TITLE: GCN CIRCULAR NUMBER: 5691 SUBJECT: GRB 061004: Swift detection of a burst DATE: 06/10/04 20:12:10 GMT FROM: David Palmer at LANL H. Ziaeepour (UCL-MSSL), D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC), S. R. Oates (UCL-MSSL), C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL), G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 19:50:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 061004 (trigger=232339). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 97.748, -45.894 {06h 30m 60s, -45d 53' 36"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a peak with a duration of about 6 sec. The peak count rate was ~5000 counts/sec (15-350 keV), at ~3 sec after the trigger. The XRT began observing the field at 19:51:30 UT, 60 seconds after the BAT trigger. XRT found a bright, variable, uncatalogued X-ray source located at RA(J2000) = 06h 31m 10.52s, Dec(J2000) = -45d 54' 24.0", with an estimated uncertainty of 6 arcseconds (90% confidence radius). This location is 124 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 4.6e-10 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 69 seconds after the BAT trigger. No afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 18.0 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.049 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5693 SUBJECT: GRB 061004: Nearby 2MASS Galaxy DATE: 06/10/04 23:41:40 GMT FROM: Derek Fox at PSU D.B. Fox (Penn State) reports: "I note the presence of a 2MASS galaxy, 2MASX J06310985-4554013, at 23 arcsec distance from the XRT position for GRB 061004 (Ziaeepour et al., GCN 5691). Estimated magnitudes of the host galaxy from the 2MASS catalog, via NED, are: J=15.17(24) mag, H=14.72(35) mag, and Ks=13.60(22) mag (uncertainties in the least significant digits are given in parentheses). The proximity of this galaxy to the X-ray afterglow may be interesting in light of the relatively short 6-s duration of GRB 061004." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5694 SUBJECT: GRB 061004, Swift BAT refined analysis DATE: 06/10/05 01:24:26 GMT FROM: Louis M Barbier at NASA/GSFC/Swift H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), C. Markwardt (GSFC/UMD), D. Palmer (LANL), 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-239.0 to T+595.8 sec from the recent telemetry downlink, we report further analysis of BAT GRB 061004 (trigger #232339) (Ziaeepour, et al., GCN Circ. 5691). The BAT ground-calculated position is RA,Dec = 97.795, -45.903 deg {6h 31m 10.8s, -45d 54' 9.8"} (J2000) +- 0.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 98%. The light curve shows a single peak, extending out to T+8 seconds. T90 (15-350 keV) is 6.2 +- 0.3 sec (estimated error including systematics). The time-averaged spectrum from T+0.2 to T+8.1 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.81 +- 0.10. The fluence in the 15-150 keV band is 5.7 +- 0.3 x 10-07 erg/cm2. The 1-sec peak photon flux measured from T+2.67 sec in the 15-150 keV band is 2.5 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5695 SUBJECT: GRB 061004: Swift-XRT Team Refined Analysis DATE: 06/10/05 01:32:12 GMT FROM: Kim Page at U.of Leicester K.L. Page, A.P. Beardmore (U. Leicester) & H. Ziaeepour (UCL-MSSL) report on behalf of the Swift-XRT Team: We have analysed the first 2 orbits of Swift-XRT data obtained for GRB 061004 (GCN Circ. 5691; Ziaeepour et al.). Using 3.8 ks of Photon Counting mode data, we derive a refined position of: RA(J2000) = 06 31 10.48 Dec(J2000) = -45 54 24.6 with an estimated error radius of 5.5 arcsec (90% confidence, including boresight uncertainties). This lies 0.7 arcsec from the original XRT position given in GCN Circ. 5691 and 14.2 arcsec from the ground-calculated BAT position in GCN Circ. 5694 (Krimm et al). The X-ray light-curve shows an initial decay of alpha = 1.62 +/- 0.14, breaking around 375 seconds after the burst to a flatter decay slope of 0.61 +/- 0.10. The WT spectrum can be modelled using a power-law of Gamma = 1.53 +/- 0.48, absorbed by the Galactic column