GRB 150305A
GCN Circular 17551
Subject
GRB 150305A: Swift XRT confirms weak INTEGRAL event as a new GRB
Date
2015-03-08T18:12:17Z (10 years ago)
From
Rhaana Starling at U of Leicester <rlcs1@star.le.ac.uk>
R. Starling (U. Leicester) reports:
On 2015-03-05T09:49:19 UT INTEGRAL recorded a 7.6 sigma event at
RA, Dec 269.78943, -41.62041 degrees (err 3.39 arcmin) and issued WEAK
Alert 6905. We triggered a Swift ToO to observe this position.
Swift observations began at 1.8E4 s after the INTEGRAL trigger with
exposure time 3ks (obsID33663). Two sources were present in the error circle.
One of these is consistent with the ROSAT source 1RXS J175914.5-423529,
which is likely associated with dwarf nova V728 CrA.
The second is a new source, with enhanced XRT position of
RA, Dec (J2000) = 17h 59m 02.60s, -42$B!k(B 39$B!l(B 49.5$B!l!l(B (269.76082, -42.66374 deg)
with an uncertainty of 3.3$B!l!l(B (radius, 90% confidence).
In this first observation the new source had a count rate 0.035 ct/s.
Further Swift observations beginning 1.1E5s post-burst with exposure time
3.7ks showed that this source had a count rate of approx. 0.007 ct/s, having
faded with a decay rate of alpha ~ -0.7.
The spectrum of the new source can be described with an absorbed power law.
The UVOT data were taken in UVM2 and UVW1 filters. A preliminary analysis
does not reveal any UV counterpart to the new XRT source.
We conclude that the INTEGRAL WEAK event was a real GRB and that the
fading source discovered by Swift XRT is the afterglow.
We thank the Swift team for carrying out these ToOs, and acknowledge use
of the UK Swift Science Data Centre in our analysis.
GCN Circular 17552
Subject
GRB 150305A: a long GRB detected by INTEGRAL
Date
2015-03-09T12:41:36Z (10 years ago)
From
Sandro Mereghetti at IASF/CNR <sandro@iasf-milano.inaf.it>
S.Mereghetti (IASF-Milano), D.Gotz (CEA, Saclay), C.Ferrigno, E.Bozzo
(ISDC, Versoix), and J.Borkowski (CAMK, Torun) on behalf of the IBAS
Localization Team report:
a gamma ray burst lasting at least 100 s has been detected by IBAS in the
IBIS/ISGRI data at 09:49:19 UT of March 5, 2015.
The refined coordinates (J2000) are:
R.A.= 269.7685 deg
DEC.= -42.6481 deg
with an uncertainty of 2.5 arcmin (90% c.l.).
The burst had a peak flux of about 0.2 counts/cm2/s (20-200 keV, 1-s
integration time) and a fluence in the same energy range of about 7e-7
erg/cmq (over 100 s).
Due to the significance of the detection below the high confidence
threshold, only an Alert Packet of WEAK type was distributed by IBAS in
real time (Packet n. 6905). The X-ray afterglow has been detected with
Swift/XRT (Starling 2015, GCN 17551).
A plot of the light curve can be found at
http://ibas.iasf-milano.inaf.it/IBAS_Results.html