GRB 090531B
GCN Circular 9461
Subject
GRB 090531B: Swift detection of a burst
Date
2009-05-31T18:44:29Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), T. Sakamoto (NASA/UMBC) and
B. Sbarufatti (INAF-IASFPA) report on behalf of the Swift Team:
At 18:35:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090531B (trigger=353728). Swift will execute a delayed slew
to the burst.
The BAT on-board calculated location is
RA, Dec 252.064, -36.025 which is
RA(J2000) = 16h 48m 15s
Dec(J2000) = -36d 01' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows an initial bright spike
at T_zero, then two much smaller spikes at T+21 sec and T+35 sec.
The peak count rate was ~7000 counts/sec (15-350 keV), at ~0 sec
after the trigger.
Due to an observing constraint, Swift will not slew until
T0+50.1 minutes. There will be no XRT or UVOT data until
this time.
Burst Advocate for this burst is J. R. Cummings (jayc 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 9462
Subject
GRB 090531B: ROTSE-III Optical Limits
Date
2009-05-31T19:20:55Z (16 years ago)
From
Brad Schaefer at LSU <schaefer@grb.phys.lsu.edu>
B. E. Schaefer (Louisiana State), T. Guver (U Arizona), S. B. Pandey (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 090531B (Swift trigger 353728; J. R. Cummings et al., GCN
9461), producing images beginning 7.3 s after the GCN notice time. An
automated response took the first image at 18:36:22.3 UT, 26.1 s after the
burst, and during the gamma-ray emission, under excellent conditions. We
took 10 5-sec, 10 20-sec and 50 60-sec exposures. These unfiltered images
are calibrated relative to USNO A2.0 (R). Imaging is on going.
Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma Swift/BAT error circle, for both single images and coadding into
sets of 10; however, we are limited as the field is somewhat crowded.
Individual images have limiting magnitudes ranging from 15.3-16.0; we set
the following specific limits.
start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
18:36:22.3 18:36:27.3 5 15.3 26.1 N
18:47:31.3 18:52:11.6 280 16.3 695.1 Y
[GCN OPS NOTE(31may09): Per author's request, the "B" was added
to the burst name.]
GCN Circular 9463
Subject
GRB 090531B: Swift-XRT candidate afterglow position
Date
2009-05-31T20:27:50Z (16 years ago)
From
Boris Sbarufatti at INAF-IASF-Pa <sbarufatti@ifc.inaf.it>
B. Sbarufatti, V. Mangano (INAF-IASFPA) and
J. R. Cummings (NASA/UMBC) report on behalf of the
Swift-XRT team
The XRT began observing the field of GRB 090531B
(trigger 353728, Cummins, et al., GCN Circ 9461) at
19:26:22 UT, 3026 seconds after the BAT trigger, as
soon as the burst went outside the Earth limb observing
constraint.
Using promptly downlinked data we find an X-ray
source with an enhanced position: RA,Dec = 252.0748, -36.0350
(degrees) which is equivalent to:
RA (J2000.0) = 16 48 17.95
DEC (J2000.0) = -36 02 06.0
with an uncertainty of 3.4 arcsec (radius, 90% containment).
This location is 47.8 arcseconds from the BAT onboard position, inside
the BAT
error circle.
This circular is an official product of the Swift-XRT team.
[GCN OPS NOTE(03sep09): Per operator's desire, the Subject line
was corrected from "090831B" to "090531B". F.Marshall and H.Krimm noticed this.]
GCN Circular 9464
Subject
Initial Swift/UVOT observations of GRB 090531B
Date
2009-05-31T20:49:26Z (16 years ago)
From
Caryl Gronwall at PSU/Swift-UVOT <caryl@astro.psu.edu>
C. Gronwall (PSU) and J. R. Cummings (NASA/UMBC) report on behalf of
the UVOT Team:
In response to GRB090531B (Swift/BAT trigger 353728; Cummings et al.,
GCN Circ. 9461)
at 18:35:56 UT, UVOT took a finding chart exposure of 150 seconds with
the White filter
starting 3848 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 (Sbarufatti et al., GCN Circ. 9463) The typical 3-sigma
upper limit has
been about 19.6 mag. No correction has been made for the expected
extinction corresponding
to E(B-V) of 1.12.
GCN Circular 9465
Subject
GRB 090531B: Swift-BAT refined analysis
Date
2009-06-01T00:03:02Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
T. N. Ukwatta (GWU), 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),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC)
(i.e. the Swift-BAT team):
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090531B (trigger #353728)
(Cummings, et al., GCN Circ. 9461). The BAT ground-calculated position is
RA, Dec = 252.070, -36.015 deg, which is
RA(J2000) = 16h 48m 16.8s
Dec(J2000) = -36d 00' 53.4"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
The mask-weighted light curve shows an initial bright spike with a total
width of 1.3 sec. It returns to baseline and then starts (!T+15 sec)
a long smooth rise to a peak around T+40 sec and a smooth decline
ending at ~T+110 sec. The spike is spectrally harder than the long smooth peak.
