GRB 180418A
GCN Circular 22697
Subject
GRB 180418A: 15 GHz upper limits from AMI
Date
2018-05-10T21:43:58Z (8 years ago)
From
Kunal Mooley at NRAO,Caltech <kmooley@caltech.edu>
J. Bright (Oxford), K. P. Mooley (NRAO, Caltech; Jansky Fellow), R. P.
Fender (Oxford)
We observed the field of GRB 180418A (D'Elia et al., GCN 22646) with the
AMI Large Array at 15.5 GHz. Our observations on 2018 Apr 18.88, Apr
20.89 and Apr 22.86 (UT) (0.61 d, 2.61 d and 4.58 post-burst) do not
reveal any radio source at the XRT location (Goad et al., GCN 22650),
with preliminary 3sigma upper limits of 99 uJy, 81 uJy and 93 uJy
respectively.
We thank the MRAO staff for scheduling these observations. Results from
the AMI short-GRB program are posted on the AMI-GRB database available
at http://4pisky.org/ami-grb/.
GCN Circular 22671
Subject
GRB 180418A: TAROT La Silla observatory early optical observations
Date
2018-04-25T00:27:40Z (8 years ago)
From
Alain Klotz at IRAP-CNRS-OMP <Alain.Klotz@free.fr>
Klotz A., Noysena.K., Atteia J.L. (CNRS-OMP-IRAP),
Boer, M., Eymar, L. (CNRS-ARTEMIS),
Gendre B. (UVI - Etelman Obs.) report:
We imaged the field of GRB 180418A detected by SWIFT
(trigger 826428) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.
The observations started 28s after the GRB trigger
(15s after the notice). The elevation of the field decreased from
6 degrees above horizon and weather conditions were good.
The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
Despite the very elevation we can measure the very
early optical light variation of the OT reported by
Zheng & Filippenko (GCNC 22647). We used NOMAD-1 1149-0186465
as reference star r(AB)=15.23 (according SDSS DR9).
Preliminary analysis gives:
start end r(AB) 1sig
(sec) (sec)
28 36 14.30 0.04
36 43 14.24 0.03
43 51 14.40 0.03
51 58 14.61 0.04
58 66 14.98 0.05
66 73 15.42 0.06
73 81 15.52 0.09
81 88 15.83 0.15
The following images are taken in tracking mode.
We used the same reference star for PSF fitting:
start end r(AB) 1sig
(sec) (sec)
100 130 15.96 0.06
141 171 16.50 0.11
181 211 16.58 0.13
221 251 17.10 0.31
262 292 16.90 0.25
302 392 17.00 0.29
Magnitudes are not corrected for galactic dust extinction.
We note that the maximum brightness of the OT
seems to occured at 40s r(AB)=14.24 followed by
a decay of about alpha=2.7 until 70s. Then the decay
is compatible with alpha=1.1 until 6 min (end of TAROT
observations because the elevation was too low).
GCN Circular 22670
Subject
GRB 180418A: MITSuME Ishigakijima Optical Observation
Date
2018-04-24T02:00:28Z (8 years ago)
From
Ryosuke Itoh at Tokyo Institute of Tech. <itoh@hp.phys.titech.ac.jp>
T. Horiuchi, H. Hanayama, M. Honma (IAO, NAOJ),
R. Itoh, K. Shiraishi, K. Murata, Y. Tachibana and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME and OISTER collaboration:
We observed the field of GRB 180418A (D'Elia et al.,GCN 22646)
with the optical three color (g', Rc and Ic) CCD camera attached
to the Murikabushi 1m telescope of Ishigakijima Astronomical
Observatory.
The observation started on 2018-04-18 13:55:32 UT, (~7 hours after
the burst). We detected the previously reported afterglow
(W. Zheng and A. Filippenko, GCNC22647) in the R band.
The photometric results of the OT are listed below.
We used UCAC-4 catalog for flux calibration.
