GRB 070110

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
G. Cusumano (INAF-IASFPA), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), C. B. Markwardt (GSFC/UMD),
T. Mineo (INAF-IASFPA), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB),
B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

At 07:22:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070110 (trigger=255445).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 0.910, -52.961 which is 
   RA(J2000)  =  00h 03m 38s
   Dec(J2000) = -52d 57' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a multi-peaked
structure with a duration of about 70 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~18 sec after the trigger. 

The XRT began observing the field at 07:24:15 UT, 93 seconds after the
BAT trigger. XRT found a bright, variable, uncatalogued X-ray source
located at RA(J2000) = 00h 03m 39.6s, Dec(J2000) = -52d 58' 29.1", with an
estimated uncertainty of 4.2 arcseconds (90% confidence radius). 
This is a ground calculated position based on prompt downlinked data. 
This location is 52 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
2.1e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 104 seconds after the BAT trigger. An
afterglow candidate is apparent at RA=0.9133 (00h 03m 39.20s),
DEC=-52.9740 (-52d 58' 26.3") with an estimated uncertainty of � 1
arcsec, which is 4.6" from the XRT position. The estimated magnitude
is 20.9 (white), with an uncertainty of � 1 mag. Additional data
products are not yet available to confirm the candidate. The
2.7'x2.7' sub-image covers 100% of the XRT error circle. No
correction has been made for the expected extinction corresponding to
E(B-V) of 0.014.

GRB 070110, Swift-BAT refined analysis

J. Cummings (GSFC/UMBC), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the data set from T-239 to T+750 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 070110 (trigger #255445)
(Krimm, et al., GCN Circ. 6005
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 ).  The BAT ground-calculated position
is RA, Dec = 0.934, -52.978 deg which is
     RA(J2000)  =  00h 03m 44.2s
     Dec(J2000) = -52d 58' 39.8"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 97%.

The mask-tagged light curve shows a very broad peak beginning at T-3 sec and
peaking at T+0 sec.  Then there is a slow exponential decline in the 
light curve
out to T+135 s, with two or three additional peaks superimposed.  T90 
(15-350 keV)
is 85 +- 5 sec (estimated error including systematics).

The time-averaged spectrum from T-2.7 to T+100.6 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.57 +- 0.12.  The fluence in the 15-150 keV band is 1.6 +- 0.1 x 
10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band is
0.6 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence level.

B. Sbarufatti, V. Mangano, T. Mineo, G. Cusumano (INAF-IASFPA),
and H. Krimm (GSFC/USRA) report on behalf of the Swift XRT Team:


We have analysed the first five orbits of XRT data of GRB07011,
consisting of 171 s of exposure in Windowed Timing (WT)
mode and 10 ks of exposure in Photon Counting (PC) mode.

The XRT refined position from the PC data is:

   RA(J2000)  =  00h 03m 39.43s
   Dec(J2000) = -52d 58' 26.7s

with an error of 3.6 arcsec (90% containment). This is 45.3 arcsec
from the refined BAT position (Cummings et al., GCN 6007
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 ),
3.0 arcsec from the preliminary  XRT position and 1.9 arcsec
from the UVOT position (Krimm et al., GCN 6005
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 ).

The 0.3-10 keV light curve shows an initial steep decay with
slope -2.53 +/- 0.07 followed by a flat decay phase with slope
-0.05 +/- 0.04, that starts 580 +/- 43 s after the trigger.
After a further break at 20.3 +/- 0.8 ks from the trigger
the light curve steepens abruptly, with a slope -7.9 +/- 0.9.
A small flare is detected at about T+380 s.

The WT and PC spectra are well fit by an absorbed power law
with photon index 2.00 +/- 0.08.
The absorption is at the level of 3e20 cm^-2, consistent with
the Galactic absorpion along the light of sight (1.8e20 cm^-2).
The average unabsorbed flux of the WT and PC spectra is
7.0e-10 and 1.7e-11 erg cm^-2 s^-1 respectively.

