GRB 091018
GCN Circular 10034
Subject
GRB 091018: Swift detection of a burst with optical afterglow
Date
2009-10-18T21:08:34Z (16 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. Stamatikos (OSU/NASA/GSFC), D. N. Burrows (PSU),
J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
C. Gronwall (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
W.B Landsman (GSFC), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
D. M. Palmer (LANL), M. Perri (ASDC), J. L. Racusin (NASA/GSFC/ORAU)
and G. Stratta (ASDC) report on behalf of the Swift Team:
At 20:48:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 091018 (trigger=373172). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 32.211, -57.526 which is
RA(J2000) = 02h 08m 51s
Dec(J2000) = -57d 31` 34``
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single smooth
FRED peak a duration of about 10 sec. The peak count rate
was ~16000 counts/sec (15-350 keV), at ~2 sec after the trigger.
The XRT began observing the field at 20:49:20.5 UT, 60.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 32.18587, -57.54749 which
is equivalent to:
RA(J2000) = 02h 08m 44.61s
Dec(J2000) = -57d 32' 51.0"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 91 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 (2.81e+20
cm^-2, Kalberla et al. 2005), with an excess column of 1.4
(+1.00/-0.93) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 4.40e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 68 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7`x2.7` sub-image at
RA(J2000) = 02:08:44.61 = 32.18588
DEC(J2000) = -57:32:53.8 = -57.54827
with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.8
arc sec. from the center of the XRT error circle. The estimated magnitude is
14.60 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03.
Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT 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 10036
Subject
GRB 091018: ROTSE-III Detection of Optical Counterpart
Date
2009-10-18T21:34:32Z (16 years ago)
From
Brad Schaefer at LSU <schaefer@grb.phys.lsu.edu>
B. E. Schaefer (Louisiana State) and 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 091018 (Swift trigger 373172, Stamatikos et al., GCN
10034). The first image was at 20:57:36.1 UT, 556.6 s after the burst
(11.1 s after the GCN notice time). The unfiltered images are calibrated
relative to USNO A2.0. We detect a new object, not visible in the DSS
(second epoch), with coordinates:
02:08:44.6 -57:32:53.6 (J2000),
with positional uncertainty of 1" or better
start UT mag mlim(of image)
----------------------------------
20:57:36.1 15.4 16.4
With this, we confirm the optical afterglow reported in GCN 10034 as a
UVOT detection. The source is rapidly fading. A jpeg image is available
at
http://www.rotse.net/images/gsb373172_3c01_img.jpg Note that the object
numbered 14 (in the lower of the two circles) is the candidate in
question.
Continuing observations are in progress.
GCN Circular 10037
Subject
GRB 091018: Enhanced Swift-XRT position
Date
2009-10-19T00:31:06Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1175 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 091018, 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 = 32.18588, -57.54825 which is equivalent
to:
RA (J2000): 02h 08m 44.61s
Dec (J2000): -57d 32' 53.7"
with an uncertainty of 1.7 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, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 10038
Subject
GRB091018: Magellan Echellette Observations
Date
2009-10-19T01:49:14Z (16 years ago)
From
Hsiao-Wen Chen at U Chicago <hchen@oddjob.uchicago.edu>
Hsiao-Wen Chen, Jennifer Helsby (UChicago), Stephen Shectman, Ian
Thompson, Jeffrey Crane (Carnegie Observatory) report on behalf of a
larger collaboration:
"We observed the afterglow of GRB091018 reported by Stamatikos et al. (GCN
10034) and confirmed by Schaefer et al. (GCN10036) using the MagE
echellette spectrograph on the Magellan Clay Telescope. The observations
started at UT 00:28 on October 19, 2009, ~ 3.5 hours after the inital
trigger. We obtained 2x900s exposures. Our preliminary reduction shows
that the afterglow spectrum displays strong absorption transitions due to
MgII, FeII, MnII at redshift z=0.971, which we tentatively identify as the
host redsdhift of the GRB.
Further analysis is underway.
This message may be cited."
GCN Circular 10039
Subject
GRB 091018: GROND observations
Date
2009-10-19T02:13:51Z (16 years ago)
From
Robert Filgas at MPI <filgas@mpe.mpg.de>
R. Filgas, T. Kruehler, A. Yoldas (all MPE Garching),
S. Klose (TLS Tautenburg), and
J. Greiner (MPE Garching), report on behalf of the GROND team:
GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted
at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile), started
follow-up observations of GRB 091018 (Stamatikos et al. 2009, GCN 10034)
on October 18, at 23:47 UTC (~4 hrs after the burst).
