GRB 161001A

K. L. Page (U Leicester), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 01:05:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 161001A (trigger=714404).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 71.913, -57.283 which is 
   RA(J2000) = 04h 47m 39s
   Dec(J2000) = -57d 16' 57"
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 3 sec.  The peak count rate
was ~11000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 01:06:21.5 UT, 65.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 71.91848, -57.26127 which is equivalent
to:
   RA(J2000)  = 04h 47m 40.44s
   Dec(J2000) = -57d 15' 40.6"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 78 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 68 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
0.01. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.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.)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 161001A, we find an
enhanced XRT position of the afterglow: RA, Dec: 71.9194, -57.2604
which is equivalent to:
   RA (J2000)  = 04 47 40.66
   Dec (J2000) = -57 15 37.3
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/714404.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

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

Using 1075 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 161001A, 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 = 71.91991, -57.26095 which is equivalent
to:

RA (J2000): 04h 47m 40.78s
Dec (J2000): -57d 15' 39.4"

with an uncertainty of 1.7 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.

N. P. M. Kuin (UCL-MSSL) and K. L. Page (U. Leicester) report on
behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 161001A
68 s after the BAT trigger (Page et al., GCN Circ. 19967
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 ). No optical
afterglow consistent with the XRT position (Osborne et al. GCN Circ.
19969
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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            68          218          147         >20.8
u_FC               281          530          246         >20.2
white               68         1183          353         >20.4
v                  611         1232           78         >19.1
b                  536         1158           58         >19.1
u                  281         5994          395         >20.2
w1                 661         1282           78         >19.2
m2                 636         1257           78         >19.2
w2                1016         1208           39         >19.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).

T. Kruehler (MPE Garching), D. Xu (NAOC/CAS), J. Bolmer (MPE Garching 
and ESO Santiago), K. Wiersema (Univ. Leicester), D. Malesani (DARK/NBI 
and DTU Space), R. Sanchez-Ramirez (IAA-CSIC), J. P. U. Fynbo 
(DARK/NBI), report on behalf of a larger collaboration:

We observed the field of GRB 1601001A (Page et al., GCN 19967
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 ) with the 
ESO Very Large Telescope Unit 2 (Kueyen) equipped with the X-shooter 
spectrograph.

Close to, but outside, the enhanced XRT position (Osborne et al., GCN 
19969
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 ), in our acquisition image we detect a bright, pointlike source at 
coordinates RA = 04:47:40.71, Dec = -57:15:36.8. This source is faintly 
visible in the archival DSS data and is pointlike in our images (0.75" 
seeing).

A spectrum was secured of this object, for a total of 4x600 s, starting 
on Oct 1.299 UT (6.1 hr after the GRB). The continuum is consistent with 
a stellar spectrum, and we conclude that this target is not associated 
with GRB 161001A.

Our slit, at a position angle of 319.6 deg (CCW from north), does 
however cover a portion of the XRT error circle. Within the wings of the 
the PSF of the DSS object, approximately 0.8 arcsec SE, we detect a 
number of emission lines which are consistent with [O II], Hbeta, [O 
III] and Halpha at a common redshift of z = 0.891, revealing the 
presence of a background object. While we cannot accurately determine 
its position from the slit information alone, that is consistent with 
being at the edge of the XRT error circle. Our images also hint a faint 
extension of the DSS object at a position consistent with that of the 
emission lines, which could represent the continuum emission of the 
object. As such, this is a candidate host galaxy of GRB 161001A.

We caution that we have no way to confirm the association between the 
emission line object and the GRB. No variability can be inferred from 
our data, and as we lack an estimate of the continuum flux, we can not 
presently quantify the chance association probability.

A finding chart showing the region surrounding the XRT position is shown 
at this URL: 
http://www.astro.ku.dk/~malesani/GRB/161001A/GRB161001A_slit.png

We acknowledge excellent support from the ESO observing staff at 
Paranal, in particular Zahed Wahhaj, Jonathan Smoker, and Claudia Cid.

A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), J.A.
Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), B.
Mingo (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester) and K.L. Page report on behalf of the Swift-XRT team:

We have analysed 6.9 ks of XRT data for GRB 161001A (Page et al. GCN
Circ. 19967
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 ), from 51 s to 34.6 ks after the  BAT trigger. The data
comprise 128 s in Windowed Timing (WT) mode (the first 7 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN Circ. 19968
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 ).

