GRB 080727B
GCN Circular 8022
Subject
GRB 080727B: Swift detection of a bright burst
Date
2008-07-27T08:30:44Z (17 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. Immler (CRESST/GSFC/UMD), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),
C. Guidorzi (INAF-OAB), S. D. Hunsberger (PSU), W.B Landsman (GSFC),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), D. Perez (U Leicester),
T. Sakamoto (NASA/UMBC) and R. L. C. Starling (U Leicester) report on
behalf of the Swift Team:
At 08:13:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080727B (trigger=318101). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 276.870, +1.172 which is
RA(J2000) = 18h 27m 29s
Dec(J2000) = +01d 10' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a double-peaked
structure with a duration of about 10 sec. The peak count rate
was ~18,000 counts/sec (15-350 keV), at 6 sec after the trigger.
The XRT began observing the field at 08:15:05.9 UT, 101.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 276.85898,
1.16304 which is equivalent to:
RA(J2000) = 18h 27m 26.16s
Dec(J2000) = +01d 09' 47.0"
with an uncertainty of 2.8 arcseconds (radius, 90% containment). This
location is 51 arcseconds from the BAT onboard position, within the BAT
error circle.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.64e+21
cm^-2, Kalberla et al. 2005), with an excess column of 4.7
(+4.37/-3.38) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 105 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 25% of the BAT error circle and 100% of
the XRT error circle. The typical 3-sigma upper limit has been about
18.5 mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 1.94.
Burst Advocate for this burst is S. Immler (immler 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 8023
Subject
GRB 080727B: REM prompt observations
Date
2008-07-27T09:11:06Z (17 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo, S. Covino, L.A. Antonelli, D. Fugazza, L. Calzoletti, S.
Campana, G. Chincarini, M.L. Conciatore, S. Cutini, V. D'Elia, F.
D'Alessio, F. Fiore, P. Goldoni, D. Guetta, C. Guidorzi, G.L. Israel,
E. Maiorano, N. Masetti, A. Melandri, E. Meurs, L. Nicastro, E. Palazzi,
E. Pian, S. Piranomonte, L. Stella, G. Stratta, G. Tagliaferri, G.
Tosti, V.Testa, S.D. Vergani, F. Vitali report on behalf of the REM team:
The robotic 60-cm REM telescope located at La Silla (Chile) observed
automatically the field of the GRB 080727B (Immler et al. GCN 8022) on
July 27 starting at 08:14:25 UT (61 seconds after the burst).
Observations were carried out at high airmass. In a series of 10s and
30s exposures we do not see any afterglow candidate inside the XRT error
box down to R > 16.0 and H > 13.0 (3sigma c.l.).
GCN Circular 8024
Subject
GRB 080727B: KAIT observations
Date
2008-07-27T10:03:20Z (17 years ago)
From
Weidong Li at UC Berkeley KAIT/LOSS <weidong@astron.berkeley.edu>
W. Li, R. Chornock, D. A. Perley, J. S. Bloom, and A. V. Filippenko,
University of California at Berkeley, on behalf of the KAIT
GRB team, report:
The robotic 0.8-m KAIT located at Lick Observatory responded to
GRB 080727B (Immler et al. GCN 8022) automatically on July 27
starting at 08:14:12 UT (48 seconds after the burst). A series of
images were taken in the V, I, and clear filters. We detected a
fading new object at the following location:
RA (J2000) = 18h27m26.05s +/- 0.3"
Dec (J2000) = +01d09'47.7" +/- 0.3" ,
suggesting that this is the optical afterglow of the GRB.
We report the following preliminary photometry (calibrated
to USNO B1):
UT start exptime filter mag err
08:14:12 2 s clear 18.20 0.16
08:14:17 2 s clear 18.38 0.16
08:14:20 2 s clear 18.45 0.23
The power-law decay index between t = 49 s and 72 s after the
burst is -1.44 +/- 0.59. Further analysis is ongoing.
GCN Circular 8026
Subject
GRB 080727B: Enhanced Swift-XRT position
Date
2008-07-27T11:40:28Z (17 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 2097 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 080727B, 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 = 276.85851, +1.16272 which is equivalent
to:
RA (J2000): 18h 27m 26.04s
Dec (J2000): +01d 09' 45.8"
with an uncertainty of 1.9 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 8030
Subject
GRB 080727B, Swift-BAT refined analysis
Date
2008-07-27T17:12:48Z (17 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
W. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-120 to T+182 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080727B (trigger #318101)
(Immler, et al., GCN Circ. 8022). The BAT ground-calculated position is
RA, Dec = 276.871, 1.173 deg which is
RA(J2000) = 18h 27m 29.1s
Dec(J2000) = +01d 10' 23.2"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 69%.
