GRB 140518A

E. Sonbas (Adiyaman Univ.), T. Guver (Istanbul Univ.), U. Temiz, F.Dolek
(Cukurova Univ.), E. Gogus (Sabanci Univ.), O. Erece (Akdeniz Univ.), O.
Basturk (Ankara Univ.) report on behalf of a larger collaboration


 We observed the field of Swift GRB 140518A (Melandri et al., GCN#16298
Loading...
 
 )
with the 1.0 meter T100 telescope (Bakirlitepe, TUBITAK National
Observatory, Turkey), starting May, 18, 21:35:41 UT (~ 12.3 hours after the
trigger). 5 x 300 s exposures were obtained in the R filter under moderate
weather conditions.


We do not detect an optical afterglow within the reported XRT error circle
down to a limiting magnitude of >20.37 (2-sigma) in the combined R band
image.


We are grateful to TUBITAK National Observatory for prompt scheduling the
observations and technical support.

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), 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 140518A (Melandri, et al., GCN 16298
Loading...
 
 ) 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 2014/05 19.24 to 2014/05 19.46 UTC (20.37 to
25.71 hours after the BAT trigger), obtaining a total of 2.47 hours
exposure in the r and i bands and 2.06 hours exposure in the Z an J bands.

For a source at the optical transient position (Zheng et al., GCN 16299
Loading...
 
 ),
in comparison with the SDSS DR9 and 2MASS, we obtain the following upper
limits (3-sigma):

  r  > 22.03
  i  > 22.20
  Z  > 21.28
  J  > 21.07

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  Compared to our observations last
night (Cucchiara, et al., GCN 16302
Loading...
 
 ), during which the source faded
approximately as t^(-0.5), the source has now apparently faded more rapidly
as t^(-1) or faster.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

T. N. Ukwatta (MSU), 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 (NASA/UMBC), C. B. Markwardt (GSFC), A. Melandri (INAF-OAB),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU),
J. Tueller (GSFC) (i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 140518A (trigger #599287)
(Melandri, et al., GCN Circ. 16298
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 227.231, 42.396 deg which is
  RA(J2000)  =  15h 08m 55.3s
  Dec(J2000) = +42d 23' 44.2"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.

The mask-weighted light curve shows multiple peaks with roughly three main pulse
structures. The first main pulse starts at ~T-4 s and ends at ~T+8 s. The second main
pulse starts at ~T+38 s, followed immediately by the third main pulse structure that
starts at ~T+48 s and ends at ~T+61 s. Additionally, each of these main pulse structure
contains several  sub-pulses. T90 (15-350 keV) is 60.5 +- 2.4 sec (estimated error
including systematics).

The time-averaged spectrum from T-4.1 to T+60.0 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.92 +- 0.61,
and Epeak of 43.9 +- 7.6 keV (chi squared 54.15 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+41.94 sec in the 15-150 keV band is
1.0 +- 0.1 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.97 +- 0.13 (chi squared 65.02 for 57 d.o.f.).  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/599287/BA/

A. Maselli  (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows
(PSU), J.A. Kennea (PSU), V. Mangano (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester) and A.
Melandri report on behalf of the Swift-XRT team:

We have analysed 8.3 ks of XRT data for GRB 140518A (Melandri  et al.
GCN Circ. 16298
Loading...
 
 ),  from 58 s to 19.5 ks after the  BAT trigger. The
data comprise 92 s in Windowed Timing (WT) mode (the first 8 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. Using 4543 s of PC mode data and 6 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 227.25249, +42.41821
which is equivalent to:

RA (J2000): 15h 09m 00.60s
Dec(J2000): +42d 25' 05.6"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.42 (+0.22, -0.19). At T+251 s  the decay
flattens to an alpha of 0.25 (+0.15, -0.18) before breaking again at
T+2747 s to a final decay with index alpha=1.51 (+0.32, -0.27).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.66 (+/-0.10). The
best-fitting absorption column is  2.5 (+1.7, -1.6) x 10^22 cm^-2, at a
redshift of 4.707, in addition to the Galactic value of 1.6 x 10^20
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.94 (+/-0.12) and a best-fitting absorption column of 2.9 (+1.7,
-1.6) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.4 x 10^-11 (3.8
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.6 x 10^20 cm^-2
Intrinsic column:    2.9 (+1.7, -1.6) x 10^22 cm^-2 at z=4.707
Photon index:	     1.94 (+/-0.12)

If the light curve continues to decay with a power-law decay index of
1.51, the count rate at T+24 hours will be 2.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.9 x
10^-14 (7.8 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/00599287.

