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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17870, 17871
Message-Id: <20260704070545.3D9832880A7B@server.astronomerstelegram.org>
Date: Sat,  4 Jul 2026 03:05:45 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17870							     ATEL #17870

Title:	Einstein Probe discovery of a new magnetar candidate in outburst:
		EP J223759.5+531421 (EP260628c)
Author:	N. Rea, F. Coti Zelati, Y. L. Wang (ICE-CSIC), H. Yang, X.
		Mao, C. Jin, H. Sun, W. Yuan (NAO, CAS), C. Dai (NJU), H. Feng, L.
		Tao (IHEP, CAS), L. Lin (BNU), Z. Li (QUT), B. Zhang (HKU), J.-U.
		Ness, A. Borghese (ESA), G. L. Israel, A. Possenti, M. Burgay, M.
		Pilia (INAF), P. Esposito, A. Geminardi  (IUSS Pavia), M. Imbrogno,
		D. De Grandis, A. Marino (ICE-CSIC), A. K.H. Kong (NTHU), S. Guillot
		(IRAP), C. Maitra (IUCAA, MPE) on behalf of the Einstein Probe collaboration
		and a larger follow-up collaboration
Queries:	rea@ice.csic.es
Posted:	3 Jul 2026; 12:47 UT
Subjects:X-ray, Transient, Magnetar

We report on follow-up X-ray observations of the newly discovered transient
EP260628c (Yang et al., Atel #17859), first detected by the Einstein Probe
mission. The source, now designated as EP J223759.5+531421,  has been observed
twice with the Einstein Probe FXT instrument (on 2026-06-29 for 2.5 ks
and on 2026-06-30 for 2.2 ks) and once with NuSTAR (2026-06-30 for ~23ks).

Timing analysis of the combined data reveals coherent X-ray pulsations
with a period of P = 5.995872(3) s (1-sigma error) referenced to EPOCH
= 61222.125540838 MJD (TDB).

The pulse profile is double peaked, which explains the tentative 3s period
reported earlier  (Yang et al., Atel #17859), and it is highly energy dependent.
Broadband spectral analysis of the NuSTAR data, together with the soft
X-ray coverage provided by FXT, shows that the spectrum is well described
by the sum of two blackbody components (kT_1~0.4keV and kT_2~1 keV) and
a power-law tail (Gamma~1.4) extending to an energy of approximately 30
keV. The absorbed 0.3-10 keV flux, extrapolated from the best-fitting model,
is ~9x10^-11 erg/cm^2/s. Serendipitous Swift XRT observations in 2017 did
not detect the source with an observed flux upper limit of about < 5x10^-13
erg/cm^2/s (3-sigma).

The combination of a slow spin period, X-ray outburst, thermal emission
with multiple blackbody components, and a hard X-ray power-law component
is characteristic of magnetar emission, supporting the classification of
EP J223759.5+531421 as a newly identified magnetar candidate. The position
of the source at Galactic latitude b = -4 points possibly to an old magnetar;
however, the possibility of a low-mass X-ray binary (i.e. an UCXB like
4U 1626-67) cannot be discarded yet.

Further observations are ongoing with EP, NuSTAR, XMM-Newton and GTC EMIR.
Multi-band follow-up observations are highly 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: Nanda Rea (rea@ice.csic.es)
https://www.astronomerstelegram.org/?read=17870
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ATEL #17871							     ATEL #17871

Title:	AT2026rdg is a heavily reddened Nova in its early phase
Author:	S. Basa (LAM), C. Adami (LAM), M. Dennefeld (IAP/CNRS &amp;
		Sorbonne U.)
Queries:	dennefeld@iap.fr
Posted:	3 Jul 2026; 17:40 UT
Subjects:Optical, Nova

We observed AT2026 at Haute-Provence Observatory (OHP) during the night
of July 2d to 3d (2026.49863) with the Mistral spectrograph attached to
the 1.93m telescope. Several exposures were obtained, covering the blue
range (400-800nm) and the red range (600-1000nm), with R~~700. The object
is a heavily reddened classical nova in its early phase. Emission lines
of Hydrogen, Helium and OI are observed, also a few weak FeII lines, and
several absorption lines as well (NaD, MgI, ...). The PCygni profiles at
Halpha, HBeta and OI-777nm indicate an expansion velocity of ~ 1100 km/sec.
The ratio of Halpha/HBeta emission is ~20, indicating a strong reddening,
also seen from the shape of the continuum. These results are consistent
with the findings of Munari et al (ATel 17867) and Tampo (ATel 17868).
In view of its brightness, the object is worth further observations and
is followed by the RAPAS group of Amateurs Astronomers.

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Password Certification: Michel Dennefeld (dennefel@iap.fr)
https://www.astronomerstelegram.org/?read=17871
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