GRB 180709A
GCN Circular 22930
Subject
GRB 180709A: Swift detection of a burst
Date
2018-07-09T11:11:25Z (7 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), P. A. Evans (U Leicester),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC)
and K. L. Page (U Leicester) report on behalf of the Neil Gehrels
Swift Observatory Team:
At 10:52:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180709A (trigger=846868). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 38.119, +60.372 which is
RA(J2000) = 02h 32m 29s
Dec(J2000) = +60d 22' 18"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multi-peaked
structure with a duration of about 30 sec. The peak count rate
was ~800 counts/sec (15-350 keV), at ~6 sec after the trigger.
The XRT began observing the field at 10:53:45.0 UT, 104.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
38.1178, 60.3490 which is equivalent to:
RA(J2000) = 02h 32m 28.27s
Dec(J2000) = +60d 20' 56.5"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 82 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density.
The initial flux in the 2.5 s image was 6.60e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 114 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag.
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain, extinction expected.
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 22933
Subject
GRB 180709A: Enhanced Swift-XRT position
Date
2018-07-09T14:25:14Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1493 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 180709A, 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 = 38.11784, +60.34912 which is equivalent
to:
RA (J2000): 02h 32m 28.28s
Dec (J2000): +60d 20' 56.8"
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 22934
Subject
GRB 180709A: COATLI Optical Observations
Date
2018-07-09T15:27:42Z (7 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
Nat Butler (ASU), Alan M. Watson (UNAM), aRosa L. Becerra (UNAM), William
H. Lee (UNAM), Carlos Rom��n-Z����iga (UNAM), Alexander Kutyrev (GSFC), and
Eleonora Troja (GSFC) report:
We observed the field of GRB 180709A (Marshall et al., GCN Circ 22930) with
the COATLI 50-cm telescope and interim imager at the Observatorio
Astron��mico Nacional on the Sierra de San Pedro M��rtir (
http://coatli.astroscu.unam.mx) from 2018-07-09 10:53:05.6 to 11:26:07.1
UTC (from 65.4 seconds after the trigger or 14.5 seconds after the alert to
0.55 hours after the trigger), obtaining a total of 695 seconds of exposure
in the w filter.
For a source within the XRT error region (Marshall et al., GCN Circ.
22930), we determine a 3-sigma upper limit of
w > 21.3
This magnitude is calibrated against the USNO-B1 catalog (adjusted to an
approximate AB system) and is not corrected for Galactic extinction in the
direction of the GRB.
We thank the COATLI technical team (Fernando ��ngeles, Oscar Chapa, Salvador
Cuevas, Alejandro Farah, Jorge Fuentes, Rosal��a Langarica, Fernando Quir��s,
and Carlos Tejada) and the staff of the Observatorio Astron��mico Nacional.
GCN Circular 22935
Subject
GRB 180709A: Optical limits
Date
2018-07-09T16:36:22Z (7 years ago)
From
Jules Halpern at Columbia U. <jph1@columbia.edu>
J. P. Halpern (Columbia U.) reports:
I observed the field of Swift GRB 180709A (Marshall et al., GCN 22930)
with an SDSS r filter using the 1.3m McGraw Hill telescope of the
MDM Observatory, beginning 17.6 minutes after the trigger.
Four 5-minute exposures were obtained in morning twilight.
Upper limits at the enhanced Swift-XRT position of Beardmore et al.
(GCN 22933) are listed below, as calibrated to Pan-STARRS1 photometry.
---------------------------------------------
Date(UT) Start(UT) Mid-time T-T0 r(mag)
---------------------------------------------
July 9 11:09:34 1194 s > 22.0
July 9 11:14:41 1501 s > 21.8
July 9 11:19:47 1807 s > 21.4
July 9 11:24:54 2114 s > 21.1
---------------------------------------------
These magnitudes are not corrected for Galactic extinction, which is
considerable at this Galactic latitude of -0.1 deg. According to the
NED implementation of Schlafly & Finkbeiner (2011), A_r = 6.1 mag.
GCN Circular 22936
Subject
GRB 180709A: Swift-XRT refined Analysis
Date
2018-07-09T20:08:00Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU),
P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), Z. Liu (NAOC /
U. Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAB) and F.E. Marshall report on behalf of the Swift-XRT team:
We have analysed 6.8 ks of XRT data for GRB 180709A (Marshall et al.
