GRB 101023A

C. J. Saxton (UCL-MSSL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
M. De Pasquale (UCL-MSSL), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), O. M. Littlejohns (U Leicester),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
S. R. Oates (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 22:50:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 101023A (trigger=436981).  Swift slewed immediately to the 
burst.
The BAT on-board calculated location is
RA, Dec 317.954, -65.394 which is
    RA(J2000) = 21h 11m 49s
    Dec(J2000) = -65d 23' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The lightcurve shows a small initial pulse at 
T+0
seconds with a large FRED pulse at about T+55 sec. The peak flux was
32000 counts/sec at T+55 sec.

The XRT began observing the field at 22:51:36.9 UT, 84.5 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 317.9704, -65.3859 which is equivalent to:
    RA(J2000)  = 21h 11m 52.89s
    Dec(J2000) = -65d 23' 09.2"
with an uncertainty of 5.3 arcseconds (radius, 90% containment). This
location is 37 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy.

UVOT took a finding chart exposure of 100 seconds with the White
filter  starting 92 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  0.03. The XRT position lies 10.6" from a catalogued USNO
object, photometry is difficult due to the bright halo of the 13th
magnitude USNO star. More data is required to determine if a new
source is present.

Burst Advocate for this burst is C. J. Saxton (cjs2@mssl.ucl.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. D'Avanzo, D. Fugazza (INAF/Brera), E. Palazzi (INAF-IASFBo) on behalf
of the REM team report:

The robotic 60-cm REM telescope located at La Silla (Chile) observed
automatically the field of GRB 101023A (Saxton et al. GCN 11363
Loading...
 
 ) with the
REMIR near-infrared camera in imaging mode.

Inspection of two set of H-band images, carried out 37 and 63 minutes post
burst, respectively, does not reveal any afterglow candidate within the
XRT error circle down to a 3sigma limiting magnitude of H~14.8 and H~15.5,
respectively (calibrated against the 2MASS catalogue).

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

Using 934 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 101023A, 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 = 317.96358, -65.38852 which is equivalent
to:

RA (J2000): 21h 11m 51.26s
Dec (J2000): -65d 23' 18.7"

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.

A.J.Levan (U. Warwick), D. Perley (U. Berkeley) and P. D'Avanzo
(INAF-OAB)  report for a larger collaboration:

"We observed the field of GRB 101023A (Saxton et al. GCN 11363
Loading...
 
 )
with GMOS on Gemini-South. We obtained a first epoch of observations
in the r-band beginning at 24 October 00:38, approximately 1.8 hours
post-burst. A second epoch was obtained at 01:26. In these two
observations we identify a fading point source at a location of

RA(J2000) 21:11:51.24 
DEC(J2000) -65:23:15.84

We identify this as the afterglow of GRB 101023A. The afterglow
fades by approximately 0.35 magnitudes between the two epochs of
observation, and has r~20.5 in our first epoch (based on archival
zeropoints). The afterglow position is ~2.8" from the refined XRT 
position of Osborne et al. (GCN 11365
Loading...
 
 ).

We thank the staff of Gemini, in particular Henry Lee, for their
help with these observations."

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
C. J. Saxton (UCL-MSSL), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+542 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 101023A (trigger #436981)
(Saxton, et al., GCN Circ. 11363
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 317.949, -65.389 deg, which is 
   RA(J2000)  =  21h 11m 47.8s 
   Dec(J2000) = -65d 23' 20.1" 
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 11%.
 
The mask-weighted light curve shows a small peak starting at ~T-10 sec, peaking
at T_zero.  The main emission starts with about 3 overaping peaks peaking at
~T+54 and ~T+58 sec and ending at ~T+140 sec.  T90 (15-350 keV) is 80.8 +- 2.2 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-11.0 to T+137.3 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.26 +- 0.15, 
and Epeak of 101.1 +- 18.9 keV (chi squared 45.1 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.7 +- 0.1 x 10^-5 erg/cm2
and the 1-sec peak flux measured from T+57.34 sec in the 15-150 keV band is
0.0 +- 0.0 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.67 +- 0.03 (chi squared 69.3 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/436981/BA/

K.L. Page (U. Leicester) and C. J. Saxton (UCL-MSSL) report on behalf of 
the Swift-XRT team:

We have analysed 961 s of XRT data for GRB 101023A (Saxton et al. GCN Circ. 
11363
Loading...
 