For the afterglow candidate reported by Stamatikos et al. we
estimate the following preliminary magnitudes (in the AB system):
g'= 19.061 +/- 0.010
r'= 18.853 +/- 0.007
i'= 18.732 +/- 0.013
z'= 18.70 +/- 0.10
J = 18.3 +/- 0.1
H = 18.2 +/- 0.1
K = 17.9 +/- 0.1
calibrated against GROND zeropoints.
GCN Circular 10040
Subject
GRB 091018: Swift-BAT refined analysis
Date
2009-10-19T02:57:39Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
C. B. Markwardt (GSFC/UMD), 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), 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-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 091018 (trigger #373172)
(Stamatikos, et al., GCN Circ. 10034). The BAT ground-calculated position is
RA, Dec = 32.191, -57.546 deg, which is
RA(J2000) = 02h 08m 45.9s
Dec(J2000) = -57d 32' 45.0"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.
The mask-weighted light curve shows the FRED peak starting at ~T-5 sec,
peaking at T+1.1 sec, and ending at ~T+20 sec. T90 (15-350 keV) is
4.4 +- 0.6 sec (estimated error including systematics).
The time-averaged spectrum from T-0.3 to T+7.7 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.77 +- 0.24,
and Epeak of 19.2 +18,-11 keV (chi squared 40.01 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+0.80 sec in the 15-150 keV band is
10.3 +- 0.4 ph/cm2/sec. A fit to a simple power law gives a photon index
of 2.30 +- 0.06 (chi squared 52.2 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/373172/BA/
GCN Circular 10041
Subject
GRB091018: Swift/UVOT observations
Date
2009-10-19T04:12:08Z (16 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W.B. Landsman (NASA/GSFC) and M. Stamatikos (OSU/NASA/GSFC) report on
behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 091018
69s after the BAT trigger (Stamatikos et al., GCN 10034). The
afterglow is well-detected in all seven UVOT filters at the position
reported by Stamatikos et al. The initial magnitudes are as follows:
Filter T_start(s) Exp(s) Mag
white 69 147 14.57 � 0.012
white 860 147 16.48 � 0.018
u 281 246 15.07 � 0.017
u 6911 197 18.04 � 0.08
v 610 19 16.4 � 0.14
b 536 19 16.4 � 0.08
uvw1 660 20 15.9 � 0.12
uvm2 635 20 15.7 � 0.16
uvw2 586 20 16.1 � 0.15
The detection in the uvw2 filter indicates a redshift less than z = 1.1,
consistent with the value of z= 0.971 reported by the Magellan group (
Chen et al., GCN 10038).
The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.029 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 10042
Subject
GRB 091018: VLT/X-shooter spectra
Date
2009-10-19T16:24:15Z (16 years ago)
From
Antonio Deugarte at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (OAB-INAF), P. Goldoni
(APC/Univ. Paris 7 and SAp/CEA), C.C. Thoene
(OAB-INAF), N. Tanvir (Univ. Leicester),
P. Jakobsson (Univ. of Iceland), S.D. Vergani
(APC/Univ. Paris 7), H. Flores (Paris Obs.)
D. Malesani (DARK/NBI), A. Levan (Univ.
Warwick) and J.P.U. Fynbo (DARK/NBI) report
on behalf of the X-shooter GRB collaboration:
X-shooter observed the afterglow of GRB 091018
(Stamatikos et al. CGN 10034) starting at 23:58 UT
of the 18th Oct 2009. The observation consisted of
4 x 600s exposures, having a mean epoch of October
19.0148 UT, 3.53 hours after the burst. In the spectra
we detect the continuum in the complete range from
3000 to 24800 Angstroms. On a preliminary analysis
we find several absorption features including AlII
(1670), AlIII (1854, 1862), FeII (2260, 2344, 2374,
2382, 2586, 2600) MnII (2576, 2594, 2606), MgII
(2797, 2803), MgI (2852), CaII (3934, 3969) at a
common redshift of 0.9710 +/- 0.0003, consistent with
the observation reported by Chen et al. (GCN 10038).
There is also a tentative detection of [OII], [OIII] and
H-alpha emission lines from the host galaxy at the
same redshift. Further analysis is ongoing.
