GRB 090418
GCN Circular 9148
Subject
GRB 090418 OA candidate
Date
2009-04-18T11:16:22Z (16 years ago)
From
Ryan Chornock at UC Berkeley <chornock@astro.berkeley.edu>
R. Chornock, S. B. Cenko, W. Li, and A. V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:
The Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory automatically
slewed to the position of GRB 090418 and discovered a new new point source not
present in the DSS at coordinates (J2000): 17:57:15.17 +33:24:21.1
at an unfiltered magnitude of approximately 15.8 at UT=11:10:57. Further
observations are in progress.
GCN Circular 9149
Subject
GRB 090418: Swift detection of a burst with optical afterglow
Date
2009-04-18T11:35:24Z (16 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
V. Mangano (INAF-IASFPA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
P.A. Curran (MSSL-UCL), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
J. Mao (INAF-OAB), P. T. O'Brien (U Leicester), D. M. Palmer (LANL),
A. M. Parsons (GSFC), M. Perri (ASDC), B. A. Rowlinson (U Leicester),
B. Sbarufatti (INAF-IASFPA), G. Tagliaferri (INAF-OAB),
T. N. Ukwatta (GSFC/GWU), L. Vetere (PSU) and H. Ziaeepour (UCL-MSSL)
report on behalf of the Swift Team:
At 11:07:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090418 (trigger=349510). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 269.334, +33.409 which is
RA(J2000) = 17h 57m 20s
Dec(J2000) = +33d 24' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows two main peaks
with a duration of about 70 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~45 sec after the trigger.
The XRT began observing the field at 11:09:16.3 UT, 96.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
269.3129, 33.4055 which is equivalent to:
RA(J2000) = 17h 57m 15.09s
Dec(J2000) = +33d 24' 19.9"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 64 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
3.55e+20 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 1.05e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 250 seconds with the u filter starting
859 seconds after the BAT trigger. An afterglow candidate has been
found in the initial data products at
RA(J2000) = 17:57:15.1 = 269.31458
Dec(J2000) = +33:24:21 = +33.40583
with an estimated uncertainty of 1.0 arcsec (radius, 90% confidence, statistical
+ systematic). This is 1.1 arcsec from the XRT position. The estimated
magnitude is u = 17.3 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.04.
Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.it).
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 9150
Subject
GRB 090418: ROTSE-III Confirmation of Optical Counterpart
Date
2009-04-18T12:10:59Z (16 years ago)
From
Fang Yuan at ROTSE <yuanfang@umich.edu>
F. Yuan (U Mich), B. E. Schaefer (Louisiana State), W. Rujopakarn
(Steward), report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
090418 (Swift trigger 349510; Mangano et al, GCN 9149) in twilight.
The first image was at 11:07:59.2 UT, 19.0 s after the burst (4.2 s
after the GCN notice time). The unfiltered images are calibrated
relative to USNO B1.0.
We detect the optical counterpart at the KAIT and UVOT position
(Chornock et al. GCN 9148; Mangano et al, GCN 9149) at the following
magnitude and limit:
start UT end UT mag magerr mlim(of image)
--------------------------------------------------------------------------------
11:07:59.2 11:09:06.3 15.9 0.1 17.0
11:09:19.6 11:14:02.1 15.9 0.1 16.8
11:14:11.3 11:25:31.5 - - 16.7
GCN Circular 9151
Subject
GRB 090418 Lick Redshift
Date
2009-04-18T12:34:39Z (16 years ago)
From
Ryan Chornock at UC Berkeley <chornock@astro.berkeley.edu>
R. Chornock, S. B. Cenko, C. V. Griffith, M. E. Kislak, I. K. W. Kleiser, and
A. V. Filippenko (UC Berkeley) report:
We obtained optical spectra of the afterglow of GRB 090418 (Chornock et al., GCN
9148; Mangano et al., GCN 9149; Yuan et al., GCN 9150) using the Kast
spectrograph on the Lick 3-meter telescope. Our first 900s exposure, starting
at 11:21:16 UT (only 816s after the burst trigger) reveals a smooth continuum
extending to the blue limit of our spectra (3450 Angs). Superposed on the
continuum are absorption lines of C IV, Mg II, Fe II, Al II, and Mg I at
z=1.608, which we suggest is the redshift of this burst. Further analysis is
ongoing.
