GRB 170827A
GCN Circular 21718
Subject
GRB 170827A: Swift detection of a burst
Date
2017-08-27T05:25:35Z (8 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
F. E. Marshall (NASA/GSFC), A. D'Ai (INAF-IASFPA),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:
At 05:12:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170827A (trigger=769567). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 276.180, -40.220 which is
RA(J2000) = 18h 24m 43s
Dec(J2000) = -40d 13' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). As is typical for an image trigger, the
immediately-available BAT lightcurve shows no obvious variation.
The XRT began observing the field at 05:14:32.5 UT, 124.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 276.1508, -40.2016 which is equivalent to:
RA(J2000) = +18h 24m 36.19s
Dec(J2000) = -40d 12' 05.8"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). This
location is 104 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 4.23e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White
filter starting 133 seconds after the BAT trigger. Only partial
images are available and neither the 2.7'x2.7' sub-image nor the 8'x8'
region for the list of sources generated on-board covers the XRT error
circle. Analysis of any potential afterglow will have to await further
data.
Burst Advocate for this burst is F. E. Marshall (marshall 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 21721
Subject
GRB 170827A: REM optical/NIR observations
Date
2017-08-27T09:28:32Z (8 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo, D. Fugazza, S. Covino (INAF/OAB) report on behalf of the REM team:
We observed the field of the short GRB 170827A (Marshall et al., GCN 21718) with the 60-cm robotic
telescope REM located at the La Silla Observatory (Chile). The observations started at 05:14:24 UT,
116 seconds after the burst, and were carried out simultaneously in the g, r, i, z and H bands.
A preliminary photometry of the first co-added images indicates that no obvious afterglow candidate
is detected within the Swift/XRT error circle (Marshall et al., GCN 21718) down to the following 3sigma
limiting AB magnitudes:
r > 19.5 at T-T0 = 720s
H > 17.5 at T-T0 = 585s
Magnitudes are in the AB system and have been calibrated with respect to the 2MASS (H-band)
and APASS (r-band) catalogues.
GCN Circular 21722
Subject
GRB 170827A: Swift/UVOT Upper Limits
Date
2017-08-27T15:15:10Z (8 years ago)
From
Frank Marshall at GSFC <femarsha@khamseen.gsfc.nasa.gov>
F. E. Marshall (NASA/GSFC) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 170827A
134 s after the BAT trigger (Marshall et al., GCN Circ. 21718).
No optical afterglow consistent with the XRT position
(Marshall et al. GCN Circ. 21718)
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and a subsequent short exposure are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 134 284 147 >19.8
u 292 298 6 >17.8
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.11 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 21724
Subject
GRB 170827A, Swift-BAT refined analysis
Date
2017-08-27T16:58:00Z (8 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+509 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170827A (trigger #769567)
(Marshall et al. GCN Circ. 21718). The BAT ground-calculated position is
RA, Dec = 276.189, -40.202 deg which is
RA(J2000) = 18h 24m 45.3s
Dec(J2000) = -40d 12' 07.9"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 98%.
The mask-weighted light curve shows a weak pulse that starts at ~T+20 s
and ends at ~T+140 s. T90 (15-350 keV) is 94.0 +- 12.5 sec (estimated error
including systematics).
The time-averaged spectrum from T+19.1 to T+138.9 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.29 +- 0.18. The fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+67.13 sec in the 15-150 keV band
is 0.4 +- 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/769567/BA/
GCN Circular 21728
Subject
GRB 170827A: ePESSTO NTT afterglow candidate
Date
2017-08-28T02:33:35Z (8 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
J. Lyman (Univ. of Warwick), D. Homan (Univ of Edinburgh), P. D'Avanzo (INAF-OAB), Patricia Schady (MPE Garching),
K. E. Heintz (DARK/NBI), E. Palazzi (INAF-IASFBo), L. Galbany (Univ. de Chile), J. Anderson (ESO), C. Inserra (Southampton),
E. Kankare (QUB), K. Maguire (QUB), S. Smartt (QUB), K. W. Smith (QUB), O. Yaron (Weizmann), D. Young (QUB),
I. Manulis (Weizmann) report:
We observed the field of GRB 170827A (Marshall et al., GCN 21718) under the extended Public ESO Spectroscopic Survey for
Transient Objects (ePESSTO; see Smartt et al. 2015, A&A, 579, 40 http://www.pessto.org ). The observations were performed on
the ESO New Technology Telescope at La Silla with the SofI and EFOSC2 instrument in imaging mode starting from 2017-08-28
at 00:47:05 UT (i.e. 19.58 hours from the burst). Observations were carried out with the Z, J, R and I filters.
Within the XRT error circle (Marshall et al., GCN 21718) we detect an object at the following coordinates:
RA(J2000), Dec(J2000) = 18:24:36.14, -40:12:06.3
(+/- 0.5"). The object has a magnitude R~21.5 (based on preliminary photometry calibrated against the USNOB1 catalogue) at
T-T0 = 20.08 hours. We cannot make any statement about variability at this time.We also notice the presence of a fainter object
about 2.4" West.
