GRB 090518
GCN Circular 9386
Subject
GRB 090518: Swift detection of a burst
Date
2009-05-18T02:09:07Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
P. A. Evans (U Leicester), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
A. Rowlinson (U Leicester), M. H. Siegel (PSU),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:
At 01:54:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090518 (trigger=352420). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 119.933, +0.768 which is
RA(J2000) = 07h 59m 44s
Dec(J2000) = +00d 46' 04"
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 5 sec. The peak count rate
was ~4000 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 01:55:57.8 UT, 73.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 119.95519, 0.75892 which
is equivalent to:
RA(J2000) = 07h 59m 49.25s
Dec(J2000) = +00d 45' 32.1"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 86 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 in excess of the Galactic value (4.65e+20
cm^-2, Kalberla et al. 2005), with an excess column of 4.9
(+3.56/-2.94) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 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 none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the XRT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.04.
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 9387
Subject
GRB 090518: Enhanced Swift-XRT position
Date
2009-05-18T08:33:11Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 3965 s of XRT Photon Counting mode data and 8 UVOT
images for GRB 090518, 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 = 119.95404, +0.75921 which is equivalent
to:
RA (J2000): 07h 59m 48.97s
Dec (J2000): +00d 45' 33.2"
with an uncertainty of 1.6 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) and Evans
et al. (2009, arXiv:0812.3662).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 9388
Subject
GRB 090518: Swift-XRT refined analysis
Date
2009-05-18T09:44:36Z (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 6.4 ks of XRT data for GRB 090518 (Evans et al. GCN
Circ. 9386), from 88 s to 13.0 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Evans et al. (GCN. Circ 9387).
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.5 (+0.4, -0.3). At T+332 s the decay
flattens to an alpha of 0.29 (+0.16, -0.38) before breaking again at
T+2743 s to a final decay with index alpha=1.1 (+/-0.3).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.4). The best-fitting
absorption column is 6.2 (+2.3, -1.9) x 10^21 cm^-2, in excess of the
Galactic value of 4.6 x 10^20 cm^-2 (Kalberla et al. 2005). The counts
to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from
this spectrum is 4.9 x 10^-11 (9.9 x 10^-11) erg cm^-2 count^-1.
If the light curve continues to decay with a power-law decay index of
1.1, the count rate at T+24 hours will be 0.0031 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x
10^-13 (3.1 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/00352420.
This circular is an official product of the Swift-XRT team.
GCN Circular 9389
Subject
GRB090518 : Optical upper limit by MOA-II telescope
Date
2009-05-18T12:03:46Z (16 years ago)
From
Takashi Sako at Nagoya U./MOA <sako@stelab.nagoya-u.ac.jp>
T. Sako, A. Fukui, K. Nishimoto (STE Lab, Nagoya Univ.)
on behalf of the MOA Collabration report:
We searched for an optical afterglow of GRB090518 (GCN 9386, Evans et al.;
GCN 9387, Evans et al.) starting from 7:02:10 UT (5 hours after the burst)
with the MOA-II 1.8m telescope at Mt.John observatory in New Zealand.
In a single image of a 300sec exposure with a wideband Red filter (center
wavelength ~ 750nm and FWHM ~ 250nm), we did not find any object
within the error circle of the Swift XRT source position (GCN 9387).
A 5 sigma upper limit is set in the I magnitude at 18.9 mag.
This photometry was done by using the DoPhoto and calibrated against the
USNO-B1.0 catalog stars, and not corrected for the Galactic extinction.
GCN Circular 9393
Subject
GRB 090518, Swift-BAT refined analysis
Date
2009-05-18T15:29:11Z (16 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), 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-119 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090518 (trigger #352420)
(Evans, et al., GCN Circ. 9386). The BAT ground-calculated position is
RA, Dec = 119.957, 0.778 deg which is
RA(J2000) = 07h 59m 49.6s
Dec(J2000) = +00d 46' 41.4"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 75%.
The mask-weighted light curve shows a FRED-like peak starting at T-0.5 sec,
peaking at T+0 sec, and ending at T+3 sec. T90 (15-350 keV) is
6.9 +- 1.7 sec (estimated error including systematics).
The time-averaged spectrum from T-2.4 to T+6.9 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.54 +- 0.14. The fluence in the 15-150 keV band is 4.7 +- 0.4 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band
is 2.4 +- 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/352420/BA/
GCN Circular 9394
Subject
GRB 090518: P60 Observations
Date
2009-05-18T21:51:50Z (16 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko (UC Berkeley) reports on behalf of a larger collaboration:
We have imaged the field of GRB090518 (Evans et al., GCN 9386) with the
automated Palomar 60-inch telescope beginning at 3:45 UT on 2009 May 18 (~
1.83 hr after the burst). Observations were taken in the r', i', and z'
filters at high airmass. We find no sources inside the enhanced XRT
error circle (Evans et al., GCN 9387), to the following limiting
magnitudes:
Filter Magnitude
--------------------------------
r' > 20.5
i' > 20.0
z' > 19.0
No correction has been applied for Galactic extinction along the line of
sight.