#T0+[hour] MID-UT T-EXP[sec] g' Rc Ic
-------------------------------------------------------------------
8.6 15:22:01 10380 >22.8 22.4+/-0.5 >22.0
-------------------------------------------------------------------
T0+ : Elapsed time after the burst [hour]
T-EXP: Total Exposure time [sec]
GCN Circular 22668
Subject
GRB 180418A : SQUEAN observations
Date
2018-04-21T15:57:47Z (8 years ago)
From
Changsu Choi at Seoul Nat U <changsu@astro.snu.ac.kr>
Changsu Choi (CEOU/SNU), Yongjung Kim (CEOU/SNU), Woojin Park (KHU), Suhyun
Shin (CEOU/SNU) and Myungshin Im (CEOU/SNU), on behalf of a larger
collaboration
We observed the field of GRB 180418A (Swift BAT trigger 826428; D'Elia et
al., GCN #22646) using SQUEAN installed at 2.1m Otto Struve telescope of
McDonald Observatory in US, on 18th and 19th April (UT).
The optical counter part of GRB180418A was clearly detected by observation
on 18th April, starting from 2018-04-18T08:18:27 to 08:31:38 UT which is
0.065 days to 0.0742 after BAT trigger.
No obvious source is found in the images taken on 2018-04-19 (UT).
The preliminary photometry results are given below.
All magnitudes are reported in AB magnitudes. The photometric calibration
is based on the stars in SDSS catalog in the observed field. No galactic
extinction correction is applied.
Date t-T0 Filter Exp. Magnitude Error
(UT, start) (mid, days) (s) (3" aperture)
2018-04-18T08:18:27 0.065 r 60*3 20.44 0.07
2018-04-18T08:22:53 0.068 i 60*3 20.34 0.04
2018-04-18T08:25:02 0.070 r 60*6 20.47 0.06
2018-04-18T08:27:48 0.072 z 60*3 20.61 0.12
2018-04-18T08:31:38 0.075 r 60*3 20.57 0.08
GCN Circular 22666
Subject
GRB 180418A: Further GROND observations
Date
2018-04-20T14:14:21Z (8 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
P. Schady and T.-W. Chen (both MPE Garching) report:
We re-observed the field of GRB 180418A (Swift trigger 826428; D'Elia et
al., GCN #22646) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) on 20th April, at a mid-time of 02UT. Observations
were performed at an average seeing of 1.2" and at an average airmass of
1.7.
Compared to the previous night of GROND observations (Schady, GCN #22662),
the target has decayed by ~0.8dex in the r'-band. Based on around 60
minutes of data, the estimated AB magnitudes from the second epoch of
GROND observations are:
g' = 24.5 +/- 0.2 mag
r' = 24.0 +/- 0.1 mag
i' = 23.4 +/- 0.2 mag
z' > 23.5 mag
J > 21.7 mag
H > 21.1 mag
K > 19.5 mag
Given magnitudes are calibrated against SDSS and 2MASS field stars, and
they are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E(B-V)=0.01 mag in the direction of the
burst (Schlafly & Finkbeiner 2011).
We thank Sam Kim for his excellent support from La Silla.
GCN Circular 22665
Subject
GRB 180418A: Swift/UVOT Detection
Date
2018-04-19T22:05:17Z (8 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 180418A
3086 s after the BAT trigger (D'Elia et al., GCN Circ. 22646).
A fading source consistent with the XRT position
(Goad et al. GCN Circ. 22650)
is detected in the initial UVOT exposures, confirming the previously
reported optical afterglows (Zheng & Filippenko, GCN Circ. 22647; Guidorzi
et al., GCN Circ. 22648; Troja et al., GCN Circ. 22652; Fong et al., GCN
Circ. 22659; Malesani et al., GCN Circ. 22660; Schady et al., GCN Circ. 22662;
Misra et al., GCN Circ. 22663).
The preliminary UVOT position is:
RA (J2000) = 11:20:29.21 = 170.12172 (deg.)
Dec (J2000) = +24:55:59.2 = 24.93311 (deg.)
with an estimated uncertainty of 0.49 arc sec. (radius, 90% confidence).
