GRB 160408A
GCN Circular 19260
Subject
GRB 160408A: Swift detection of a short burst
Date
2016-04-08T06:39:08Z (9 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
P.A. Evans (U Leicester), S. D. Barthelmy (GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:
At 06:25:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160408A (trigger=682059). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 122.557, +71.140, which is
RA(J2000) = 08h 10m 14s
Dec(J2000) = +71d 08' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a single spike
with a duration of about 0.5 sec. The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 06:27:18.5 UT, 94.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 122.6235, 71.1284 which
is equivalent to:
RA(J2000) = 08h 10m 29.64s
Dec(J2000) = +71d 07' 42.3"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 87 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. We
cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.18 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.9
(+3.04/-2.61) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 98 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 none of
the XRT error circle. 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 expected
extinction corresponding to E(B-V) of 0.03.
Burst Advocate for this burst is P.A. Evans (pae9 AT star.le.ac.uk).
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 19261
Subject
GRB 160408A: Enhanced Swift-XRT position
Date
2016-04-08T09:58:51Z (9 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 1293 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 160408A, 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 = 122.62470, +71.12831 which is equivalent
to:
RA (J2000): 08h 10m 29.93s
Dec (J2000): +71d 07' 41.9"
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) 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 19262
Subject
GRB 160408A: Gemini optical observations
Date
2016-04-08T10:45:28Z (9 years ago)
From
Andrew Levan at U.of Leicester <A.J.Levan@warwick.ac.uk>
A.J. Levan (U. Warwick) and N.R. Tanvir (U. Leicester) report for a larger collaboration:
���We observed the location of the short GRB 160408A (Evans et al. GCN 19260) with Gemini-North and GMOS. Observations were taken in the r-band, starting at 07:23 UT, approximately 58 minutes after the burst. Several objects are present in the field close to the refined XRT position (Osborne et al. GCN 19261). The closest objects are a compact source (A) and a more extended galaxy (B). The locations of these sources are:
Source A:
RA(J2000) 08h 10m 29.81s
DEC(J2000) 71d 07��� 43.7���
Source B:
RA(J2000) 08h 10m 29.32s
DEC(J2000) 71d 07��� 40.5���
with an uncertainty of approximately 0.3��� in each co-ordinate. Conditions were not photometric at the time of the observations, but comparison with USNO-B1 sources in the field of view suggests that source A has a magnitude of r~24.5, source B is approximately a magnitude brighter.
We thank the Gemini staff for the rapid execution of these observations.���
GCN Circular 19263
Subject
GRB 160408A: Swift-BAT refined analysis
Date
2016-04-08T13:13:33Z (9 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
P.A. Evans (U Leicester), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-120 to T+302 sec from the recent telemetry downlinks,
we report further analysis of BAT GRB 160408A (trigger #682059)
(Evans, et al., GCN Circ. 19260). The BAT ground-calculated position is
RA, Dec = 122.561, 71.128 deg, which is
RA(J2000) = 08h 10m 14.6s
Dec(J2000) = +71d 07' 40.0"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 33%.
The mask-weighted light curve starts at ~T0, peaks at ~T+0.1 sec, and
ends at ~T+0.4 sec. T90 (15-350 keV) is 0.32 +- 0.04 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.02 to T+0.37 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
0.85 +- 0.25. The fluence in the 15-150 keV band is 1.6 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.30 sec in the 15-150 keV band
is 2.1 +- 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/682059/BA/
We note that this burst was detected by Fermi-GBM, CALET-GBM, Swift-BAT,
and INTEGRAL-SPIACS.
GCN Circular 19265
Subject
GRB 160408A: Fermi GBM detection
Date
2016-04-08T15:23:19Z (9 years ago)
From
Oliver Roberts at UCD/Fermi <oliver.roberts@ucd.ie>
O.J. Roberts (UCD) reports on behalf of the Fermi GBM Team:
"At 06:25:43.86 UT on the 8th of April 2016, the Fermi
Gamma-Ray Burst Monitor triggered and located GRB 160408A
(trigger 481789547 / 160408268), which was also detected by
Swift (Evans et al. 2008, GCN 19620). The GBM on-ground
location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger
time using the Swift XRT position is about 7 degrees.
The GBM light curve consists of two bright, short emission
episodes, with a duration (T90) of about 0.9 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.384 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.76 +/- 0.10 and
the cutoff energy, parameterized as Epeak, is 914 +/- 184 keV.
