GRB 101219B

J. M. Gelbord (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), D. M. Palmer (LANL) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 16:27:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 101219B (trigger=440635).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 12.257, -34.532 which is 
   RA(J2000)  =  00h 49m 02s
   Dec(J2000) = -34d 31' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  This is an image trigger so as is typical,
the BAT lightcurve does not show anything. 

The XRT began observing the field at 16:30:19.8 UT, 146.3 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 12.2306, -34.5662 which is equivalent to:
   RA(J2000)  = 00h 48m 55.34s
   Dec(J2000) = -34d 33' 58.3"
with an uncertainty of 5.6 arcseconds (radius, 90% containment). This
location is 145 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 150 seconds with the White filter
starting 156 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:48:55.35 =  12.23061
  DEC(J2000) = -34:33:59.5  = -34.56652
with a 90%-confidence error radius of about 0.62 arc sec. This position is 1.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.84 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is J. M. Gelbord (jgelbord AT astro.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.)

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
N. Gehrels (GSFC), J. M. Gelbord (PSU), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+766 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 101219B (trigger #440635)
(Gelbord, et al., GCN Circ. 11473
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 ).  The BAT ground-calculated position is
RA, Dec = 12.259, -34.556 deg which is 
   RA(J2000)  =  00h 49m 01.9s 
   Dec(J2000) = -34d 33' 21.6" 
with an uncertainty of 3.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 7%.
 
The mask-weighted light curve shows a broad peak starting at ~T+20 sec
and ending at ~T+60 sec.  However, given that there was a pre-planned slew
ending just before T_zero, we can not rule out that was actvitity before
this source came into the BAT FoV.  T90 (15-350 keV) is 34 +- 5 sec
(estimated error including systematics).
 
The time-averaged spectrum from T+10 to T+60 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.56 +- 0.16.  The fluence in the 15-150 keV band is 2.1 +- 0.4 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+26.84 sec in the 15-150 keV band
is 0.6 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

A.J. van der Horst (USRA) reports on behalf of the Fermi GBM Team:

"At 16:28:13.12 UT on 19 December 2010, the Fermi Gamma-Ray Burst
Monitor triggered and located GRB 101219B (trigger 314468895 /
101219686), which was also detected by the Swift/BAT (GCN 11473
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 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 59 degrees.

The GBM light curve consists of one peak with a duration (T90)
of 51 +/- 2 s (50-300 keV). The time-averaged spectrum from
T0-4.1 s to T0+47.1 s is best fit by a Band function with
Epeak = 70 +/- 8 keV, alpha = 0.33 +/- 0.36, and beta = -2.12 +/- 0.12.
The event fluence (10-1000 keV) in this time interval is
(5.5 +/- 0.4)E-6 erg/cm^2. The 1-sec peak photon flux
measured starting from T0+5.6 s in the 10-1000 keV band is
2.0 +/- 0.2 ph/s/cm^2.

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

F. Olivares E. (MPE Garching), A. Rossi (TLS Tautenburg), and J.
Greiner (MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 101219B (Swift trigger 440635; Gelbord et
al., GCN #11473
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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 MPI/ESO telescope at La
Silla Observatory (Chile).

Observations started during twilight at 00:33 UT on December 20, 8.1
hours after the GRB trigger, and were performed at an average seeing
of 1" and an average airmass of 1.05.

We confirm the optical afterglow candidate reported by Gelbord et
al.(GCN #11473
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 ). The afterglow faded, however, it is well detected in
all seven GROND optical/NIR bands.

Based on 141 s of total exposure in g'r'i'z' and 240 s in JHK, taken
at 00:36 UT mid-time, we estimate preliminary magnitudes (all in the
AB system) of:

g' = 20.4 +/- 0.1
r' = 20.0 +/- 0.1
i' = 20.0 +/- 0.2
z' = 19.6 +/- 0.1
J =�19.2 +/- 0.1
H =�18.8 +/- 0.1 and
K = 18.6 +/- 0.1

A second epoch was obtained at 03:10 UT mid-time, with total exposure
time of 1500 s in in g'r'i'z' and 1200 s seconds in JHK. The afterglow
has faded by ~0.3 mag in the r' and J bands, which yields a temporal
decay index of alpha = 1.0 between our two epochs.

Given magnitudes are calibrated against GROND zero points and 2MASS
field stars. The error in the optical bands is dominated
by the zero-point uncertainty. Magnitudes are not corrected for the
expected Galactic foreground extinction corresponding to a reddening
of E(B-V)=0.02 mag in the direction of the burst (Schlegel et al.
1998).

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

Using 2429 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 101219B, 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 = 12.23064, -34.56688 which is equivalent
to:

RA (J2000): 00h 48m 55.35s
Dec (J2000): -34d 34' 00.8"

with an uncertainty of 1.6 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.M. Gelbord (PSU) reports on behalf of the Swift-XRT team:

We have analysed 17 ks of XRT data for GRB 101219B (Gelbord et al.
GCN Circ. 11473
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 ), from 136 s to 65.2 ks after the BAT trigger. The
data comprise 415 s in Windowed Timing (WT) mode (the first 9 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
Beardmore et al. (GCN. Circ 11480).

