROM: Elena Pian at ITESRE-CNR,Bologna A. Pastorello (MPA), K. Kawabata (Hiroshima Univ.), E. Pian, (INAF-OATs), K. Nomoto (Tokyo Univ.), P. Mazzali (INAF,MPA,Tokyo), T. Hattori, M. Iye, T. Sasaki (Subaru,NAOJ), on behalf of a larger collaboration, report: On August 10, 2005, at 07.7 UT we observed the field of GRB050724 with Subaru+FOCAS and I filter. The exposure time was 2 minutes. The seeing was 0.4". No object is detected at the position of the optical transient reported by Berger et al. (submitted to Nature, astro-ph/0508115). The 3-sigma upper limit is I = 23 (this is not corrected for the Galactic reddening). This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3886 SUBJECT: GRB050824: First 2 hours of power low optical decay? DATE: 05/08/26 17:27:26 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, V.Kornilov, N.Tyurina, A.Belinski, E.Gorbovskoy, D.Kuvshinov Sternberg Astronomical Institute, Moscow Union "Optic" We have analysed all photometric points obtained during first 2 hours (see picture http://observ.pereplet.ru/images/GRB050824/2.jpg ) from ROTSE (GCN Circ 3867), MASTER (GCN Circ 3883), J. Gorosabel et al. (GCN Circ 3865) and Swift UVOT(GCN Circ 3880) in similar colors . The upper limits of ROTSE and MASTER for 500-750 sec (GRB time) are in agreement. Both instrumental systems are more or less similar. There is some contradiction with J. Gorosabel et al. (GCN 3865) and MASTER data (GCN Circ 3880) for 24 - 47 minutes. But there is no error bar in J. Gorosabel et al.(GCN 3865). The SWIFT UVOT V-band is most closed to MASTER in color sense. If we include only 2 MASTER points and Swift UVOT V-point we can obtain next power low: m = 2.1(+-0.2) log (t) + 19.5 , t in hours. This corresponds to usual flux power law F ~ t^-0.9 However there is strong contradiction with ROTSE (11 min) uper limit and J. Gorosabel et al. (GCN 3865) point. JPG-images are available at http://observ.pereplet.ru/images/GRB050824/2.jpg . This work is supported by RFFI 04-02-16411 grant. This message can be cited. Mailto: lipunov@sai.msu.ru