GRB 150423A
GCN Circular 17803
Subject
GRB 150423A: GMG observation limit
Date
2015-05-05T02:09:50Z (11 years ago)
From
Jirong Mao at Yunnan Obs <jirongmao_obs@ynao.ac.cn>
J. Mao, Y. Fan and J.-M. Bai (YNAO) report:
We observed the field of GRB 150423A (Pagani et al., GCN 17728) with the 2.4-meter optical telescope at Gao-Mei-Gu (GMG) station of Yunnan Observatory. Observations began from 17:11:14 UT, May 2nd, 2015, about 9 days after the trigger. We did not
detect any source / rebrightening feature at the afterglow position down to a limit of z~21.0 mag with poor observational condition.
GCN Circular 17801
Subject
GRB 150423A: Chandra X-ray Observation
Date
2015-05-03T16:46:10Z (11 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
E. Berger, R. Margutti (Harvard), and W. Fong (Univ. of Arizona) report:
"We observed the location of the short GRB 150423A (GCN #17728) with the
Chandra X-ray Observatory ACIS-S instrument starting on 2015 May 2.308 UT
for a total of 23.3 ksec. At the location of the optical afterglow (GCNs
#17732, 17733) we detect no significant X-ray emission, and place an upper
limit on the count rate of 1.3e-4 cps (1" radius aperture). Using the
spectral properties determined from the Swift/XRT data (GCN #17737) we
place an upper limit on the flux of the X-ray afterglow at 9.17 days
post-burst of 1.7e-15 erg/s/cm^2 (0.3-10 kev).
We thank Belinda Wilkes, Harvey Tananbaum, and the Chandra X-ray
Observatory staff for approving and carrying out this Director's
Discretionary Time observation."
GCN Circular 17798
Subject
GRB 150423A: JCMT SCUBA-2 sub-mm observation
Date
2015-05-01T22:08:22Z (11 years ago)
From
Ian Smith at Rice U <ian@spacsun.rice.edu>
I.A. Smith (Rice U.), N.R. Tanvir (U. of Leicester) report:
We observed the location of the short GRB 150423A (Pagani et al.,
GCN Circ. 17728) using the SCUBA-2 sub-millimeter continuum camera
on the James Clerk Maxwell Telescope. The observation started at
07:21 UT on 2015-04-23, corresponding to 53 minutes after the burst
trigger. Exposures totaling 2.0 hours were made in good weather
conditions. No source was detected, with the RMS background noise
being 1.5 mJy/beam at 850 microns and 17.4 mJy/beam at 450 microns.
We thank Callie Matulonis, Angus Mok, and Iain Coulson for the
prompt support of these observations that were taken under project
M15AI86.
GCN Circular 17763
Subject
GRB 150423A: MITSuME Akeno Optical observation
Date
2015-04-27T05:50:43Z (11 years ago)
From
Taketoshi Yoshii at Tokyo Tech <yoshii.t.ac@m.titech.ac.jp>
S.Harita, T.Fujiwara, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, Y. Yano,
S. Kurita, Y.Ono, Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:
We searched for the optical counterpart of GRB 150423A (C. Pagani et al. GCN Circular #17728) with the
optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan.
The observation started on 2015-04-23 13:03:48 UT (~6.6 h after the burst).
We did not find any new point source within XRT circle in all three bands.
We obtained following limits for the magnitudes.
T0+[sec] MID-UT T-EXP[sec] g' Rc Ic
---------------------------------------------------------------------------------------
23744 16:26:45 2940 >19.4 >19.3 > 18.4
---------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used GSC2.3 catalog for flux calibration
GCN Circular 17755
Subject
GRB 150423A: VLT/X-shooter spectroscopy and tentative redshift
Date
2015-04-24T22:10:20Z (11 years ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
D. Malesani (DARK/NBI), T. Kruehler (ESO), D. Xu (NAOC/CAS), G. Pugliese (API/Uva), D. Watson, J. P. U. Fynbo, B. Milvang-Jensen (DARK/NBI), A. de Ugarte Postigo (IAA/CSIC and DARK/NBI), N. R. Tanvir (U. Leicester), V. D'Elia (ASI/ASDC and INAF/Roma), K. Wiersema (U. Leicester), J. Greiner(MPE Garching), J. Japelj (U. Ljubljana) report on behalf of a larger collaboration:
We observed the optical afterglow (Varela et al., GCNs 17729, 17732, Perley, GCN 17733, Littlejohns et al. GCN 17736, Kann et al. GCN 17738, Fong & Milne GCN 17741) of the Swift short-GRB 150423A (Pagani et al. GCN 17728) with the VLT equipped with the X-shooter spectrograph in the rapid response mode (RRM).