The mask-weighted light curve shows two big FRED-like pulses from
T-0.5 to T+3 sec and from T+5.5 to T+9.5 sec. There are several
pulses starting at T+2.5, T+7.2, T+7.5, and T+8.8 sec.
T90 (15-350 keV) is 8.6 +- 0.2 sec (estimated error including systematics).
The time-averaged spectrum from T-0.2 to T+9.4 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 0.80 +- 0.17,
and Epeak of 226.6 +- 120.2 keV (chi squared 43.60 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 3.1 +- 0.1 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T-0.04 sec in the 15-150 keV band is
7.6 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index
of 1.12 +- 0.04 (chi squared 54.09 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/318101/BA/
GCN Circular 8031
Subject
GRB 080727B: Swift-XRT refined analysis
Date
2008-07-27T17:16:40Z (17 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P.A. Evans (U. Leicester) and S. Immler (CRESST/GSFC/UMD) report
on behalf of the Swift-XRT team:
We have analysed 1.6 ks of XRT data for GRB 080727B (Immler et al., GCN
Circ 8022). The data were taken in two snapshots; the first started 105
s after the trigger and contained 51 s of Windowed Timing mode data
followed by 500 s of Photon Counting (PC) mode data. The second snapshot
began at T0+11 ks, and contained 1.2 ks of data, all in PC mode.
The UVOT-enhanced XRT position has been given by Goad et al. (GCN Circ.
8026).
The light curve shows an initial steep decay with a power-law index of
2.47 (+1.38, -0.39), with a break to a shallower decay of 1.05 (+0.20,
-0.13). The break occurred at T0+267 (+89, -100) s.
A spectrum formed from all available PC mode data can be modelled by an
absorbed power law with a photon index on 1.61 (+0.43, -0.38). The best
fitting absorption column is 8.7 (+4.1, -2.9) x 10^21 cm^-2, in excess
of the Galactic value in the direction of the burst (3.6 x 10^21,
Kalberla et al. 2005). The counts to observed 0.3-10 keV flux
conversion factor deduced from this spectrum is 5.0 x 10^-11 erg cm^-2
s^-1 count^-1.
If the light curve continues to decay with a slope of 1.05, the count
rate at 24 hours post-trigger will be 1.8 x 10^-3, corresponding to an
observed (unabsorbed) flux of 9.0 x 10^-14 (4.2 x 10^-13) erg cm^-2
s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular 8033
Subject
GRB 080727B: Swift/UVOT Upper Limits
Date
2008-07-27T18:25:27Z (17 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W.B. Landsman (NASA/GSFC/Adnet) and S. Immler (PSU) report on behalf of
the Swift/UVOT team:
The Swift/UVOT observed the field of GRB 080727B starting 105s after the
BAT trigger (Immler et al., GCN Circ. 8022). We do not find any
source, in any of the UVOT observations, at either the UVOT-enhanced XRT
position of the afterglow (Goad et al. GCN Circ. 8026) or the proposed
KAIT afterglow position (Li et al., GCN 8024). The 3-sigma upper
limits for detecting a source at this location in single exposures are:
Filter T_start Exp(s) Mag (3-sigma upper limit)
----------------------------------------------------------
v 211 393 >20.6
uvw1 642 15 >17.9
uvm2 617 19 >17.6
white 105 98 >21.0
----------------------------------------------------------
The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a large
reddening of E_{B-V} = 1.9 mag. All photometry is on the UVOT flight
system described in Poole et al. (2008, MNRAS, 383, 627).
Combining the UVOT upper limits with the KAIT detection at R~18.3 (Li et
al., GCN 8024) suggest that there is either high extinction, very fast
decline in brightness (the UVOT observations began 57 seconds after the
KAIT observations ), or high redshift. The UVOT results are
obtained at shorter wavelengths, and for example, the UVOT v filter is
expected to suffer an additional ~1.4 mag of extinction, assuming that
E(B-V) = 1.9 and that the KAIT clear filter corresponds roughly to the R
band. The results may also be consistent with a high redshift burst
(5.5 < z <6.5) which is only observable at wavelengths longward of ~6000 A.
GCN Circular 8037
Subject
GRB 080727B: REM NIR afterglow prompt detection
Date
2008-07-28T07:27:46Z (17 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo, S. Covino, L.A. Antonelli, D. Malesani, D. Fugazza, L.
Calzoletti, S. Campana, G. Chincarini, M.L. Conciatore, S. Cutini, V.
D'Elia, F. D'Alessio, F. Fiore, P. Goldoni, D. Guetta, C. Guidorzi,
G.L. Israel, E. Maiorano, N. Masetti, A. Melandri, E. Meurs, L.