Preliminary detections 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 (fc) 3087 3236 147 19.19+-0.11
white 3087 4470 344 19.45+-0.09
white 49806 72093 4850 >22.62
v 3243 4835 347 >19.53
b 4064 4264 196 >20.19
b 15510 16114 590 >20.82
u (fc) 3859 4059 196 19.35+-0.24
u 14598 31858 894 >20.73
uvw1 3655 3855 196 19.19+-0.28
uvw1 9720 27635 1206 20.02+-0.21
uvm2 3450 3649 196 18.93+-0.27
uvm2 8814 26975 2165 20.65+-0.26
uvw2 4476 4676 196 >19.69
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 22664
Subject
GRB 180418A: Continued RATIR Optical Observations
Date
2018-04-19T13:35:19Z (8 years ago)
From
Eleonora Troja at GSFC <eleonora.troja@nasa.gov>
Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM),
Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB),
Antonino Cucchiara (UVI), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM),
Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and
Vicki Toy (UMD) report:
We re-observed the field of GRB 180418A (D'Elia, et al., GCN 22646) 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 2018/04 19.13 to 2018/04 19.41 UTC
(20.47 to 27.09 hours after the BAT trigger), obtaining a total of
4.17 hours exposure in the r and i bands.
The optical afterglow (Zheng & Filippenko, GCN 22647) is detected in all
bands and significantly faded with respect to our first night of
observations (Troja et al., GCN 22652). In comparison with the
SDSS DR9 catalog, we obtain the following detections:
�� r = 23.63 +/- 0.22
�� i = 23.14 +/- 0.16
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.
GCN Circular 22663
Subject
GRB 180418A: Imaging of the optical afterglow with the 1.3 m DFOT and 3.6 m DOT in ARIES, India
Date
2018-04-19T10:24:49Z (8 years ago)
From
Kuntal Misra at ARIES,India <kuntal@aries.res.in>
Kuntal Misra, Abhishek Paswan, Mridweeka Singh, S. B. Pandey, T. S. Kumar, Amitesh Omar (ARIES, Nainital, India) report
We observed the field of GRB 180418A (D���Elia et al. GCN 22646) with the facilities at the Devasthal Observatory, operated by ARIES India, located in the Central Himalayan region. Observations were triggered around 2018-04-18T14:41 UT (nearly 8 hours after the burst) with the 1.3 m Devasthal Fast Optical Telescope (DFOT) in r and i bands and with the newly commissioned 3.6 m Devasthal Optical Telescope (DOT) in griz bands. The afterglow is not detected in co-added images in r and i bands of 3x300 sec each taken with DFOT. However, we detect a faint source consistent with the position of the optical afterglow (Zheng et al. GCN 22647, Guidorzi et al. GCN 22648, Troja et al. GCN 22652, Fong et al. GCN 22659, Malesani et al. 22660) at a magnitude of 22.3+/-0.1 in r band with the ARIES Devasthal Faint Object Spectrograph Camera (ADFOSC) mounted on the 3.6 m DOT. The magnitudes are calibrated with respect to the nearby stars and are not corrected for Galactic extinction.
Further analysis is in progress and more observations are planned to get deeper images.
We thank the DOT operation team for successfully conducting the observations.
GCN Circular 22662
Subject
GRB 180418A GROND observations
Date
2018-04-19T10:03:15Z (8 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
The field of GRB 180418A (Swift trigger 826428; D'Elia et al., GCN #22646)
was observed 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 01:27 UT on 19th April, 18.7 hours after the GRB
trigger. They were performed at an average seeing of 1.5" and at an
average airmass of 1.7.
A source is detected in the g'r'i' bands at a position consistent with the
X-ray and optical afterglow (Zheng et al., GCN #22647; Goad et al., GCN
#22650). The source is not clearly point-like, and it is therefore
possible that some host galaxy light is contributing to the flux. Based on
22 min of exposure in g'r'i'z' and 20 min in JHK, the estimated AB
magnitudes are:
g' = 23.60 +/- 0.14 mag
r' = 23.24 +/- 0.13 mag
i' = 22.88 +/- 0.21 mag
z' > 22.96 mag
J > 21.16 mag
H > 20.67 mag
K > 18.82 mag
Given magnitudes are calibrated against SDSS for g'r'i'z' and 2MASS field
stars for JHK, and they are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E(B-V)=0.01 mag in
the direction of the burst (Schlafly & Finkbeiner 2011).
I thank Sam Kim for his excellent support from La Silla.