A series of individual spectra with a total exposure time of around 5000 s were obtained starting on 2015-04-23 06:50 UT, which is 22 minutes after the BAT trigger.
A preliminary analysis of the spectrum reveals a faint and blue continuum detected down to 3200 AA. This sets a robust upper limit of z < 2.5 to the redshift of the GRB. Similarly to Perley (GCNs 17733, 17744), we do not detect obvious absorption or emission features in our spectra. There is, however, a tentative detection of a doublet in absorption at around 6900 AA. If real, the lines match the Mg II doublet at a redshift of z = 1.394.
We acknowledge the excellent support provided by Paranal staff, and in particular Fernando Selman and Emanuela Pompei.
GCN Circular 17754
Subject
GRB 150423A: Continued RATIR optical afterglow monitoring
Date
2015-04-24T19:01:43Z (11 years ago)
From
Owen Littlejohns at Az State U <olittlej@asu.edu>
Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM),
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), 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 again observed the field of GRB 150423A (Pagani, et al., GCN 17728)
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 2015/04 24.18 to 2015/04 24.48
UTC (21.74 to 28.97 hours after the BAT trigger), obtaining a total of
5.69 hours exposure in the r, i and z bands.
For a source within the Swift-XRT error circle (Evans, et al., GCN
17735), in comparison with the SDSS DR9, we obtain the following upper
limits (3-sigma):
r > 24.82
i > 24.79
z > 22.07
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. In comparison to the earlier
epoch of RATIR observations (Littlejohns, et al., GCN 17736), these upper
limits indicate fading of at least 1 magnitude in the r and i bands. This
implies a continuing power-law decay temporal power-law index of t^-0.5
or steeper, which is consistent with the comparison between the first
epoch of RATIR observations and the earlier GROND measurements (Varela,
et al., GCN 17732). The magnitude of source 2, as reported in the GROND
observations, is consistent with being constant in both epochs of RATIR
data.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro
M�rtir.
GCN Circular 17750
Subject
GRB 150423A: TSHAO optical observations
Date
2015-04-24T14:37:06Z (11 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
E. Mazaeva (IKI), A. Volnova (IKI), A. Kusakin (Fesenkov Astrophysical
Institute), A. Pozanenko (IKI) report on behalf of larger GRB follow-up
collaboration:
We observed the field of GRB 150423A (Pagani et al., GCNC 17728) with
Zeiss-1000 (East) 1-m telescope of Tien Shan Astronomical Observatory
starting on Apr. 23 (UT) 17:43:02. We obtained several images in R-filter.
In a combined image we marginally detect the source S2 and do not detect the
afterglow (Varela et al., GCN 17729). Coordinates of the S2 (J2000) 14 46
18.94 +12 17 04.4 with an uncertainty of 0.4" is marginally coincide with
coordinates reported by Varela et al. (GCN 17729).