This circular is an official product of the Swift-XRT team.

A. Trotter, A. LaCluyze, J. Haislip, D. Reichart, K. McLin, L. Cominsky, 
H. T. Cromartie, A. Foster, N. Frank, K. Ivarsen, M. Maples, J. Moore, 
M. Nysewander, R. Beauchemin, T. Berger, A. Dow, M. Hinckle, A. 
Patterson, H. Pegues, J. Pozo, D. Waddell, and J. A. Crain report:

Skynet observed the Swift-XRT localization of GRB 140518A (Melandri et 
al., GCN 16298
Loading...
 
 , Swift trigger 599287) with the 14" GLAST Optical Robotic 
Telescope (GORT) at the Hume observatory in CA, USA. Observations began 
at t=130s and continued until 2.4h post-trigger. Skynet took alternating 
exposures in the Rc and Ic bands, increasing from 10s to 160s. In early 
Ic and Rc images, and in later stacked Ic images, we detect an 
uncatalogued fading optical source at a position consistent with the 
afterglow candidate reported by Zheng et al. (GCN 16299
Loading...
 
 ).

The source faded from Ic=16.8 at t=130s to Ic > 18.7 at a mean time 
t~70m. In Rc band, we detect the source marginally at Rc~18.3 at t=4m, 
with Rc>20.1 at a mean time t~55m.

A preliminary light curve is at:
http://www.skynet.unc.edu/grb/grb140518a.png

Photometry is calibrated to six APASS-DR7 stars in the field, and has 
not been corrected for the Galactic foreground extinction corresponding 
to E(B-V)=0.016 (Schlegel et al. 1998).

No further Skynet observations are scheduled.

N. P. M. Kuin (UCL-MSSL) and A. Melandri (INAF-OAB) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 140518A  77 s after the BAT trigger (Melandri et al.,
GCN Circ. 16298
Loading...
 
 ).  No optical afterglow consistent with the
XRT position (Melandri et al. GCN Circ. 16298
Loading...
 
 ) 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            77          226          147         >20.7
u_FC               289          539          246         >20.7
white               77        13719         1583         >22.6
v                  619         7499          568         >20.2
b                  545        12953         1060         >22.0
u                  289        12041         1286         >21.6
w1                 668         7910          568         >21.4
m2                1071         7705          413         >21.1
w2                 595         7295          510         >21.3

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).

A. Cucchiara (NASA/GSFC), 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), 
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), 
José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), 
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:

We observed the field of GRB 140518A (Melandri, et al., GCN 16298
Loading...
 
 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2014/05 18.41 to 2014/05 18.46 UTC (0.60
to 1.75 hours after the BAT trigger), obtaining a total of 0.71 hours
exposure in the r and i bands and 0.30 hours exposure in the Z,
Y, J, and H bands.

We detect the fading source identified by Zheng et al. (GCN 16299
Loading...
 
 ) and 
Perley et al. (GCN 16300
Loading...
 
 ) within the Swift-XRT error circle.
We confirm this to be the optical afterglow of GRB 140518A.

In comparison with the SDSS DR9 and 2MASS, we
obtain the following detections:

  r 20.50 +/- 0.04
  i 19.00 +/- 0.02
  Z 18.59 +/- 0.03
  Y 18.19 +/- 0.03
  J 18.13 +/- 0.02
  H 17.80 +/- 0.02

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
Based on these observations, and using our automatic photo-z
analysis tool (Littlejohns et al. arXiv:1312.3967) we determine two possible
photometric redshifts: assuming a Milky Way extinction curve for the GRB 
host we derive a photo-z of z=1.88 (+- 0.06) and A_V=1.8, while a SMC 
extinction law gives a z=4.63 (+- 0.11) and A_V=0.5. 
The second solution is consistent with the spectroscopic redshift
reported by Chornock et al. (GCN 16301
Loading...
 
