GRB 160409A

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

Swift has initiated a ToO observation of the Swift/BAT GRB 160409A. 
Automated analysis of the XRT data will be presented online at
http://www.swift.ac.uk/ToO_GRBs/00020604

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. These are
not necessarily related to the Swift/BAT event. Any X-ray source
considered to be a probable afterglow candidate will be reported via a 
GCN Circular after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

GRB 160409A found in Swift BAT ground analysis

P.A. Evans (U. Leicester),  J.P. Osborne (U Leicester), 
K. L. Page (U Leicester), and  D.M. Palmer (LANL)
report on behalf of the Swift Team

At 05:54:14 UT on 2016-04-09 BAT triggered and located
GRB 160409A (trigger #682162).  Swift did not immediately 
slew to this source because its location approximately
matched a known source (4U 1916-053) in its on-board catalog.  
The BAT on-board calculated location is 
RA, dec 289.705,-5.390 which is 
RA(J2000) = 19h 18m 49s
Dec(J2000) = -5d 23' 24"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
peak structure with a duration of about 30 sec.  The peak count rate
was ~1300 counts/sec (15-350 keV), at ~2 sec after the trigger.

The catalogued source, 4U 1916-053, is identified by Simbad as being
the LXB V* V1405 Aql.  However, this object is 9 arcminutes from the 
BAT position, and well outside the error circle.  BAT has detected a burst
from that source (1.1 arcmin offset from the V1405 Aql location)
in April 2006.  During the 6-minute accumulation that overlaps the
trigger, SAX J2103.5+4545 is detected (at lower significance and 
correspondingly larger position uncertainty) with a 3.3 arcmin offset.
Therefore we can confidently state that this trigger did not come
from the location of V1405 Aql and is due to a different source.

A Swift Target of Opportunity was requested and XRT began
observing the field at 00:34:58 UT on 2016-04-12, which is
2.8 days after the BAT trigger. No unknown sources were 
detected in the 3 kiloseconds of data, although two known 
sources and possible scattered X-rays from V1405 Aql were seen.
No new sources were detected in UVOT down to a limiting
magnitude of 21.3 in white.

Qualitatively, about half of long GRBs would be visible in a 
3 ks XRT observation at that delay after the trigger, so the 
non-detection of an afterglow does not rule out a GRB.

A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia
(ASDC), A. D'Ai (INAF-IASFPA), T.G.R. Roegiers (PSU), L.M. McCauley
(PSU), J.A. Kennea (PSU), S.L. Gibson (U. Leicester) and P.A. Evans (U.
Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Swift/BAT-detected burst GRB 160409A, collecting 3.0 ks of Photon
Counting (PC) mode data between T0+240.0 ks and T0+246.7 ks. 

No uncatalogued X-ray sources have been detected inside or close to the
Swift/BAT error region. The 3-sigma upper limit in the field ranges
from ~0.004 to ~0.005 ct s^-1, corresponding to a 0.3-10 keV observed
flux of 1.7e-13 to 2.1e-13 erg cm^-2 s^-1 (assuming a typical GRB
spectrum).

A previously-catalogued X-ray source has been detected inside or close
to the Swift/BAT error region, however because it is a catalogued
object it is unlikely to be the afterglow.

An uncatalogued was detected, however this was too far from the GRB
position to be the afterglow.

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
http://www.swift.ac.uk/ToO_GRBs/00020604.

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

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

The long-duration GRB 160409A (Swift-BAT ground detection:
Evans et al., GCN 19304
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 ) triggered Konus-Wind
at T0=21254.430 s UT (05:54:14.430).

The KW light curve shows single structure-less pulse with
a total duration of ~35 s.
The emission is visible up to ~7 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160409_T21254/

As observed by Konus-Wind, the burst had a fluence
of 1.8(-0.3,+0.3)x10^-5 erg/cm2, and a 64-ms peak flux,
measured from T0+4.846 s, of 1.5(-0.2,+0.2)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+24.832 s)
is best fit in the 20 keV - 15 MeV range
by the cutoff power law with the following model parameters:
the photon index alpha = -0.68(-0.16,+0.18),
and the peak energy Ep = 209(-18,+22) keV,
chi2 = 107/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep with an upper limit on beta of -2.1

The spectrum near the peak count rate (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range
by the cutoff power law with the following model parameters:
the photon index alpha = -0.72(-0.17,+0.19),
and the peak energy Ep = 252(-26,+32) keV,
chi2 = 122/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep with an upper limit on beta of -2.0

All the quoted errors are at the 1 sigma confidence level.
All the quoted values are preliminary.