Nicastro, E. Palazzi, E. Pian, S. Piranomonte, L. Stella, G. Stratta,
G. Tagliaferri, G. Tosti, V.Testa, S.D. Vergani, F. Vitali report on
behalf of the REM team:
Following the KAIT detection of the optical afterglow of GRB 080727B (Li
et al. GCN 8024) we performed a detailed off-line analysis of our REM
images (D'Avanzo et al., GCN 8023). While we confirm the non-detection
of the optical afterglow in the R-band down to the 16th magnitude (30 s
of total exposure), we find a barely visible object in our coadded
H-band frame (50 s of total exposure) with a magnitude of H = 11.8 � 0.2
(calibrated against the 2MASS catalogue) at a position consistent with
the one reported by Li et al.
Unfortunately, just after taking the first R and H-band images, the
telescope experienced tracking problems, due to the low altitude of the
object with respect to the horizon, and we do not have more images of
this GRB. The inferred unabsorbed color (R-H = 3.24 mag) is consistent
with the hypothesis of an highly absorbed or high redshift event
(Landsman et al. GCN 8033).
GCN Circular 8042
Subject
Konus-Wind observation of GRB 080727B
Date
2008-07-28T12:43:57Z (17 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team, report:
The long GRB 080727B (Swift-BAT trigger #318101: Immler et al., GCN
8022, Baumgartner et al., GCN 8030) triggered Konus-Wind at T0=29609.825
s UT (08:13:29.825).
The burst light curve shows two multipeaked pulses with a total duration
of ~9 s.
As observed by Konus-Wind the burst
had a fluence of 9.46(-0.84, +0.98)x10^-6 erg/cm2,
and a 64-ms peak flux measured from T0+6.080 s
of 5.14(-0.10, +0.11)x10^-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+8.448 s) is well be fitted (in the 20 keV - 2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.85(-0.18, +0.16),
and Ep = 282(-37, +52) keV (chi2 = 56.6/60 dof).
Fitting by GRBM (Band) model yields:
the low-energy photon index is alpha = -0.73(-0.24, +0.29),
the high energy photon index beta < -2.08,
the peak energy Ep = 242(-48, +69) keV (chi2 = 54.8/59 dof).
All the quoted errors are at the 90% confidence level.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB080727_T29609/
GCN Circular 8045
Subject
GRB 080727B: GROND redshift limit
Date
2008-07-28T21:21:10Z (17 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
T. Kruehler, J. Greiner, F. Schrey, C. Clemens, A. Yoldas (all MPE Garching),
A. Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on
behalf of the GROND team:
Since telescope pointing constraints did not allow a prompt observation of
GRB 080727B (Swift trigger 318101, Immler et al. 2008, GCN #8022), GROND
(Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI telescope
at La Silla Observatory (Chile), started observations in g'r'i'z'JHK only
on Jul 27, 23:08 UT, nearly 15 hrs after the burst. Under mediocre conditions
a total of 90 min effective exposure in g'r'i'z' and 76 min in JHK was
collected. Correcting for foreground extinction of A_V = 6.15 (Schlegel et al.
1998), we measure the following AB magnitudes/limits:
g'>17.7, r'>19.7, i'>19.9, z'=19.8+-0.1, J=19.45+-0.15, H=19.2+-0.1,
K=19.0+-0.15.
The corresponding SED is well fit by a single power law with slope 0.85,
with no evidence of additional (intrinsic) extinction, and with the
i'-limit being consistent with that power law. Our SED power law has an
extinction-corrected R-H=1.0. The best fit Hyper-z redshift to our data
gives z=5.5-6.5, with a firm upper limit of 6.7. Given the non-constraining
upper limits at i' and bluer, no lower limit can be placed. If the color
R-H = 3.24 mag from the combination of KAIT (Li et al. 2008, GCN #8024)
and REM data (D'Avanzo et al. 2008, GCN #8037) is correct, then the redshift
of GRB 080727B would be larger than 5.8.