The late-time light curve (from T0+5.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.40 (+0.17, -0.16).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.07 (+0.16, -0.15). The
best-fitting absorption column is  4.9 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.90 (+/-0.16) and a
best-fitting absorption column of 6.5 (+1.2, -1.1) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.6 x 10^-11 (7.4 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.5 (+1.2, -1.1) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^20 cm^-2
Excess significance: 9.7 sigma
Photon index:	     1.90 (+/-0.16)

If the light curve continues to decay with a power-law decay index of
1.40, the count rate at T+24 hours will be 5.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.5 x
10^-13 (4.0 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/00714404.

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

P Veres, M Stanbro and C Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 01:05:16.72 UT on 01 October 2016, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 161001A (trigger 496976720 / 161001045) which
was also detected by the Swift/BAT (Page et al., GCN 19967
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 ).
The GBM on-ground location is consistent with the Swift position.


The angle from the Fermi LAT boresight at the GBM trigger time is 37
degrees.



The GBM light curve consists of a dominant pulse preceded by weaker emission
with a duration (T90) of about 2.2 s (50-300 keV).
The time-averaged spectrum from T0-1.1 s to T0+2.9 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.89 +/- 0.10 and
the cutoff energy, parameterized as Epeak, is 313 +/- 54 keV.

The event fluence (10-1000 keV) in this time interval is
(2.3 +/- 0.2)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.2 s in the 10-1000 keV band
is 6.9 +/- 0.3 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),

J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC),

H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC),

J. P. Norris (BSU), K. L. Page (U Leicester)

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-274 to T+962 sec from the recent telemetry downlink,

we report further analysis of BAT GRB 161001A (trigger #714404)

(Page, et al. GCN Circ. 19967
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 ).  The BAT ground-calculated position is

RA, Dec = 71.923, -57.261 deg which is

  RA(J2000)  =  04h 47m 41.5s

  Dec(J2000) = -57d 15' 39.8"

with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 78%.


The mask-weighted light curve shows several overlapping pulses

that stars at ~T-0.3, and ends at ~T+3 s. The highest peak occurs at

~ T+1.6 s. T90 (15-350 keV) is 2.6 +- 0.4 sec (estimated error including

systematics).


The time-averaged spectrum from T-0.2 to T+3.1 sec is best fit by a simple

power-law model.  The power law index of the time-averaged spectrum is

1.14 +- 0.09.  The fluence in the 15-150 keV band is 6.7 +- 0.4 x 10^-7 erg/cm2.

The 1-sec peak photon flux measured from T+1.40 sec in the 15-150 keV band

is 3.5 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence

level.


Using a 16-ms binned light curve, the lag analysis finds a lag of

7 (+/- 13) ms for the 100-350 keV to 25-50 keV band, and -7.5 (+26, -19) ms

for the 50-100 keV to 15-25 keV band, which is consistent with

those of a short GRB.


The results of the batgrbproduct analysis are available at

http://gcn.gsfc.nasa.gov/notices_s/714404/BA/

T.-W. Chen (MPE Garching), S. Klose, A. Nicuesa Guelbenzu (TLS), 
J. Bolmer (MPE Garching and ESO Vitacura), T. Kruehler and 
J. Greiner (both MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 161001A (Swift trigger 714404; Page et
al., GCN #19967
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner
et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the
ESO La Silla Observatory (Chile).

Observations started at 02:48 UT on 2016-10-01, 1.71 hours
after the GRB trigger. They were performed at an average 
seeing of 2" and at an average airmass of 2.3.

We found a faint singular point source which is south-west 2.2 arcsec 
away from the photometric center of nearby bright DSS2 object
for which Kruehler et al. (GCN #19971
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 ) reported X-Shooter spectroscopy.
The position is within the 2.3" Swift-XRT error circle reported by 
Evans et al. (GCN #19968
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 ) and also within the 1.9" enhanced XRT position 
(Osborne et al., GCN 19969
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 ), at
RA (J2000.0) = 04 h 47 m 40.57 s   
DEC (J2000.0) = -57d 15' 39.2
with an uncertainty of 0.5" in each coordinate.

Based on images with 36 min of total exposure in g'r'i'z'
and 30 min in JHK at a mid-time of 03:58 UT on 2016-10-01,
we derive the following preliminary magnitudes and upper limits
(all in the AB system):

g' = 23.1 +- 0.2 mag,
r' = 22.5 +- 0.1 mag,
i' = 21.6 +- 0.1 mag,
z' = 21.5 +- 0.1 mag,
J > 21.3 mag,
H > 20.3 mag, and
K > 18.7 mag.