The light curve (from T0+425 s) can be modelled with a series of
power-law decays. The decay from T+425 s is steep, with an index of
alpha=4.16 (+2.3, -0.50).  At T+638 s the decay flattens to an
alpha of 2.35 (+0.31, -0.46).  Another break at T+4.7 ks is
followed by a flatter decay of alpha = 0.23 (+/-0.15).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.68 (+/- 0.04). The
best-fitting absorption column is consistent with the Galactic value
of 3.14 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has
a photon index of 1.69 (+0.12, -0.11) and a best-fitting absorption
column consistent with the Galactic value. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.1 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+0.9, -3.1) x 10^20 cm^-2
Galactic foreground: 3.14 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.69 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
0.23, the count rate at T+24 hours will be 0.0060 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (1.3 x 10^-13) erg cm^-2 s^-1.  The count rate at T+48 hours
would be 0.0051 count s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00440635.

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

N.P.M. Kuin (MSSL/UCL) and J.M. Gelbord (PSU) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 101219B
156 s after the BAT trigger (Gelbord et al., GCN Circ. 11473
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 ).
The optical afterglow is at 7 arcsec distance of a 16th magnitude star.
Special care has been taken to subtract the estimated contribution
of the neghboring star.  The data suggest that after an initial
brightening, there was a dimming around T+550s followed by a
second brightening.

Preliminary magnitudes of the GRB, using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC)
exposure and some selected subsequent exposures are:

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

white_FC           156          306        147.4       17.87   0.06
white              768          788         19.5       17.59   0.10
white             6686         6886        196.6       18.58   0.06
v                  820          840         19.5       17.55   0.27
v                 7097         7296        196.6       18.39   0.15
b                  570          590         19.5       18.79   0.30
b                  744          764         19.4       18.00   0.19
u                  718          738         19.5       17.25   0.18
u                 1298         1318         19.5       17.26   0.18
uvw1              1446         1465         19.4       17.43   0.28
uvw1             16352        16861        501         18.40   0.11
uvm2              7301         7392         89.6       18.15   0.24
uvm2             51175        52075        856         19.54   0.16
uvw2              6892         7092        197         18.04   0.13
uvw2             56901        57801        886         20.21   0.20

The values quoted above 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).

N.P.M. Kuin (MSSL/UCL) and J.M. Gelbord (PSU) report on behalf of
the Swift/UVOT team:

As reported earlier (Gelbord et al., GCN Circ. 11473
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 ; Kuin et al.,
GCN Circ. 11482
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 ), Swift/UVOT observations of GRB 101219B detected an
optical afterglow in all its bands with initial magnitudes of about
18 mag. The optical afterglow has been unusually slow to decay, and
is around 23 mag at present in the u and uv bands. The UVOT has
obtained a good light curve in all bands up to about 300ks, with
continuing detections through 1000ks in u, uvw1, uvm2, and uvw2 (v
and b measurements after 300ks are significantly affected by the PSF
wings of a B = 15.5 mag star located 7 arcsec to the SW). The light
curve still appears to be decaying and there is some indication that
this decay may not be smooth.

GRB 101219B is further interesting because the UVOT light curve
exhibits an early decay to about 600 seconds after the trigger time
T, after which a second brightness rise to a maximum around T+850s
occurs. A corresponding break is found in the X-ray light curve, in
that the decay observed by XRT flattens approximately at T+700s.

The only constraint on the redshift of this burst is an upper limit
around 1.5 implied by the detection in uvw2, as there have not been
any spectroscopic observations announced to date. However, if this
burst is bright because it is close, then we might detect a supernova
bump in the coming days.

We consider this an interesting burst and would like to bring this
to the attention of the community as an opportunity for further
observations.

Dale A. Frail (NRAO) reports on behalf of a larger collaboration:

"We responded to a request (GCN#11516
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 ) for further observations of the
long-lived optical afterglow of GRB 101219B. The Expanded Very Large
Array (EVLA) observed a field toward this GRB (GCN#s 11473, 11482)
on 2011 January 7.03 UT at a center frequency of 8.46 GHz.

In a preliminary reduction of the data, we detect a weak radio source
(Flux=71+/-15 uJy) at RA(J2000)=00:48:55.40 (+/-0.01) and
Dec(J2000)=-34:34:00.1 (+/-0.7) that may be the afterglow of
GRB 101219B.

No further observations are planned.

N.P.M. Kuin (MSSL/UCL) and J.M. Gelbord (PSU) report
on behalf of the Swift/UVOT team:

Observations of GRB 101219B from 0.86Ms to 2.45Ms after the
BAT trigger (T) continued in the u and uvw2 filter. The
uvw2 light curve has been flat since T+1Ms. The late time
uvw2 image obtained by summing the late time data in uvw2
shows that the likely host is offset from the GRB position
by 1.2" with an estimated distance error (90% confidence)
of 0.5".

The host position is:

RA = 00h 48m 54.37s
Dec = -34d 33m 58.3s (J2000),

which is (12.23069, -34.56620) in decimal degrees.

