Gamma-ray Burst 070920B

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Sep 07 21:04:49 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     291728,   Seg_Num: 0
GRB_RA:            0.144d {+00h 00m 35s} (J2000),
                   0.243d {+00h 00m 58s} (current),
                  -0.497d {-00h 01m 58s} (1950)
GRB_DEC:         -34.819d {-34d 49' 06"} (J2000),
                 -34.776d {-34d 46' 31"} (current),
                 -35.097d {-35d 05' 48"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       5480 [cnts]    Image_Peak=223 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   137     E_range: 15-50 keV
BKG_INTEN:       34983 [cnts]
BKG_TIME:        75853.76 SOD {21:04:13.76} UT
BKG_DUR:         8 [sec]
GRB_DATE:        14363 TJD;   263 DOY;   07/09/20
GRB_TIME:        75872.38 SOD {21:04:32.38} UT
GRB_PHI:         155.61 [deg]
GRB_THETA:         7.84 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     14.10 [sigma]
IMAGE_SIGNIF:    7.94 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +1  +3  +0  +0 +82  +1 
SUN_POSTN:       177.73d {+11h 50m 54s}   +0.99d {+00d 59' 08"}
SUN_DIST:        146.13 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      282.35d {+18h 49m 24s}  -27.31d {-27d 18' 45"}
MOON_DIST:        65.49 [deg]
MOON_ILLUM:      62 [%]
GAL_COORDS:      354.57,-76.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      344.66,-31.65 [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 = 4.42,19.93 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Thu 20 Sep 07 21:08:09 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     291728,   Seg_Num: 0
GRB_RA:            0.144d {+00h 00m 35s} (J2000),
                   0.243d {+00h 00m 58s} (current),
                  -0.497d {-00h 01m 58s} (1950)
GRB_DEC:         -34.819d {-34d 49' 06"} (J2000),
                 -34.776d {-34d 46' 31"} (current),
                 -35.097d {-35d 05' 48"} (1950)
GRB_DATE:        14363 TJD;   263 DOY;   07/09/20
GRB_TIME:        75872.38 SOD {21:04:32.38} UT
TRIGGER_INDEX:   137
GRB_PHI:         155.61 [deg]
GRB_THETA:         7.84 [deg]
DELTA_TIME:      58.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     14.10 [sigma]
IMAGE_SIGNIF:    7.94 [sigma]
LC_URL:          sw00291728000msb.lc
SUN_POSTN:       177.73d {+11h 50m 55s}   +0.98d {+00d 59' 05"}
SUN_DIST:        146.13 [deg]   Sun_angle= 11.8 [hr] (West of Sun)
MOON_POSTN:      282.38d {+18h 49m 32s}  -27.31d {-27d 18' 31"}
MOON_DIST:        65.47 [deg]
MOON_ILLUM:      62 [%]
GAL_COORDS:      354.57,-76.68 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      344.66,-31.65 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        SWIFT-BAT GRB Lightcurve.  
COMMENTS:           
COMMENTS:        The next comments were copied from the BAT_POS Notice:  
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 = 4.42,19.93 [deg].

GCN Circular #6808
J. L. Racusin (PSU), S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/GSFC/USRA), H. A. Krimm (GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC), C. Pagani (PSU), D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the Swift Team:
At 21:04:32 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 070920B (trigger=291728). The BAT on-board calculated location is RA, Dec 0.144, -34.819 which is
```
   RA(J2000)  = 00h 00m 35s
   Dec(J2000) = -34d 49' 06"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a single peak with a duration of about 35 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger.
Because Swift is in the process of returning to normal operations, automatic slewing to GRBs is currently disabled. Therefore, there are no prompt XRT or UVOT observations of this burst.
Burst Advocate for this burst is J. L. Racusin (racusin AT astro.psu.edu). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular #6809
A. de Ugarte Postigo, J. Gorosabel, M. Jelinek, A.J. Castro-Tirado (IAA-CSIC, Granada), D. Perez-Ramirez (U. Jaen), R. Corradi (ING, La Palma), T. Liimets (ING, La Palma and Tartuu Obs.) report:
We have observed the field of GRB070920B (Racusin et al., GCNC 6808) using the 2.5m NOT telescope (+ALFOSC) at Roque de los Muchachos Observatory in V, R and I bands (180 s each) at high airmass. The mean time of the observations was 21.0486 Sep. 2007 (UT), ~4.1 hours after the burst. We do not detect any bright afterglow candidate within the Swift/BAT error box. However, we do see a red, stationary object (detected in R and I bands) slightly over the DSS2 limit that does not seem to have its correspondent in the DSS2 images. The coordinates of this object are (J2000 +/- 0.5"):
```
R.A.: 00:00:34.56
Dec.: -34:49:08.4
```
Further observations are needed to confirm wether this could be the optical afterglow of GRB 070920B.
A finding chart comparing with the DSS2 can be found at:
www.iaa.es/~deugarte/GRBs/070920B/GRB070920B.jpg
This message can be quoted.
