GRB 170524A

K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender
(Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D.
Titterington, S. H. 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
170524A (Gropp et al., GCN 21135
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 ) 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 May 25.03, May 26.26, May
28.18 and Jun 01.20 (UT) do not reveal any radio source at the XRT
location (Evans et al., GCN 21136
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 ), with 3sigma upper limits of 162 uJy,
207 uJy, 120 uJy and 126 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/.

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), Eleonora
Troja (GSFC), 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 (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 170524A (Gropp, et al., GCN 21135
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 ) 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 2017/05 25.40 to 2017/05 25.46 UTC (13.79 to
15.29 hours after the BAT trigger), obtaining a total of 1.06 hours
exposure in the r and i bands and 0.36 hours exposure in the Z, Y, J, and H
bands.

We again observed from 2017/05 26.32 to 2017/05 26.47 UTC (35.77 to 39.48
hours after the BAT trigger), obtaining a total of 2.42 hours exposure in
the r and i bands and 1.01 hours exposure in the Z, Y, J, and H bands.

For a source within the Swift-XRT error circle (Evans, et al., GCN 21136
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 ),
in comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
upper limits (3-sigma):

     5/25      5/26
  r  > 24.45   > 25.66
  i  > 23.25   > 24.52
  Z  > 21.72   > 23.00
  Y  > 21.26   > 22.57
  J  > 18.16   > 21.25
  H  > 17.83   > 21.50

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.

E. Mazaeva (IKI), S. Nazarov (CrAO), A. Kusakin (Fesenkov Astrophysical 
Institute),  A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of 
larger GRB follow-up collaboration:

We observed the field of the Swift GRB 170524A (trigger=754322) (Gropp 
et al., GCN 21135
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 )  with Zeiss-1000 (East) of Tien Shan Astronomical 
Observatory and AZT-8 telescope of CrAO. We obtained several images in R 
filter. The TSHAO observations started on 2017-05-24 (UT) 20:31:45 under 
not optimal weather conditions.  Observations in CrAO started on 
2017-05-25 (UT) 00:18:50. Within enhanced XRT position (Evans et al. GCN 
21136
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 )  we did not detect any  optical source in the first epoch. In the 
second epoch (CrAO observation) we detected an object which is on the 
edge of the  enhanced XRT position. The object has coordinates (J2000) 
21:17:56.30 +48:36:27.9 with uncertainties of about 1 arcsec in each 
coordinate and brightness of R=20.10 +/- 0.15 at 0.1992 days after the 
Swift trigger. For now we can not say anything about the object 
variability. However the object is barely visible in DSS2 (Red).
The preliminary results of field photometry are as follows

Date       UT start   t-T0   Filter  Exp.      UL(3 sigma)
                       (mid, days)    (s)

2017-05-24 20:31:45 0.06857  R       46*120    20.3
2017-05-25 00:18:50 0.19920  R       10*180    21.5

Photometry is based on nearby USNO-B1.0 stars

USNO-B1.0_id    R2

1386-0392957 16.69

1385-0394718 17.29

1386-0392907 17.11


The finding chart of the object can be found at
http://grb.rssi.ru/GRB170524A/GRB170524A_CrAO_170524.png

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), J.G. Gropp (PSU),
H. A. Krimm (NSF/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170524A (trigger #754322)
(Gropp et al., GCN Circ. 21135
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 ).  The BAT ground-calculated position is
RA, Dec = 319.488, 48.603 deg which is
  RA(J2000)  =  21h 17m 57.2s
  Dec(J2000) = +48d 36' 12.5"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.

The mask-weighted light curve shows a double peaked structure
with the first pulse from ~T0 to ~T+0.05, and second pulse from ~T+0.05 to ~T+0.1.
T90 (15-350 keV) is 0.10 +- 0.02 sec (estimated error including systematics).

The time-averaged spectrum from T+0.00 to T+0.12 sec fit by a simple
power-law model shows the power law index of 1.07 +- 0.24 (chi squared 47.68 for 57 d.o.f.).
The fluence in the 15-150 keV band is 3.7 +- 0.6 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.44 sec in the 15-150 keV band
is 0.5 +- 0.1 ph/cm2/sec.

