GRB 180510B

B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), P.A. Evans (U.
Leicester), S.L. Gibson (U. Leicester), Z. Liu (NAOC / U. Leicester),
A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and A.
Tohuvavohu report on behalf of the Swift-XRT team:

We have analysed 2.6 ks of XRT data for GRB 180510B (Tohuvavohu et al.
GCN Circ. 22696
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 ), from 3.0 ks to 10.2 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Beardmore et al. (GCN Circ.
22698
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.48 (+/-0.12).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.83 (+/-0.12). The
best-fitting absorption column is  1.3 (+0.4, -0.3) x 10^21 cm^-2, in
excess of the Galactic value of 2.5 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 3.7 x 10^-11 (4.5 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.3 (+0.4, -0.3) x 10^21 cm^-2
Galactic foreground: 2.5 x 10^20 cm^-2
Excess significance: 5.0 sigma
Photon index:	     1.83 (+/-0.12)

If the light curve continues to decay with a power-law decay index of
1.48, the count rate at T+24 hours will be 9.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.4 x
10^-13 (4.1 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/00831816.

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

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
A. Tohuvavohu (PSU), 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 180510B (trigger #831816)
(Tohuvavohu et al. GCN Circ. 22696
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 ).  The BAT ground-calculated position is
RA, Dec = 77.965, -62.320 deg which is
  RA(J2000)  =  05h 11m 51.6s
  Dec(J2000) = -62d 19' 13.0"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 41%.

The mask-weighted light curve shows a weak pulse that starts at ~T-20 s and peaks
at ~T+1 s. The main pulse ends at ~ T+40 s, and there is some low-level emission
that lasts until ~T+140 s. T90 (15-350 keV) is 134.3 +- 48.2 sec (estimated error including systematics).

The time-averaged spectrum from T-19.92 to T+137.10 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.00 +- 0.17.  The fluence in the 15-150 keV band is 2.1 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.96 sec in the 15-150 keV band
is 1.2 +- 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/831816/BA/

J. Palmerio (IAP, Paris), A. Rossi (INAF-OAS), D. Malesani (DAWN/NBI and 
DARK/NBI), N. R. Tanvir (Univ. Leicester), V. D'Elia (ASI-SSDC), A. de 
Ugarte Postigo (HETH/IAA-CSIC and DARK/NBI), S. D. Vergani (GEPI/Obs. 
Paris), D. Xu (NAOC), D. A. Kann (HETH/IAA-CSIC), J.P.U. Fynbo 
(DAWN/NBI), and B. Sbarufatti (PSU), report on behalf of the Stargate 
Consortium:

We observed the optical afterglow of GRB 180510B (Tohuvavohu et al., GCN 
22696
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 ; Schady et al., GCN 22701
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 ) with the ESO VLT/X-shooter 
spectrograph, covering the wavelength range 3000-21000 AA.
The afterglow is clearly detected in the 10s acquisition images taken 
starting at 23:09 UT (~3.7 hours after the GRB trigger) with brightness 
R~19.8 (Vega), calibrated against USNO-B1 stars in the field. 
Spectroscopy started at 23:19 UT on 2018-05-10 (~3.9 hours after the GRB 
trigger) and consisted of 2 exposures of 600 s.

Preliminary analysis of the spectrum reveals continuum flux down to 3600 
AA, which sets an upper limit to the redshift z <~ 2 via the lack of any 
obvious DLA feature. In addition, we identify several absorption lines 
at a common redshift of z=1.305, the most prominent being ZnII/CrII, 
FeII, MgII, and MgI. Moreover, we also identify another absorption 
system at z=0.63 based on the detection of the MgII doublet. Therefore, 
we propose the most probable redshift of the GRB to be z=1.305, with an 
intervening system at 0.638.

We acknowledge the excellent support from the ESO staff, particularly 
Boris Haeussler, Karleyne Silva and Emanuela Pompei in obtaining these 
observations.

P. Schady (MPE, Garching) reports:

We observed the field of GRB 180510B (Swift trigger 831816; Tohuvavohu et
al., GCN #22696
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 ) 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 23:14 UT on 10th May, 3.0 hours after the GRB
trigger. They were performed at an average seeing of 1.3" and at an
average airmass of 1.8.

A single point source is present within the 1.5" Swift-XRT error circle
reported by Beardmore et al. (GCN #22698
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 ) at

RA (J2000.0) = 05:11:52.66
DEC (J2000.0) = -62:19:26.4

with an uncertainty of 0.2" in each coordinate.

Based on 6.6 min of total exposures in g'r'i'z' and 6 min in JHK, the
estimated AB magnitudes are

g' = 20.5 +/- 0.1 mag
r' = 20.0 +/- 0.1 mag
i' = 19.8 +/- 0.1 mag
z' = 19.6 +/- 0.1 mag
J = 18.8 +/- 0.1 mag
H = 18.5 +/- 0.1 mag
K = 18.0 +/- 0.1 mag

Given magnitudes are calibrated against GROND zeropoints as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.02 in the direction
of the burst (Schlafly & Finkbeiner 2011).

I would like to thank Markus Rabus for his excellent support from La Silla.

Klotz A., Noysena.K., Atteia J.L. (CNRS-OMP-IRAP),
Boer, M., Eymar, L. (CNRS-ARTEMIS),
Gendre B. (UWA - Univ. Western Australia) report:

We imaged the field of GRB 180510B detected by SWIFT
(trigger 831816) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 2.88h after the GRB trigger
just after the dusk. The elevation of the field
decreased from 38 degrees above horizon weather conditions
were good.

We co-added a series of exposures but we we cannot
detect the OT reported by Tohuvavohu et al. (GCNC 22696)
Preliminary analysis gives:

start  end    rlim(AB)
(hour) (hour)
2.88   3.62   19.0

Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 2476 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 180510B, 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 = 77.96901, -62.32411 which is equivalent
to:

RA (J2000): 05h 11m 52.56s
Dec (J2000): -62d 19' 26.8"

with an uncertainty of 1.5 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.

A. Tohuvavohu (PSU), A. Deich (PSU), J.D. Gropp (PSU),
J. A. Kennea (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and
B. Sbarufatti (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 20:15:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 180510B (trigger=831816). Due to an observing constraint
Swift did not slew immediately to the burst. 

The BAT on-board calculated location is 
RA, Dec 77.989, -62.335 which is 
   RA(J2000) = 05h 11m 57s
   Dec(J2000) = -62d 20' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 20 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 21:04:52.4 UT, 2950.1 seconds
after the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 77.96962, -62.32356 which
is equivalent to:
   RA(J2000)  = 05h 11m 52.71s
   Dec(J2000) = -62d 19' 24.8"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 52 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (2.54 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.8
(+3.31/-2.67) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 2953 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	05:11:52.64 =  77.96932
  DEC(J2000) = -62:19:26.3  = -62.32396
with a 90%-confidence error radius of about 0.76 arc sec. This position is 4.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.25 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03. 

Burst Advocate for this burst is A. Tohuvavohu (aaronb AT swift.psu.edu). 
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.)