GCN Circular 8046
Subject
GRB 080727B: KAIT photometry and an early lightcurve break
Date
2008-07-28T23:49:10Z (17 years ago)
From
Weidong Li at UC Berkeley KAIT/LOSS <weidong@astron.berkeley.edu>
W. Li, R. Chornock, D. A. Perley, J. S. Bloom, and A. V. Filippenko,
University of California at Berkeley, on behalf of the KAIT GRB team;
D. A. Kann, TLS Tautenburg, report:
We have analyzed the KAIT observations of the OA of GRB 080727B
as reported in Li et al. (GCN 8024). The imaging sequence started
with 10 x 2 s unfiltered exposures, with the OA detected on each
frame. A series of 20 s V, I, and unfiltered images were then
obtained, and the OA was detected in the first couple of I and
unfiltered images. Additional photometry (calibrated to USNO B1):
UT start exptime filter mag err
08:14:46 2 s clear 18.98 0.28
08:16:03 20 s clear 19.64 0.07
08:17:35 20 s clear 20.68 0.23
Our GRB pipeline used more than 100 USNO B1 stars in calculating the
photometric zero point. However, we suspect that the USNO B1 calibration
for the GRB field may be significantly off. Based on our experience in
the limiting magnitude of the KAIT 2 s and 20 s unfiltered images, we
estimate that the above photometry and those reported in GCN 8024 should
be made brighter by 1.0 - 2.0 mag. The corrected KAIT photometry, together
with the REM NIR detection (D'Avanzo et al. GCN 8037), suggests an
optical - NIR color of R-H (Vega) = 1.2 to 2.2 mag, which is consistent
with the SED fit from the GROND observations (predicted R-H (AB) = 1.0 mag;
Kruehler et al. GCN 8045).
The KAIT unfiltered light curve of GRB 080727B can be well fit by
a broken power-law with an index of 1.08 +/- 0.07 between t = 49 s
to 169 s, and 1.88 +/- 0.21 between t= 169 s and 524 s. Such an
early break in the light curve is quite extraordinary.
We plan to obtain photometric calibrations of the GRB field in the
upcoming photometric nights at Lick Observatory.
GCN Circular 8049
Subject
GRB 080727B: IR photometry
Date
2008-07-29T15:15:00Z (17 years ago)
From
Andrew Levan at U.of Leicester <anl@star.le.ac.uk>
A.J. Levan (U. Warwick) and K. Wiersema (U. Leicester) report for
a larger collaboration:
We observed the location of GRB 080727B (Immler et al. GCN 8022)
using UKIRT. The automatic observations begin at 08:27:13 UT, roughly
800 seconds after the burst. An initial set of K-band observations
were acquired, followed by a shallower JHK sequence. At the location
of the X-ray (Goad et al. GCN 8026) and optical/IR afterglows
(D'Avanzo et al. GCN 8023; Li et al. GCN 8024) we clearly identify
the fading afterglow of GRB080727B in all filters. The photometry,
calibrated against several 2MASS stars within the field of view is
shown below:
===========================================
T_s T_s-T_b Band Mag err
===========================================
08:27:13 0.00959 K 13.952 0.03
08:31:38 0.01266 K 14.243 0.03
08:36:03 0.01573 K 14.392 0.03
08:50:08 0.02551 K 14.952 0.05
09:00:10 0.03248 K 15.276 0.05
09:10:09 0.03940 K 15.549 0.05
===========================================
08:47:04 0.023389 H 16.144 0.06
08:58:06 0.031042 H 16.560 0.06
09:07:05 0.037280 H 16.775 0.08
==========================================
08:43:13 0.02071 J 17.855 0.10
08:53:15 0.02767 J 18.300 0.10
09:03:16 0.03463 J 18.626 0.11
===========================================
*Data have not been corrected for the significant foreground
extinciton
The K-band is suggestive of a break occurring at t_b ~ 1600s, with
pre- and post-break slopes of alpha_1 =0.84 and alpha_2 =1.26. The
initial slope is significantly shallower than that suggested by the
KAIT observations (Li et al GCN 8046), and implies either that the
afterglow decay flatenned after those observations, or that the
optical and IR were not tracking eachother in this case.
We thank the staff of UKIRT for their rapid response to these alerts.
GCN Circular 8074
Subject
GRB 080727B: Late VLT imaging
Date
2008-08-06T05:38:15Z (17 years ago)
From
Thomas Kruehler at MPE/MPI <kruehler@mpe.mpg.de>
T. Kruehler, J. Greiner (MPE Garching) and S. Klose (Tautenburg) report:
We triggered VLT/FORS imaging of the field of the Swift GRB 080727B
(Immler et al. 2008, GCN #8022). A series of exposures were obtained in
Rc (6*120s), Bessel I (5*120s) and Gunn z (4*120s) starting from 06:19 UT
on 2008-07-29, roughly 46 hours after the burst. We marginally detect the
optical afterglow (Li et al, 2008, GCN #8024) in the stacked I and z
frames at 24.7 +- 0.3 mag (I) and 23.9 +- 0.5 mag (z), calibrated
against USNO-B1 stars.
Given the large errors and the uncertain and high foreground extinction,
this is consistent with the power law reported in Kruehler et al (2008,
GCN #8045) and puts the upper redshift limit to ~5. The 3 sigma upper
limit in Rc (>25.5 mag) is above that power law and does not constrain
the shape of the spectral energy distribution or the redshift.
We thank the ESO/VLT staff for the perfect support.