of 5.7e20 cm^-2. There is no evidence for any excess NH. The mean observed (unabsorbed) flux over 0.3-10 keV for this spectrum (spanning a time of 68-86 seconds after the trigger) is 2.83e-10 (3.07e-10) erg cm^-2 s^-1. If the decay continues with a slope of alpha ~ 0.61, the count rate at 24 hours after the burst is predicted to be 0.012 count s^-1. Using a conversion factor of 1 count s^-1 being approximately equivalent to 4.6e-11 erg cm^-2 s^-1 (observed flux), this corresponds to a flux of 2.8e-11 erg cm^-2 s^-1 (over 0.3-10 keV). The predicted unabsorbed flux at 24 hours is 3.2e-11 erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5696 SUBJECT: GRB061004: Swift/UVOT optical observations DATE: 06/10/05 11:38:35 GMT FROM: Samantha Oates at MSSL S. R. Oates (UCL-MSSL), H. Ziaeepour (UCL-MSSL) report on behalf of the Swift UVOT team The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of GRB061004 at 19:51:14 UT, ~51 seconds after the initial Swift BAT trigger (Ziaeepour et al, GCN 5691). No optical counterpart was detected at the XRT position (Page et al, 6595) within the coadded images or with the V and white finding charts. The 3 sigma upper limits are provided for the coadded images and the finding charts below: Filter Start Stop Exposure 3SigmaUL -------------------------------------------------------- WHITE (finding) 68 168 100 18.4 V (finding) 174 574 400 20.0 V 704 24752 1477 18.9 B 652 13187 928 19.9 U 625 18969 1225 20.5 UVW1 604 18895 2121 21.2 UVM2 580 17988 1357 20.4 UVW2 680 24092 1337 20.5 WHITE 665 6706 520 20.3 -------------------------------------------------------- The values quoted above are not corrected for the expected Galactic extinction of E_{B-V}=0.049. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5697 SUBJECT: GRB 061004: Las Campanas Optical/NIR Observations DATE: 06/10/05 17:05:04 GMT FROM: Edo Berger at Carnegie Obs E. Berger (Carnegie), S. Gonzalez, and W. Krzeminski (LCO) report: "We observed the XRT position (GCN 5695) of GRB 061004 (GCN 5694) using the du Pont 100-inch telescope in K-band and the Swope 40-inch telescope in r-band. A total of 1215 sec and 1200 sec were obtained in each filter, respectively, starting on 2006 Oct 5.313 and Oct 5.338 UT. We do not detect any sources within the XRT error circle to a 3-sigma limit of K=18.9 mag and r=22.0 mag." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5698 SUBJECT: GRB 061004: Optical afterglow candidate and redshift DATE: 06/10/05 21:08:41 GMT FROM: Pall Jakobsson at U Hertfordshire Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo, Brian L. Jensen , Jens Hjorth (DARK, NBI), Andrew Levan (U. Hertfordshire), Nial Tanvir (U. Leicester), Paul Vreeswijk and Cedric Ledoux (ESO) report on behalf of a larger collaboration: Using FORS1 on the Very Large Telescope, we have imaged the GRB 061004 field (Ziaeepour et al. GCN 5691) on Oct 5.369 (0.542 days post-burst). Inside the revised XRT circle (Page et al. GCN 5695) we find an R ~ 23 mag point source, using photometric zeropoints from the ESO webpages. At present we cannot confirm that the source is fading. Its coordinates are: R.A.(J2000) = 06:31:10.71 Dec(J2000) = -45:54:28.7 with a 0.3" error in each coordinate. We obtained a 30 min spectrum (300V grating) of this source immediately after imaging. The spectrum displays an absorption feature around 5230 A, with the flux dropping substantially blueward of this feature. Associating it with Ly-alpha gives a redshift of z ~ 3.3 for this proposed afterglow candidate. A finding chart can be found at: http://www.dark-cosmology.dk/~brian_j/grb/grb061004.827/ We thank the Paranal staff, especially Chris Lidman and Rachel Gilmour for excellent support. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5774 SUBJECT: GRB 061004: Swift/XRT Astrometry Correction DATE: 06/10/31 23:38:37 GMT FROM: Judith Racusin at PSU J. L. Racusin (PSU), D. N. Burrows (PSU), K. L. Page (U Leicester), H. Ziaeepour (UCL-MSSL), and N. Gehrels (NASA/GSFC) report on behalf of the Swift XRT team: We have re-analyzed the full XRT data set of GRB 061004. XRT observed the field of GRB 061004 for a total exposure time of 61 ks between October 4 and October 10, 2006 in Photon Counting mode. Applying the new XRT boresight definition (Burrows et al., GCN 5750), we find a boresight corrected position of RA(J2000): 06h 31m 10.68s, Dec(J2000): -45d 54' 22.7", with an estimated uncertainty of 3.6 arcseconds (radius, 90% containment). To further improve the accuracy of this position, we performed an astrometry correction using 54 ks of the total exposure time (when the satellite position was stable). In this data set we find 26 serendipitous X-ray sources detected with the XIMAGE detect algorithm with S/N > 3, 5 of which have near-by optical counterparts in the USNO-B1 catalog. We match these sources to obtain a best fit mean frame shift, carefully accounting for several instrumental factors including exposure map correction, and additional hot pixel removal. We calculate the statistical position errors using the empirical fits as described in Moretti et al. (2006, A&A, 448, L9), assuming that the astrometric correction removes the 3.5" systematic error normally applied to XRT positions to account for errors in the star tracker attitude solution. The result of this analysis leads to a mean frame shift from the previously reported position (Page et al., GCN 5695), of: RA offset: +0.49s +/- 0.07s Dec offset: +1.3" +/- 1.0" and a new XRT astrometry corrected position of: RA(J2000): 06h 31m 10.94s Dec(J2000): -45d 54' 23.3" with an estimated uncertainty of 2.0 arcseconds (radius, 90% containment). This position is 5.0 arcseconds from the original refined XRT position given in Page et al. (GCN 5695), 2.8 arcseconds from the boresight corrected XRT position, and 5.9 arcseconds from the faint VLT optical object described in Jakobsson et al. (GCN 5698). A figure comparing all of these positions is available at: http://www.swift.psu.edu/images/grb061004_astrometry.gif This Circular is an official product of the Swift XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 5782 SUBJECT: GRB 061004: Further VLT/NTT observations DATE: 06/11/02 13:34:24 GMT FROM: Pall Jakobsson at U Hertfordshire Pall Jakobsson (U. Hertfordshire), Johan P. U. Fynbo, Brian L. Jensen , Jens Hjorth, Maximilian D. Stritzinger (DARK, NBI), Andrew Levan (U. Hertfordshire), Nial Tanvir (U. Leicester), Paul Vreeswijk, Cedric Ledoux (ESO), Houri Ziaeepour (UCL-MSSL) and Mathew Smith (U. Portsmouth) report on behalf of a larger collaboration: We have performed follow-up observations of the GRB 061004 optical afterglow candidate (S1) reported in Jakobsson et al. (GCN 5698). The S1 flux is roughly constant between the three epochs of observations: Tel/inst Date (UT) Delta-t Exp. time Magnitude (days) (s) -------------------------------------------------------------- VLT/FORS1 Oct 5.366 0.539 2*300 22.55 +/- 0.09 VLT/FORS1 Oct 7.344 2.517 2*300 + 120 22.82 +/- 0.07 NTT/EMMI Oct 15.352 10.525 3*500 22.73 +/- 0.20 In addition, S1 is 3.9" from the edge of the revised XRT error circle (Racusin et al. GCN 5774). The most likely conclusion is that S1 is not associated with the GRB. There is no evidence for other sources inside the revised XRT error circle. The limiting magnitude of our first epoch observation is R > 25.1 (2 sigma). The corresponding upper limit on beta_OX is 0.42, rendering the burst dark according to the definition proposed by Jakobsson et al. (2004, ApJ, 617, L21). Considering the brightness of S1, it is unlikely that it is a normal galaxy if z ~ 3.3 (GCN 5698). The relatively low S/N of the VLT spectrum makes it difficult to reach a firm conclusion on the reality of absorption features (apart from the feature around 5230 A). The lack of broad emission lines and the marginal evidence for optical variability might indicate that S1 is a blazar. An alternative scenario is that S1 is at a lower redshift. The 5230 A feature could be the Balmer/4000 A break, indicating a redshift of z ~ 0.3. We thank Kim Page for providing us with the afterglow X-ray flux.