GCN Circular 22661
Subject
GRB 180418A: Xinglong TNT optical upper limit
Date
2018-04-19T02:51:03Z (8 years ago)
From
L.P. Xin at NAOC <xlp@nao.cas.cn>
L. P. Xin, J. Z. Yan, J. Y. Wei, Y. L. Qiu, J. S. Deng,
J. Wang, X. H. Han, X. M. Meng, C. Wu, D. TURPIN, H. L. Li report:
We began to observe GRB 180418A (D'Elia et al., GCN 22646)
with Xinglong 0.8-m TNT telescope, China, at 2018-04-18, 14:23:11(UT),
about 7.8 hours after the burst.
We obtained 10 R-band images with an exposure time of 300 sec for each frame.
The optical afterglow (Zheng & Filippenko, GCN 22647;
Guidorzi et al., GCN 22648; Troja et al., GCN 22652; Fong et al., GCN
22659; Malesani et al., GCN 22660 ) was not detected in our stacked image with 10*300 sec.
The 3 sigma upper limit is estimated to be about R~20 mag calibrated
by USNO B1.0 R2 mag at about 8.2 hours after the burst,
We acknowledge the excellent support from Xinglong staff YunPeng Wang.
GCN Circular 22660
Subject
GRB 180418A: NOT optical observations
Date
2018-04-19T00:20:53Z (8 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
Daniele Malesani (DAWN/NBI and DARK/NBI), Kasper Elm Heintz (Univ.
Iceland and DAWN/NBI), Maria Stone (Univ. Turku), and James Stone,
report on behalf of a larger collaboration:
We observed the optical afterglow (Zheng & Filippenko, GCN 22647;
Guidorzi et al., GCN 22648; Troja et al., GCN 22652; Fong et al., GCN
22659) of GRB 180418A (D'Elia et al., GCN 22646) with the 2.5-m Nordic
Optical Telescope (NOT) equipped with StanCam.
Observations were carried out in the Bessel R filter, but calibrated
against SDSS r-band Pan-STARRS local photometry. A low S/N source is
detected at a position consistent with previous reports.
At a mid time of April 18.936 UT (15.72 hr after the trigger), we
measure for the counterpart r = 22.70 +- 0.15 AB.
Compared to the Gemini-North measurement (Fong et al., GCN 22659), we
infer a decay slope alpha = 0.75 +- 0.17, assuming F(t) propto t^-alpha.
GCN Circular 22659
Subject
GRB 180418A: Gemini-North imaging and spectroscopy
Date
2018-04-18T22:46:13Z (8 years ago)
From
Wen-fai Fong at Northwestern U <wfong@northwestern.edu>
W. Fong (Northwestern Univ.), N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick), and R. Chornock (Ohio Univ.) report on behalf of a larger collaboration:
"We observed the location of the short-duration GRB 180418A (D'Elia et al., GCN 22646) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini-North 8-meter telescope. We obtained 4x120-sec each in the griz-bands at a mid-time of 2018 April 18.451 UT (4.09 hr post-burst) in 0.7-1" seeing over an airmass range of 1.2-1.5. We detect the optical afterglow (Zheng et al., GCN 22647, Guidorzi et al., GCN 22648, Troja et al., GCN 22652) in all bands with the following preliminary magnitudes:
g = 22.0 +/- 0.1
r = 21.6 +/- 0.2
i = 21.2 +/- 0.2
z = 21.9 +/- 0.4
All magnitudes are reported in the AB system, calibrated to SDSS, and not corrected for Galactic extinction. Notably, the most nearby source in projection is 13.3" from the optical afterglow position, although it is difficult to tell whether the source is point-like or extended in our images. There are otherwise no clearly-extended sources within 30" of the optical afterglow position (corresponding to 185 kpc at z~0.5) to 3-sigma limits of g>23.4 AB mag, r>22.5 AB mag.
In addition, we obtained 4x900-sec of GMOS spectroscopy of the optical afterglow at a mid-time of 2018 April 18.382 UT (2.44 hr post-burst) at an airmass of 1.1. No prominent features can be identified, beyond a blue continuum. Analysis is ongoing.
Further observations are planned. We thank the Gemini staff, and in particular observers Jason Chu and Michael Hoenig, for their assistance with these observations."