GCN Circular 9395
Subject
GRB090518: GROND upper limits
Date
2009-05-19T02:37:52Z (16 years ago)
From
Andrea Rossi at TLS Tautenburg <rossi@tls-tautenburg.de>
A. Rossi (Tautenburg), P. Afonso and J. Greiner( both MPE Garching) report
on behalf of the GROND team:
GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile), observed the field of GRB 090518
(P. Evans et al. 2009, GCN #9386) simultaneously in the g'r'i'z'JHK
bands. Observations started on May 18, at 23:01 UTC, 21.1 h after the burst.
In stacked images of 49 min total integration time in griz and 40 min in
JHK, we do not detect any new object inside the enhanced XRT error circle
(P. Evans et al., GCN #9387), down to the following limiting magnitudes
(all in the AB system):
g' > 24.5
r' > 24.9
i' > 24.2
z' > 23.8
J > 22.4
H > 22.1
K > 21.2
The upper limits have been obtained using GROND zero points and 2MASS
field stars as reference. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.04 mag.
GCN Circular 9397
Subject
GRB 090518: Swift/UVOT Upper Limits
Date
2009-05-19T11:50:39Z (16 years ago)
From
Frank Marshall at GSFC <marshall@milkyway.gsfc.nasa.gov>
F.E. Marshall (NASA/GSFC) and P. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT observed the field of GRB 090518 starting 77 s after
the BAT trigger (Evans et al., GCN Circ. 9386). No optical afterglow
is detected in the initial UVOT exposures at the position
of the X-ray afterglow (Evans et al., GCN Circ. 9387).
Three-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC)
exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white (FC) 77 227 147 >20.7
white 77 1367 373 >21.3
v 620 1417 97 >19.3
b 545 1341 78 >19.7
u 290 1316 304 >20.0
uvw1 669 1466 97 >19.7
uvm2 644 1442 97 >21.2
uvw2 596 1392 97 >20.0
The values quoted above are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 9419
Subject
GRB 090518: Fermi GBM detection
Date
2009-05-22T16:29:30Z (16 years ago)
From
Bill Paciesas at UAH <bill.paciesas@nasa.gov>
W. Paciesas (UAH) reports on behalf of the Fermi GBM Team:
"At 01:54:44.52 UT on 18 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090518 (trigger 264304486 / 090518080).
which was also detected by the SWIFT-BAT
(Evans et al. 2009, GCN 9386)
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 53 degrees.
The GBM light curve consists of a single asymmetric peak
with a duration (T90) of about 9 s (8-1000 keV).
The time-averaged spectrum from T0-2.048 s to T0+7.04 s is
adequately fit by a simple power law function with index -1.59 +/- 0.06
(chi squared 688 for 688 d.o.f.).
The event fluence (8-1000 keV) in this time interval is
(1.60 +/- 0.05)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.64 s in the 8-1000 keV band
is 4.7 +/- 0.1 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 9423
Subject
GRB 090518 - NOT upper limit
Date
2009-05-26T07:21:31Z (16 years ago)
From
Johan U. Fynbo at U.Copenhagen <jfynbo@astro.ku.dk>
C. C. Thoene (INAF/OAB), E. Kankare (NOT), J. P. U. Fynbo, D. Malesani
(DARK/NBI), A. J. Levan (Univ. Warwick), P. Jakobsson (Univ. Iceland),
J. Hjorth (DARK/NBI) report:
We observed the field of GRB 090518 (GCN 9386, Evans et al.) with
ALFOSC/NOT on La Palma starting May 18, 20:54 UT (21 h after the burst).
Observations were obtained in R (3x300s), I (3x300s) and z (6x200s)
filters at high airmass.
We do not detect any new source at the XRT position (GCN 9387, Evans et
al.) in the summed image of each filter. The following upper limits were
obtained (based on USNO B1.0 reference stars and a NOT z-band archival
zeropoint):
R > 23.7 mag
I > 21.8 mag
z(AB) > 22.5 mag
GCN Circular 10002
Subject
GRB 090518: Skynet/PROMPT Observations
Date
2009-10-09T03:19:09Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, 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 090518 (Evans et al., GCN
9386) with four of the 16" PROMPT telescopes at CTIO beginning 3.3 minutes
after the trigger in UVRI.
We do not detect the afterglow (Evans et al., GCN 9386) within the enhanced
Swift/XRT localization (Evans et al., GCN 9387). 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)
5.2 PROMPT-4 4 x 40 I 18.2 229 USNO B1 0.372 0.001
+ 1 x 10
5.8 PROMPT-5 2 x 40 V 18.3 72 NOMAD 0.146 0.001
6.4 PROMPT-2 1 x 80 R 19.3 217 USNO B1 0.305 0.001
+ 2 x 40