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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17428, 17429
Message-Id: <20251003071122.6D44D2880485@server.astronomerstelegram.org>
Date: Fri,  3 Oct 2025 03:11:22 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17428							     ATEL #17428

Title:	EP250630b: A new Be white dwarf binary in outburst in the LMC
Author:	C. Maitra (IUCAA, MPE), F. Haberl (MPE), A. Udalski (Univ.
		of Warsaw), C. Jin (CAS)
Queries:	cmaitra@mpe.mpg.de
Posted:	2 Oct 2025; 17:02 UT
Subjects:X-ray, Binary, Transient

EP250630b  was discovered as a new long-term X-ray transient by EP-WXT
on 2025-06-30T09:23:01 (ATEL#17306). A follow-up observation with the Follow-up
X-ray Telescope (FXT) indicated 
two possible counterparts, a nova candidate AT 2025ggn and a Be star both
located in the LMC.

We followed up EP250630b with a 60 ks XMM-Newton ToO observation on 2025-08-30.
The source was detected at the following position (after astrometrical
corrections):

RA (J2000) = 5:03:37.63 , DEC (J2000) = -69:24:09.64

with a 0.5" statistical uncertainty (including 1 sigma statistical and
systematics). This favours the Be star candidate 2MASS J05033739-6924111
(V=15.7 mag) as the likely 
counterpart of the X-ray source as opposed to AT 2025ggn which falls outside
the 3 sigma error circle.

A 2 ks Chandra HRC-I DDT observation was performed on 2025-09-11 in which

the source was detected at the following position:

RA (J2000) = 5:03:37.28 , DEC (J2000) = -69:24:10.48

with a 0.21" statistical uncertainty ( 1 sigma). This further 
favours the Be star as the possible optical counterpart.

The X-ray spectrum is typical of a Supersoft X-ray source with an absorbed
luminosity (0.2-5 keV) of ~ 1e37 erg/s assuming a distance of 50 kpc to
the LMC.

OGLE-IV I-band light curve of the Be star (OGLE J05033753-6924110) revealed
high variability and a 2.9 mag outburst observed just before the X-ray
brightening, and a possible orbital period of ~13 or ~40 days.

All of the above indicates that EP250630b is a candidate Be white dwarf
binary in outburst in the LMC. This discovery makes it only the fifth known
in this rare class of systems in the LMC (and 5 in the SMC). Detailed analysis
of the EP, XMM, Chandra and OGLE observations will be published elsewhere.

We thank the XMM-Newton and Chandra SOC teams for the quick scheduling
of the observations.

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Password Certification: Chandreyee Maitra (cmaitra@mpe.mpg.de)
https://www.astronomerstelegram.org/?read=17428
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ATEL #17429							     ATEL #17429

Title:	Fermi-LAT detection of renewed gamma-ray activity from the
		high-redshift FSRQ PKS 0601-70
Author:	S. Lopez-Perez (LLR, Ecole Polytechnique &amp; CNRS/IN2P3),
		A. Holzmann Airasca (University of Trento &amp; INFN Bari), and F.
		Casaburo (INAF-OAR &amp; INFN Roma Tor Vergata &amp; University of
		Roma La Sapienza), on behalf of the Fermi Large Area Telescope Collaboration
Queries:	lopez@llr.in2p3.fr
Posted:	2 Oct 2025; 19:08 UT
Subjects:Gamma Ray, >GeV, Request for Observations, Blazar, Quasar

The Large Area Telescope (LAT), one of the two instruments on the Fermi
Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from
a source positionally consistent with the flat-spectrum radio quasar PKS
0601-70, also known as 4FGL J0601.1-7035 (Abdollahi et al. 2022, ApJS,
260, 53), with coordinates R.A. = 90.29717 deg, Dec. = -70.60239 deg (J2000;
Healey et al. 2007, ApJS, 171, 61), and redshift z=2.409 (Shaw et al. 2012,
ApJ, 748, 49).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on October 1, 2025, with a daily averaged gamma-ray flux
(E>100MeV) of (1.5+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty
only). This corresponds to a flux increase of a factor of 40 relative to
the average flux reported in the fourth data release of the Fermi-LAT catalog
(4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546).  This is the highest
LAT daily flux ever observed for this source. The corresponding photon
index is 2.1+/-0.1, indicating a harder spectrum than the 4FGL-DR4 value
of 2.37 +/- 0.02. The Fermi-LAT Collaboration has previously reported enhanced
activity from this source in ATels #13506 and #17359.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue. A preliminary light curve for
PKS 0601–70 can be accessed via the Fermi-LAT Light-Curve Repository
at <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J0601.1-7035">4FGL
J0601.1-7035</a>.  This source will be added to the list of Fermi-LAT daily
monitored sources. We encourage multifrequency observations of this source.
For this source, the Fermi-LAT contact person is I. Mereu (isabella.mereu@pg.infn.it).

The Fermi-LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an international
collaboration between NASA and DOE in the U.S. and many scientific institutions
across France, Italy, Japan and Sweden.

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