A preliminary photometry is following
date UT start t-T0 Filter Exp. S1 S2
S2_err
(mid, days) (s)
2015-04-23 17:43:02 0.57561 R 25*600 >22.7 22.7 0.3
and based on nearby SDSS DR9 stars:
SDSS9_id R(Lupton)
J144606.22+121513.3 15.42
J144647.40+121502.9 17.54
J144648.52+121523.3 15.15
GCN Circular 17747
Subject
GRB 150423A: WHT observations
Date
2015-04-24T11:35:37Z (11 years ago)
From
Klaas Wiersema at U Leicester <kw113@leicester.ac.uk>
K. Wiersema (Leicester), A. Levan (Warwick), N. Tanvir (Leicester), C. MacLeod
(IfA Edinburgh), F. Riddick (ING) report:
We observed the position of GRB 150423A (Pagani et al. GCN 17728) using the
ACAM instrument on the William Herschel Telescope, at La Palma. We obtained
images with 5 x 300 sec exposure time in both sloan g and z bands, starting at
22:30 UT on 23 April 2015. The nearby galaxy (Varela et al. GCN 17732; Perley et
al. GCN 17744) is clearly detected, but the afterglow (Varela et al. GCN 17732)
is not significantly detected, with a 5 sigma limit of g~25.3 (calibrated using
SDSS field objects). A low significance object may be present near the afterglow
position in g band, as well as some faint galaxies, which may be candidate hosts.
See here for an image of the field:
http://www2.le.ac.uk/departments/physics/people/klaaswiersema/wht-observations-of-grb-150423a/view
GCN Circular 17744
Subject
GRB 150423A: Keck redshift of neighboring galaxy
Date
2015-04-24T09:15:25Z (11 years ago)
From
Daniel Perley at Caltech <dperley@astro.caltech.edu>
D. A. Perley (Caltech) reports:
Further to GCN 17733, I report analysis of the spectroscopy acquired of
S2, the neighboring object located 4.0 arcseconds northeast of the
optical afterglow of GRB 150423A, first announced by Varela et al. (GCN
17732).
The spectrum of this object shows weak emission lines from OII (3727),
OIII (5007), Halpha (6563), and marginally Hbeta (4861), all at a common
redshift of z=0.456. No features are visible in the trace of S1 at any
of the same wavelengths (or elsewhere in its spectrum).
At this redshift, the offset between the sources corresponds to 23 kpc
in projection.
Further observations of S1 will be necessary to determine whether it is
entirely afterglow or if it also contains flux from a (coincident) host
galaxy, perhaps at a different redshift.
GCN Circular 17742
Subject
GRB 150423A: MITSuME Okayama upper limits
Date
2015-04-24T06:46:33Z (11 years ago)
From
Daisuke Kuroda at OAO/NAOJ <dikuroda@oao.nao.ac.jp>
D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of MITSuME and OISTER collaboration:
We observed the field of GRB 150423A (Pagani et al., GCNC 17728)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2015-04-23 17:04:40 UT, (~10.6 h after the burst).
We could not detect the previously reported afterglow (Varela et al., GCNC
17729,17732; Perley, GCNC 17233) in all the three bands.
Three sigma upper limits of the OT are listed below.
We used SDSS-DR8 catalog for flux calibration.
#T0+[day] MID-UT T-EXP[sec] g' Rc Ic
-----------------------------------------------------
0.49107 18:15:13 7200.0 >20.8 >20.8 >19.9
-----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]
GCN Circular 17741
Subject
GRB 150423A: UKIRT NIR observations
Date
2015-04-24T02:53:39Z (11 years ago)
From
Wen-fai Fong at U of Arizona <wfong@email.arizona.edu>
W. Fong and P. Milne (University of Arizona) report on behalf of a larger
collaboration:
"We observed the field of the Swift short-duration GRB 150423A (Pagani et
al., GCN 17728) with UFTI mounted on the 3.8-m United Kingdom Infrared
Telescope (UKIRT) on Mauna Kea beginning on 2015 April 23.337 UT, at an
average airmass of 1.1 in 0.55" seeing. We obtained 6600 sec of J-band
imaging at a mid-time of 2.72 hr post-burst, and 6300 sec of K-band imaging
at a mid-time of 4.93 hr post-burst. The afterglow (Source 1; Varela et
al., GCN 17732; Perley, GCN 17733; Littlejohns et al., GCN 17736; Kann et
al., GCN 17738) is weakly detected in both the J- and K-bands. We cannot
establish fading over the course of our observations due to the weak
detection of the source. We note that Source 2 (Varela et al., GCN 17732)
is only detected in K-band.
Further observations are planned."