GCN Circular 22658
Subject
GRB 180418A: Swift-BAT refined analysis
Date
2018-04-18T22:09:29Z (8 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), V. D'Elia (ASDC),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), J. P. Norris (BSU),
T. Sakamoto (AGU), M. Stamatikos (OSU), 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 downlink,
we report further analysis of BAT GRB 180418A (trigger #826428)
(D'Elia et al., GCN Circ. 22646). The BAT ground-calculated position is
RA, Dec = 170.132, 24.925 deg which is
RA(J2000) = 11h 20m 31.6s
Dec(J2000) = +24d 55' 28.9"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
The mask-weighted light curve shows a single FRED-like pulse that starts
at ~T0, peaks at ~T+0.4 s, and ends at ~T+3.5 s. T90 (15-350 keV)
is 2.29 +- 0.83 sec (estimated error including systematics).
The time-averaged spectrum from T+0.10 to T+3.50 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.44 +- 0.12. The fluence in the 15-150 keV band is 3.2 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.23 sec in the 15-150 keV band
is 3.0 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The duration and hardness of this burst show it to be intermediate between the
short and long burst populations.
Using a 16-ms binned light curve, the lag analysis finds a lag of 0.1000 +/- 0.026 s
for the 100-350 keV to 25-50 keV band, and 0.088 +/- 0.026 s for the 50-100 keV
to 15-25 keV band. These values are also intermediate between canonical short and
long GRBs.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/826428/BA/
GCN Circular 22657
Subject
GRB 180418A: 1.5m OSN optical observations
Date
2018-04-18T20:57:12Z (8 years ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
A. Sota, Y. Hu, J. C. Tello, I. Carrasco and A. J. Castro-Tirado
(IAA-CSIC), on behalf of a larger collaboration, report: "Following the
detection of GRB 180418A with the Neil Gehrels Swift Observatory (D'Elia
et al. GCNC 22646), I-band observations at the 1.5m telescope at
Observatorio de Sierra Nevada (Granada, Spain) have been gathered on Apr
18 starting at 19:49 UT (13 hr post burst). At the position of the
optical afterglow (Zheng and Filippenko, GCNC 22647; Guidorzi et al.,
GCNC 22648; Troja et al., GCNC 22652), no counterpart is detected down
to I = 21.0 in the coadded image (5x300s)."
GCN Circular 22656
Subject
GRB 180418A: Fermi GBM observation
Date
2018-04-18T20:00:05Z (8 years ago)
From
Peter Veres at UAH <veresp@gmail.com>
E. Bissaldi (Politecnico & INFN Bari) and P. Veres (UAH)
report on behalf of the Fermi GBM Team:
"At 06:44:06.28 UT on 18 April 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180418A (trigger 545726651 / 180418281),
which was also detected by the Swift/BAT (D'Elia et al. 2018, GCN 22646).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight at the GBM trigger time is 78 degrees.
The GBM light curve consists of a signle FRED-like peak,
with a duration (T90) of about 2.5 s (50-300 keV).
The time-averaged spectrum from T0-0.06 s to T0+0.77 s is
adequately fit by a simple power law function with index -1.52 +/- 0.03.
The event fluence (10-1000 keV) in this time interval is
(7.6 +/- 0.4)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.26 s in the 10-1000 keV band
is 7.56 +/- 1.13 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 22655
Subject
GRB 180418A: Swift-XRT refined Analysis
Date
2018-04-18T19:38:07Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
Z. Liu (NAOC / U. Leicester), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte
(PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and V.
D'Elia report on behalf of the Swift-XRT team:
We have analysed 6.7 ks of XRT data for GRB 180418A (D'Elia et al. GCN
Circ. 22646), from 3.1 ks to 31.9 ks after the BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Goad et al. (GCN Circ. 22650).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.09 (+0.18, -0.16).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.02 (+0.28, -0.26). The
best-fitting absorption column is 8.0 (+7.1, -5.8) x 10^20 cm^-2, in
excess of the Galactic value of 1.1 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 3.2 x 10^-11 (3.8 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 8.0 (+7.1, -5.8) x 10^20 cm^-2
Galactic foreground: 1.1 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index: 2.02 (+0.28, -0.26)
If the light curve continues to decay with a power-law decay index of
1.09, the count rate at T+24 hours will be 3.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (1.3 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/00826428.
This circular is an official product of the Swift-XRT team.