This lightcurve is consistance with a short hard burst with an extended emission.
T90 (15-350 keV) is 80 +- 23 sec (estimated error including systematics).
The time-averaged spectrum from T-13.0 to T+67.0 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.51 +- 0.22. The fluence in the 15-150 keV band is 7.1 +- 0.9 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.2 sec in the 15-150 keV band
is 1.25 +- 0.1 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/353728/BA/
GCN Circular 9469
Subject
GRB 090531B: Swift/UVOT Upper Limits
Date
2009-06-01T10:06:42Z (16 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and J. R. Cummings (NASA/UMBC) report on behalf of
the Swift/UVOT team:
The Swift/UVOT observed the field of GRB 090531B starting 3924 s after the
BAT trigger (Cummings et al., GCN Circ. 9461), once the GRB came out of
Earth limb observing constraint. No optical afterglow is detected in any
of the UVOT exposures at the position of the X-ray afterglow (Sbarufatti
et al., GCN Circ. 9463), with the following three-sigma upper limits:
Filter T_mid(s) Exp(s) 3-sig Mag UL
white 3934 74 > 20.52
v 4105 98 > 19.08
b 4926 98 > 20.06
u 4721 98 > 19.74
uvw1 4515 98 > 19.65
uvm2 4310 98 > 19.32
uvw2 5336 98 > 19.61
The values quoted above are not corrected for the large Galactic
extinction due to the reddening of E(B-V)=1.12 in the direction of the
burst (Schlegel et al. 1998). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular 9470
Subject
GRB 090531B, RIMOTS optical upper limits
Date
2009-06-01T13:32:06Z (16 years ago)
From
Eri Sonoda at U of Miyazaki/Japan <sonoda@astro.miyazaki-u.ac.jp>
E. Sonoda, K. Noda, N. Ohmori, K. Kono, H. Hayasi,
A. Daikyuji, Y. Nisioka, M. Yamauchi
(University of Miyazaki)
We have observed the field covering the error circle of
GRB090531B (Swift trigger 353728, GCN 9461(J. R. Cummings et al.))
with the unfiltered CCD camera on the 30-cm telescope
at University of Miyazaki.
The observation was started 18:37:28 UT (92 s after the Swift trigger),
under cloudy condition.
First image was obtained at 18:41:05 UT (309 s after the Swift trigger).
We have compared our data of 30 sec exposures with the USNO-A2.0 catalog.
There is no new source at the reported position.
(GCN 9462(B. E. Schaefer et al.), GCN 9464(C. Gronwall et al.)
GCN 9465(T. N. Ukwatta et al.), GCN 9469(P. Schady et al.))
Preliminary analysis shows there is no new source brighter than 14.6 mag.
GCN Circular 9471
Subject
Corrections to GRB 090531B Swift/UVOT Upper Limits
Date
2009-06-01T14:29:44Z (16 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and J. R. Cummings (NASA/UMBC) report on behalf of
the Swift/UVOT team:
We report a mistake in a few of the times provided in GCN 9469, including
the start time of the observations, which was in fact 3849 s after the BAT
trigger (Cummings et al., GCN Circ. 9461). Also, the exposure times of the
UVOT observations should have been two times the values given.
The corrected 3-sigma upper limits for the UVOT observations of the field
of GRB 090531B are provided below.
Filter T_mid(s) Exp(s) 3-sig Mag UL
white 3924 147 > 20.52
v 4105 197 > 19.08
b 4926 197 > 20.06
u 4721 197 > 19.74
uvw1 4515 197 > 19.65
uvm2 4310 197 > 19.32
uvw2 5336 197 > 19.61
The values quoted above are not corrected for the large Galactic
extinction due to the reddening of E(B-V)=1.12 in the direction of the
burst (Schlegel et al. 1998). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular 9475
Subject
GRB 090531B: Swift/BAT spectral lag results
Date
2009-06-01T15:55:43Z (16 years ago)
From
Tilan Ukwatta at GSFC/GWU <tilan.ukwatta@gmail.com>
T. N. Ukwatta (GWU/GSFC), S. D. Barthelmy (GSFC), J. R. Cummings
(NASA/UMBC), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU),
N. Gehrels (GSFC) (for the Swift-BAT team):
For GRB 090531B (Cummings et al. GCN 9461), the BAT team has
analyzed spectral lags for the data from T-1.0 sec to T+2.0 sec
using non-mask weighted light curves with 16 msec time binning.