Second-epoch observations were performed at a mean time 
of 09:19 UT at an average seeing 1.1" and at an average airmass of 1.1.
At that time the source seems to have faded to:

r' = 22.9 +- 0.1 mag

Given magnitudes are calibrated against USNO as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V) = 0.01 mag in the
direction of the burst (Schlafly & Finkbeiner 2011).

R.Podesta, C.Lopez, F. Podesta
Observatorio Astronomico Felix Aguilar (OAFA)

H. Levato, C. Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

D.Buckley, S. Potter,
South African Astronomical Observatory

E.Gorbovskoy, V. Lipunov, N.Tyurina, V.Kornilov,
O.Gress, P.Balanutsa, A.Kuznetsov, D.Kuvshinov
Lomonosov Moscow State University, Sternberg Astronomical Institute

R. Rebolo, M. Serra Ricart, N. Lodieu, G. Israelian
The Instituto de Astrofisica de Canarias

K.Ivanov, J.Rabinovich, N.M.Budnev,
Irkutsk State University

A. Tlatov, V.Senik, D. Dormidontov, A.Parkhomenko
Kislovodsk Solar Station of the Pulkovo Observatory

V.Yurkov, Yu.Sergienko, A.Gabovich
Blagoveschensk Educational State University, Blagoveschensk

MASTER-OAFA  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in OAFA was pointed to the  GRB161001A 29 sec after notice 
time and 41 sec after trigger time at 2016-10-01 01:05:57UT. On our 
first (10s exposure)  set we  not found OT within 6 square degrees 
field around  SWIFT BAT  error-box (Page et al., GCN 19967
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 ; Markwardt et 
al.,GCN 19974 ) brighter then 16.7  unfiltered magnitude.

MASTER-SAAO  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in SAAO was pointed to the  GRB161001A 167 sec after notice time 
and 176 sec after trigger time at 2016-10-01 01:08:17 UT. On our first 
(40s exposure)  set we haven`t found optical transient  within SWIFT 
error-box.

The 5-sigma upper limit has been about 18.4 mag

We found optical object at first hour coadded images  by both MASTERs 
telescopes at coordinates Ra 04:47:40.83 Dec -57:15:38.07 (+-0.7 arcsec 
error) with unfiltered magnitude:

0.8R +0.2B = 20.6 (+0.1 -0.4)

with respect to USNO B stars. We  have archival images in MASTER SAAO 
DataBase at 2016-04-09  with 20.9 3-SIGMA limit. We see same object at 
same position.

We note that our scale is 1 pix ~ 2 arcsec . So the DSS2 object  (Kruehler 
et al., GCN 19971
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 )  and GROND afterglow candidate (Chen et al., GCN 19975
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 ) 
are inside the our pixel.

The message may be cited.

D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

GRB 161001A (Swift/BAT detection: Page et al., GCN 19967
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 ;
Fermi GBM observation: Veres et al., GCN 19973
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 )
triggered Konus-Wind at T0=3919.479 s UT (01:05:19.479).

The light curve shows a short pulse with a total duration
of ~0.5 s.
The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst had a fluence of
(1.8 �� 0.5)x10^-6 erg/cm2 and a 16-ms peak energy flux,
measured from T0-0.016, of (8.0 �� 3.5)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The spectrum of the burst (measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 10 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -0.46(-0.36,+0.48),
and the peak energy Ep = 437(-117,+190) keV,
chi2 = 30.0/36 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep with only an upper limit on beta of -2.1,
chi2 = 30.0/35 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB161001_T03919/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.

K. L. Murata (Nagoya University),  K. Miyakawa (Tokyo Institute of
Technology), and T. Nagayama (Kagoshima University)

We observed the field of GRB 161001A ( Page et al., GCN Circular #19967
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 )
with the near-infrared (J, H, Ks) simultaneous imaging camera SIRIUS
attached to 1.4 m telescope IRSF ( InfraRed Survey Facility) in Sutherland
observatory, South Africa.

The observations started on 2016-10-01 02:41:46 UT (~ 95 min. after the
burst). We could not detect  the afterglow within the enhanced XRT error
circle (Osborne et al., GCN Circular #19969
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 ) in the three bands. We have
obtained the following preliminary upper limits (Vega magnitude system):

 J > 14.61
 H >14.19
 Ks > 14.01

Given magnitudes were calibrated against 2MASS point sources in this field.
The upper limits were determined as the magnitudes of the fainter star
within 1 arcmin from the enhanced XRT position.

This observation was carried out by IRSF and OISTER collaboration.