GRB 090309
GCN Circular 8964
Subject
GRB 090309: Swift detection of a burst
Date
2009-03-09T23:50:52Z (16 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
P. A. Evans (U Leicester), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), W.B Landsman (GSFC),
F. E. Marshall (NASA/GSFC), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
B. A. Rowlinson (U Leicester), T. Sakamoto (NASA/UMBC),
M. H. Siegel (PSU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:
At 23:29:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090309 (trigger=345945). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 284.981, -25.264 which is
RA(J2000) = 18h 59m 55s
Dec(J2000) = -25d 15' 50"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a peak with a
with a duration of about 3 sec. There is a hint of a secondary peak
around T+25 sec with a duration of 10 sec. The peak count rate
was ~1400 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 23:30:32.5 UT, 79.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 284.9730, -25.2611
which is equivalent to:
RA(J2000) = 18h 59m 53.51s
Dec(J2000) = -25d 15' 39.8"
with an uncertainty of 3.3 arcseconds (radius, 90% containment). This
location is 28 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.07e+21 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 81 seconds after the BAT trigger. No credible 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 upper limit for this image is approximately
white = 19 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.23.
Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.ac.uk).
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 8967
Subject
GRB 090309, Swift-BAT refined analysis
Date
2009-03-10T14:02:00Z (16 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
D. M. Palmer (LANL), 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), A. M. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), 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-240 to T+362 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090309 (trigger #345945)
(Evans, et al., GCN Circ. 8964). The BAT ground-calculated position is
RA, Dec = 284.978, -25.274 deg which is
RA(J2000) = 18h 59m 55.5s
Dec(J2000) = -25d 16' 42.0"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 61%.
The mask-weighted light curve shows a single peak starting at T-1 sec,
peaking around T+1 sec, and ending at T+2 sec.
T90 (15-350 keV) is 3.0 +- 1.4 sec (estimated error including systematics).
The time-averaged spectrum from T-0.8 to T+2.2 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.36 +- 0.33. The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.18 sec in the 15-150 keV band
is 0.9 +- 0.2 ph/cm2/sec. 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/345945/BA/
GCN Circular 8969
Subject
GRB 090309: Enhanced Swift-XRT position
Date
2009-03-10T15:00:31Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1230 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 090309, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 284.97425, -25.26099 which is equivalent
to:
RA (J2000): 18h 59m 53.82s
Dec (J2000): -25d 15' 39.6"
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 8970
Subject
GRB 090309: Swift-XRT refined analysis
Date
2009-03-10T15:43:56Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team:
We have analysed 5.5 ks of XRT data for GRB 090309 (Evans et al. GCN
Circ. 8964), from 86 s to 12.4 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Goad et al. (GCN. Circ 8969).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.38 (+0.08, -0.09).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+/-0.3). The best-fitting
absorption column is 2.8 (+1.5, -1.1) x 10^21, in excess of the Galactic
value of 1.1 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to
observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from
this spectrum is 4.0 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1.
If the light curve continues to decay with a power-law decay index of
0.38, the count rate at T+24 hours will be 0.012 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.8 x
10^-13 (8.2 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00345945.
This circular is an official product of the Swift-XRT team.
GCN Circular 8973
Subject
GRB 090309: Swift/UVOT Upper Limits
Date
2009-03-10T22:03:58Z (16 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W.B. Landsman (NASA/GSFC) and P. Evans (U. Leicester) report on behalf
of the Swift/UVOT team:
The Swift/UVOT observed the field of GRB 090309 starting 82 s after the
BAT trigger (Evans et al., GCN Circ. 8964). No optical afterglow is
detected in the initial UVOT exposures at the refined position of the
X-ray afterglow (Goad et al., GCN Circ. 8969). An r~19 field star (
GSC S9QR039837) is detected 3" from the XRT position. Three-sigma
upper limits using the UVOT photometric system (Poole et al. 2008,
MNRAS, 383, 627) in a 2" radius aperture for the first finding chart
(FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white (FC) 82 231 147 >21.0
white 82 6136 564 >21.8
v 624 17530 1317 >20.7
b 549 23995 1088 >21.4
u 294 23315 2241 >21.5
uvw1 673 22401 1998 >21.6
uvm2 648 18210 1875 >21.6
uvw2 599 16617 1318 >21.6
The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.23 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 8982
Subject
GRB 090309, Swift-BAT lag analysis
Date
2009-03-13T09:58:16Z (16 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
T. Sakamoto (GSFC/UMBC), J. P. Norris, T. N. Ukwatta (GWU/GSFC),
S. D. Barthelmy (GSFC), N. Gehrels (GSFC), M. Stamatikos (GSFC/ORAU)
(for the Swift-BAT team):
For GRB 090309 (Evans et al. GCN Circ. 8964), we are unable to determine
if this is a short or long burst. The reasons are as follows: (1) the
spectral lag is 0.044 +/- 0.16 sec (between the 50-100 and 15-25 keV).
(2) The T90 duration is 3.0 +- 1.4 sec (Palmer et al. GCN Circ. 8967)
which is midway between the two T90 distributions. (3) The photon index
is 1.36 +/- 0.33 (Palmer et al. GCN Circ. 8967) is also in the middle of
the short and hard distributions (Figure 13 of Sakamoto et al., ApJS, 175, 179).