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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17817, 17818
Message-Id: <20260528070543.ECB3E28807C2@server.astronomerstelegram.org>
Date: Thu, 28 May 2026 03:05:43 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17817							     ATEL #17817

Title:	ATLAS-Teide Detects Centaur (60558) 174P/Echeclus in Ongoing
		Outburst
Author:	J. Licandro (IAC, ULL), V. Kuksenko (UCB), Miquel Serra-Ricart,
		Miguel R. Alarcon (Light Bridges, IAC, ULL), P. Nichita (IAC, ULL),
		J. Tonry, L. Denneau, (IfA, University of Hawaii)
Queries:	jlicandr@iac.es
Posted:	27 May 2026; 13:28 UT
Subjects:Optical, Asteroid, Comet, Planet (minor), Solar System Object

We report that Centaur 174P/Echeclus has been detected in outburst in four
30s images obtained on 2026 May 11.9 UTC with the 2nd module of the ATLAS-Teide
instrument (Licandro et al. 2025, EPSC-DPS2025-538, 10.5194/epsc-dps2025-538)
installed at Teide Observatory (Tenerife, Spain). Echeclus was detected
unexpectedly bright at magnitude 18.28 +/- 0.07. When observed it was at
r = 14.042 and Delta = 14.326 au, where r and Delta are the heliocentric
and geocentric distances respectively and a phase angle of 3.917 deg. If
it were inactive, a brightness of V ~ 21 mag is expected given its absolute
magnitude Hv = 9.97 +/- 0.03 (Pereira et al., 2023, MNRAS, 527(2), 3624).
That means that Echeclus was > 13-times brighter than expected, meaning
that it is in an active phase. No coma is detected above the noise level
of the ATLAS images. An image produced by stacking the 4 ATLAS ones and
centered on Echeclus is included. 
Such activity is not surprising for this object. This Centaur has displayed
recurrent cometary outbursts of varying intensity, the most notable being
a ~7 mag brightening in late 2005 at 13 au (Choi et al. 2006, CBET, 355,1).
Subsequent outbursts were recorded in 2011 (~3 mag outburst, Jaeger et
al., 2011, IAU Circ., 9213, 2), 2016 (~3 mag brightening, Miles, 2016,
CBET, 4313), 2017 (~4 mag event post-perihelion, James, 2018, J. Br. Astron.
Assoc., 128, 51). In all cases the object showed an extended coma.  
ATLAS-Teide is an array of 16 RASA11 telescopes (see Licandro, J. et al.
2023, 10.48550/arXiv.2302.07954 for details) equipped with QHY600PRO cameras,
based on sCMOS sensors Sony IMX455  (Alarcon, M. R., et al. 2023, PASP,
135, 055001). Images are obtained using a Luminance (UV/IR cut) filter.
ATLAS-Teide is the 5th unit of the ATLAS survey (Tonry, J.L., et al. 2018,
PASP 130, 988, 064505 , see http://www.fallingstar.com for more information).
All frames were bias-subtracted and flat-fielded following standard procedures.
Point-source photometry was performed with a GPU-accelerated pipeline using
PSF-matched detection and S/N-driven aperture photometry with PSF-based
aperture corrections. Field stars were matched to Pan-STARRS DR1 to derive
per-image photometric zero-points.

ATLAS-Teide image of Echeclus obtained on 2026 May 11.9 UTC.: https://drive.google.com/file/d/1KOsCMLqRzq8-p0hwZv20yqOPzo0o56IW/view?usp=drive_link
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Password Certification: Javier Licandro (jlicandr@iac.es)
https://www.astronomerstelegram.org/?read=17817
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ATEL #17818							     ATEL #17818

Title:	Einstein Probe catches the onset of a new outburst from the
		NS LMXB MXB 1730-335 (Rapid Burster)
Author:	Alessio Marino, Francesco Coti Zelati, Nanda Rea, Yilong Wang,
		Giulia Illiano (ICE-CSIC), Minghao Zhang (NAO, CAS), Chen Wang (IHEP,
		CAS), Biao Zhang, Jiapei Feng (USTC), Haiwu Pan (NAO, CAS) 
Queries:	marino@ice.csic.es
Posted:	27 May 2026; 15:18 UT
Subjects:X-ray, Binary, Neutron Star, Transient

We report on the detection of a new outburst from the neutron star low-mass
X-ray binary MXB 1730-335 (a.k.a. the Rapid Burster) with the Wide-field
X-ray Telescope (WXT) onboard Einstein Probe (EP). Located in the globular
cluster Liller 1, the system is unique among Galactic X-ray bursters in
exhibiting both thermonuclear Type-I and accretion-driven Type-II bursts
(e.g. Bagnoli et al. 2015). Its previous outburst was reported in September
2025 (ATel #17388).

EP-WXT detected the onset of a new outburst on 2026 May 25, with the 0.5-4
keV observed flux rising from 9.5e-11 erg cm-2 s-1 to 2e-10 erg cm-2 s-1
within about one day. An EP-FXT follow-up observation performed on 2026-05-26
at 12:47:42 UTC confirmed the continued brightening of the source, with
a measured 0.5-10 keV observed flux of 1e-09 erg cm-2 s-1.

A 2.5 ks light curve reveals several Type II X-ray bursts, confirming that
the peculiar bursting behavior of the source has already resumed.

Multi-wavelength follow-up observations are encouraged.

Launched on January 9, 2024, EP is a space X-ray observatory designed to
monitor the soft X-ray sky with rapid X-ray follow-up capability (Yuan
et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission
of the Chinese Academy of Sciences in collaboration with ESA, MPE, and

CNES.

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Password Certification: Alessio Marino (marino@ice.csic.es)
https://www.astronomerstelegram.org/?read=17818
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