GCN Circular 17740
Subject
GRB 150423A: Swift-BAT refined analysis
Date
2015-04-23T22:07:16Z (11 years ago)
From
Tilan Ukwatta at LANL <tilan.ukwatta@gmail.com>
T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
C. Pagani (U Leicester), 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+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 150423A (trigger #638808)
(Pagani, et al., GCN Circ. 17728). The BAT ground-calculated position is
RA, Dec = 221.601, 12.264 deg which is
RA(J2000) = 14h 46m 24.2s
Dec(J2000) = +12d 15' 50.6"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.
BAT light curve shows a single peak starting around T+0.0 sec
and ending around T+0.25 sec. T90 (15-350 keV) is 0.22 +- 0.03 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.01 to T+0.24 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
0.84 +- 0.24. The fluence in the 15-150 keV band is 6.3 +- 1.0 x 10^-08
erg/cm2.
The 1-sec peak photon flux measured from T-0.37 sec in the 15-150 keV band
is 0.9 +- 0.1 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/638808/BA/
GCN Circular 17739
Subject
GRB 150423A: Swift/UVOT Upper Limits
Date
2015-04-23T21:00:00Z (11 years ago)
From
Frank Marshall at GSFC <femarsha@khamseen.gsfc.nasa.gov>
F.E. Marshall (NASA/GSFC) and C. Pagani (U. Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150423A
74 s after the BAT trigger (Pagani et al., GCN Circ. 17728).
No optical afterglow consistent with the optical position
(Source 1 in Varela et al. GCN Circ. 17732; Perley GCN Circ. 17733)
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) exposures and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 74 223 147 >20.8
u_FC 286 535 246 >20.2
white 74 6067 733 >21.5
v 615 6477 452 >20.9
b 541 5862 255 >20.9
u 286 6924 513 >20.8
w1 665 6887 452 >20.9
m2 5048 6682 393 >20.8
w2 591 6273 432 >21.6
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 17738
Subject
GRB 150423A: VLT detection
Date
2015-04-23T20:20:49Z (11 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann (TLS Tautenburg), T. Kruehler (ESO Chile), S. Klose (TLS
Tautenburg) and J. Greiner (MPE Garching) report:
We obtained a photometry sequence in BVRIz with VLT FORS2 of the optical
afterglow (Varela et al., GCN # 17729, # 17732; Perley, GCN # 17733;
Littlejohns et al., GCN # 17736) of the short GRB 150423A (Swift-638808,
Pagani et al., GCN # 17728).
Observations started on April 23, 2015, 08:02:19 UT, 94 minutes after the
GRB. Seeing was 1".0 and airmass was 1.7.
The afterglow is clearly detected in BVR. Analysis of Iz is pending.
We find Rc = 22.8 +/- 0.1 in the first image (calibrated against SDSS
standard stars transformed to Rc) and find it fades by approximately 0.4
magnitudes in the course of an hour (see also Perley, GCN # 17733;
Littlejohns et al., GCN # 17736).
We are indebted to Jonathan Smoker and Fernando Selman for VLT UT1 support.
GCN Circular 17737
Subject
GRB 150423A: Swift-XRT refined Analysis
Date
2015-04-23T19:06:53Z (11 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
K.L. Page (U. Leicester), M. de Pasquale (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
C. Pagani report on behalf of the Swift-XRT team:
We have analysed 8.1 ks of XRT data for GRB 150423A (Pagani et al. GCN
Circ. 17728), from 78 s to 28.7 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Evans et al. (GCN Circ. 17735).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.86 (+/-0.09).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.53 (+0.32, -0.21). The
best-fitting absorption column is 2.9 (+10.0, -1.2) x 10^20 cm^-2,
consistent with the Galactic value of 1.8 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 4.2 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 2.9 (+10.0, -1.2) x 10^20 cm^-2
Galactic foreground: 1.8 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.53 (+0.32, -0.21)
If the light curve continues to decay with a power-law decay index of
0.86, the count rate at T+24 hours will be 1.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.0 x
10^-14 (6.2 x 10^-14) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00638808.
This circular is an official product of the Swift-XRT team.