 ), from 88 s to 6.0 ks after the BAT trigger. The data comprise 109 s in 
Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The 
enhanced XRT position for this burst was given by Osborne et al. (GCN. Circ 
11365).

The light curve can be modelled with an initial power-law decay with an index 
of alpha=4.30 (+0.11, -0.13), followed by a break at T+174 s to an alpha of 
1.22 (+0.03, -0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed 
power-law with a photon spectral index of 1.99 (+/-0.06). The best-fitting 
absorption column is 1.93 (+/-0.16) x 10^21 cm^-2, in excess of the 
Galactic value of 2.6 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode 
spectrum has a photon index of 2.15 (+0.22, -0.21) and a best-fitting 
absorption column of 2.1 (+/-0.6) x 10^21 cm^-2. The counts to observed 
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum 
is 3.8 x 10^-11 (6.1 x 10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of 
1.22, the count rate at T+24 hours will be 0.020 count s^-1, corresponding 
to an observed (unabsorbed) 0.3-10 keV flux of 7.6 x 10^-13 (1.2 x 10^-12) 
erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_products/00436981.

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

M. Nardini, F. Olivares E., and J. Greiner (all MPE Garching) report
on behalf of the GROND team:

We observed the field of GRB 101023A (Swift trigger 436981; Saxton et
al., GCN #11363
Loading...
 
 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et
al. 2008, PASP, 120, 405) mounted at the 2.2 m ESO/MPI telescope at La
Silla Observatory (Chile). Observations started on October 23 at 23:59
UT, 1.2 hours after the GRB trigger, and were performed at an average
seeing of 1.4" and at an average airmass of 1.3.

We detect the afterglow reported by Levan et al. (GCN #11366
Loading...
 
 ) in all
GROND bands. Co-added images of 24 min of integration time in g'r'i'z'
and 20 min in JHK with midtime at 01:47 UT yield the following
magnitudes in the AB system:

g' = 21.16 +/- 0.04,
r' = 20.50 +/- 0.02,
i' = 20.00 +/- 0.02,
z' = 19.59 +/- 0.02,
J = 19.08 +/- 0.04,
H = 18.76 +/- 0.06, and
K = 17.64 +/- 0.06,

calibrated against GROND zeropoints and 2MASS field stars. We notice
that the K-band magnitude might be contaminated by the near bright
star. Between Oct 24 at 00:03 UT and Oct 24 at 1:47 UT the afterglow
faded of ~0.75 mag in 1.75h.

No corrections for the expected Galactic foreground extinction were
made, which corresponds to a reddening of E(B-V)=0.033 mag in the
direction of the burst (Schlegel et al. 1998). Observations are
continuing.

M. De Pasquale, C. Saxton  and S. Oates (UCL-MSSL)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB
101023A 93 s after the BAT trigger (Saxton et al, GCN Circ. 11363
Loading...
 
 )
with a 100s finding chart in the white filter.
UVOT detected a fading optical source, with a position consistent
with the enhanced XRT position (Osborne et al, GCN Circ. 11365
Loading...
 
 ), in
the white filter exposures and, very marginally, in the first u
band exposure. We identify this object as the optical afterglow
of GRB101023A.
There is no detection of this source in other filters, either in
single or summed up exposures.

The position of this optical afterglow is

RA =21h 11m 51.26s (317.96360)
Dec = -65d 23m 15.7s (-65.38769) (J2000)

with an estimated uncertainty of 0.6 arcsec. This position is
consistent with the source identified by Gemini (Levan et al,
GCN Circ. 11366
Loading...
 
 ) and GROND Nardini et al., GCN 11369
Loading...
 
 ). We caution
that the photometry of this object is rather complicated by the
presence of a bright star 13rd magnitude star, which is located
about 15 arcseconds from the optical afterglow.

Preliminary magnitudes and 3-sigma upper limits using the UVOT
photometric system (Poole et al, 2008, MNRAS, 383, 627) for the
initial exposures are:

Filter      T_start(s)  T_stop(s)   Exp(s)        Mag

white (fc)      93        193        100     19.4 +/- 0.2
white         5895      10094        960     21.7 +/- 0.4 (2.8 sigma)
v             3524      15873       1082         >20.2
b             4344       4483        137         >20.2
u             4139       4339        200     20.5 +/- 0.6 (2 sigma)
u            21640      22548        882         >21.1
w1            3934      21633       1126         >21.1
m2            3728      16778       1082         >21.2
w2           10101      10653        544         >21.0


The values quoted above 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).