A single blackbody fit to the time-averaged spectrum shows the blackbody
temperature of 21.09 +- 3.99 keV (chi squared 51.91 for 57 d.o.f.).
A thermal bremsstrahlung model fit shows the temperature of 199.36 +- -80.44 keV
(chi squared 57.87 for 57 d.o.f.).  A double blackbody fit shows the lower temperature
of 5.84 (error not unconstrained) keV and the higher temperature of 25.96 +15.56 keV
(chi squared 45.99 for 55 d.o.f.).  All the quoted errors are at the 90% confidence level.

The photon index of ~ 1 using the simple power-law model is consistent with those from
the BAT-detected short GRBs (Lien & Sakamoto et al. 2016), and harder than
the spectra of many BAT-detected SGRs, which have photon index ~ 3.
In addition, the double-peaked structure seen in this burst is not commonly observed in
the BAT light curves of SGRs (with time bins >= 2 ms).

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/754322/BA/

S.W.K. Emery (UCL-MSSL) and J.G. Gropp (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170524A
67 s after the BAT trigger (Gropp et al., GCN Circ. 21135
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 ).
No optical afterglow consistent with the XRT position
(Evans et al. GCN Circ. 21136
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 )
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            67          217          147         >20.4
u_FC               280          529          246         >19.5
white               67         1007          334         >20.6
v                  610         1058           58         >17.9
b                  535         1157           58         >18.7
u                  280         1132          285         >19.5
w1                 660         1107           58         >18.3
m2                1063         1082           19         >17.3
w2                 586         1033           58         >18.6

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 2.82 in the direction of the burst
(Schlegel et al. 1998).

Jan ��trobl, Ren�� Hudec and Martin Jel��nek (AS�� CAS, Ond��ejov, CZ)

We observed the location of the recently discovered GRB 170524A (Gropp et
al., GCNC 21135) with the 0.5m robotic telescope D50 located in Ond��ejov,
Czech Republic. The unfiltered CCD observations started 4 hours after the
trigger, once the position got available above local horizon, and had to be
interrupted after 20 minutes because of passing clouds. The sum of all
images obtained has a mean exposure time 00:02:23UT, i.e. 4.22h after the
GRB, and a limiting magnitude of R>20.2. No object was detected within the
XRT errorbox (Evans et al., GCNC 21136).

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), A. Cholden-Brown (PSU), S.L. Gibson
(U. Leicester) and J.G. Gropp report on behalf of the Swift-XRT team:

We have analysed 9.9 ks of XRT data for GRB 170524A (Gropp et al. GCN
Circ. 21135
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 ), from 69 s to 46.6 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. 21136
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 ). There is
evidence that the source may be fading, however we cannot constrain the
decay at the current time

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00754322.

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

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

Using 467 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 170524A, 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 = 319.48641, +48.60687 which is equivalent
to:

RA (J2000): 21h 17m 56.74s
Dec (J2000): +48d 36' 24.7"

with an uncertainty of 4.3 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.

J.G. Gropp (PSU), S. D. Barthelmy (GSFC), C. Gronwall (PSU),
J. A. Kennea (PSU), H. A. Krimm (NSF/USRA), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (GSFC/UMBC) and D. M. Palmer (LANL) report on behalf of the
Swift Team:

At 19:49:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170524A (trigger=754322).  Swift slewed immediately to the source. 
The BAT on-board calculated location is 
RA, Dec 319.456, +48.587, which is 
   RA(J2000)  =  21h 17m 49s
   Dec(J2000) = +48d 35' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 0.25 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 19:50:16.0 UT, 60.7 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 319.4869, 48.6065 which
is equivalent to:
   RA(J2000)  = 21h 17m 56.86s
   Dec(J2000) = +48d 36' 23.4"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 101 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 does not constrain the column density. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 67 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 large, but uncertain extinction expected. 

We note that this is a short burst, close to the Galactic plane 
(lat = -0.5 degrees), although far from the Galactic center
(lon = 91 degrees).  Thus there is a possibility that this
is a previously unknown Soft Gamma Repeater (SGR). 
However, the preliminary 4-energy lightcurve shows more
flux above 100 keV than is typical for an SGR burst. 

Burst Advocate for this burst is J.G. Gropp (jdg44 AT 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.)