If decaying at the present rate the source will reach a count rate
of 4e-6 counts/s  in the 0.3-10 keV  band at T+24 hr, which
corresponds to an unabsorbed 0.3-10 keV flux of 2e-16 erg cm^-2 s^-1.

All quoted errors are the 90% confidence level.

This circular is an official product of the Swift XRT Team.

P. Roming (PSU), P. T. Boyd, and H. Krimm (NASA/GSFC) report on behalf of 
the Swift UVOT team:

The Swift/UVOT began settled observations of GRB 070110 104 seconds after 
the BAT trigger (Krimm et al., GCN Circ.6005
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 ). Analysis of the merged 
Swift/UVOT data obtained on 2007-01-10 shows that the candidate optical 
afterglow was detected in the White, V, B, and U filters, but not in the UV 
filters. The photometry results are given for the 7 UVOT filters below:

Filter	   Tstart    Tstop    Exp       Mag    Error    Significance
White   104        5882     590	     20.0    0.14     9.1
V           210        23205   2065   20.3    0.20     5.7
B           4046     29593   1568   20.9    0.17     7.1
U           5274     35376   3166   20.4    0.10     11.6
UVW1   5069     34757   3758   20.8 (3-sigma UL)
UVM2    4864     33850   2739   21.1 (3-sigma UL)
UVW2   4456     39315   1853   20.9 (3-sigma UL)

There is marginal evidence for fading of the optical candidate but 
confirmation of its fading is pending further analysis. The values quoted 
above are not corrected for the expected extinction corresponding to E(B-V) 
of 0.014.

A.O. Jaunsen (Univ. Oslo), D. Malesani, J.P.U. Fynbo, J. Sollerman
(DARK/NBI), P.M. Vreeswijk (ESO), report on behalf of a larger
collaboration.

We observed the optical afterglow of GRB 070110 (Krimm et al., GCN 6005
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 ;
Roming et al., GCN 6009
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 ) with the ESO VLT equipped with FORS2.
Observations started on 2007 Jan 11.04 UT (17.6 hr after the GRB). Three
1800-s spectra were acquired in the range 3800-8500 AA.

Based on the detection of a DLA and several metallic lines (among which
SiII 1260, SiIV 1394,1403, CIV 1548,1551 and many others), we infer a
redshift z = 2.352 +- 0.001. We also detect Lyalpha in emission
superimposed on the DLA trough. We caution that the wavelength calibration
has been performed using archival lamps.

We acknowledge the excellent support from the ESO/Paranal staff.

H. A. Krimm (GSFC/USRA) , P. Boyd (GSFC), V. Mangano (INAF-IASFPA),
F. Marshall (GSFC), B. Sbarufatti (INAF-IASFPA), N. Gehrels (GSFC)
report on behalf of the Swift Team

Based on its unusual afterglow light curve, the Swift team declares
GRB 070110 to be a "burst of interest".  Although the burst is
59 degrees from the Sun and moving closer to the Sun, we will
continue observations of the afterglow in the U filter over the next
several days.  We  encourage multiwavelength observations of this
unusual burst throughout its lightcurve.

Swift observations of GRB 070110 are discussed in GCN Report 26.2
(http://gcn.gsfc.nasa.gov/report_archive.html)

As reported previously, after a very steep drop, the XRT light curve
started to rise at T+35 ksec, reaching 3.2 X 10^-2 counts/sec.
Then between T+45 ksec and T+75 ksec, the light curve again turned
over, dropping to 6 X 10^-3 counts/sec at 100 ksec, before flattening
again.  Although flares have been observed in other bursts at
times > 10 ksec, such behavior (a steep drop followed by a slow rise)
has not before been observed in a Swift burst (see for example
P. O'Brien et al (2006), ApJ 647, 1213).

