GRB 150727A
GCN Circular 18076
Subject
GRB 150727A: Swift detection of a burst with an optical counterpart
Date
2015-07-27T19:24:14Z (10 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
S. B. Cenko (GSFC), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), J. L. Racusin (NASA/GSFC) and M. H. Siegel (PSU)
report on behalf of the Swift Team:
At 19:02:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150727A (trigger=650530). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 203.990, -18.355, which is
RA(J2000) = 13h 35m 58s
Dec(J2000) = -18d 21' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a large FRED-like peak
structure with a duration of about 60 sec. The peak count rate
was ~2795 counts/sec (15-350 keV), at ~4 sec after the trigger.
The XRT began observing the field at 19:03:19.5 UT, 77.2 seconds after
the BAT trigger. XRT found a bright, fading, uncatalogued X-ray source located
at RA, Dec 203.9705, -18.3259 which is equivalent to:
RA(J2000) = +13h 35m 52.92s
Dec(J2000) = -18d 19' 33.2"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 124 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 8.93e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 86 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 13:35:52.52 = 203.96883
DEC(J2000) = -18:19:31.4 = -18.32539
with a 90%-confidence error radius of about 0.62 arc sec. This position is 6.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.31 with a 1-sigma error of about 0.15. No correction has been made for
extinction.
Burst Advocate for this burst is S. B. Cenko (brad.cenko 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 18079
Subject
GRB 150727A: Enhanced Swift-XRT position
Date
2015-07-27T23:59:12Z (10 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.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 1662 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 150727A, 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 = 203.96843, -18.32576 which is equivalent
to:
RA (J2000): 13h 35m 52.42s
Dec (J2000): -18d 19' 32.7"
with an uncertainty of 1.8 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 18080
Subject
GRB 150727A: VLT/X-shooter redshift
Date
2015-07-28T05:14:42Z (10 years ago)
From
Nial Tanvir at U.Leicester <nrt3@star.le.ac.uk>
N. R. Tanvir (U. Leicester), D. Xu (NAOC/CAS), T. Zafar (ESO), S. Covino (INAF/OABr), S. Schulze (PUC, MAS) report for a larger collaboration:
We observed the afterglow of GRB 150727A (Cenko et al. GCN 18076) with VLT/X-shooter, beginning at 2015-07-28 00:01 UT, about 5 hr after the burst.
Preliminary analysis of the spectrum reveals emission lines of Halpha, Hbeta and [OIII] 4959/5007 at a redshift of z=0.313. There is only marginal evidence of the [OII] 3727 doublet, suggesting the emission lines are coming from a dust obscured region (consistent also with a high Ha:Hb ratio). The continuum is faint with no clear absorption lines, but can be traced in the blue as far as the instrumental cut-off at about 3100A. Despite the absence of detected absorption features, it is likely that the emission lines are from the host galaxy and therefore that this redshift is also that of the GRB.
GCN Circular 18081
Subject
GRB 150727A: Fermi GBM detection
Date
2015-07-28T06:25:51Z (10 years ago)
From
George A. Younes at George Washington U <gyounes@email.gwu.edu>
G. Younes (GWU) reports on behalf of the Fermi GBM Team:
"At 19:01:56.35 UT on July 27 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150727A (trigger 459716520/150727793), which
was also detected by Swift (Cenko et al. 2015, GCN 18076). The GBM
on-ground location, using the Fermi GBM trigger data, is consistent
with the Swift/XRT location.
The angle of the burst direction to the Fermi LAT boresight
is 46 degrees.
The GBM light curve shows a FRED-like (fast-rise exponential-decay)
pulse with a duration (T90) of about 50s (50-300 keV). The
time-averaged spectrum from T0-4s to T0+56s is well fit by a power
law with an exponential high-energy cutoff. The power law index is
-0.7 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 149 +/-
10 keV.
The event fluence (10-1000 keV) in this time interval is
(7.9 +/- 0.3)E-06 ergs/cm^2. The 1.0-sec peak photon flux measured
starting from T0+5.0s in the 10-1000 keV band
is 2.1 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 18082
Subject
GRB 150727A: Swift-XRT refined Analysis
Date
2015-07-28T08:24:02Z (10 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. D'ai
(INAF-IASFPA), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), J.A.
Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P.
Beardmore (U. Leicester) and S.B. Cenko report on behalf of the
Swift-XRT team:
We have analysed 8.0 ks of XRT data for GRB 150727A (Cenko et al. GCN
Circ. 18076), from 68 s to 32.5 ks after the BAT trigger. The data
comprise 523 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN Circ. 18079).