GCN Circular 22652
Subject
GRB 180418A: RATIR Optical Observations
Date
2018-04-18T12:45:53Z (8 years ago)
From
Eleonora Troja at GSFC <eleonora.troja@nasa.gov>
Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM),
Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB),
Antonino Cucchiara (UVI), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM),
Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and
Vicki Toy (UMD) report:
We observed the field of GRB 180418A (D'Elia, et al., GCN 22646) 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 2018/04 18.28 to 2018/04 18.43 UTC
(1.8 minutes to 3.64 hours after the BAT trigger), obtaining a total of
2.57 hours exposure in the r and i bands.
At the position of the optical afterglow (Zheng & Filippenko, GCN 22647),
in comparison with the SDSS DR9 catalog, we obtain the following
detection:
�� r������ = 19.95 +/- 0.01
This magnitude is in the AB system and is not corrected for Galactic
extinction in the direction of the GRB.
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.
Further observations are planned.
GCN Circular 22650
Subject
GRB 180418A: Enhanced Swift-XRT position
Date
2018-04-18T10:19:03Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.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 1679 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 180418A, 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 = 170.12153, +24.93309 which is equivalent
to:
RA (J2000): 11h 20m 29.17s
Dec (J2000): +24d 55' 59.1"
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 22649
Subject
GRB 180418A: Swift-XRT observations
Date
2018-04-18T08:12:24Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne (U. Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU), G.
Cusumano (INAF-IASF PA), M. Perri (ASDC) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:
The XRT began observing the field of GRB 180418A at 07:35:27.5 UT,
3081.4 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 170.12059,
24.93276 which is equivalent to:
RA(J2000) = 11h 20m 28.94s
Dec(J2000) = +24d 55' 57.9"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 88 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 consistent with the Galactic value of 1.07
x 10^20 cm^-2 (Willingale et al. 2013).
GCN Circular 22648
Subject
GRB 180418A: LCO FTN afterglow confirmation
Date
2018-04-18T07:47:13Z (8 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell
(U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a
large collaboration report:
The LCO 2-m Faulkes Telescope North (Hawaii) began observing Swift short
GRB 180418A (D'Elia et al. GCN 22646) on April 18, 07:18:19 UT (34
minutes since the GRB) with the SDSS-I filter. We clearly detect the
optical afterglow (Zheng et al. GCN 22647) with the following magnitude:
Mid time since GRB���� Exp������� Filter�������� Magnitude
(hrs)����������������� (s)
------------------------------------------------------------
0.62������������������ 5x60������ SDSS-I�������� 19.2 +- 0.1
------------------------------------------------------------
as calibrated against nearby SDSS objects.
GCN Circular 22647
Subject
GRB 180418A: KAIT Optical Afterglow Candidate
Date
2018-04-18T07:18:14Z (8 years ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
GRB 180418A: KAIT Optical Afterglow Candidate
WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 180418A (D'Elia et al.,
GCN 22646 starting at 06:46:41 UT, 125 s after the burst.
Observations were performed with an automatic sequence in the
clear (roughly R), V, and I filters, and the exposure time was 20 s
per image. Inside the Swift/BAT position error circle we
detected an afterglow candidate at position:
RA: 11:20:29.20 (j2000)
Dec: 24:55:58.8 (j2000)
The clear band magnitude declined from Mag ~15.8 to ~17.2 during our
observations.
Observation are on going, multi-band follow-ups are encouraged.
GCN Circular 22646
Subject
GRB 180418A: Swift detection of a short burst
Date
2018-04-18T06:55:40Z (8 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), P. A. Evans (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), B. Sbarufatti (PSU),
M. Stamatikos (OSU/NASA/GSFC) and A. Tohuvavohu (PSU) report on behalf
of the Neil Gehrels Swift Observatory Team:
At 06:44:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180418A (trigger=826428). Swift could not immediately slew
to the burst due to an observing constraint.
The BAT on-board calculated location is
RA, Dec 170.112, +24.956 which is
RA(J2000) = 11h 20m 27s
Dec(J2000) = +24d 57' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single peak
structure with a duration of about 1.5 sec. The peak count rate
was ~8000 counts/sec (15-350 keV), at ~0 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+49.6
minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it).
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.)