The spectral lags were measured between standard canonical BAT
energy bands: channel 1 (15-25 keV), 2 (25-50 keV), 3 (50-100 keV)
and 4 (100-350 keV) are given below.
Lag Ch3-Ch2 : -2 +/- 9 msec
Lag Ch4-Ch2 : 11 +/- 5 msec
Lag Ch4-Ch3 : 8 +/- 3 msec
The signal-to-noise ratio in channel 1 is too weak to make a
lag measurement.
These lag values are consistent with lags observed for short
hard burst with extended emission.
GCN Circular 9480
Subject
GRB 090531B: GROND observation
Date
2009-06-02T11:58:24Z (16 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
A. Rossi (Tautenburg), F. Olivares, T. Kruehler and J. Greiner (all
MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 090531B (Swift trigger 353728, Cummings et al.
2009, GCN #9461) simultaneously in g'r'i'z'JHK with GROND
(Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPI/ESO telescope
at La Silla Observatory (Chile).
Observations started on 1 June 2009 at 00:03 UT, 5.5 hours after the burst and
continued until 00:50 UT under mediocre seeing (~1.5), cirrus and Moon light.
A second epoch started at 04:33 UT under better conditions, consisting of
72 min exposure in g'r'i'z' and 60 min in JHK.
We find three objects within the XRT error circle (Sbaruffatti et al. 2009,
GCN #9463), and another three at the outer circumference of the error circle
(see finding chart on http://www.mpe.mpg.de/~jcg/grb090531B.html). Within
+-0.2 mag, none of these objects shows any variability between 5.5 and 10 hrs
post-burst, and thus are most likely foreground objects.
In empty regions of the error circle, the first epoch yields the following
upper limits (all AB):
g' > 22.9
r' > 22.6
i' > 22.1
z' > 22.8
J > 20.1
H > 19.8
K > 19.2
which were obtained using the USNO and 2MASS field stars as reference.
However, given the poor conditions and preliminary photometric calibration,
a variable object might be hidden behind one of the foreground objects,
and masked in the difference image due to the distorted PSF from the first
epoch. In that case, the upper limits would be about 2 mag brighter.
No correction has been applied for the strong foreground reddening of
E(B-V)=1.11 mag (Schlegel et al. 1998).
GCN Circular 9481
Subject
GRB 090531b, SMARTS optical/IR observations
Date
2009-06-02T21:50:32Z (16 years ago)
From
Bethany Cobb at UC Berkeley <bcobb@astro.berkeley.edu>
B. E. Cobb (UC Berkeley) reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained
optical/IR imaging of the error region of GRB 090531b (GCN 9461, Cummings
et al.) over two epochs with mid-exposure times of 2009-06-01 02:56 UT
and 2009-06-02 05:26 UT (8.3 and 34.8 hours post-burst). Total summed
exposure times for each observation amounted to 36 minutes in R and
30 minutes in J.
While there are a number of sources in and around the position of
the GRB X-ray afterglow (GCN 9463, Sbarufatti et al.; GCN 9480, Rossi
et al.), image differencing of the two epochs using the ISIS image
subtraction program does not reveal any significant variable source. The
sky limiting magnitude of the images is I>21.1 and J>18.5 (where optical
photometry is calibrated using USNO-B1 stars and IR photometry with 2MASS;
these limits have not been corrected for Galactic reddening).
GCN Circular 9501
Subject
GRB 090531B: Fermi GBM detection
Date
2009-06-10T01:07:56Z (16 years ago)
From
Sylvain Guiriec at UAH <sylvain.guiriec@lpta.in2p3.fr>
S. Guiriec (UAH)
reports on behalf of the Fermi GBM Team:
"At 18:35:56.49 UT on 31 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090531B (trigger 265487758 / 090531775)
which was also detected by the SWIFT-BAT (Cummings et al. 2008, GCN 9461).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 25 degrees.
The GBM light curve consists of a single peak with a duration (T90) of
about 2 s (8-1000 keV).
The time-averaged spectrum from T0-0.23 s to T0+0.77 s is
adequately fit by a Band function with Epeak = 2166(+675-408) keV,
alpha = -0.71(+0.10-0.10), and beta = -2.47(+0.25-0.46)
(Castor C-Stat 780 for 602 d.o.f.).
The event fluence (8-1000 keV) in this time interval is
(6.20 +/- 0.18)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.23 s in the 8-1000 keV band is 1.49 +/- 0.04 ph/s/cm^2.
The spectral and temporal analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."