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.2 (+/-0.4). At T+93.8 s the decay
steepens to an alpha of 2.72 (+0.11, -0.08). The light curve breaks
again at T+195 s to a decay with alpha=1.42 (+0.07, -0.06), and again
at T+3169 s s to alpha=8.0 (+0.0, -5.8), before a final break at
T+4539 s s after which the decay index is 0.5 (+/-0.3).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.39 (+/-0.04). The
best-fitting absorption column is 2.0 (+/-1.5) x 10^20 cm^-2, at a
redshift of 0.313, in addition to the Galactic value of 9.8 x 10^20
cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum is 2.7 x
10^-11 (3.9 x 10^-11) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus:
Galactic foreground: 9.8 x 10^20 cm^-2
Intrinsic column: 2.0 (+/-1.5) x 10^20 cm^-2 at z=0.313
Photon index: 2.39 (+/-0.04)
If the light curve continues to decay with a power-law decay index of
0.5, the count rate at T+24 hours will be 8.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.4 x
10^-13 (3.4 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/00650530.
This circular is an official product of the Swift-XRT team.
GCN Circular 18083
Subject
GRB 150727A: LCOGT-Cerro Tololo observations
Date
2015-07-28T10:03:02Z (10 years ago)
From
Simone Dichiara at Ferrara U/Italy <dichiara@fe.infn.it>
S. Dichiara, C. Guidorzi (U. Ferrara), C.G. Mundell (U. Bath),
S. Kobayashi (LJMU), A. Gomboc (U. Ljubljana) on behalf of
a large collaboration report:
Using a 1-m LCOGTN telescope in Cerro Tololo (Chile),
we began observing GRB 150727A (Cenko et al. GCN 18076;
Younes et al. GCN 18081) on July 28 01:23:01 UT
(~6.3 hours after the burst trigger) with r' and i' filters.
We did not detect the UVOT counterpart (Cenko et al. 2015, GCN 18076)
down to the following limit:
Mid time from Total Exp Filter Magnitude
trigger (hr) (s)
-------------------------------------------------
6.71 120x10 r' > 18.9
6.76 120x9 i' > 16.5
-------------------------------------------------
Values have been calibrated against nearby USNOB-1 stars
(R2 and I).
GCN Circular 18084
Subject
GRB 150727A: Swift/UVOT Detection
Date
2015-07-28T10:38:48Z (10 years ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
A. A. Breeveld (UCL-MSSL) and S. B. Cenko (GSFC) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150727A
86 s after the BAT trigger (Cenko et al., GCN Circ. 18076).
A fading source consistent with the enhanced XRT position (Osborne et
al. GCN Circ. 18079) is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 13:35:52.52 = 203.96885 (deg.)
Dec (J2000) = -18:19:31.3 = -18.32536 (deg.)
with an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence).
Preliminary detections in the white, u and uvw2 filters and 3-sigma
upper limits using the UVOT photometric system (Breeveld et al. 2011,
AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 86 236 147 18.28 �� 0.06
white 578 598 20 18.75 �� 0.24
v 4036 4236 197 >18.7
b 554 574 19 >18.5
u 298 548 246 18.75 �� 0.16
m2 4241 4379 136 >19.1
w2 3831 4031 197 19.53 �� 0.36
The magnitudes in the table are not corrected for the Galactic
extinction due to the reddening in the direction of the burst.
GCN Circular 18085
Subject
GRB 150727A: Watcher optical upper limit
Date
2015-07-28T10:39:46Z (10 years ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
A. Martin-Carrillo (UCD), D. Murphy (UCD), L. Hanlon (UCD), M. Topinka (CTU), H. J. van Heerden (UFS), B. van Soelen (UFS) and P. J. Meintjes (UFS):
We observed the field of GRB 150727A (Cenko et al., GCN Circ. #18076) using the 40cm UCD Watcher telescope at Boyden Observatory in South Africa.
Observations started at 19:19:55 UT, 1073 seconds after the burst trigger. A series of 60 sec images were taken in the SDSS r' filter using an Andor CCD camera.
No afterglow candidate is detected in any of the individual images at the UVOT location. A 3sigma upper limit for a combined 180 second exposure is given below.
Start | End | Exposure | Filter | Magnitude
-------------------------------------------------------------------------------------------------
19:19:55 UT | 19:25:20 UT | 3x60 sec | r' | >17.59 (3sigma upper limit)
The upper limit was calculated using nearby stars from the APASS catalogue.
This message can be cited in publications.
GCN Circular 18086
Subject
GRB 150727A: Swift-BAT refined analysis
Date
2015-07-28T12:05:52Z (10 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlinks,
we report further analysis of BAT GRB 150727A (trigger #650530)
(Cenko, et al., GCN Circ. 18076). The BAT ground-calculated position is
RA, Dec = 203.968, -18.320 deg, which is
RA(J2000) = 13h 35m 52.3s
Dec(J2000) = -18d 19' 11.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 68%.