GCN Circular 9152
Subject
GRB 090418: PAIRITEL NIR detection
Date
2009-04-18T14:13:00Z (16 years ago)
From
Bethany Cobb at UC Berkeley <bcobb@astro.berkeley.edu>
B. E. Cobb and J. S. Bloom (UC Berkeley) report:
We observed the optical afterglow of GRB 090418 (Mangano et al., GCN 9149)
with the 1.3-m Peters Automated Infrared Imaging Telescope (PAIRITEL)
beginning at 2009-04-18 11:34 UT, 26 minutes after the Swift
Trigger. We detect the afterglow (Chornock et al., GCN 9148; Yuan et al.,
GCN 9150) in 651 sec mosaics of 7.8 sec simultaneous individual exposures
in the J, H, and Ks filters. Preliminary photometry for the afterglow in
these
mosaics, with midtime 2009-04-18 11:43 UT (35 minutes post-burst), yields
J = 17.7 +- 0.4, H = 17.5 +- 0.4, and Ks = 16.1 +- 0.4
(all magnitudes given in the Vega system), calibrated to the 2MASS system.
GCN Circular 9154
Subject
GRB 090418: Enhanced Swift-XRT position
Date
2009-04-18T16:00:43Z (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 2594 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 090418, 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 = 269.31329, +33.40607 which is equivalent
to:
RA (J2000): 17h 57m 15.19s
Dec (J2000): +33d 24' 21.8"
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, arXiv:0812.3662).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 9157
Subject
GRB 090418: Swift-BAT refined analysis
Date
2009-04-18T17:54:33Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
E. E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), V. Mangano (INAF-IASFPA), 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+705 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090418 (trigger #349510)
(Mangano, et al., GCN Circ. 9149). The BAT ground-calculated position is
RA, Dec = 269.320, 33.407 deg, which is
RA(J2000) = 17h 57m 16.8s
Dec(J2000) = +33d 24' 24.4"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 31%.
The mask-weighted light curve shows two clusters of peaks. The first
starts at ~T-8 sec, peaks at ~T+1 sec, and reaches a minimum at T+15 sec.
The second cluster peaks at around T+40 sec and returns to background
at ~T+70 sec. T90 (15-350 keV) is 56 +- 5 sec (estimated error
including systematics).
The time-averaged spectrum from T-8.5 to T+61.1 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.48 +- 0.07. The fluence in the 15-150 keV band is 4.6 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.06 sec in the 15-150 keV band
is 1.9 +- 0.3 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/349510/BA/
GCN Circular 9163
Subject
GRB 090418: Swift XRT refined analysis
Date
2009-04-19T16:55:19Z (16 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
Mangano V., Sbarufatti B. (INAF-IASFPA) report on behalf of the
Swift XRT Team:
We have analysed the first four orbits of Swift-XRT data obtained from
GRB 090418 (trigger 349510; Mangano, et al., GCN Circ. 9149),
comprising 116 s taken in Windowed Timing (WT) mode, from T+102 s to
T+218 s, and a total exposure of 8.5 ks in Photon Counting (PC)
mode from T+219 s to the end of the observation at T+18 ks.
The best position of the X-ray afterglow is the UVOT enhanced XRT
position given in Goad, et al., GCN Circ. 9154, that is
RA, Dec = 269.31329, +33.40607 which is equivalent to:
RA (J2000): 17h 57m 15.19s
Dec (J2000): +33d 24' 21.8"
with an uncertainty of 1.7 arcsec (radius, 90% confidence).
The 0.3-10 keV X-ray light curve is well fitted by a doubly broken
pawer law, with a initial decay slope alpha1=1.7+/-0.1,
a first breal at about T+245 s, an intermediate decay slope
alpha2=0.35 -0.1+0.06, a second break at about T+2 ks and
a final decay slope alpha3=1.39+/-0.06
If decaying at this rate, the afterglow will reach a count-rate of
6.1E-3 counts/s at T+48h.
