//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6156 SUBJECT: GRB 070227: Swift detection of a burst in ground analysis DATE: 07/02/28 06:42:44 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC), D. M. Palmer (LANL), T. Sakamoto (NASA/ORAU) and L. Vetere (PSU) report on behalf of the Swift Team: At 2007-02-27 22:21:59 Swift-BAT detected GRB 070227 (trigger 262347). The burst was not found automatically onboard, because a planned slew terminated the trigger prematurely. The burst was found later in ground analysis. Swift did not slew to the burst, and a target of opportunity observation for this burst will be uploaded at the next command opportunity (around 1400 UT). The BAT position is RA, Dec 120.566, -46.305 (J2000) RA: +08h 02m 16s Dec: -46d 18' 17" with an estimated error circle of 3 arcmin. The burst was in the extreme partially coded field of view, the coding was 3.4%. The burst as seen by BAT was a single peak at least 8 seconds long. We have detailed information for only T-2 to T+8 sec. Since the burst was weak and on the edge of the FOV, and because of the subsequent slew, we can not determine if additional emission occurred. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6157 SUBJECT: GRB070227: possible X-ray afterglow detection DATE: 07/02/28 19:17:26 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani, D. Grupe, D.N. Burrows (PSU) report on behalf of the Swift/XRT Team: The Swift BAT detected GRB 070227 at 22:21:59 UT (GCN 6156). The Swift observatory did not slew promptly because a planned slew terminated the trigger prematurely. The burst was found later in ground analysis. The XRT began taking data at 2007-02-28 13:51:31 UT, approximately 15 hours and 30 minutes after the trigger. In a preliminary data analysis of the first 2.6ks of PC data we detect an uncataloged X-ray source located at RA, Dec 120.5808 -46.3135 which is RA(J2000) = 08h 02m 19.4s Dec(J2000) = -46d 18' 48.7" We estimate an uncertainty of 8 arcseconds radius (90% containment). This position is 48 arcseconds from the BAT position (GCN 6156). The source count rate is approximately 0.005 counts/s. Observations are still underway and further ground analysis will be performed to determine if this X-ray source is fading. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6158 SUBJECT: GRB 070227, Swift-BAT refined analysis DATE: 07/02/28 21:20:42 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), C. Pagani (PSU), 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-2.0 to T+8.1 sec, we report further analysis of BAT GRB 070227 (trigger #262347) (Pagani, et al., GCN Circ. 6156). The BAT ground-calculated position is RA, Dec = 120.566, -46.305 (J2000) RA: +08h 02m 16s Dec: -46d 18' 17" with an uncertainty of 2.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 3%. Because this was a failed trigger on-board, this is all the detailed BAT data we are going to get on this burst. The burst had two weak overlapping peaks with spectral evolution. The larger peak was at T+1 and the smaller at T+6 sec. There is no additional strong emission at times later than T+8, but we cannot rule out weak emission. T90 (15-350 keV) is 7 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T+0.0 to T+8.0 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.27. The fluence in the 15-150 keV band is 1.6 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+0.00 sec in the 15-150 keV band is 2.7 +- 0.4 ph/cm2/sec. The quoted errors are at the 90% confidence level considering the statistical and usual systematic effects. However, because of the extreme partial coding of this burst, and particularly the reduced sensitivity to low energy photons at the edge of the FOV, we expect an extra systematic uncertainty contribution of about 10%. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6159 SUBJECT: GRB 070227: TAROT La Silla observatory optical observations DATE: 07/02/28 21:51:23 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 070227 detected by SWIFT (trigger 262347) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 7.76 hours after the GRB trigger (5.2s after the notice). The elevation of the field decreased from 41 degrees above horizon, weather conditions were excellent and the moon elevation was less than 10 degrees. The date of trigger : t0 = 2007-02-27T22:21:58.752 We co-added a series of 26 long exposures taken between t0+7.76h and t0+8.98h. The co-added image has a limiting magnitude R~20.2. The field is very crowded. We do not detect any OT in the BAT refined error box (Barbier et al. GCNC 6158) nor in the XRT one (Pagani et al. GCNC 6157). Concerning the XRT error box, we detected clearly all stars present in the USNO-B1 catalog or in the DSS-R image. Magnitudes are not corrected for galactic dust extinction. N.B. Galactic coordinates are lon=261.2574 lat= -8.2038 and the galactic extinction in R band is 0.7 magnitudes estimated from D. Schlegel et al. 1998ApJ...500..525S. