Gamma-ray Burst 090531

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN/BACODINE POSITION NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 01:45:38 UT
NOTICE_TYPE:     Swift-BAT GRB Position
TRIGGER_NUM:     353627,   Seg_Num: 0
GRB_RA:          178.687d {+11h 54m 45s} (J2000),
                 178.808d {+11h 55m 14s} (current),
                 178.046d {+11h 52m 11s} (1950)
GRB_DEC:          +7.799d {+07d 47' 58"} (J2000),
                  +7.747d {+07d 44' 49"} (current),
                  +8.078d {+08d 04' 40"} (1950)
GRB_ERROR:       3.00 [arcmin radius, statistical only]
GRB_INTEN:       4861 [cnts]    Image_Peak=179 [image_cnts]
TRIGGER_DUR:     1.024 [sec] 
TRIGGER_INDEX:   146     E_range: 25-100 keV
BKG_INTEN:       33058 [cnts]
BKG_TIME:        6299.21 SOD {01:44:59.21} UT
BKG_DUR:         8 [sec]
GRB_DATE:        14982 TJD;   151 DOY;   09/05/31
GRB_TIME:        6317.38 SOD {01:45:17.38} UT
GRB_PHI:         -77.76 [deg]
GRB_THETA:        20.45 [deg]
SOLN_STATUS:     0x3
RATE_SIGNIF:     9.00 [sigma]
IMAGE_SIGNIF:    7.22 [sigma]
MERIT_PARAMS:     +1  +0  +0  +0  +2  -3  -5  +0 +27  +0 
SUN_POSTN:        68.11d {+04h 32m 25s}  +21.91d {+21d 54' 44"}
SUN_DIST:        105.94 [deg]   Sun_angle= -7.4 [hr] (East of Sun)
MOON_POSTN:      159.40d {+10h 37m 35s}   +5.40d {+05d 23' 43"}
MOON_DIST:        19.42 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:      265.53, 66.46 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      175.68,  6.63 [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 = 242.95,-7.18 [deg].

red DSS finding chart ps-file

GCN NOTICE

TITLE:           GCN/SWIFT NOTICE
NOTICE_DATE:     Sun 31 May 09 01:48:50 UT
NOTICE_TYPE:     Swift-BAT GRB Lightcurve
TRIGGER_NUM:     353627,   Seg_Num: 0
GRB_RA:          178.687d {+11h 54m 45s} (J2000),
                 178.808d {+11h 55m 14s} (current),
                 178.046d {+11h 52m 11s} (1950)
GRB_DEC:          +7.799d {+07d 47' 58"} (J2000),
                  +7.747d {+07d 44' 49"} (current),
                  +8.078d {+08d 04' 40"} (1950)
GRB_DATE:        14982 TJD;   151 DOY;   09/05/31
GRB_TIME:        6317.38 SOD {01:45:17.38} UT
TRIGGER_INDEX:   146
GRB_PHI:         -77.76 [deg]
GRB_THETA:        20.45 [deg]
DELTA_TIME:      -57.00 [sec]
TRIGGER_DUR:     1.024 [sec] 
SOLN_STATUS:     0x3
RATE_SIGNIF:     9.00 [sigma]
IMAGE_SIGNIF:    7.22 [sigma]
LC_URL:          sw00353627000msb.lc
SUN_POSTN:        68.11d {+04h 32m 26s}  +21.91d {+21d 54' 45"}
SUN_DIST:        105.94 [deg]   Sun_angle= -7.4 [hr] (East of Sun)
MOON_POSTN:      159.43d {+10h 37m 42s}   +5.38d {+05d 22' 55"}
MOON_DIST:        19.40 [deg]
MOON_ILLUM:      49 [%]
GAL_COORDS:      265.53, 66.46 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      175.68,  6.63 [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 = 242.95,-7.18 [deg].