 ).


We thank the staff of the Observatorio Astronómico Nacional in San Pedro 
Mártir.

[GCN OPS NOTE(19may14):  Per author's request, the "9.90 to 11.05"
was changed to "0.60 to 1.75".]

R. Chornock (Harvard), D. B. Fox (Penn State), A. Cucchiara (Goddard), D. A. 
Perley (Caltech), and A. Levan (Warwick) report on behalf of a larger collaboration:

We obtained 2x900s of spectroscopy of the optical afterglow (Zheng et al., GCN 
16299
Loading...
 
 ; Perley et al., GCN 16300
Loading...
 
 ) of GRB140518A (Melandri et al., GCN 16298
Loading...
 
 ) 
using GMOS on the 8-m Gemini-North telescope starting at 12:22 UT on May 18. Our 
spectra covered the wavelength range 5900-10150 Angstroms at a resolution of 
R~1200. A damped Lyman-alpha system is present near 6940 Angs, corresponding to 
z~4.71.  A fit to the absorber gives z=4.706 and the log of the HI column 
density (in cm^-2) is 21.65 +- 0.1. Strong narrow absorption lines of S II, Si 
II, Si II*, O I, O I*, Si IV, C II, C IV, Fe II, and Al II associated with this 
absorption system have a common redshift of z=4.707.  The combination of the DLA 
and the excited fine structure lines allow us to identify this as the redshift 
of the GRB.

We thank the Gemini staff, in particular Rachel Mason and Joy Chavez, for their 
assistance with these observations.

D. A. Perley (Caltech) reports on behalf of a larger collaboration

The Palomar 60-inch telescope responded automatically to the Swift 
trigger for GRB 140518A (Melandri et al., GCN 16298
Loading...
 
 ) and began a 
repeating cycle of 60-second exposures in r, i, and z-band observations 
at 09:22:28 UT, 4.70 minutes after the burst.

We weakly detect the afterglow reported by Zheng et al. (GCN 16299
Loading...
 
 ) in 
the i and z filters, but not in r-band.   Only marginal detections are 
evident in any individual exposure in any filter, but a stack of the 
first six exposures in each band gives magnitudes (calibrated relative 
to SDSS) of:

r > 20.31  (2 sigma)
i = 19.03 +/- 0.16
z = 18.20 +/- 0.17

at a mid-time of approximately 16 minutes after the burst.

WeiKang Zheng, Alexei V. Filippenko, Adam Morgan (UC Berkeley), and
S. B. Cenko (NASA/Goddard Space Flight Center) report on behalf of the
KAIT GRB team:

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to GRB 140518A (Swift trigger 599287;
Melandri et al., GCN 16298
Loading...
 
 ) starting at 09:22:16 UT, 270 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. We detect a faint object within XRT error
circle at J2000 coordinates of:

RA =  15:09:00.62
DEC= +42:25:05.9

with uncertainty of about 1". The object was only detected in the
first clear band single image with mag R~18.3, no detection in
following single images. But it is marginally detected in the co-add
of next 5 single images with mag R~19.0. We suggest this to be the
afterglow of the GRB. All mags are calibrated to USNO B1.0 catalog. 

[GCN OPS NOTE(18may14): Per author's request, the Subject-line was
corrected from "140418A" to "140518A".]

A. Melandri (INAF-OAB), M. G. Bernardini (INAF-OAB),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D. Malesani (DARK/NBI),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 09:17:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 140518A (trigger=599287).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 227.269, +42.416 which is 
   RA(J2000) = 15h 09m 05s
   Dec(J2000) = +42d 24' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a multiple-peaked
structure with a  duration of about 60 s.  The peak count rate
was ~1500 counts/s (15-350 keV) at ~0 sec after trigger. 

The XRT began observing the field at 09:18:55.0 UT, 69 seconds
after the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 227.2519,
42.4185 which is equivalent to:
   RA(J2000)  = 15h 09m 00.45s
   Dec(J2000) = +42d 25' 06.6"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
position may be improved as more data are received; the latest position
is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.56 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.5
(+2.30/-2.03) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 3.67e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 76 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 expected extinction corresponding to E(B-V) of
0.02. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.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.)