We thank the ESO observing staff, in particular A.
Smette, C. Martayan and C. Cid.
GCN Circular 10043
Subject
GRB 091018: BOOTES-3 observations
Date
2009-10-19T19:49:59Z (16 years ago)
From
Antonio Deugarte at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (INAF-OAB), P. Kubanek (U. Valencia, IAA-CSIC),
M. Jelinek, A.J. Castro-Tirado, J. Gorosabel, R. Cunniffe, S. Guziy
(IAA-CSIC),
B.A. Allen (Vintage Lane Obs.) and P. Yock (Auckland Univ.) report:
We have observed the afterglow of GRB 091018 (Stamatikos et al. CGN
10034) with the 0.6m Yock-Allen telescope (BOOTES-3) located in
Blenheim (New Zealand). A combination of 21x30s unfiltered images with
mean epoch Oct. 19.625 UT (18.2 hours after the burst) shows the
afterglow
at a magnitude of R=20.0+/-0.3. The photometry has been obtained using
as comparison 5 USNO-B1.0 stars. This magnitude implies a rough
decay slope of alpha = 0.7 +/- 0.2 (with F ~ t^(-alpha)) as compared to
the values of Filgas et al. (GCN 10039). Further analysis is ongoing.
GCN Circular 10044
Subject
GRB 091018 : Faulkes Telescope South Observations
Date
2009-10-19T20:37:10Z (16 years ago)
From
Zach Cano at ARI/John Moores Liverpool <zec@astro.livjm.ac.uk>
Z. Cano (Liverpool JMU), C. Guidorzi (U. Ferrara), D. Bersier, N.R. Clay,
S. Kobayashi, A. Melandri, C.G. Mundell, C.J. Mottram, R.J. Smith, I.A.
Steele (Liverpool JMU), A. Gomboc (U. Ljubljana), N.R. Tanvir (U.
Leicester) on behalf of a larger collaboration report:
The Faulkes Telescope South (Australia) observed the field of GRB 091018
(Swift trigger=373172, Stamatikos et al., GCN 10034) on 2009 October 19.
We clearly detect the afterglow candidate (Schaefer & Pandey, GCN 10036;
Chen et al., GCN 10038; Filgas et al., GCN 10039; Landsman & Stamatikos,
GCN 10041; A. de Ugarte Postigo et al., GCN 10042 & GCN 10043) in the Ri'
filters with the following magnitudes:
Filter mag merr T-To (hr)
---------------------------------------
I 19.73 0.06 15.17
I 20.13 0.08 20.95
R 19.67 0.06 15.72
R 20.06 0.08 20.95
As calibrated against nearby USNO object 0342-0026807 (R2 = 16.34, I2 =
16.22).
From the images obtained on FTS we derive preliminary decay rates of:
alpha_I = 1.1 +/- 0.3 & alpha_R = 1.2 +/- 0.3.
GCN Circular 10045
Subject
Konus-RF observation of GRB 091018
Date
2009-10-19T21:35:13Z (16 years ago)
From
Valentin Pal'shin at Ioffe Inst <lanzelot@mail.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
P. Oleynik, M. Ulanov, and D. Svinkin on behalf of
the Konus-RF team, report:
The soft GRB 091018 (Swift-BAT trigger #373172: Stamatikos et al.,
GCN 10034, Markwardt et al., GCN 10040) triggered Konus-RF
at T0=74900.651 s UT (20:48:20.651).
The burst light curve shows a single pulse with a duration of ~5 s.
As observed by Konus-RF the burst
had a fluence of 1.44(-0.16, +0.19)x10^-6 erg/cm2,
and a 256-ms peak flux measured from T0-0.280 s
of 4.32(-0.94, +0.97)x10^-7 erg/cm2/s
(both in the 20 keV - 1 MeV energy range).
The time-integrated spectrum of the burst (from T0-2s to T0+3s)
is well fitted (in the 10 keV - 1 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -1.53(-0.39, +0.59), and
Ep = 28(-16, +10) keV (chi2 = 83.4/94 dof).
Fitting by GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -2.44 (chi2 = 81.7/93 dof).
All the quoted values are preliminary.
All the quoted errors are at the 90% confidence level.
Assuming z = 0.971 (Chen et al., GCN 10038) and
a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27,
Omega_Lambda = 0.73, the isotropic energy release E_iso ~3.7x10^51 erg,
the peak luminosity (L_iso)_max ~2.2x10^51 erg/s,
and Ep_rest ~55 keV.