Michael S. Briggs (UAHuntsville) reports on behalf of the Fermi GBM Team:

"At 22:50:04.73 UT on 23 October 2010, the Fermi Gamma-ray Burst Monitor
(GBM) triggered and located GRB 101023A (trigger 309567006 / 101023.951).

The burst was also detected by the SWIFT-BAT (C. J. Saxton et al. 2010,
GCN 11363
Loading...
 
 ).  The GBM on-ground location is consistent with the Swift
position.

The GBM light curve shows two major pulses, the first from 0 to 25 s
relative to the trigger time, the second from 45 to 100 seconds, with
the GRB having a T90 duration of 77 +/- 8 s (50-300 keV).
The spectrum from 0 to 95 s is well fit with a cutoff power law with
an index of -1.64 +/- 0.01 and an Epeak of 277 +/- 14 keV.   The fluence
(10-1000 keV) for the t90 time interval is (6.4 +/- 0.1) E-05 erg/cm^2.

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

K. Motohara, T. Tanabe, S. Koshida, T. Morokuma,
T. Minezaki, and Y. Yoshii (University of Tokyo),
report on behalf of the TAO project team:

We observed GRB 101023A (Saxton et al., GCN 11363
Loading...
 
 ) with
the near-infrared camera ANIR mounted on the miniTAO 1.0m
telescope at the University of Tokyo Atacama Observatory
on the summit of Co. Chajnantor (5640m altitude) in
the northern Chile.

The J-, H-, and Ks-band observations started from
2010-10-24 02:48 UT (3hours after the burst), and total
exposure time was 540sec for each band. The afterglow was
detected in all the three bands at the position reported
by Levan et al. (GCN 11366
Loading...
 
 ). The seeing was 0.9-1.0arcsec
throughout the observations, and the image of the afterglow
was clearly separated from the nearby bright star.

AB magnitudes are are listed below, where the flux calibrations
were carried out using 2MASS stars within the FoV.

Band   Mid-UT    AB-Mag
----------------------------
Ks      02:53:05  19.40 +/- 0.10
H       03:07:41  20.28 +/- 0.27
J       03:24:36  19.92 +/- 0.14
----------------------------

S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long GRB 101023A, (Swift/BAT trigger=436981:
Saxton, et al., GCN 11363
Loading...
 
 ; Stamatikos et.al, GCN 11367
Loading...
 
 )
triggered Konus-Wind at T0=82264.703s UT (22:51:04.703)

The burst light curve started, at ~T0-65s, with a weak
initial pulse, followed by a much brighter and harder
emission episode, peaked at ~T0+5s.
The total duration of the burst is ~100 s.
The emission is seen up to 2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB101023_T82264/

As observed by Konus-Wind the burst
had a fluence of (6.6 � 0.5)x10-5 erg/cm2,
and a 256-ms peak flux, measured from T0+4.096s,
of (7.1 � 0.5)x10-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of major part of the burst
(from T0 to T0+29.952 s) is best fit
in the 20 keV - 2 MeV range by the GRB (Band)
model, for which:
the low-energy photon index alpha = -1.07 (-0.07, +0.08),
the high energy photon index beta = -2.5 (-0.3, +0.7),
the peak energy Ep = 200(-16, +17) keV (chi2 = 73/57 dof).

The spectrum at the maximum count rate
(measured from T0+0.256 to T0+6.400 s) is best fit
in the 20 keV - 2 MeV range by the GRB (Band)
model, for which:
the low-energy photon index alpha = -0.84 (-0.07, +0.08),
the high energy photon index beta = -2.8 (-0.4, +0.2),
the peak energy Ep = 239(-17, +18) keV (chi2 = 56/57 dof).

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

R. Ruffini, L. Izzo, A. Penacchione, S.K. Chakrabarti on behalf of ICRAnet
reports:

We have tentatively identified the redshift factor z of GRB 101023A (GCN
11363
Loading...
 
 , 11364
Loading...
 
 , 11365
Loading...
 
 , 11366
Loading...
 
 ) to be between 0.7 to 1.0 from Amati relation. This
GRB had two major pulses whose E_iso appear to be ~10^52 ergs and ~2x10^53
ergs respectively. Despite being bright and nearby, no Supernovae has been
reported for this source. We encourage anyone having data especially around
1st to 7th of November, 2010, on this object on supernovae association (either
way) to report them to facilitate understanding this object.