Gamma-ray Burst 070227

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Wed 28 Feb 07 06:07:42 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     262347,   Seg_Num: 0
GRB_RA:          120.566d {+08h 02m 16s} (J2000),
                 120.622d {+08h 02m 29s} (current),
                 120.176d {+08h 00m 42s} (1950)
GRB_DEC:         -46.305d {-46d 18' 17"} (J2000),
                 -46.325d {-46d 19' 30"} (current),
                 -46.164d {-46d 09' 50"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       2936 [cnts]    Image_Peak=100 [image_cnts]
TRIGGER_DUR:     3.000 [sec] 
TRIGGER_INDEX:   0     E_range: 15-25 keV
BKG_INTEN:       0 [cnts]
BKG_TIME:        0.00 SOD {00:00:00.00} UT
BKG_DUR:         0 [sec]
GRB_DATE:        14158 TJD;    58 DOY;   07/02/27
GRB_TIME:        80518.89 SOD {22:21:58.89} UT
GRB_PHI:         168.69 [deg]
GRB_THETA:        57.09 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     9.00 [sigma]
IMAGE_SIGNIF:    11.30 [sigma]
MERIT_PARAMS:     +0  +0  +0  +0  +0  +0  +0  +0  +0  +0 
SUN_POSTN:       340.85d {+22h 43m 23s}   -8.09d {-08d 05' 40"}
SUN_DIST:        114.84 [deg]   Sun_angle= -9.3 [hr] (East of Sun)
MOON_POSTN:      119.97d {+07h 59m 52s}  +24.67d {+24d 40' 00"}
MOON_DIST:        70.99 [deg]
MOON_ILLUM:      87 [%]
GAL_COORDS:      261.26, -8.20 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      143.69,-64.15 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Coordinates.  
COMMENTS:        This is a rate trigger.  
COMMENTS:        A point_source was found.  
COMMENTS:        This does not match any source in the on-board catalog.  
COMMENTS:        This does not match any source in the ground catalog.  
COMMENTS:        This is a GRB.  
COMMENTS:        This trigger occurred at longitude,latitude = 0.00,0.00 [deg].  
COMMENTS:        This Notice was ground-reprocessed from flight-data.  
COMMENTS:          
COMMENTS:        This is a ground-generated notice    
COMMENTS:        A point_source was found in ground analysis.    
COMMENTS:        Onboard analysis was limited by the occurrence of a slew  
COMMENTS:        This source is close to a known high proper motion star   
COMMENTS:        The MERIT_PARAMS values are probably wrong

red DSS finding chart ps-file
GCN Circular #6156
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.
GCN Circular #6157
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.
GCN Circular #6158
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%.
GCN Circular #6159
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.
GCN Circular #6160
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).
GCN Circular #6161
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.]
GCN Circular #6163
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 Circular #6167
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.
GCN Report 37.1
GCN_Report 37.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_37_1.pdf by C. Pagani at PSU titled: "Swift Observations on GRB 070227"

Back to JG's homepage

Jochen Greiner, last update: 07-Mar-2007 [Disclaimer]