GCN Circular 21729
Subject
GROND observations of GRB170827A
Date
2017-08-28T09:40:33Z (8 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
P. Schady (MPE Garching) reports
I observed the field of GRB 170827A (Swift trigger 769567; Marshall et
al., GCN #21718) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla
Observatory (Chile).
Observations started at 00:44 UT on 28-08-2017, 19.5 hours after the GRB
trigger. They were performed at an average seeing of 1.5" and at an
average airmass of 1.0.
A point source is present within the 4.9" Swift-XRT error circle (Marshall
et al., GCN #21718) in the g'r'i'z' GROND images, consistent with the
ePESSTO position reported by Lyman et al. (GCN #21728).
Based on a total exposure time of 36 min in g'r'i'z' and 30 min in JHK,
the estimated preliminary magnitudes and upper limits (all in AB system)
are
g' = 22.8 +/- 0.1 mag
r' = 21.9 +/- 0.1 mag
i' = 21.6 +/- 0.1 mag
z' = 21.4 +/- 0.1 mag
J > 21.1 mag
H > 20.6 mag
K > 20.1 mag
Given magnitudes are calibrated against GROND zeropoints as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.09 mag in the
direction of the burst (Schlafly & Finkbeiner 2011).
A second fainter source is also detected within the XRT error circle at
around 2.3" west of the ePESSTO afterglow candidate. No statement can be
made at this time on the variability of either source.
I acknowledge the excellent help provided by the support astronomer in La
Silla, Markus Rabus, in obtaining these data.
GCN Circular 21730
Subject
GRB 170827A: Swift-XRT refined Analysis
Date
2017-08-28T13:23:16Z (8 years ago)
From
Antonino D'Ai at IASF-PA <antonino.dai@ifc.inaf.it>
A. D'Ai (IASF-PA), V. D'Elia (ASDC), F. E. Marshall (NASA/GSFC) reports
on behalf of the Swift-XRT team:
We have analysed 1.1 ks of XRT data for GRB 170827A (Marshall et al.
GCN Circ. 21718), from 113 s to 17.3 ks after the BAT trigger. The
data comprise 165 s in Windowed Timing (WT) mode (the first 9 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode.
The initial light curve from T0+130s to T0+295s can be modelled with a
power-law decay with a decay index of alpha=1.19 (+/-0.08). In the
following observation at T0+16.1 ks the afterglow is not detected with
a 3-sigma upper limit of 1.6 x 10^-2 count^-1 s^-1.
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.23 (+0.06, -0.05). The
best-fitting absorption column is 1.46 (+/-0.15) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.0 x 10^-11 (4.2 x 10^-11) erg
cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
Total column: 1.46 (+/-0.15) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^21 cm^-2
Excess significance: 3.0 sigma
Photon index: 2.23 (+0.06, -0.05)
Given the lack of detection in the second observation, no reliable
estimate of the X-ray count rate for the following days is possible.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00769567.
This circular is an official product of the Swift-XRT team.
GCN Circular 21743
Subject
GRB170827A: Further GROND follow-up observations
Date
2017-08-29T07:29:05Z (8 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
P. Schady (MPE Garching) reports
I re-observed the field of GRB 170827A (Swift trigger 769567; Marshall et
al., GCN #21718) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) on 29-08-2017, 1.8 days after the GRB trigger and 1
day after the first set of GROND observations (Schady, GCN #21729) .
Observations were performed at an average seeing of 1.4" and at an average
airmass of 1.0.
The two point sources detected within the 4.9" XRT error circle (Marshall
et al., GCN #21718) in the first epoch of GROND observations (Schady, GCN
#21729) are still seen in the second epoch of GROND observations and they
remain at the same magnitude. Neither of these sources are therefore
likely to be the optical counterpart of GRB 170827A.
I acknowledge the excellent help provided by the support astronomer in La
Silla, Markus Rabus, in obtaining these data.
GCN Circular 21807
Subject
GRB 170827A: LCO Observations
Date
2017-09-04T11:43:05Z (8 years ago)
From
Antonino Cucchiara at UVI <antonino.cucchiara@uvi.edu>
A. Cucchiara, D. Morris, J. Staff, and B. Gendre (U. Virgin
Islands) report on behalf of a larger collaboration:
"On August 27.71 UT (T_0 +12.0h) we began observing the
center of the field of GRB 170827A (Marshall et al.
GCN 21718, D'Ai et al. GCN 21730) using the Las Cumbres
Observatory 1m telescope located in Sutherland Observatory.
We performed a series of 5x240s observations in SDSS r' and
i��� bands for a total of 20 minutes on sky in each filter at
average airmass of 1.05.
In the full median stacked images we identified no optical
counterpart within the center of the Swift-XRT refined position
or at the ePESSTO NTT optical counterpart location (Evans et al.
GCN 21413, Lyman et al. GCN 21728) at the following
3-sigma limits:
r' > 20.6 mag
i' > 19.6 mag
These values are consistent with the limits and detections
reported by other observatories (D'Avanzo et al. GCN 21721,
Schady et al. GCN 21729, 21743).
These magnitudes are calibrated against nearby USNO-B1 sources,
converted in SDSS bands, and not corrected for Galactic extinction."