GCN Circ. 22930), from 111 s to 24.8 ks after the BAT trigger. The
data comprise 277 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Beardmore et al. (GCN Circ. 22933).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.95 (+0.09, -0.08).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.41 (+/-0.20). The
best-fitting absorption column is 1.9 (+/-0.4) x 10^22 cm^-2, in
excess of the Galactic value of 8.9 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.7 (+0.5, -0.4) and
a best-fitting absorption column of 3.5 (+1.2, -1.0) x 10^22 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 8.4 x 10^-11 (1.6 x 10^-10) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.5 (+1.2, -1.0) x 10^22 cm^-2
Galactic foreground: 8.9 x 10^21 cm^-2
Excess significance: 4.3 sigma
Photon index: 1.7 (+0.5, -0.4)
If the light curve continues to decay with a power-law decay index of
1.95, the count rate at T+24 hours will be 2.1 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x
10^-15 (3.4 x 10^-15) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00846868.
This circular is an official product of the Swift-XRT team.
GCN Circular 22937
Subject
GRB 180709A: Swift/UVOT Upper Limits
Date
2018-07-09T20:38:53Z (7 years ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
A. A. Breeveld (UCL-MSSL), S. W. K. Emery (UCL-MSSL) and F. E. Marshall
(NASA/GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 180709A
115 s after the BAT trigger (Marshall et al., GCN Circ. 22930).
No optical afterglow consistent with the XRT position (Beardmore et al.,
GCN Circ. 22933) 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 subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 115 264 147 >20.5
u_FC 273 523 246 >19.6
v 604 797 39 >18.0
b 529 723 39 >19.0
uvw1 654 846 39 >17.7
The magnitudes in the table are not corrected for the Galactic
extinction due to the reddening of E(B-V) = 2.72 in the direction of the
burst (Schlegel et al. 1998).
GCN Circular 22938
Subject
GRB 180709A: Swift-BAT refined analysis
Date
2018-07-09T20:48:13Z (7 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
M. Stamatikos (OSU), 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), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180709A (trigger #846868)
(Marshall et al., GCN Circ. 22930). The BAT ground-calculated position is
RA, Dec = 38.086, 60.333 deg which is
RA(J2000) = 02h 32m 20.7s
Dec(J2000) = +60d 19' 59.4"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 81%.
The mask-weighted light curve shows a single-peaked structure that starts
at ~T0 and peaks at ~T+10 s. The main structure ends at ~T+40 s, with some
tail emission lasting till ~T+240 s. T90 (15-350 keV) is 215.1 +- 28.9 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.54 to T+243.46 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.37 +- 0.23. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+8.73 sec in the 15-150 keV band
is 0.6 +- 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/846868/BA/
GCN Circular 22939
Subject
GRB 180709A: BOOTES-5/JGT optical observations
Date
2018-07-09T21:54:44Z (7 years ago)
From
Irene Carrasco at Inst.De Astrofisica de Andalucia <irene@iaa.es>
I. Carrasco (Univ. de Malaga), Y. Hu, E. Fernandez-Garcia, J. C. Tello
and A. J. Castro-Tirado (IAA-CSIC), D. Hiriart and
W. H. Lee (UNAM), S. Jeong and I. H. Park (SKKU), M. D. Caballero-Garcia
(ASU-CAS, CZ) and R. Cunniffe (Inst. of Physics, CZ) on behalf of a
larger collaboration, report:
The 60 cm BOOTES-5/JGT at Observatorio Astronomico Nacional in San Pedro
Martir (Mexico) automatically responded in 21s (and 74s after the GRB
onset) to the Swift trigger of GRB 180709A (Marshall et al., GCN
22930). The first unfiltered images (10 s exposures) were obtained at
10:53:14 UT. At the position of the Swift X-ray afterglow, no optical
afterglow is detected down 18.1 mag. Furthermore, on the co-add of the
images obtained until 11:43:04 UT no afterglow is detected down to 21
mag, consistent with the limits reported by Butler et al. (GCN 22934),
Halpern (GCN 22935) and Breeveld et al. GCN 22937).
We thank the staff at Observatorio Astronomico Nacional in San Pedro
Martir for its excellent support.