GRB 170325A

GRB 170325A, Swift-BAT detection of a short GRB
 
D. M. Palmer (LANL), S. D. Barthelmy (GSFC), 
J. R. Cummings (CPI), N. Gehrels (GSFC),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
 
GRB 170325A was detected by Swift/BAT at 2017-03-25 07:56:57.95 UTC.  
Because the spacecraft was slewing at that time, there was no onboard triggers, 
and the burst was found later in the ground analysis in response to
Fermi-GBM trigger #512121423.

Using the data set from T-16 to T+92 sec from the recent telemetry downlink,
The BAT ground-calculated position is
RA, Dec = 127.483, 20.526 deg which is 
   RA(J2000)  =  08h 29m 55.9s 
   Dec(J2000) = +20d 31' 32.5" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
 
The mask-weighted light curve shows a single FRED-like pulse that
starts and peaks at ~T0, and ends at ~T+0.4 s. T90 (15-350 keV) is 0.3 +- 0.1 sec 
(estimated error including systematics).
 
The time-averaged spectrum from T+0.0 to T+0.4 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.06 +- 0.26.  The fluence in the 15-150 keV band is 8.8 +-1.3 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.30 sec in the 15-150 keV band
is 1.1 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

E. Bissaldi (Politecnico & INFN Bari), M. Stanbro,
and C. Meegan (UAH) report on behalf of the Fermi GBM Team:

"At 07:56:58.04 UT on 25 March 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170325A (trigger 512121423/170325331),
which was also detected by the Swift/BAT (Palmer et al. 2017, GCN 20938
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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 60 degrees.

The GBM light curve consists of a single peak
with a duration (T90) of about 0.58 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.192 s is
adequately fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.7 +/- 0.2 and
the cutoff energy, parameterized as Epeak, is 600 +/- 200 keV.

The event fluence (10-1000 keV) in this time interval is
(4.8 +/- 0.6)E-7 erg/cm^2. The 64-ms peak photon flux, measured
starting from T0 in the 10-1000 keV band, is 7.6 +/- 1.1 ph/s/cm^2.


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

K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender 
(Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D. 
Titterington, S. H. Carey, J. Hickish, Y. C. Perrott, N. Razavi-Ghods, 
P. Scott (Cambridge), K. Grainge, A. Scaife (Manchester)

We followed up the short GRB 170325A, detected in the Swift/BAT 
ground-based analysis (Palmer et al., GCN 20938
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 ), with the AMI Large 
Array as part of the 4pisky program. We note that this GRB was also 
detected by Fermi/LAT (Bissaldi et al., GCN 20940
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 ). Our observations at 
15 GHz on 2016 Mar 27.01, Mar 27.84 and Mar 29.83 (UT; 1.7d, 2.5d and 
4.5d post-burst respectively) do not reveal any transient source in the 
BAT error circle (Palmer et al., GCN 20938
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 ), which allows us to place 
3sigma upper limits of 113 uJy, 85 uJy and 117 uJy respectively on the 
radio afterglow of the GRB.

We thank the AMI staff for scheduling these observations. The AMI-GRB 
database is a log of all GRB follow up observations with the AMI, and is 
available at http://4pisky.org/ami-grb/.

E. Mazaeva (IKI), A. Pozanenko (IKI), V. Rumyantsev (CrAO), P. Minaev 
(IKI),  E. Klunko (ISTP), A. Volnova (IKI), M. Eselevich (ISTP)   report 
on behalf of larger GRB follow-up collaboration:

��e followed up the short GRB 170325A (Palmer et al., GCN  20938
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 ) with 
AZT-33IK telescope of Sayan observatory (Mondy) an ZTSh telescope of 
CrAO observatory. The burst was detected by GBM/Fermi (Bissaldi et al., 
GCN 20940
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 ) and also detected as 5.5 sigma non-triggered IBAS event of 
0.1 s duration of SPI-ACS/INTEGRAL (see 
http://grb.rssi.ru/GRB170325A/GRB170325_SPI-ACS.png).

We obtained several images in R-filter  on  March 26, March 29, and 
April 1 and cover all 90% error box of the BAT/Fermi (Palmer et al., GCN 
  20938
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 ).  We investigated variability of sources in the BAT/Fermi error 
box between the three epochs. One source exhibits marginal fading 
between first and second epochs. Preliminary photometry of the source is 
following

Date       UT start   t-T0    Filter  Exp.     OT     Err.  UL
                      (mid, days)      (s)

2017-03-26 14:10:51  1.28049  R      3600    21.94   0.15  22.2
2017-03-29 21:00:52  4.56314  R      3240    22.27   0.10  23.6
2017-04-01 15:46:59  7.35072  R      4100    22.45   0.25  22.6

the photometry is based on nearby SDSS-DR9 stars

SDSS-DR9_id         R(Lupton transformations)
J082954.53+203317.9 18.69
J083002.05+203031.2 16.74
J082950.18+203013.8 18.25
J082949.90+203106.9 16.65

Coordinates of the source are  (J2000) 08:29:57.677   +20:30:51.75 with 
uncertainty of  0.7 arcsec in both coordinates. The finding chart can be 
found in
http://grb.rssi.ru/GRB170325A/GRB170325A_Mondy_170326_2.png
http://grb.rssi.ru/GRB170325A/GRB170325A_CrAO_170329.png

The source is not presented in SDSS-DR9, but clearly visible in 
r(=22.59), i(=22.10) filters, barely visible in u-filter (23.1), and not 
detected in g and z of SDSS images.

We suggest the source is an afterglow and host candidates of the short 
GRB 170325A.