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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17934, 17935
Message-Id: <20260802070600.48523288078E@server.astronomerstelegram.org>
Date: Sun,  2 Aug 2026 03:06:00 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17934							     ATEL #17934

Title:	The FAST POP-discovered FRB 20251125A remains active in continued
		FAST observations
Author:	Y. C. Zhang(NAOC), L. Qian(NAOC), P. Jiang, G. Y. Zhang(NAOC),
		L. Y. Wang(NAOC), X. Y. Zhang(NAOC), B. Liu(NAOC), Z. Pan(NAOC)
Queries:	lqian@nao.cas.cn
Posted:	1 Aug 2026; 10:04 UT
Subjects:Radio, Fast Radio Burst

We report the continued FAST tracking observations of FRB 20251125A (DFC005;
J2000 RA = 10:23:47.53, J2000 Dec = +09:51:24.74), discovered in the FAST
POP (Piggyback Observation of Pulsars, https://fast.bao.ac.cn/cms/article/2034282224688386050)
survey (ATel #17837) and subsequently confirmed as a repeating source (ATel
#17898).

We detected 436 bursts with S/N higher than 7.0 in the FAST L-band tracking
observations between 2026 July 14 and 31, with a total exposure of ~30
h. The event rate is 14.51 bursts h^-1, the mean DM is ~578 pc cm^-3 and
the mean pulse width is ~16.8 ms. We estimate a DM-inferred redshift of
z is 0.51~0.65.

As the discovery team of FRB 20251125A, we are performing a follow-up observation
with FAST and the FAST Core Array, together with detailed burst analysis
and interferometric localization. An accurate position and other follow-up
results will be reported upon completion.

This work made use of the data from FAST (Five-hundred-meter Aperture Spherical
radio Telescope) (https://cstr.cn/31116.02.FAST). FAST is a Chinese national
mega-science facility, operated by the National Astronomical Observatories,
Chinese Academy of Sciences.

POP, Piggyback Observation of Pulsars: https://fast.bao.ac.cn/cms/article/2034282224688386050
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Password Certification: Lei Qian (lqian@nao.cas.cn)
https://www.astronomerstelegram.org/?read=17934
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ATEL #17935							     ATEL #17935

Title:	Einstein Probe X-ray detection of the FSRQ 4C +10.45 following
		renewed gamma-ray activity
Author:	J. W. Hu, C. C. Jin (NAO, CAS), H. Feng (IHEP, CAS), R. D.
		Liang, W. Chen, H. W. Pan (NAO, CAS), Y. J. Zhang (PKU) on behalf
		of the Einstein Probe Collaboration,  Adithiya Dinesh (Universidad
		Complutense de Madrid), Janeth Valverde (Marquette University), Chiara
		Bartolini (INFN Bari), G. La Mura (INAF - Astronomical Observatory
		of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration.
Queries:	adinesh@ucm.es
Posted:	1 Aug 2026; 21:00 UT
Subjects:X-ray, Gamma Ray, AGN, Blazar, Quasar

On July 23, 2026, the Large Area Telescope (LAT), one of the two instruments
on the Fermi Gamma-ray Space Telescope, observed gamma-ray flaring activity
from a source positionally consistent with the flat-spectrum radio quasar
4C +10.45, also known as 4FGL J1608.7+1029 (Abdollahi et al. 2022, ApJS,
260, 53), with coordinates R.A. = 242.19251 deg, Decl. = +10.48549 deg
(J2000; Le Bail et al. 2016, AJ, 151, 79L), and redshift z = 1.233 (SDSS-DR13,
Albareti et al. 2017, ApJS, 233, 25). The gamma-ray activity was reported
in ATel #17924. Enhanced optical activity from the source was also reported
in ATel #17916 on July 21, 2026 from Hans-Haffner-Sternwarte observatory.

Following these reports, a one-orbit target-of-opportunity observation
of 4C +10.45 was performed with the Follow-up X-ray Telescope (FXT) on
board Einstein Probe, starting at 2026-07-25 22:43:07 (UTC), with an exposure
time of approximately 1.6 ks. An X-ray source positionally consistent with
4C +10.45 was significantly detected. The average FXT 0.5-10 keV spectrum
can be fitted with an absorbed power-law model with a fixed Galactic hydrogen
column density of 5 X 10^20 cm^-2 and a photon index of 1.38 (+0.20/-0.19).
The derived average unabsorbed 0.5-10 keV flux is 4.16 (+1.07/-0.82) X
10^-12 erg cm^-2 s^-1. The uncertainties quoted above are at the 90% confidence
level.

The source has previously been detected with the Neil Gehrels Swift Observatory
and is listed in the Second Swift-XRT Point Source Catalogue as 2SXPS J160846.0+102907.
The catalogue reports an unabsorbed 0.3-10 keV flux of (2.34+/-0.05) X
10^-12 erg cm^-2 s^-1.

During July 25, 2026, which covered the Einstein Probe observation, 4C
+10.45 was not significantly detected by the Fermi-LAT. Assuming a power-law
spectrum with photon index 2.0, the corresponding 95% confidence upper
limit on the photon flux (E>100MeV) is 0.8 X 10^-6 photons cm^-2 s^-1.
However, preliminary analysis of the three-day interval from July 23 to
July 25, 2026, indicates significant gamma-ray emission from 4C +10.45,
with an average gamma-ray flux (E > 100 MeV) of (0.5 +/- 0.1) x 10^-6 photons
cm^-2 s^-1 and TS around 70. This corresponds to a flux increase by a factor
of approximately 20 relative to the 4FGL-DR4 average, while the corresponding
photon index of 2.55 +/- 0.20 is consistent with the catalog value of 2.53
+/- 0.03.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue. A preliminary light curve for
4C +10.45 can be accessed via the <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1608.7+1029">Fermi-LAT
Light-Curve Repository</a> and via the <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/4C_p10d45">Monitored
Source List</a>. For this source, the Fermi-LAT contact person is Adithiya
Dinesh (adinesh@ucm.es).

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. We further acknowledge the commitment
of the Einstein Probe Team, Observatory Duty Scientists, and PI, who made
these observations possible.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor
the soft X-ray sky with 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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