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6160 SUBJECT: GRB 070227: Swift/UVOT Upper Limits DATE: 07/02/28 23:52:35 GMT FROM: Shashi Pandey at MSSL S. B. Pandey (UCL-MSSL) and C. Pagani (PSU) report on behalf of the Swift/UVOT Team: The Swift/UVOT started observing the field of GRB 070227 (trigger 262347) 56680 s after the BAT trigger (Pagani et al., GCN Circ. 6156). UVOT observations started late because the BAT observation did not result in an automated response, but was found during the ground analysis. The 3-sigma upper limits for detecting a source inside the XRT error circle (Pagani, Grupe & Burrows, GCN Circ. 6157) in the co-added exposures are: Filter T_start T_stop Exp(s) Mag (3-sigma upper limit) --------------------------------------------------------------- V 56680 57586 885 20.90 B 63392 64113 702 21.58 U 62480 63386 885 21.31 UVW1 61573 62473 886 21.17 UVM2 57592 58329 726 21.34 UVW2 55773 56673 886 21.04 --------------------------------------------------------------- Caution should be taken due to the presence of a nearby bright star. The XRT error circle lies lies within the wings of the PSF of the bright star in all the UVOT frames. This complicates the photometry, so these limits could possibly be underestimated. The values quoted above are not corrected for the expected Galactic extinction E_{B-V} = 0.34 mag towards the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6161 SUBJECT: GRB 070227: optical observations DATE: 07/03/01 01:10:18 GMT FROM: Alan Gilmore at U of Canterbury,Mt John Obs A. C. Gilmore and P. M. Kilmartin (Mt John Observatory of the University of Canterbury) report: We stacked 20 x 60 second clear exposures with an Apogee U-47 CCD on a 0.6-m f/13.5 reflector at Mt John Observatory, centred on February 28 09:54 UT (11.5 hours after the burst.) Our images do not show any new object in or near the Swift-BAT error circle when compared with DSS-2 red and DSS-2 infra-red images. This message may be cited. [GCN OPS NOTE (28feb07): This message was delayed ~20 hrs due to unknown internet delivery problems.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6163 SUBJECT: GRB 070227: optical observations DATE: 07/03/01 06:23:32 GMT FROM: Alan Gilmore at U of Canterbury,Mt John Obs A. C. Gilmore and P. M. Kilmartin (Mt John Observatory of the University of Canterbury) report: We stacked 20 x 60 second clear exposures with an Apogee U-47 CCD on a 0.6-m f/13.5 reflector at Mt John Observatory, centred on February 28 09:54 UT (11.5 hours after the burst.) Our images do not show any new object in or near the Swift-BAT error circle when compared with DSS-2 red and DSS-2 infra-red images. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6167 SUBJECT: GRB070227: Swift-XRT refined analysis DATE: 07/03/05 21:07:47 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani, J. L. Racusin, L. Vetere, D. Grupe, D. N. Burrows (PSU), report on behalf of the Swift XRT team: We have analysed the Swift-XRT Photon Counting data of GRB 070227 (GCN Circ. 6156) from T+56ks to T+386ks (where T is the BAT trigger time). The candidate X-ray afterglow reported in GCN Circ. 6157 has faded from the initial count rate of ~ 0.01 counts/s to a count rate of 0.002 counts/s. Using 39ks of PC data the refined XRT position is RA,Dec= 120.5805, -46.3135 which is: RA(J2000): 08h 02m 19.33s Dec(J2000): -46d 18' 48.7" with an uncertainty of 4 arcseconds (90% containment). This position is 47 arcseconds from the refined BAT position given in GCN Circ. 6158 and 0.7 arcseconds from the XRT position given in GCN Circ. 6157. The light-curve shows an initial flat phase during the first 20ks of XRT obervations ending at about 80ks after the burst, followed by a decay that can be fitted with a power law with index 0.9+/-0.2. The spectral fit to the PC data is not very well constrained due to the low number of afterglow events. The fit with an absorbed power law, applying C-statistics, gives a photon index of 2.9 (+0.8/-0.5) in the [0.3-10] keV band, and a column density of (0.57 +0.26/-0.18)e22 cm^-2 (compared with the Galactic value in this direction of 0.31e22 cm^-2). The average estimated unabsorbed 0.3-10 keV flux from T+56ks to T+386ks of XRT Photon Counting observations was 3.6e-13 erg cm^-2 s^-1. This Circular is an official product of the Swift XRT Team.