The event fluence (10-1000 keV) in this time interval is
(1.25 +/- 0.08)E-06 erg/cm^2. The 64 ms peak photon flux
measured starting from T0+0 s in the 10-1000 keV band,
is 12.4 +/- 1.4 ph/s/cm^2.
A Band function fits the spectrum equally well, with
Epeak = 765 +/- 198 keV, alpha = -0.70 +/- 0.12, and
beta = -2.27 +/- 0.41.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 19266
Subject
GRB 160408A: Swift-XRT refined Analysis
Date
2016-04-08T18:14:24Z (9 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. D'Ai
(INAF-IASFPA), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), D.N.
Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.2 ks of XRT data for GRB 160408A (Evans et al. GCN
Circ. 19260), from 103 s to 23.4 ks after the BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Osborne et al. (GCN Circ. 19261).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.3 (+/-0.3).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.1 (+/-0.4). The
best-fitting absorption column is 1.6 (+1.4, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 4.2 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 3.4 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.6 (+1.4, -1.1) x 10^21 cm^-2
Galactic foreground: 4.2 x 10^20 cm^-2
Excess significance: 1.9 sigma
Photon index: 2.1 (+/-0.4)
If the light curve continues to decay with a power-law decay index of
1.3, the count rate at T+24 hours will be 8.4 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x
10^-15 (3.8 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/00682059.
This circular is an official product of the Swift-XRT team.
GCN Circular 19267
Subject
GRB 160408A: Swift/UVOT Upper Limits
Date
2016-04-08T20:15:45Z (9 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and P. A. Evans (U Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 160408A
98 s after the BAT trigger (Evans et al., GCN Circ. 19260).
No optical afterglow consistent with the XRT position
(Osborne et al. GCN Circ. 19261) or the possible
optical counterparts (Levan et al., GCN Circ. 19262)
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 98 248 147 >21.0
u_FC 311 561 246 >19.7
white 98 1365 373 >21.8
v 641 1414 97 >19.4
b 566 1340 78 >19.6
u 311 1316 304 >19.9
w1 691 1291 58 >19.5
m2 838 1092 39 >18.8
w2 617 1390 97 >19.9
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 19268
Subject
GRB 160408A: TLS Tautenburg observations
Date
2016-04-09T09:34:20Z (9 years ago)
From
Sebastian Schmidl at TLS Tautenburg <schmidl@tls-tautenburg.de>
J. I. Avalos (University of Leipzig), N. P. Plaza (Universidad Autonoma de
Madrid), M. Blunck (University of Leipzig), L. Lalounta (University of
Patras), E. Komucyeya (Mbarara University), S. Schmidl, S. Klose, D. A.
Kann, A. Nicuesa Guelbenzu, and F. Ludwig (all TLS Tautenburg) report:
We observed the field of the short GRB 160408A (Evans et al., GCN
19260) with the Tautenburg 1.34-m Schmidt telescope at as mid-time of about
15.3 hrs after the GRB trigger, at a mean airmass of 1.2. We obtained 10 x
300 sec exposures in the Ic band.
Inside the 1".9 enhanced XRT error circle (Osborne et al.,GCN 19261),
we do not detect the possible optical counterparts reported by Levan et
al. (GCN Circ. 19262). We estimate a preliminary upper limit of Ic > 21.3
mag, calibrated against USNO-B1 field stars.
These observations were performed as part of the Tautenburg Observing
School at the Thueringer Landessternwarte.
[GCN OPS REPORT(14apr16): Per author's request, the institutional affiliations
of the authors was corrected, and the last sentence was added.]