GCN Circular 17736
Subject
GRB 150423A: RATIR optical afterglow monitoring
Date
2015-04-23T17:47:09Z (11 years ago)
From
Owen Littlejohns at Az State U <olittlej@asu.edu>
Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM),
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), 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 150423A (Pagani, et al., GCN 17728) 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 2015/04 23.41 to 2015/04
23.48 UTC (3.30 to 5.01 hours after the BAT trigger), obtaining a
total of 1.42 hours exposure in the r, i and z bands.
For a source within the Swift-XRT error circle (Evans, et al., GCN
17735), in comparison with the SDSS DR9, we obtain the following
detections and upper limits (3-sigma):
r 23.77 +/- 0.23
i 23.62 +/- 0.26
z > 20.33
These magnitudes are in the AB system and are not corrected for
Galactic extinction in the direction of the GRB. Of the two sources
reported by GROND (Varela, et al., GCN 17732), this source is at the
position of source 1. Our observations show a fading of 0.8 magnitudes
in the i band, implying a power-law decay with a temporal index,
t^-0.5. Similarly to the Keck observations (Perley, GCN 17733), we
also find source 2 reported by GROND to have remained at approximately
constant brightness.
Continued observations are planned.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro
M�rtir.
GCN Circular 17735
Subject
GRB 150423A: Enhanced Swift-XRT position
Date
2015-04-23T15:48:49Z (11 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 2017 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 150423A, 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 = 221.57899, +12.28349 which is equivalent
to:
RA (J2000): 14h 46m 18.96s
Dec (J2000): +12d 17' 00.6"
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 17733
Subject
GRB 150423A: Keck optical afterglow confirmation
Date
2015-04-23T14:34:27Z (11 years ago)
From
Daniel Perley at Caltech <dperley@astro.caltech.edu>
D. A. Perley (Caltech) reports:
I acquired observations of the optical afterglow candidate of GRB
150423A (Pagani et al., GCN 17726; Varela et al., GCN 17732) using the
Low Resolution Imaging Spectrometer (LRIS) on the Keck I 10m telescope.
Two epochs of V- and i-band imaging were acquired, the first beginning
at UT 07:13 (approximately 0.75 hours after the trigger, as soon as the
target cleared the telescope Nasmyth limit), the second beginning at UT
13:12 (approximately 6.75 hours after the trigger).
The sources mentioned by Varela et al. are well-detected in both epochs.
Source 2 remains constant between the frames, while Source 1 declines
by approximately 0.9 magnitude in both V- and i-band, confirming that it
is the optical afterglow.
Shortly after the second imaging epoch, I also acquired 1600 seconds of
low-resolution spectroscopy with the slit oriented to cover both S1 and
S2. A faint trace is detected for both sources. Source 2 shows a clear
emission line in the blue arm and at least one marginal emission line in
the red arm, indicating a low to moderate redshift. Source 1 (the
afterglow) shows no clear features in emission or absorption, but the
signal is very weak. Further analysis will reported at a later time
pending wavelength calibration of the spectra.
GCN Circular 17732
Subject
GRB 150423A: GROND afterglow candidate
Date
2015-04-23T13:27:32Z (11 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
K. Varela, F. Knust, and J. Greiner (all MPE Garching)
report on behalf of the GROND team:
Further to Varela et al. (GCN #17729), we report continued observations
of the field of GRB 150423A (Swift trigger 638808; Pagani et al., GCN #17728)
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). The
observations were performed at an average seeing of 1.0 and at an average
airmass of 1.5.
We detect 2 faint sources within or close to the 2.2" XRT error circle:
Source #1, within the XRT error circle:
RA (2000.0) = 14h 46m 18.86s
Decl (2000.0) = +12d 17' 00.7"
with an error of 0.3".
Source #2, just outside the XRT error circle:
RA (2000.0) = 14h 46m 19.04s
Decl (2000.0) = +12d 17' 03.4
with an error of 0.3". This source matches an object visible in the SDSS.
Based on 25.1 min of total exposure time in g'r'i'z' and 20.0 min in JHK,
centered 58 min after the GRB, we estimate the following preliminary magnitudes
(all in AB system).