GCN Circular #6811
S.D. Barthelmy (GSFC), L. Barbier (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), J.L. Racusin (PSU), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from recent telemetry downlinks, we report further analysis of BAT GRB 070920 (trigger #291728) (Racusin, et al., GCN Circ. 6808). The BAT ground-calculated position is RA, Dec = 0.127, -34.844 deg which is
```
   RA(J2000)  =  00h 0m 30.5s 
   Dec(J2000) = -34d 50' 39" 
```
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 100%.
The mask-weighted lightcurve shows a symmetrical peak starting at ~T-20 sec, peaking at ~T+1 sec, and ending at ~T+17 sec. T90 (15-350 keV) is 20.2 +- 0.2 sec (estimated error including systematics).
The time-averaged spectrum from T-11.2 to T+13.4 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.67 +- 0.58, and Epeak of 41.3 +- 4.5 keV (chi squared 45.21 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 6.6 +- 0.5 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T-0.49 sec in the 15-150 keV band is 0.8 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.00 +- 0.10 (chi squared 67.16 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.
GCN Circular #6812
E. Berger (Princeton,OCIW) and W. Krzeminski (LCO) report:
"We observed the BAT error circle of GRB 070920b (GCN 6808) with the Swope 40-inch telescope at Las Campanas Observatory starting on 2007 Sep. 21.22 UT (8.2 hours after the burst). A total of 30 minutes were obtained in R-band in mediocre seeing conditions (~1.5"). A comparison to DSS reveals no new objects within the revised BAT error circle (GCN 6811)."
GCN Circular #6814
B. E. Cobb, part of the larger SMARTS consortium, reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical imaging of the error region of GRB 070920b (Racusin et al. GCN 6808) with a mid-exposure time of ~4.4 hours post-burst (2007-09-21 01:29 UT). The total summed exposure time amounted to 36 minutes in I, but images were taken under poor weather conditions.
Comparison to the DSS reveals no new sources in the refined GRB error region (Barthelmy et al. GCN 6811). Our I-band limiting magnitude is I~20.8 (calibrated using several USNO-B1.0 stars).
GCN Circular #6816
Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:
We imaged the field of GRB 070920B detected by SWIFT (trigger 291728) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile.
The observations started 2.7h after the GRB trigger (beginning of the night). The elevation of the field increased from from 27 degrees above horizon and weather conditions were good but the moon (phase=0.58) was only at 68 degrees of the field, limiting the detectivity.
We co-added a series of 8 x 180s unfiltered exposures. We do not detect any OT in the refined position provided by Barthelmy et al. (GCNC 6811) nor the source reported by de Ugarte Postigo et al. (GCNC 6809):
t0+2.7h to t0+3.6h : R > 18.2
Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction (which is very low along the line of sight).
This message may be cited.
GCN Circular #6820
J. L. Racusin (PSU) reports on behalf of the Swift-XRT team:
We have analysed 9.7 ks of Swift XRT data for GRB 070920B (Racusin et al., GCN 6808) beginning 64 ks after the BAT trigger. The data are entirely in Photon Counting mode, and reveal a faint uncatalogued X-ray source at RA, Dec= 0.13029, -34.85284 degrees, which is equivalent to:
```
RA (J2000) =  00h 00m 31.27s
Dec(J2000) = -34d 51' 10.2"
```
with an estimated uncertainty of 8.0 arcsec (radius, 90% containment including boresight uncertainty). This is 33 arcsec from the refined BAT position (Barthelmy et al. GCN 6811). The source has a count rate of 2.1e-3 +/- 0.6e-3 counts s-1. At present we are unable to determine whether the source is fading, however observations are ongoing.
This circular is an official product of the Swift-XRT team.
GCN Circular #6824
H. Swan (U Mich), E.S. Rykoff (UCSB), F. Yuan (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 070920B (Swift trigger 291728; J. L. Racusin, GCN 6808), producing images beginning 8.5 s after the GCN notice time. An automated response took the first image at 21:05:16.5 UT, 44.1 s after the burst, under partly cloudy conditions. We took 10 5-sec, 10 20-sec and 386 60-sec exposures. These unfiltered images are calibrated relative to USNO A2.0 (R). We lost internet contact with ROTSE-IIIc shortly after the GCN trigger, thus we were unable to retrieve the burst data until Sept. 25.
Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma Swift/BAT error circle or the XRT error circle , (J. L. Racusin, GCN 6820) for both single images and coadding into sets of 10; the field is not crowded. Individual images have limiting magnitudes ranging from 12.8-17.8; we set the following specific limits.
```
start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
21:05:16.5   21:05:21.5         5     15.7           44.1       N
21:05:16.5   21:06:34.5        78     16.7           44.1       Y
21:29:06.7   21:34:44.6       337     17.8         1474.3       Y
```
GCN Report 84.1
GCN_Report 84.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_84_1.pdf by J.L. Racusin at PSU titled: "Swift Observations of 070920B"

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Jochen Greiner, last update: 27-Sep-2007 [Disclaimer]