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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17268, 17269
Message-Id: <20250705071112.4C6032880A19@server.astronomerstelegram.org>
Date: Sat,  5 Jul 2025 03:11:12 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17268							     ATEL #17268

Title:	EP J171203.4-333221.5: Archival radio observations from ASKAP
		VAST
Author:	Akash Anumarlapudi (UWM), David Kaplan (UWM), Dougal Dobie
		(U. Sydney/OzGrav), and Tara Murphy (U. Sydney), on behalf of the
		VAST collaboration.
Queries:	aakash@uwm.edu
Posted:	5 Jul 2025; 03:27 UT
Subjects:Radio, X-ray, Neutron Star, Transient, Variables

On June 23, 2025, Einstein Probe (EP) discovered a X-ray transient  EP250623a
(EP J171203.4-333221.5; ATel #17247). Follow-up observations by the Follow-up
X-ray Telescope (FXT) on board EP and the Swift X-ray telescope (XRT) revealed
that the source is likely Galactic (ATel #17255) and could be an eclipsing
neutron-star binary system. Following this, MeerKAT performed radio observations
of this source at 1.4 GHz and found a weak radio source (5.3 sigma) with
a flux density of 108 uJy (ATel #17258) at the location of the EP transient.

Here we report the archival radio observations of this source taken at
the Australian SKA Pathfinder (ASKAP) observations as part of the Variable
And Slow Transients Survey (VAST; Murphy et al. 2021) at 887.5 MHz.

The position of the source was observed for 64 epochs, roughly with a two-week
cadence between January 2020 and October 2024. Each observation lasted
approximately 12 minutes, reaching a sensitivity (noise level) of 250 uJy.
The source was not detected in any of the single-epoch images. We stacked
the individual exposures, which also resulted in a non-detection. The 1-sigma
noise level at the location of the source is 40 uJy, a factor 2-3 deeper
than the transient's brightness reported by MeerKAT in the ATel #17258,
although at a slightly different frequency.

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Password Certification: Akash Anumarlapudi (aakash@uwm.edu)
https://www.astronomerstelegram.org/?read=17268
==============================================================================
ATEL #17269							     ATEL #17269

Title:	EP250702a/GRB 250702B,C,D,E: Archival radio observations from
		ASKAP VAST
Author:	Akash Anumarlapudi (UNC Chapel Hill), David Kaplan (UWM),
		Igor Andreoni (UNC Chapel Hill), Dougal Dobie (U. Sydney/OzGrav),
		Tara Murphy (U. Sydney) on behalf of the VAST collaboration.
Queries:	aakash@uwm.edu
Posted:	5 Jul 2025; 03:36 UT
Subjects:Radio, X-ray, Transient

Fermi Gamma-ray Burst Monitor (GBM) reported the discovery of four possible
long-durational GRBs, GRB 250702B,C,D,E, that might likely be coming from
the same source (GCN #40891). Further X-ray observations by the Einstein
Probe (EP; GCN #40906), MAXI (GCN #40910), Konus-WIND (GCN #40914), and
SVOM (GCN #40923) resulted in the discovery of an X-ray counterpart. Data
from the Wide-field X-ray Telescope (WXT) aboard EP revealed that the source
was active in X-rays even a day before the Fermi GBM discovery. Follow-up
observations from the Follow-up X-ray Telescope on EP (FXT, GCN #40906)
constrained the position of the source to 20 arcseconds (90% confidence).
The inferred line of sight column density is slightly higher than the expected
column density, not ruling out a Galactic origin. No optical counterparts
were reported down to i=22.0 (GCN #40918), but infrared observations have
resulted in the discovery of a candidate counterpart (GCN #40924) with
Ks~17.3 Vega, which is very red in color and rapidly fading (GCN #40961).
Subsequent analysis of GBM data suggested that the burst GRB 250702C is
likely not related to GRB 250702 B/D/E, but an unrelated short GRB (GCN
#40931).

Here we report the archival radio observations of this source taken at
the  Australian SKA Pathfinder (ASKAP) observations as part of the Variable
And Slow Transients Survey (VAST; Murphy et al. 2021) at 887.5 MHz.

The position of the source was observed for 13 epochs, roughly with a two-week
cadence between March 2024 and December 2024. Each observation lasted approximately
12 minutes, reaching a sensitivity (noise level) of 250 uJy. The source
was not detected in any of the single-epoch images. We stacked the individual
exposures, which also resulted in a non-detection. The 1-sigma noise level
at the location of the source is 75 uJy, and hence we place a limit on
the persistent radio flux density (5-sigma) of the source to be < 375 uJy.

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