The Konus-RF light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB091018_T74900/KRF/
GCN Circular 10046
Subject
GRB 091018: Skynet/PROMPT Observations of Fading
Date
2009-10-19T23:59:19Z (16 years ago)
From
Aaron LaCluyze at U.North Carolina <lacluyze@physics.unc.edu>
A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, 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 091018 (Stamatikos et
al., GCN 10034) with four of the 16" PROMPT telescopes at CTIO beginning
3.0 hours after the the trigger in BVRI.
We detect the afterglow (Stamatikos et al., GCN 10034) in all filters.
Between 3.0 and 12.3 hours after the trigger, the afterglow faded with
periods of rebrightening (1) beginning around 5 hours and peaking around 6
hours, and (2) beginning around 8 hours and peaking around 9 hours.
Overall, if fitted with a power law, the afterglow faded with a power-law
index of about -0.95 in BVR but only about -0.65 in I. I - R brightened by
about 0.45 mag over the course of 12 hours.
At 12.3 hours after the trigger, the afterglow's magnitude was R = 19.82
+0.14 -0.12 (statistical) +/- 0.56 (systematic; calibrated to 115 USNO B1
stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb091018.png
GCN Circular 10047
Subject
GRB 091018: miniTAO/ANIR Observations
Date
2009-10-20T05:47:04Z (16 years ago)
From
Takeo Minezaki at U.of Tokyo/Astro <minezaki@mtk.ioa.s.u-tokyo.ac.jp>
K. Motohara, M. Konishi, K. Toshikawa, N. Mitani,
T. Minezaki, S. Koshida, D. Kato, Y. Yoshii$B!!(B(University of Tokyo),
Y. Ita (National Astronomical Observatory of Japan)
on behalf of the TAO project team:
We report the NIR imaging observation of GRB 091018 carried out
from October 19 2:09 to 2:57 (UTC), using NIR Camera ANIR
(Motohara et al. 2008, Proc. SPIE 7014, 70142T) mounted on
the 1.0m miniTAO telescope (Sako et al. 2008, Proc. SPIE7012, 70122T)
at the University of Tokyo Atacama Observatory on the summit
of Co. Chajnantor (5640m altitude) in the northern Chile.
The preliminary magnitudes (AB system) for the afterglow candidate
reported by Stamatikos et al. 2009 (GCN 10034) are ;
Y = 18.98 +/- 0.14
J = 19.40 +/- 0.19
H = 18.93 +/- 0.17
Ks = 18.22 +/- 0.07
which are taken with the MKO filter system.
GCN Circular 10055
Subject
GRB 091018: Swift XRT refined analysis
Date
2009-10-21T11:55:55Z (16 years ago)
From
Giulia Stratta at ASDC <giulia.stratta@gmail.com>
G. Stratta (ASDC) reports on behalf of the Swift-XRT team:
The Swift-XRT began observing GRB 091018 (trigger=373172) on
2009-10-18 at 20:49:20.5 UT, 60.9 seconds after the BAT trigger
(Stamatikos et al., GCN Circ. 7226). The data have been
taken in Windowed Timing (WT) mode from T + 67 s to T + 144 s
and in Photon Counting (PC) mode later on.
Enhanced position of the detected, bright X-ray afterglow
was given by Osborne et al. (GCN Circ. 10037)
The X-ray light curve from T + 67 s to T + 53.3 ks is well
fit by a broken power law model (chi^2 = 115 for 128 degrees
of freedom) with a temporal break at tb = T + (500 +/- 100) s and
decay indices alpha1 = -0.4 +/- 0.1 and alpha2 = -1.17 +/- 0.03
before and after the break, respectively.
The 0.3-10 keV spectrum from T + 156 s to T + 7.1 ks
is well fit by an absorbed power law (reduced chi2 of 1.0, with
50 degrees of freedom). The best fit photon index is 1.9 +/- 0.1,
with an hydrogen column density at the burst rest frame
(z=0.971, Hsiao-Wen Chen et al. GCN Circ.10038) of
NHz = (1.4 +/- 0.8)e21 cm^-2 in addition to the Galactic column
along the line of sight, that is NH = 2.8e20 cm^-2
(Kalberla et al. 2005). Errors are given at 90% confidence level.