The UVOT light curve is even more extraordinary.  The afterglow
was originally detected at V=20 at T+104 sec and continues to be
detectable in all visible filters (V, B and U) with a common power
law decay index of -0.47 +- 0.02 in all three filters.  At T+203 ksec,
the afterglow is seen at V=21.6. Thus the optical light curves do not show
any of the extreme variability seen in the X-rays.  It is very rare that
a burst which was first detected at V=20 is still detectable at
T >200 ksec. The afterglow was not detected in the UVW1 filter, with
a 3-sigma upper limit of 22.26 for a 4071-sec exposure beginning at T+75 ks.
This non-detection is consistent with the redshift z=2.352 reported 
for the burst (Jaunsen et al, GCN 6010
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 ).

[GCN OPS NOTE(12jan07): Per request of one of the authors of GCN 6010
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and with the concurance of the GCN admistrator, the author for the 
6010 reference was changed from Malesani to Jaunsen.]

D. Malesani (NBI/DARK), A.O. Jaunsen (Univ. Oslo), and P.M. Vreeswijk 
(ESO), report:

We have analyzed the VLT acquisition images of the spectrum of GRB 
070110 (Jaunsen et al., GCN 6010
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 ). We provide the following astrometric 
position for the afterglow (J2000):

alpha = 00:03:39.27
delta = -52:58:26.9

with an error of 0.3". This is consistent with, and improves, the UVOT 
position (Krimm et al., GCN 6005
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 ). The object appears pointlike with a 
seeing of 0.75".

Based on instrumental zeropoints, we also report a magnitude R~21 on 
2006 Jan 11.030 UT (17.34 hr after the GRB). Such a bright magnitude is 
consistent with the slow decay reported by UVOT (Krimm et al., GCN 
report 26).

L. Amati (INAF/IASF Bologna), F. Frontera (Univ. Ferrara and INAF/IASF 
Bologna), C. Guidorzi (Univ. Milano Bicocca and INAF/OAB), E. Montanari 
(Univ. Ferrara and ITA "Calvi") report:

"Based on the correlation between power-law photon index and peak energy 
of GRB spectra measured by Swift/BAT in 15-150 keV (Zhang et al. 2006, 
astro-ph/0612238, and Sakamoto et al., ApJ, submitted), the photon index 
of 1.57+/-0.12 measured by BAT for GRB 070110 (Cummings et al, GCN 6007
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 ) 
corresponds to a peak energy Ep of ~110+/-50 keV. From this spectral 
information and the reported 15-150 keV fluence of (1.6+/-0.1)x10^-6 
erg/cm2 (GCN 6007
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 ), by assuming a Band spectral shape and by taking into 
account the redshift of 2.352 (Jaunsen et al., GCN 6010
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 ), it is then 
possible to estimate the values of the intrinsic peak energy, Ep,i ~ 
370+/-170 keV, and of the isotropic equivalent radiated energy in the 
1-10000 keV cosmological rest frame, Eiso ~ (5.5+/1.5)x10^52 erg (the 
uncertainties on Ep,i and Eiso take approximately into account the 
measurements errors, the scatter of the photon index - peak energy 
correlation and the dependence of Eiso on the values assumed for alpha and 
beta in the Band spectral model).

These values are consistent within 2 sigma with the Ep,i-Eiso correlation.

If, conservatively, we assume a Band model with alpha equal to the power-law 
spectral index measured by BAT and beta = -2.3, we find that GRB 070110 is 
consistent with the Ep,i-Eiso correlation within 2 sigma for a measured Ep up 
to ~170 keV (E0 ~400 keV), and within 3 sigma for a measured Ep up to ~280 keV 
(E0 ~650 keV). These values of E0 are well above the upper bound of the BAT 
energy band used for spectral analysis (150 keV).

Thus, we conclude that, despite the very peculiar behaviour shown by its 
X-ray afterglow after ~20 ks from the burst onset (Krimm et al., 
GCN_Report 26.2), GRB 070110 seems to be a common long event from the 
point of its position in the Ep,i-Eiso plane. This, together with the 
standard behaviour of the early afterglow light curve (steep decay, flat 
decay) could indicate that the emission mechanisms / environment 
originating the prompt emission are not necessarily linked to those 
producing the LATE afterglow emission."