The host magnitude is uvw2 = 23.4 +/- 0.3, which
corresponds to a flux density at 1.477 x 10^15 Hz of
(3.4 +/- 1.0)x10^(-4) mJy. In the u band (1.477 x 10^15 Hz)
the observations terminated earlier than the in the uvw2.
However, the u band data obtained between T+0.86Ms and
T+1.8Ms give a 3-sigma upper limit of u > 23.3 with a
corresponding flux density < 6.4 x 10^(-4) mJy.

Observation in the uvw2 filter limits the redshift z < 1.4.

N.P.M. Kuin (MSSL/UCL) reports on behalf of the Swift/UVOT Team

A typographical error slipped into the sexagesimal position given
for the possible host in GCN 11575
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 . The position should read:

RA = 00h 48m 55.37s
DEC = -34d 33m 58.3s (J2000)

The position given in degrees was correct.

Thanks go to Daniele Malesani for pointing this out.

F. Olivares E., P. Schady, T. Kruehler, J. Greiner (all MPE Garching),
S. Klose, and D. A. Kann (Tautenburg Observatory) report on behalf of
the GROND team:

GROND continues to observe the field of the Swift GRB 101219B (Gelbord
et al., GCN #11473
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 ) simultaneously in g'r'i'z'JHK. The light curve of
the optical transient associated with this GRB (Olivares E. et al.,
GCN #11478
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 , Kuin & Gelbord, GCNs 11482
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 , 11516
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 , 11575
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 , 11576
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 ) started
as a single power-law decay, but flattens at around day five at a
preliminary AB magnitude of r' ~ 22.7. In addition there is a clear
color change associated with the flattening.

Starting at day 15, the light curve again decreases in all optical
bands to a magnitude of r' ~ 23.7 at 27 days after the burst. This
light curve shape is typical for GRB/SN events (e.g., Zeh et al. 2004,
ApJ, 609, 952), and we hence interpret these observational features as
signatures of an emerging and decaying supernova underlying the
afterglow emission of GRB 101219B.

Assuming a luminosity equal to that of SN 1998bw for the SN component,
as well as negligible dust extinction along the line of sight, a
conservative redshift range of 0.4 < z < 0.7 is derived for GRB
101219B. We note that the peak time rather short (around 14 days after
burst, see Ferrero et al. 2006, A&A, 457, 857), which further suggests
a low redshift for this GRB.

We stress that at this stage, a possible host contribution and the SN
component cannot be accurately disentangled and all results should be
considered preliminary.

Photometric and in particular spectroscopic observations with larger
aperture telescopes aiming at the detection of the fading SN and/or
host galaxy are highly encouraged.

Antonio de Ugarte Postigo (DARK/NBI), Paolo Goldoni (APC/Univ. Paris 7 
and SAp/CEA), Bo Milvang-Jensen, Daniele Malesani, Martin Sparre, Johan 
P.U. Fynbo, Giorgos Leloudas (DARK/NBI), Stefano Covino (INAF/OABr), 
Hector Flores (GEPI/Obs. de Paris), Valerio D'Elia (ASI/ASDC and 
INAF/Roma), Andrew Levan (Univ. Warwick), report on behalf of the 
X-shooter GTO GRB collaboration:

We observed the afterglow of GRB 101219B (Gelbord et al., GCN 11473
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 ) 
with the X-shooter spectrograph mounted on the ESO-VLT UT2. Observations 
were taken on two epochs, 2010 Dec 20.17 and 2011 Jan 5.09 UT (11.6 hr 
and 16.4 days after the burst, respectively). Exposure times were 80 and 
120 min, respectively.

In the first-epoch spectrum, the afterglow is detected over the full 
spectral range from about 3200 to 22,000 AA. A careful analysis provides 
a tentative redshift z=0.5519 based on detection of weak Mg II and Mg I. 
No other clear features can be found at the same redshift either in 
absorption or emission.

The second-epoch spectrum was taken 16.4 days after the GRB, which 
corresponds to 10.6 days in the rest frame at z=0.55. The continuum is 
again detected, over the wavelength range 3500 to 22,000 AA, and is 
substantially redder. No narrow emission lines can be distinguished, but 
broad SN-like undulations are apparent, particularly around 8000 AA. We 
carried out a comparison of our spectrum with those of SN 1998bw (Patat 
et al. 2001, ApJ, 555, 900) transformed at various redshifts. We find a 
convincing match at z~0.55 after comparing with a spectrum taken on 1998 
May 4 (i.e., 12 days after the GRB). The observed flux is consistent 
assuming a roughly equal contribution from a SN as bright as SN 1998bw 
and an underlying host galaxy. The match of the spectral shape, 
brightness, and spectral epoch together strenghten both the redshift 
determination and the existence of a SN associated with GRB 101219B.

Our findings are in good agreement with the GROND observations reported 
by Olivares et al. (GCN 11578
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 ).

Further observations are planned. We acknowledge the assistence of the 
ESO observing staff at Paranal, in particular Dimitri Gadotti, Leonel 
Rivas, Thomas Rivinius, Maja Vuckovic, and Thomas Szeifert.