GCN Circular 19269
Subject
GRB 160408A: Gemini afterglow confirmation
Date
2016-04-09T15:04:49Z (9 years ago)
From
Andrew Levan at U.of Leicester <A.J.Levan@warwick.ac.uk>
A.J. Levan (U. Warwick), N.R. Tanvir (U. Leicester), A. Cucchiara (GSFC/STScI), W. Fong (Arizona), D. Perley (DARK/NBI) report for a larger collaboration:
���We obtained a second epoch of Gemini-North observations of the short GRB 160408A (Evans et al. GCN 19260, Palmer et al. GCN 19263) on 9 April 2016, approximately 22 hours after our previous observations. Although the images are somewhat shallower than the first epoch, the previously identified source A (Levan & Tanvir GCN 19262) has clearly faded by at least a magnitude between the two epochs, and is not detected in our new imaging. This confirms it as the optical afterglow of GRB 160408A.���
GCN Circular 19270
Subject
GRB 160408A: GMG observation limit
Date
2016-04-10T02:50:48Z (9 years ago)
From
Jirong Mao at Yunnan Obs <jirongmao_obs@ynao.ac.cn>
W.-M. Yi, J. Mao and J.-M. Bai (YNAO) report:
We observed the field of GRB 160408A (Evans et al., GCN 19260) with the 2.4-meter optical telescope at Gao-Mei-Gu (GMG)
station of Yunnan Observatories. Observations began from 15:10:26 UT, Apr. 8th, 2016, about 9 hours after the trigger.
We did not detect any source at the afterglow position (Levan et al. GCN 19269) down to a limit of R~23.3 mag.
GCN Circular 19294
Subject
GRB 160408A: 6.0 GHz VLA upper limit
Date
2016-04-11T19:13:39Z (9 years ago)
From
Wen-fai Fong at U of Arizona <wfong@email.arizona.edu>
W. Fong (University of Arizona) reports:
"We observed the field of the short-duration GRB 160408A (Evans et al., GCN
19260) with the Karl G. Jansky Very Large Array (VLA) beginning on 2016 Apr
8.889 UT (14.91 hr post-burst) at a mean frequency of 6.0 GHz. In 1 hour of
observations, we do not detect any radio source within or around the
enhanced XRT position (Osborne et al., GCN 19261) or the optical afterglow
position (Levan et al., GCNs 19262, 19269) to a 3-sigma limit of 21.5
microJy. We therefore place a 3-sigma limit of 21.5 microJy on the radio
afterglow of GRB 160408A at 14.91 hr after the burst.
We thank the VLA staff for quickly executing these observations."
GCN Circular 19297
Subject
GRB 160408A: CALET Gamma-Ray Burst Monitor detection
Date
2016-04-12T02:48:31Z (9 years ago)
From
Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>
W. Ishizaki (ICRR), A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama,
Y. Yamada (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), I. Takahashi (IPMU),
Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena)
and the CALET collaboration:
The short-duration GRB 160408A (Swift, Evans et al. GCN Circ. 19260;
Fermi-GBM, Roberts et al. GCN Circ. 19265; INTEGRAL-ACS, Trigger #7441)
triggered the CALET Gamma-Ray Burst Monitor (CGBM) at 6:25:37.4 on
8 April 2016. The burst signal was detected by all CGBM instruments.
The light curve of the SGM shows a single peak. The emission starts at T0+6.4 sec,
peaks at T0+6.5 sec and ends at T0+7.1 sec. The T90 duration
measured by the SGM data is 0.38 +- 0.18 sec (40-1000 keV).
The CGBM data used in this analysis are provided by the Waseda CALET Operation Center
located at the Waseda University.
GCN Circular 19508
Subject
GRB 160408A: 15 GHz upper limits from AMI
Date
2016-06-08T15:12:47Z (9 years ago)
From
Kunal Mooley at Oxford U <kunal.mooley@physics.ox.ac.uk>
K. P. Mooley, T. D. Staley, R. P. Fender (Oxford), G. E. Anderson
(Curtin), T. Cantwell (Manchester), C. Rumsey, D. Titterington, S.
Carey, J. Hickish, Y. C. Perrott, N. Razavi-Ghods, P. Scott (Cambridge),
K. Grainge, A. Scaife (Manchester)
The AMI Large Array robotically triggered on the Swift alert for GRB
160408A (Evans et al., GCN 19260) as part of the 4pisky program, and
subsequent follow up observations were obtained up to 10 days
post-burst. Our observations at 15 GHz on 2016 Apr 08.61, Apr 09.77, Apr
13.87, Apr 15.74, and Apr 19.78 (UT) do not reveal any radio source at
the XRT location (Osborne et al., GCN 19261), with 3sigma upper limits
of 117 uJy, 144 uJy, 102 uJy, 204 uJy, and 145 uJy respectively.
We thank the AMI staff for scheduling these observations. The AMI-GRB
database is a log of all GRB follow up observations with the AMI, and is
available at http://4pisky.org/ami-grb/.