The observed (unabsorbed) flux in the 0.3-10 keV band is
1.5(1.8)e-10 erg cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular 10061
Subject
GRB 091018: Skynet/PROMPT Continued Observations of Fading
Date
2009-10-23T14:36:01Z (16 years ago)
From
Aaron LaCluyze at U.North Carolina <lacluyze@physics.unc.edu>
A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, A. Foster, J.
Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M.
Nysewander report:
Skynet has continued to observed the afterglow (Stamatikos et al., GCN
10034) of GRB 091018 (Stamatikos et al., GCN 10034) with four of the 16"
PROMPT telescopes at CTIO in BVRI.
After fading with a power-law index of about -0.95 in BVR between 3 and 12
hours after the trigger (LaCluyze et al., GCN 10046), the afterglow faded
with a steeper power-law index of about -1.3 in BR between 12 hours and 1.5
days after the trigger, which is consistent with the findings of Cano et
al. (GCN 10044).
However, between 1.5 days and 3.4 days after the trigger, the afterglow
faded with a shallower power-law index of about -0.9 in R.
The I - R color of the afterglow, which brightened by about 0.45 mag
between 3 and 12 hours after the trigger (LaCluyze et al., GCN 10046), has
faded by about 0.1 +/- 0.3 mag between 12 hours and 3.4 days after the
trigger, which is consistent with no additional color change, but the
uncertainty is large.
At 3.4 days after the trigger, the afterglow's magnitude was R = 22.27
+0.28 -0.23 (statistical) +/- 0.56 (systematic; calibrated to 115 USNO B1
stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb091018.png
Continued observations with larger telescopes are encouraged.
GCN Circular 10110
Subject
GRB 091018, SMARTS optical/IR afterglow observations
Date
2009-10-29T21:47:42Z (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 091018 (GCN 10034,
Stamatikos et al.) over several epochs, starting ~3.9 hours post-burst.
For the first epoch, several dithered images were obtained in each filter,
with total summed exposure times of 180s in each of BRIJK and 120s in each
of H and V. For later epochs, total summed exposure times amounted to 15
minutes in I and V and 12 minutes in J and K.
At a mid-exposure time of 2009-10-19 00:57 UT (4.1 hrs post-burst), the
GRB afterglow (e.g. GCN 10034, Stamatikos et al., GCN 10036, Schaefer et
al., GCN 10039, Filgas et al.) is detected with the following magnitudes:
B = 19.59 +/- 0.04
V = 19.27 +/- 0.05
R = 18.88 +/- 0.04
I = 18.44 +/- 0.04
J = 18.0 +/- 0.2
H = 17.1 +/- 0.2
K = 16.1 +/- 0.2
Between 4.1 hrs and 33.0 hrs post-burst, the GRB afterglow fades with a
decay rate of approximately alpha = -1.3 (where afterglow flux is
proportional to t^alpha).
time
post-burst I-band magnitude
4.1 hrs 18.44 +/- 0.04
5.5 hrs 18.82 +/- 0.04
8.0 hrs 19.26 +/- 0.04
9.7 hrs 19.49 +/- 0.05
28.6 hrs 21.04 +/- 0.06
33.0 hrs 21.27 +/- 0.08
(Optical photometry is calibrated against Landolt standard stars
and IR photometry is calibrated against 2MASS stars in the field.)
GCN Circular 10112
Subject
GRB 091018: Skynet/PROMPT Observations of Possible Host Galaxy
Date
2009-10-30T04:17:19Z (16 years ago)
From
Aaron LaCluyze at U.North Carolina <lacluyze@physics.unc.edu>
A. LaCluyze, D. Reichart, J. Haislip, K. Ivarsen, R. Egger, A. Foster, J.
Moore, A. Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M.
Nysewander report:
Skynet has continued to observed the afterglow (Stamatikos et al., GCN
10034) of GRB 091018 (Stamatikos et al., GCN 10034) with two of the 16"
PROMPT telescopes at CTIO in RI (LaCluyze et al., GCNs 10046, 10061).
Between 3.2 and 7.5 days after the trigger, the light curve is consistent
with constant emission, which suggests that we are observing the host
galaxy.
If so, we measure its brightness to be:
R = 22.30 +/- 0.11 (statistical) +/- 0.56 (systematic; calibrated to 115
USNO B1 stars).
and
I = 21.78 +/- 0.16 (statistical) +/- 0.54 (systematic; calibrated to 67
USNO B1 stars).