//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3723 SUBJECT: GRB 050801: ROTSE-III Detection of Possible Counterpart DATE: 05/08/01 18:34:58 GMT FROM: Eli Rykoff at U of Michigan/ROTSE E.S. Rykoff (U Mich), S.A. Yost (U Mich), W. Rujopakarn (U Mich) report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, responded to GRB 050801 (Swift trigger 148522). The first image was at 18:28:23.9 UT, 21.9 s after the burst (7.9 s after the GCN notice time). The unfiltered images are calibrated relative to USNO A2.0. We detect a new object, not visible in the DSS (second epoch), with coordinates: 13:36:35.4 -21:55:42.0 (J2000) start UT mag mlim(of image) ---------------------------------- 18:28:23.9 15.0 17.0 Continuing observations are in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3724 SUBJECT: GRB050801: GCN XRT position is incorrect DATE: 05/08/01 18:50:03 GMT FROM: Jamie A. Kennea at PSU/Swift-XRT J.A. Kennea and D.N. Burrows (PSU) The XRT position sent through GCN for GRB050801 is not correct due to the XRT centroiding on a artifact in the CCD, and not the afterglow. The current best position for this from Swift is the BAT position. [GCN OPS NOTE(01aug05): Per author's request, "050701" was changed to "050801" in both places.] //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3725 SUBJECT: GRB050801: Swift-BAT detection of a burst DATE: 05/08/01 19:25:50 GMT FROM: Scott Barthelmy at NASA/GSFC D.L. Band (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), C. Gronwall (PSU) S. Hunsberger (PSU), J. Kennea (PSU), D. Palmer (LANL), M. Perri (ASDC) on behalf of the Swift team: At 18:28:02.07 UT, Swift-BAT triggered and located GRB050801 (trigger=148522). The spacecraft slewed immediately. The BAT on-board calculated location is RA,Dec 204.139d,-21.950d {+13h 36m 33s,-21d 57' 00"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows a single FRED structure with a total duration of 3 sec. The peak count rate was ~900 counts/sec (15-350 keV), which peaks at ~T+0.5 seconds. The XRT began observing at 18:29:03 UT, 61 seconds after the BAT trigger. XRT did centroid on a position, but on-ground examination of the image revealed that the object found by the centroiding algorithm is a CCD artifact (Kennea, GCN 3724). Swift-UVOT began observations of GRB 050801 after the slew, however, the UVOT dark burst image did not come down via TDRSS so no information is available at this time. Detailed analysis will be performed when data is available after the next Malindi pass. Because of orbit trajectory with respect to the Malindi ground station, we will not have access to the full data sets to produce the refined analyses for several hours. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3726 SUBJECT: GRB 050801: ROTSE-III Early Afterglow Break DATE: 05/08/01 19:50:15 GMT FROM: Eli Rykoff at U of Michigan/ROTSE E.S. Rykoff (U Mich), S.A. Yost (U Mich), W. Rujopakarn (U Mich), H. Swan (U Mich), K. Alatalo (Berkeley), R. Quimby (U Texas) report on behalf of the ROTSE collaboration: ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, is observing the optical counterpart to GRB 050801 (Swift trigger 148522, Band et al, GCN 3725). The early afterglow reported in GCN 3723 is characterized by a broken power-law, which does not decay significantly from t+21s to t+200s, followed by a decline with a power law index of ~-1.1. Our preliminary photometry, relative to the USNO A2.0 catalog, also shows some possible sub-structure to the lightcurve. tstart-tburst exptime mag --------------------------------- 21.8 5.0 14.99+/-0.06 203.0 20.0 15.01+/-0.03 1590.3 60.0 17.29+/-0.15 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3728 SUBJECT: GRB 050801, afterglow observations DATE: 05/08/01 20:54:15 GMT FROM: Arne A. Henden at AAVSO B. Monard (Bronberg Observatory) reports on behalf of the AAVSO International High Energy Network: We observed the afterglow (Rykoff et. al., GCN 3723) for the Swift burst GRB 050801 (Band et al., GCN 3725), using the 30cm telescope plus ST-7XME CCD camera