GCN Circular #9454
M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC), C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC), V. Mangano (INAF-IASFPA) and D. M. Palmer (LANL) report on behalf of the Swift Team:
At 01:45:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090531 (trigger=353627). Swift could not immediately slew to the burst location. The BAT on-board calculated location is RA, Dec 178.687, +7.799 which is
```
   RA(J2000) = 11h 54m 45s
   Dec(J2000) = +07d 47' 58"
```
with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single-peaked structure with a duration of about 50 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~10 sec after the trigger.
Because of a Moon constraint, Swift could not slew, and there will be no XRT or UVOT observations until June 3.
Burst Advocate for this burst is M. Stamatikos (michael AT milkyway.gsfc.nasa.gov). 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 #9455
S. B. Cenko (UC Berkeley) reports on behalf of a larger collaboration:
We have imaged the field of GRB090531 (Stamatikos et al., GCN 9454) with the automated Palomar 60 inch telescope. Observations began at 4:47 UT on 2009 May 31 (~ 4.03 hr after the burst trigger) and were taken in the Sloan r', i', and z' filters. In coadded images, we find no new sources inside the BAT error circle to the following limits (calculated with reference to the SDSS DR7):
```
Filter		Magnitude		Time Since Burst (hours)
----------------------------------------------------------------------
r'		> 21.5			4.22
i'		> 21.3			4.25
z'		> 20.5			4.30
```
GCN Circular #9456
A. Rossi (Tautenburg), F. Olivares, and J. Greiner (both MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 090531 (Swift trigger 353627, Stamatikos et al., GCN #9454) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m MPI/ESO telescope at La Silla Observatory (Chile). Observations started on 31 May 2009 at 01:47 UT, 2 minutes after the burst and continued until 03:29 UT.
We do not find any new source within the BAT error circle. Image subtraction between the first and last images of each band does not reveal any variable source. The first image , consisting of 4.4 min exposure in g'r'i'z' and 4 min in JHK, yields the following upper limits (all AB):
```
g' > 22.6
r' > 22.8
i' > 22.4
z' > 22.0
J  > 21.5
H  > 20.9
K  > 20.2
```
which were obtained using the SDSS and 2MASS field stars as reference.
GCN Circular #9460
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team):
Using the data set from T-60 to T+243 sec from recent telemetry downlinks, we report further analysis of BAT GRB 090531 (trigger #353627) (Stamatikos, et al., GCN Circ. 9454). The BAT ground-calculated position is RA, Dec = 178.672, 7.824 deg, which is
```
   RA(J2000)  =  11h 54m 41.4s 
   Dec(J2000) = +07d 49' 27.0" 
```
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 73%.
The mask-weighted light curve shows a single peak starting at ~T-25 sec, peaking at T+9 sec, and ending at ~T+60 sec. There is a possible (2.5 sigma CL) episode of emission from T+80 to ~T+140 sec. T90 (15-350 keV) is 32 +- 6 sec (estimated error including systematics).
The time-averaged spectrum from T-12.6 to T+29.4 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.86 +- 0.42, and Epeak of 64.7 +- 14.3 keV (chi squared 51.91 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.3 +- 0.1 x 10^-6 erg/cm2 and the 1-sec peak flux measured from T+9.29 sec in the 15-150 keV band is 1.3 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.68 +- 0.09 (chi squared 65.50 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/353627/BA/
GCN Circular #9476
Gary Henson, Shannon Hall, Mark Gorski (ETSU/SARA REU), Adria Updike, Dieter Hartmann (Clemson University) report:
The 0.9m SARA telescope located at Kitt Peak National Observatory began imaging the field of GRB 090531A (Stamatikos et al., GCN 9454) about 2.5 hours after the burst under decent weather conditions. In one hour of stacked exposures, we detect no new sources down to a limiting magnitude of R > 20.5 (with respect to the USNO B.1 catalog). No further observations are planned.
GCN Circular #9525
B. Sbarufatti, V. Mangano (INAF-IASFPA) on behalf of the Swift-XRT team.
The XRT onboard Swift observed the field of GRB 090531A on 2009 June 10 and 2009 June 17, after it came outside the Moon observing contstraint, for a total exposure of 35.5 ks in Photon Counting mode.
Three significant sources are detected inside the initial BAT error circle (Stamatikos, et al., GCN circ. 9454). Two of them, detected at a level of 1.2E-3 counts/s and 9.0E-4 counts/s, are compatible with a stable count-rate and are found outside the BAT refined error circle (Sakamoto, et al., GCN circ. 9460). The third source, detected at a level of 6.5E-4 counts/s is too faint to estimate if it is fading or not, and it is found just inside the BAT refined error circle, at a distance of 64.8 arcsec from the BAT refined position. Its coordinates are RA,Dec = 178.65539, +7.81671 which is:
```
RA(J2000)  =  11h 54m 37.29s
Dec(J2000) = +07d 49' 00.2"
```
with an uncertainty of 4.8 arcsec (radius, 90% confidence).
This circular is an official product of the Swift-XRT team.

GCN Circular #10016
A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, A. Foster, J. Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander report:
Skynet observed the Swift/BAT localization of GRB 090531A (Stamatikos et al., GCN 9454) with three of the 16" PROMPT telescopes at CTIO beginning 6.1 minutes after the trigger in UVRI.
We do not detect the afterglow (Sbarufatti & Mangano, GCN 9525). Stacking only images that increase the limiting magnitude yields:

mean                                                1-sig.  1-sig.
time                             3-sig.             sys.    stat.
since                            lim.    cal.       cal.    cal.
trig.  tel.      exp.      fil.  mag.    stars*     unc.    unc.
(m)              (# x s)                            (mag)   (mag)

6.5    PROMPT-5  1 x 40    I     17.6    32 SDSS 7  0.055   0.002
15.3   PROMPT-5  11 x 80   I     19.4    32 SDSS 7  0.055   0.000
84.0   PROMPT-3  75 x 80   U     19.3    7 SDSS 7   0.037   0.001
92.6   PROMPT-5  85 x 80   I     20.5    32 SDSS 7  0.055   0.000
                  + 1 x 40
94.1   PROMPT-4  43 x 80   V     21.1    37 SDSS 7  0.007   0.000
104.8  PROMPT-4  54 x 80   R     21.3    40 SDSS 7  0.018   0.000

* Transformed using Jester et al., 2005, ApJ, 130, 873.

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Jochen Greiner, last update: 11-Oct-2009 [Disclaimer]