The mask-weighted light curve shows a FRED-like peak starting at ~T-8 sec,
peaking at ~T+5 sec, and ramping down to a flat level at ~T+80 sec.
There is a second, small peak at ~T+90 sec. The low level emission
continues (with a weak decline) out to T+870 sec when observations stop
due to an observing constraint.
T90 (15-350 keV) is 88 +- 13 sec (estimated error including systematics).
The time-averaged spectrum from T-8.70 to T+95.94 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.14 +- 0.07. The fluence in the 15-150 keV band is 3.7 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+9.21 sec in the 15-150 keV band
is 1.0 +- 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/650530/BA/
[GCN OPS NOTE(29jul15): Per author's request, the typo on the uncertainty
in the T90 value was changed from 133 to 13 sec.]
GCN Circular 18089
Subject
GRB 150727A: RATIR Optical Observations
Date
2015-07-28T16:43:42Z (10 years ago)
From
Alan M. Watson at Instituto de Astronomia UNAM <alan@astro.unam.mx>
Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara
(ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos� A. de Diego (UNAM), Leonid Georgiev (UNAM),
Jes�s Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Neil Gehrels (GSFC),
and Harvey Moseley (GSFC) report:
We observed the field of GRB 150727A (Cenko et al., GCN 18076) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astron�mico Nacional on
Sierra San Pedro M�rtir from 2015/07 28.15 to 2015/07 28.21 UTC (8.65 to
9.95 hours after the BAT trigger), obtaining a total of 1.07 hours
exposure in the r, i, and z bands.
We detect a source at the edge of the Swift/XRT error circle (Osborne et
al., GCN 18079), at RA, Dec (J2000) = 13:35:52.52, -18:19:31.4 (�0.5"). In
comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
detections and upper limits (3-sigma):
r 21.13 � 0.19
i 21.40 � 0.13
z > 19.57
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
Our detections appear to be consistent with the non-detections at
shallower depths reported by Dichiara et al. (GCN 18083). Tanvir et al.
(GCN 18080) report a tentative spectroscopic redshift of 0.313.
Further observations are planned.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro
M�rtir.
GCN Circular 18095
Subject
GRB 150727A: Continued RATIR Optical Observations - Fading
Date
2015-07-29T20:03:54Z (10 years ago)
From
Alan M. Watson at Instituto de Astronomia UNAM <alan@astro.unam.mx>
Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC),
William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori
Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino
Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU),
Enrico Ramirez-Ruiz (UCSC), Jos� A. de Diego (UNAM), Leonid Georgiev
(UNAM), Jes�s Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Neil Gehrels
(GSFC), and Harvey Moseley (GSFC) report:
We observed the field of GRB 150727A (Cenko et al., GCN 18076) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on
the 1.5m Harold Johnson Telescope at the Observatorio Astron�mico
Nacional on Sierra San Pedro M�rtir from 2015/07 29.15 to 2015/07 29.19
UTC (32.64 to 33.50 hours after the BAT trigger), obtaining a total of
0.70 hours exposure in the r, i, and z bands.
We no longer detect the source seen on the previous night (Watson et
al., GCN 18089). In comparison with the USNO-B1 and 2MASS catalogs, we
obtain the following upper limits (3-sigma):
r > 22.27
i > 22.61
z > 19.11
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
The source has faded by at least 1 magnitude in both r and i. We
therefore suggest that it it corresponds to the afterglow.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro
M�rtir.
GCN Circular 18113
Subject
GRB 150727A: IRSF NIR observation
Date
2015-08-04T08:45:32Z (10 years ago)
From
Daisuke Kuroda at OAO/NAOJ <dikuroda@oao.nao.ac.jp>
K. L. Murata (Nagoya U.), T. Kusune (Nagoya City U.), H. Onozato (Tohoku U.) and T. Nagayama (Kagoshima U.)
We observed the field of GRB 150727A (Cenko et al., GCN Circular #18076) with the near-infrared (J, H, Ks) simultaneous imaging polarimeter SIRPOL attached to 1.4 m telescope IRSF (InfraRed Survey Facility) in Sutherland observatory, South Africa.
The observations started on 2015-07-27 19:25:30 UT (~ 9 min. after the burst).
We detected an uncatalogued source within 5 arcsec from the Swift/UVOT preliminary position reported in the GCN circular of Breeveld et al. (GCN Circular #18084).
We have obtained the following preliminary magnitude (Vega magnitude system):
J = 18.9 +- 0.2
H = 18.1 +- 0.1
Ks = 17.1 +- 0.2
Given magnitudes were calibrated against 2MASS point sources in this field.
This observation was carried out by IRSF and OISTER collaboration.