of Bronberg Observatory. Using the UCAC2 star at 13:36:40.87 -21:55:58.6 as having a derived Rc magnitude of 14.5, we obtain the following photometry: UT / CR mag 19:03.0 17.5 19:05.5 17.7 19:08.0 17.9 19:10.5 18.1 19:14.5 18.4: Uncertainty in timing : 30sec absolute, 10 sec relative Uncertainty in magnitude : 0.3 in accuracy, 0.1 in precision No further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3729 SUBJECT: GRB 050801, SMARTS optical/IR afterglow observations DATE: 05/08/02 02:37:50 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 050801 (GCN 3725, Band et al.) with a mid-exposure time of 2005-08-02 00:01 UT, which is ~5.5 hours post-burst. Total summed exposure times amounted to 15 minutes in I and V and 12 minutes in J and K. The afterglow of GRB 050801 (GCN 3723, Rykoff et al.) is detected in our optical images. However, the afterglow is not significantly detected in our IR images. Preliminary photometry, obtained in comparison with USNO-B1.0 stars, indicates the magnitude of the afterglow at ~5.5 hours post-burst to be I = 20.2+/-0.2. The afterglow is not bright enough in the individual optical frames to significantly measure its decay over our ~40 minutes of observations. In comparison with 2MASS stars, the limiting IR magnitudes are J > 18.6+/-0.2 and K > 17.0+/-0.2. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3730 SUBJECT: GRB 050801: Swift-BAT refined analysis DATE: 05/08/02 03:50:15 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (GSFC/NRC), C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), F. Marshall (GSFC), D. Palmer (LANL), A. Parsons (GSFC), G. Sato (ISAS), T. Takahashi (ISAS), J. Tueller (GSFC), on behalf of the Swift-BAT team: At 18:28:02 UT Swift-BAT detected GRB 050801 (trigger=148522) (GCN Circ 3725, Band, et al.). The refined BAT ground position is (RA,Dec) = 204.140, -21.937 [deg; J2000] {13h36m33.6s,-21d59'14.7"} +-3 arcmin, (95% containment). The partial coding was 99 %. The light curve shows two peaks which are separated by about 3 seconds. The second peak is weaker and has a softer spectrum than the first peak. T90 (15-350 keV) is (20 +- 3) seconds (estimated error including systematics). The power law index of the time-averaged spectrum is 2.0 +- 0.2. The fluence in the 15-350 keV band is (4.4 +- 1.0) x 10^-7 erg/cm2. The 1-s peak photon flux measured from T0+0.27 second in the 15-350 keV band is (1.7 +- 0.2) ph/cm2/s. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3731 SUBJECT: GCN 050801: early Swift XRT analysis results DATE: 05/08/02 04:38:24 GMT FROM: Matteo Perri at ISAC/ASDC M. Perri, M. Capalbi, P. Giommi (ASDC), J. Kennea, D.N. Burrows, P. Meszaros (PSU), K. Hinshaw (GSFC-SPSYS) report on behalf of the Swift XRT team: We have analyzed the Swift XRT data from the first orbit observation of GRB 050801 (Band et al., GCN 3725). A fading, previously uncatalogued, point source at the following coordinates is detected in the field: RA(J2000) = 13h 36m 36.0s Dec(J2000) = -21d 55' 42" This position is 83 arcseconds from the BAT position given in GCN 3725 (Band et al.) and 8.5 arcsec from the ROTSE-III position reported in GCN 3723 (Rykoff et al.). The source is close to a bad column of the CCD and we estimate an uncertainty of 10 arcseconds radius in the derived position. Data in Photon Counting (PC) mode starts at 18:29:31 UT, 89 seconds from the BAT trigger. The 0.3-10 keV afterglow light curve shows a flat slope from T+89s to T+300s and then declines following a power law with decay index alpha=-1.3+/-0.3 up to T+990s, when first orbits ends. A preliminary spectral fit in the 0.3-10 keV energy band to the first orbit gives a spectral power law photon index of 1.8+/-0.3 with Nh=5.7E20 cm^-2. In the time range 89-990 seconds from trigger the average unabsorbed 0.5-10 keV flux is 2.6E-11 erg cm^-2 s^-1. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3733 SUBJECT: GRB050801: Swift/UVOT Optical and UV detections DATE: 05/08/02 07:57:28 GMT FROM: Alexander Blustin at MSSL-UCL A. J. Blustin (UCL-MSSL), D. Band (GSFC), S. Hunsberger (PSU), C. Gronwall (PSU), M. Carter (UCL-MSSL), P. Smith (UCL-MSSL) on behalf of the Swift/UVOT team report: The Swift/UVOT began observing the afterglow of GRB050801 at 2005-08-01T18:32:00, 238 s after the BAT trigger (Band et al., GCN 3725). The afterglow was detected in all six optical and UV filters at a position (J2000, corrected to the DSS coordinates) of: RA 13:36:35 (+/- 1 arcsec) DEC -21:55:41 (+/- 1 arcsec) We give two lightcurve points for each filter in the table below so that decay slopes may be determined. Filter T_mid Exp Magnitude V 244 9.78 15.9 +/- 0.2 V 919 9.77 17.9 +/- 0.8 B 215 9.78 16.0 +/- 0.1 B 890 9.78 18.0 +/- 0.4 U 201 9.78 15.20 +/- 0.09 U 961 9.76 17.2 +/- 0.3 UVW1 187 9.78 15.5 +/- 0.1 UVW1 11316 899.77 20.1 +/- 0.3 UVM2 173 9.78 16.0 +/- 0.2 UVM2 6590 337.06 20.6 +/- 0.9 UVW2 230 9.78 17.4 +/- 0.4 UVW2 4524 670.56 21.0 +/- 0.4 Where Tmid is the midpoint of the exposure post-trigger in seconds. The magnitudes are based on preliminary zero points, measured in orbit, and will require refinement with further calibration. All magnitudes are uncorrected for Galactic reddening. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3736 SUBJECT: GRB050801: Optical photometry and decay index DATE: 05/08/02 15:01:05 GMT FROM: Brian Lindgren Jensen at U.of Copenhagen GRB050801.769: Optical photometry and decay index J. P. U. Fynbo, B. L. Jensen, J. Hjorth, K. G. Woller, D. Watson (Niels Bohr Institute), P. Fouque (Obs-MiP, Toulouse), M. I. Andersen (Potsdam, AIP) report on behalf of the DARK Cosmology Centre: "We obtained BVR-band imaging of the XRT error circle of GRB050801.769 (Band et al. GCN#3725, Perri et al. GCN#3731) with the Danish 1.5m (La Silla) on Aug. 2.0 UT (approx. 6hr after the burst). We detect the optical afterglow candidate source reported by Rykoff et al. (GCN#3726), with position (RA, Dec)(J2000.0) 13:36:35.363, -21:55:42.03 Based on a preliminary std. star calibration, we obtain the following photometry of the afterglow candidate: Date (UT): Filter: Exptime: Mag. Aug 1.997 B 600s 22.36+-0.05 Aug 2.012 V 600s 21.03+-0.05 Aug 1.989 R 600s 20.75+-0.04 Aug 2.005 R 600s 20.87+-0.04 Aug 2.020 R 600s 20.94+-0.05 (in this calibration, we obtain B=20.95, V=19.74, R=19.63 for the star at: (RA, Dec) = (13:36:33.657, -21:55:29.55)). Fitting a power-law to our three R-band data points gives a lightcurve, which intersects the R=17.29 ROTSE-III (Rykoff et al. GCN#3726) data point at t-t0=1590s, to within the errors of that data point. Including the ROTSE-III data point in the fit, we find an R-band decay slope of -1.29 +-0.05. A findingchart of the field is shown at: http://www.astro.ku.dk/~brian_j/grb/grb050801.769/ " //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3743 SUBJECT: GRB050801: Unchanged decay slope DATE: 05/08/03 10:00:32 GMT FROM: Brian Lindgren Jensen at U.of Copenhagen GRB050801.769: Unchanged decay slope J. P. U. Fynbo, B. L. Jensen, J. Hjorth, K. G. Woller, D. Watson, J. Sollerman (Niels Bohr Institute), P. Fouque (Obs-MiP, Toulouse), M. I. Andersen (Potsdam, AIP) report on behalf of the DARK Cosmology Centre: "We have obtained additional DK-1.5m R-band imaging (Aug 3.0 UT) of the optical afterglow (Rykoff et al. GCN#3726) of GRB050801.769 (Band et al. GCN#3725). Extending the fit from Fynbo et al. (GCN#3726) yields a smooth well-fitting power-law from t-t0=0.44h to 29.5h, with an R-band decay slope of -1.31 +- 0.04. The lightcurve is shown at: http://www.astro.ku.dk/~brian_j/grb/grb050801.769/ " //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3762 SUBJECT: GRB050801: Radio Observation DATE: 05/08/04 17:57:34 GMT FROM: Patrick B. Cameron at Caltech P. B. Cameron (Caltech) reports on behalf of the Caltech-NRAO-Carnegie collaboration: "We observed the field of GRB050801 (GCN 3725) with the Very Large Array at 8.5 GHz beginning August 2.06 UT. No radio source is detected at the position of the optical source (GCN 3723) with a 2-sigma upper limit of 60 uJy. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc."