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From: atel@astronomerstelegram.org
Subject: ATel 17321, 17322
Message-Id: <20250806071121.EDAB528806DE@server.astronomerstelegram.org>
Date: Wed, 6 Aug 2025 03:11:21 -0400 (EDT)

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ATEL #17321							     ATEL #17321

Title:	XB-NEWS detects a new outburst of Aql X-1
Author:	Kevin Alabarta, David M. Russell,  Sandeep K. Rout, Payaswini
		Saikia, D. M. Bramich (NYU Abu Dhabi), M. Cristina Baglio (INAF-OAB),
		Stefanie Fijma (Anton Pannekoek Institute for Astronomy, University
		of Amsterdam), Alessio Marino (ICE-CSIC), and Fraser Lewis (Faulkes
		Telescope Project &amp; The Schools’ Observatory, LJMU)
Queries:	kalabarta@nyu.edu
Posted:	5 Aug 2025; 18:55 UT
Subjects:Optical, Binary, Neutron Star, Transient

Aquila X-1 (Aql X-1) is a neutron star low-mass X-ray binary (LMXB) that
undergoes outbursts with a recurrence time of approximately one per year.
The previous outburst was first detected in X-rays with Einstein Probe
on September 14, 2024 (MJD 60567; ATel #16821) and optical with the Las
Cumbres Observatory (LCO) network (ATel #16822), being later also detected
with VLA (ATel #16823), Swift/XRT (ATel #16826), SAO RAS (ATel #16840),
OAN-SPM (ATel #16841), SVOM/ECLAIRs (ATel #16843) and MeerKAT (ATel #16888).
This outburst lasted approximately two months, until November 12, 2024
(MJD 60626.24). After its return to quiescence, we continued to observe
the source with LCO.

On August 04, 2025 (MJD 60891.27), XB-NEWS detected an increase of the
optical flux in the g', r', i' and zs bands with magnitudes
19.41 +/- 0.02, 18.46 +/- 0.01, 17.94 +/- 0.01 and 17.63 +/- 0.01, respectively.
One day later, the source further brightened to g' = 19.27 +/- 0.09, V
= 18.76 +/- 0.07, r' = 18.26 +/- 0.04, R = 17.99 +/- 0.04, i' = 17.80 +/-
0.04 and zs = 17.50 +/- 0.05 mag.

Relative to the long-term quiescent averages (ATel #16822, Alabarta et
al., in prep.) the optical flux increases are &Delta;g' = 0.59 +/- 0.16,
&Delta;V = 0.56 +/- 0.14, &Delta;r' = 0.52 +/- 0.07, &Delta;R = 0.53 +/-
0.11, &Delta;i' = 0.47 +/- 0.10 and &Delta;zs = 0.42 +/- 0.07.
All values exceed the quiescent level by more than 3&sigma;, confirming
that the source has entered a new outburst phase. Although there is a hint
of a stronger brightening at bluer bands (&Delta;g' - &Delta;zs
~ 0.17 mag), the difference is less than 2&sigma; and therefore not yet
significant.

Aql X-1 is being monitored with the 1m and 2m optical telescopes of the
Las Cumbres Observatory (LCO) network (see e.g. ATel #1970, #9306, #13953,
#14563), as part of an ongoing monitoring of ~50 LMXBs (<a href="http://arxiv.org/abs/0712.2751">Lewis
et al. 2008</a>). All the obtained images are analysed with the real-time
data analysis pipeline "X-ray Binary New Early Warning System" developed
in-house (XB-NEWS; see <a href="https://ui.adsabs.harvard.edu/abs/2019AN....340..278R/abstract">Russell
et al. 2019</a>, <a href="https://ui.adsabs.harvard.edu/abs/2020MNRAS.498.3429G/abstract">Goodwin
et al. 2020</a>, Alabarta et al., in prep, and ATel #13451 for details).

Multi-wavelength observations are encouraged to study the rise of the outburst.

A link to the light curve is below.

LCO optical light curves of Aql X-1: https://xbnews.abudhabi.nyu.edu/static/data/website.plots/quick.results.AqlX1_2025Aug05.png
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Password Certification: Kevin Alabarta (kalabarta@nyu.edu)
https://www.astronomerstelegram.org/?read=17321
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ATEL #17322							     ATEL #17322

Title:	Non-detection of radio pulses from CXOU J164710.2-455216 with
		Murriyang
Author:	Marcus E. Lower (Swinburne), Fernando Camilo (SARAO), Paul
		Scholz (YorkU), George Younes (UMBC-CSST/NASA Goddard), John E. Reynolds
		(CSIRO), John M. Sarkissian (CSIRO)
Queries:	mlower@swin.edu.au
Posted:	6 Aug 2025; 02:17 UT
Subjects:Radio, Soft Gamma-ray Repeater, Pulsar, Magnetar

Following reports of renewed bursting activity (GCN #41172, ATel #17311)
and enhanced X-ray emission (ATel #17312) from the magnetar CXOU J164710.2-455216
(J1647 hereafter), we conducted a targeted search for radio pulses using
the Ultra-Wideband Low (UWL; Hobbs et al. 2020) receiver system installed
on Murriyang, the Parkes 64-m radio telescope.

We observed J1647 for 1798 seconds starting at UTC 2025-07-29-07:00:48.
Total intensity pulsar search-mode data were collected with 256 microsecond
sampling and 3328 frequency channels each 1 MHz wide covering the 704-4032
MHz UWL band. The data were searched for single pulses using the TransientX
package (Men & Barr 2024) for single pulses with widths ranging between
0.5 to 100 ms and dispersion measure (DM) values of 100 to 2000 pc cm^-3.
We also searched for periodic, pulsed radio emission using the fast-folding
algorithm based approach implemented in the Riptide package (Morello et
al. 2020). For this, we looked for signals with a period between 10.5 to
10.7 seconds over a DM range of 100 to 2000 pc cm^-3 with incremental steps
of 1 pc cm^-3. Two separate runs of the periodic search were conducted
on both the full 704-4032 MHz UWL band, and one focusing on the upper 2500-4032
MHz band. The latter was conducted to avoid the potential influence of
pulse scatter broadening due to multi-path propagation in the ionised interstellar
medium.

No significant single pulses above a S/N threshold of 10 were identified.
We also did not detect any periodic radio emission in either the full-band
or upper-band searches.

Using the radiometer equation, we set a tentative 2368 MHz upper-limit
of 7.9 uJy on the flux density of any periodic emission (assuming a 10
percent duty cycle and limiting S/N of 7) when averaging over the full
UWL band.

We thank Kaustubh Rajwade and Emma Carli for advice on searching the data
using TransientX. Murriyang, CSIRO’s Parkes radio telescope, is part
of the Australia Telescope National Facility which is funded by the Australian
Government for operation as a National Facility managed by CSIRO. We acknowledge
the Wiradjuri people as the traditional owners of the Observatory site.

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https://www.astronomerstelegram.org/?read=17322
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