GRB 170330A

A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama, Y. Yamada (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), I. Takahashi (IPMU),
Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
W. Ishizaki (ICRR), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The long-duration GRB 170330A (D'Avanzo et al. GCN Circ. 20944
Loading...
 
 ;
Sharma et al. GCN Circ. 20969
Loading...
 
 ; Kozlova et al. GCN Circ. 20974
Loading...
 
 ) triggered
the CALET Gamma-ray Burst Monitor (CGBM) at 22:27:27.91 on 30 March 2017.
The burst signal was seen by all CGBM instruments.

The light curve of the SGM shows several peaks.  The bright burst episode
starts at T-5 sec and ends at T+20 sec.  Two late time emissions at T+120 s
and T+150 s, which triggered Swift/BAT, are barely visible in the HXM data.
The T90 duration measured by the SGM data is 18.5 +- 2.4 sec (40-1000 keV).

The light curve is available at

http://cgbm.calet.jp/cgbm_trigger/flight/1174947694/

The CALET data used in this analysis are provided by the Waseda
CALET Operation Center located at the Waseda University.

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

The long-duration GRB 170330A (Swift-BAT trigger #744773:
D'Avanzo et al., GCN 20944
Loading...
 
 ; Lien et al., GCN 20968
Loading...
 
 ;
AstroSat CZTI detection: Sharma et al., GCN 20969
Loading...
 
 )
triggered Konus-Wind at T0=80850.946 s UT (22:27:30.946).

The burst light curve shows a single multi-peaked pulse
with a total duration of ~12 s. The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.85(-0.54,+0.42)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+4.912 s,
of 4.91(-2.23,+2.17)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 5 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.22(-0.67,+0.88),
the high energy photon index beta = -1.98(-0.84,+0.17),
the peak energy Ep = 226(-66,+190) keV
(chi2 = 69/76 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170330_T80850/

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

V. Sharma (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed clear detection of GRB 170330A (Swift burst detection: P. D'Avanzo et al., GCN Circ. 20944
Loading...
 
 ) in the 40-200 keV energy range. The light curve shows multiple peak structure with peak counts at 22:27:36.000 UT, around ~35 s after the Swift trigger time i.e. ~T-170 s (Swift-BAT refined analysis: A. Y. Lien et al., GCN Circ. 20968
Loading...
 
 ) and it also coincides with the Swift main peak. The light curve doesn't show excess counts above the background for last ~100 s. The measured peak count rate is 163.2 counts/s above the background in combined data of four quadrants, with a total 1389 counts. The local mean background count rate was 358.8 counts/s. Using cumulative rates, we measure a T90 of 15.6 s.

It was clearly detected in the CsI anticoincidence detector (Veto) also as bright detection in the 100-500 keV energy range.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), P. D'Avanzo (INAF-OAB),
N. Gehrels (GSFC), 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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170330A (trigger #744773)
(D'Avanzo et al., GCN Circ. 20944
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 283.331, -13.458 deg which is
  RA(J2000)  =  18h 53m 19.4s
  Dec(J2000) = -13d 27' 29.2"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 46%.

The mask-weighted light curve shows a multi-peaked structure that lasts
until ~T+126 s, with the main peak occurs around ~T-135 s. The burst came
into the BAT field of view at ~T-170 s during a pre-planned spacecraft slew.
Therefore, the burst emission might have started before ~T-170 s.
T90 (15-350 keV) is 144.73 +- 3.51 sec (estimated error including systematics).

The time-averaged spectrum from T-143.2 to T+126.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.38 +- 0.09.  The fluence in the 15-150 keV band is 5.6 +- 0.3 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-134.71 sec in the 15-150 keV band
is 4.5 +- 0.3 ph/cm2/sec.  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/744773/BA/

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D.N. Burrows
(PSU), A. Cholden-Brown (PSU), S. J. LaPorte (PSU), B. Mingo (U.
Leicester) and	report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 7.3 ks of XRT data for GRB 170330A, from 89 s to 53.1
ks after the  BAT trigger. The data comprise 404 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 light curve can be modelled with an initial power-law decay with an
index of alpha=0.71 (+0.07, -0.06), followed by a break at T+439 s to
an alpha of 1.061 (+0.029, -0.025).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.00 (+/-0.10). The
best-fitting absorption column is  4.0 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 3.0 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.88 (+0.12, -0.11)
and a best-fitting absorption column of 4.0 (+/-0.6) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.2 x 10^-11 (6.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.0 (+/-0.6) x 10^21 cm^-2
Galactic foreground: 3.0 x 10^21 cm^-2
Excess significance: 2.6 sigma
Photon index:	     1.88 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.061, the count rate at T+24 hours will be 0.021 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.7 x
10^-13 (1.3 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/00744773.

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

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

Using 3111 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 170330A, 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 = 283.33044, -13.43115 which is equivalent
to:

RA (J2000): 18h 53m 19.30s
Dec (J2000): -13d 25' 52.1"

with an uncertainty of 1.5 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.

S.W.K. Emery (UCL-MSSL) and P. D'Avanzo (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170330A
109 s after the BAT trigger (D'Avanzo et al., GCN Circ. 20944
Loading...
 
 ).
A fading source consistent with the XRT position
(Evans GCN Circ. 20945
Loading...
 
 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  18:53:19.36 = 283.33067 (deg.)
    Dec (J2000) = -13:25:51.2  = -13.43090 (deg.)
with an estimated uncertainty of 0.46 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

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

white_FC           109          258          147         18.42 +/- 0.08
u_FC               266          516          246         >19.9
white              547         1368          225         19.94 +/- 0.21
v                  596         1418           97         >18.4
b                  522         1344           78         >19.3
u                  266         1484          336         >20.0
w1                 646         1467           97         >19.0
m2                 621         1442           97         >18.9
w2                 572         1393           78         >19.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.45 in the direction of the burst
(Schlegel et al. 1998).

C. Guidorzi (U. Ferrara), S. Kobayashi, I.A. Steele (LJMU), A. Gomboc 
(U. Nova Gorica), C.G. Mundell (U. Bath) on behalf of a large 
collaboration report:

We observed Swift GRB 170330A (D'Avanzo et al. GCN 20944
Loading...
 
 ) on March 31, 
07:00 UT (8.5 hours since the GRB) with one 1-m LCO unit in Cerro Tololo 
with the SDSS i filter. Comparing with the PanSTARRS archive data, 
within the XRT error circle we do not find any new/variable source down 
to i>20.5 mag (with a total exposure of 10x120s at 8.7 hours mid time) 
as calibrated against nearby PanSTARRS sources.

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

Using  promptly downlinked XRT event data for GRB 170330A, we find an
enhanced XRT position of the afterglow: RA, Dec: 283.3308, -13.4310
which is equivalent to:
   RA (J2000)  = 18 53 19.39
   Dec (J2000) = -13 25 51.7
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/744773.

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.

P. D'Avanzo (INAF-OAB), S. D. Barthelmy (GSFC),
A. Cholden-Brown (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 22:29:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170330A (trigger=744773).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 283.326, -13.437, which is 
   RA(J2000)  =  18h 53m 18s
   Dec(J2000) = -13d 26' 12"
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 10 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 22:31:29.6 UT, 98.4 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 283.3323, -13.4301 which is equivalent to:
   RA(J2000)  = +18h 53m 19.75s
   Dec(J2000) = -13d 25' 48.4"
with an uncertainty of 5.9 arcseconds (radius, 90% containment). This
location is 33 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 108 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. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the expected extinction corresponding
to E(B-V) of 0.45. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.it). 
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.)