This message may be cited.

H. A. Krimm (GSFC/USRA),  D. N. Burrows (PSU), M. Chester (PSU),
D. Grupe (PSU), V. Mangano (INAF-IASFPA), F. Marshall (GSFC),
J. Nousek (PSU), B. Sbarufatti (INAF-IASFPA), N. Gehrels (GSFC)
report on behalf of the Swift Team

GRB070110 has been identified as a "Swift Burst of Interest"
(Krimm et al, GCN 6014
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 ) due to the remarkable irregular light curve
seen in X rays, and the long duration and slow fading of the optical
emission.  We report that the U band emission has now faded below
the  UVOT threshold of detectability (roughly 23rd magnitude),
so the UVOT can no longer follow this GRB, but we project that the
optical brightness will continue to slowly fade, making it a possible
candidate for late-time optical detection.  We are continuing
observations with the XRT and we encourage ground-based observers
to attempt measurements of the afterglow, if they are capable of
detecting an afterglow to our estimate of V=22.7 over the next five days.

The UVOT light curves (Figure 4 in GCN Report 26.3
http://gcn.gsfc.nasa.gov/reports/report_26_3.pdf )  show
power-law decays with the following indices.  V and B bands
(T+1ksec to T+200 ksec): -0.5; U band (T+ 10 ksec to T+500 ksec):
-0.7.  Converting to magnitudes using the zero points for the
filters yields the following fits:
Vmag = 21.2 + 1.25*log10(t)
Bmag = 21.9 + 1.25*log10(t)
Umag = 21.8 + 1.75*log10(t).
where the time, t, is measured in days from the trigger.  For example
at 7:00 UT on Jan. 20, 2007, the predicted V magnitude is 22.4.

The X-ray light curve (see Figure 2 in GCN Report 26.3) is decaying
very slowly and in fact the three most recent data points suggest a
slight upward trend.  Fitting the data after the steep drop in flux
(from T+35 ksec to T+800 ksec), but excluding the big rise at
around T+65 ksec, the best fit decay index is -0.6 +/- 0.1.  If the
source follows this decay law we predict a count rate in the XRT
(0.3-10.0 keV) of 1.5 X 10^-3 cts/sec on Jan. 22, 2007.  If it
continues to decay at this rate, the source will continue to be bright
enough to be observed with the XRT during the month of February 2007.

We note that this source (RA/dec:   0h 03m 39.27s, -52s 58' 26.9",
epoch 2000.0) is currently observable from an observatory at
-29 degrees latitude and is currently above 30 degrees elevation
for approximately 2 hours after astronomical twilight.  This time
will be only about one hour by the end of January.

D. Malesani, J.P.U. Fynbo (NBI/Dark), A.O. Jaunsen (Univ. Oslo), and 
P.M. Vreeswijk (ESO), report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 070110 (Krimm et al., GCN 6005
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 ) 
with the ESO VLT + FORS1. BVRI photometry was secured around Jan 21.05 
UT (~10.7 days after the GRB).

Afterglow photometry in the V band shows its magnitude to be V ~ 24, 
significantly fainter than expected based on the extrapolation of the 
UVOT decay, which would predict V ~ 22.5 (Krimm et al., GCN 6019
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 ; see 
also GCN report 26.3). We also measure the relative decay in the R band 
based on comparison with our previous images (Jaunsen et al., GCN 6010
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 ; 
Malesani et al., GCN 6015
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 ), and find it steeper than the value reported 
by UVOT in the U, B and V bands.

The above evidence supports a steepening of the optical light curve of 
GRB 070110, which possibly occurred some 5 days after the GRB, the time 
at which the UVOT light curves end.

Further observations are encouraged. We acknowledge excellent support 
from the observing staff at Paranal.