The average WT spectrum (corresponding to the initial steep decay phase)
is best fitted by an absorbed power-law model, with photon index 2.0+/-0.2,
and intrinsic NH=(6+/-3)E21 cm-2 (at the redshift z=1.608,
Chornock, et al., GCN circ. 9151) in excess with respect to the galactic
absorption value of 3.6E20 cm-2 (Kalberla et al. 2005).
The average observed(unabsorbed) flux in the 0.3-10 keV band is
3.5(4.6)E-10 ergs cm-2 s-1.
The average PC spectrum of the first orbit (covering the intermediate
slowly decaying phase) is well fitted by an absorbed power-law model,
with photon index 2.1+/-0.1, intrinsic NH=(1.2+/0.3)E22 cm-2
and average observed(unabsorbed) flux in the 0.3-10 keV band of
1.5(2.2)E-10 ergs cm-2 s-1.
Finally, the average PC spectrum from T+4.2 ks to T+18 ks (orbits 2-4)
is well fitted by an absorbed power-law model,
with photon index 2.0+/-0.1, intrinsic NH=(1.1+/0.2)E22 cm-2
and average observed(unabsorbed) flux in the 0.3-10 keV band of
1.3(1.8)E-11 ergs cm-2 s-1.
The average count-rate to observed(unabsorbed) flux conversion factor
is 4.5(6.5)E-11.
All quoted errors are at 90% confidence level.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00349510.
This circular is an official product of the Swift-XRT team.
GCN Circular 9166
Subject
VLA radio detection of GRB 090418
Date
2009-04-19T23:59:16Z (16 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
Poonam Chandra (RMC) and Dale A. Frail (NRAO) report on
behalf of a larger collaboration:
"We used the Very Large Array to observe the field of view toward the
GRB 090418 (GCN 9149) at a frequency of 8.46 GHz on 2009 Apr.19.46 UT.
We observed the radio afterglow of the GRB at a position J2000
RA 17:57:15.156, Dec 33:24:20.78 which is 0.39" away from the KAIT
optical afterglow position reported by Chornock et al. (GCN 9148).
The GRB radio afterglow flux density is 219+/-44 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 9168
Subject
GRB 090418: Optical observations with MITSuME Okayama and Ishigaki 1m telescope
Date
2009-04-20T07:23:37Z (16 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
D. Kuroda, M. Yoshida, M. Isogai, K. Yanagisawa, Y. Shimizu,
S. Nagayama, H. Toda, M. Isogai (NAOJ) and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:
We observed the field of GRB 090417B (Mangano et al. GCN 9149)
with optical three color (g', Rc and Ic) CCD cameras attached to
the MITSuME 50cm telescope of Okayama Astrophysical Observatory
and the 1m telescope of Ishigaki-Jima Observatory.
We started the observation at 13:26:42 UT, 8342s after the burst
at Okayama. We could not find a new source at the position of the
afterglow (Chornock et al. GCN 9148; Mangano et al. GCN 9149;
Goad et al. GCN 9154). 3-sigma upper limits to our observations
are the following. We used GSC2.3 catalog for flux calibration.
Okayama MITSuME observation
Mid-UT Td(day) EXP-T g' Rc Ic
-------------------------------------------------------------
13:56:41 0.11736 2940s (49x60s) >19.2 >19.1 >19.0
16:27:25 0.22204 5880s (98x60s) >20.5 >20.3 >20.1
-------------------------------------------------------------
Ishigaki-Jima 1m telescope observation
Mid-UT Td(day) EXP-T g' Rc Ic
-------------------------------------------------------------
14:48:36 0.15342 3000s (10x300s) >20.6 >20.9 >19.9
-------------------------------------------------------------
GCN Circular 9170
Subject
GRB 090418: Erratum in GCN 9168
Date
2009-04-20T08:33:35Z (16 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
M. Yoshida on behalf of the MITSuME collaboration:
I made a typo in GCN 9168. We observed "GRB 090418 (Mangano et al.
GCN 9149)" instead of "GRB 090417B". I apologize for my carelessness.