Source #1:
g' = 23.2 +/- 0.2 mag,
r' = 23.1 +/- 0.2 mag,
i' = 22.8 +/- 0.2 mag,
z' = 22.6 +/- 0.2 mag,
J > 21.6 mag,
H > 21.0 mag, and
Ks > 18.5 mag,
Source #2:
g' = 24.2 +/- 0.2 mag,
r' = 23.3 +/- 0.2 mag,
i' = 23.4 +/- 0.3 mag,
z' = 22.9 +/- 0.2 mag,
J > 21.6 mag,
H > 21.0 mag, and
Ks > 18.5 mag.
The spectral energy distribution of source #1 is best fit with a
power-law of slope beta = 0.8+-0.3 (without significant dust extinction),
typical for GRB afterglows. Also, source #1 is brighter than source #2,
but not visible in the SDSS. While we cannot establish clear fading, we
suggest this object as the afterglow of GRB 150423A.
Given magnitudes are calibrated against SDSS (g'r'i'z') as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.03 mag in the
direction of the burst (Schlegel et al. 1998).
GCN Circular 17730
Subject
GRB 150423A: KAIT Optical Upper Limit
Date
2015-04-23T07:45:42Z (11 years ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
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 150423A (Pagani et al.,
GCN 17728) starting at 06:30:00 UT, 116 s after the burst, under
thin-cloudy condition. 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. We do not detect the optical
source reported by Varela et al. (GCN 17729), in our images, nor
any other new source within the XRT error circle. The typical
limiting magnitude of our single clear image is about 17.0
calibrated to USNO B1.0.
GCN Circular 17729
Subject
GRB 150423A: GROND observation
Date
2015-04-23T07:35:54Z (11 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
K. Varela, F. Knust, J. Bodensteiner and J. Greiner (all MPE Garching)
report on behalf of the GROND team:
We observed the field of GRB 150423A (Swift trigger 638808; Pagani et al.,
GCN #17728) 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 06:32 UT on 2015-04-23, 4 min after the GRB
trigger. They were performed at an average seeing of 0".8 and at an
average airmass of 1.5.
We detect a faint source within the 2.2" XRT error circle, at position
RA (2000.0) = 14h 46m 18.9s
Decl (2000.0) = +12d 17' 00"
with an error of 0.5", about 1" away from the XRT centroid position.
Based on 7.7 min of total exposure time in g'r'i'z' and 8.0 min in JHK,
centered 24 min after the GRB, we estimate the following preliminary
magnitudes (all in AB system):
g' = 23.2 +/- 0.2 mag,
r' = 23.1 +/- 0.2 mag,
i' = 22.5 +/- 0.2 mag,
z' = 22.0 +/- 0.2 mag,
J = 19.3 +/- 0.4 mag,
H > 18.4 mag, and
K > 17.5 mag.
No statement can be made about fading at this stage. Since there is a
faint source also in the SDSS, this might be the host galaxy rather than
the afterglow.
Given magnitudes are calibrated against SDSS (g'r'i'z') as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.03 mag in the
direction of the burst (Schlegel et al. 1998).
GCN Circular 17728
Subject
GRB 150423A: Swift detection of a short burst
Date
2015-04-23T06:42:58Z (11 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
C. Pagani (U Leicester), V. D'Elia (ASDC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and T. N. Ukwatta (LANL) report on behalf of the
Swift Team:
At 06:28:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150423A (trigger=638808). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 221.600, +12.288 which is
RA(J2000) = 14h 46m 24s
Dec(J2000) = +12d 17' 18"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single peak
with a duration of about 0.5 sec. The peak count rate was ~6400
counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 06:29:14.8 UT, 70.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 221.5787, 12.2833 which
is equivalent to:
RA(J2000) = 14h 46m 18.90s
Dec(J2000) = +12d 16' 60.0"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 76 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 1.77
x 10^20 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 73 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 29% 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 expected extinction corresponding to E(B-V) of
0.03.
Burst Advocate for this burst is C. Pagani (cp232 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.)