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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel 17134, 17135, 17136
Message-Id: <20250407071633.48A7B28809E8@server.astronomerstelegram.org>
Date: Mon, 7 Apr 2025 03:16:33 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17134							     ATEL #17134

Title:	The blazar 3C345 - the highest brightness over almost two decades
Author:	V. V. Vlasyuk, O. I. Spiridonova, A. S. Moskvitin and T. A.
		Fatkhullin (Special Astrophysical Observatory of the Rus. Ac. Sci.)
Queries:	mosk@sao.ru
Posted:	6 Apr 2025; 08:06 UT
Subjects:Optical, Blazar

Our BVRI-monitoring of the bright blazars sample using our 1-meter and
0.5-meter reflectors is in progress. As it was noted in March (ATels #17059
and #17085), the blazar 3C345 is undergoing an epoch of exceptionally high
optical activity. The last estimates of its brightness were performed with
1-meter reflector only with different photometers, which are equipped by
conventional CCD and EM CCD detectors.

After achieving R = 15.83 mag at MJD 60738.12 the blazar became fainter
by 1 magnitude within one week (R = 16.76 mag at MJD 60744.07) according
to our estimates. The current most powerful re-brightening phase for 3C
345 started in the middle of March --- from level R=16.29 mag on March
14/15 night.

Now the 3C 345 is undergoing a phase of exponential growth with a slope
between 0.15 and 0.2 mags per day. The highest level R=14.99 mag was detected
within our last night observations (MJD 60770.94). We have detected the
higher blazar brightness (R between 14.45 and 14.70) as far as 19 years
ago --- within the course of its 2006 June-August outburst.

The monitoring of 3C 345 is continuing; the most of data presented were
taken under good weather conditions (seeing (FWHM) < 2 arcsec and normal
transparency) and have typical accuracy about 0.01 mags. We strongly encourage
further multi-wavelength studies.

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Password Certification: Alexander Moskvitin (mosk@sao.ru)
https://www.astronomerstelegram.org/?read=17134
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ATEL #17135							     ATEL #17135

Title:	Fermi-LAT detection of renewed gamma-ray activity from the
		FSRQ PKS 0235-618
Author:	Adithiya Dinesh (Universidad Complutense de Madrid), Janeth
		Valverde (Marquette University),  on behalf of the Fermi Large Area
		Telescope Collaboration
Queries:	adinesh@ucm.es
Posted:	7 Apr 2025; 01:04 UT
Subjects:Gamma Ray, >GeV, VHE, Request for Observations, AGN, Blazar,
		Quasar

The Large Area Telescope (LAT), one of the two instruments on the Fermi
Gamma-ray Space Telescope, has observed renewed gamma-ray activity from
a source positionally consistent with the flat-spectrum radio quasar PKS
0235-618, also known as 4FGL J0236.8-6136 (4FGL; The Fermi-LAT collaboration
2020, ApJS, 247, 33), with coordinates R.A. = 39.22186 deg, Dec. = -61.60422
deg (J2000; Xu et al., 2019, ApJS, 242, 5), and redshift z=0.465 (Healey,
S. et al. 2008, ApJS, 175, 97).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on April 5, 2025, with a daily averaged gamma-ray flux (E>100MeV)
of (0.7+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only).
This corresponds to a flux increase of a factor of 50 relative to the average
flux reported in the 4FGL-DR4 (Ballet, J. et al. 2023). The corresponding
photon index is 1.9+/-0.1, indicating a significantly harder spectrum than
the 4FGL value of 2.29+/-0.03. We have reported previous flares from this
source in ATel #2669 and #16994.

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 0235-618 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_J0236.8-6136">LCR</a>,
and via the Monitored Source List at <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0235-618">MSL</a>.
We encourage multifrequency observations of this source. For this source,
the Fermi-LAT contact person is Sara Cutini (sara.cutini@asdc.asi.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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Password Certification: Janeth Valverde (valverde@llr.in2p3.fr)
https://www.astronomerstelegram.org/?read=17135
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ATEL #17136							     ATEL #17136

Title:	XRISM/Xtend Transient Search (XTS) detected an X-ray flare
		from a YSO
Author:	H. Sugai (Chuo U.), K. Fukushima, K. Hayashi, Y. Kanemaru,
		S. Ogawa, T. Yoshida (JAXA), M. Audard (U. de Geneve), E. Behar (Technion),
		S. Inoue (Kyoto U.), Y. Ishihara (Chuo U.), T. Kohmura (TUS), Y. Maeda
		(JAXA), M. Mizumoto (UTEF), N. Nagashima (Chuo U.), M. Nobukawa (NUE),
		K. Pottschmidt (UMBC, NASA GSFC, CRESST), M. Shidatsu (Ehime U.),
		Y. Terada (Saitama U.), Y. Terashima (Ehime U.), Y. Tsuboi (Chuo U.),
		H. Uchida (Kyoto U.), T. Yoneyama (Chuo U.), M. Yoshimoto (Ehime U.),
		Y. Fujita (TMU) 
Queries:	tyoneyama263@g.chuo-u.ac.jp
Posted:	7 Apr 2025; 01:33 UT
Subjects:X-ray, Transient, Variables, Young Stellar Object

XRISM/Xtend Transient Search (XTS) detected an X-ray flare from an X-ray
source XRISM J1712-2310 on 2025-04-05 TT. The source position is determined
to be (R.A., Dec.) = (258.042, -23.162), with a systematic error of &sim;
40 arcsec. A plausible counterpart is a YSO CD-23 13197, whose distance
is 115 pc. CD-23 13197 is located &sim; 20 arcsec apart from the position
of XRISM J1712-2310.

The flare started at 2025-04-05 at &sim; 23:50 TT. The flare reached its
peak on 2025-04-06 at &sim; 01:10. The flare was still ongoing at the end
of the XRISM observation, but the e-folding time is estimated to be &sim;
20 ks. 
The peak flux is estimated as 1 &times; 10-12 erg s-1
cm-2 (0.4 &ndash; 10.0 keV). Corresponding luminosity is 2 &times;
D120pc<sup2> &times; 1030 erg s-1
by assuming the distance to XRISM J1712-2310 of D120pc.

We derived the above systematic error for the flux by comparing our derived
values for the sources detected with XTS in several observations with those
for the corresponding X-ray counterparts. We estimated the systematic error
for the source position from the separations between the detected sources
with the corresponding counterparts in the same field of view.

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Password Certification: Tomokage Yoneyama (tyoneyama263@g.chuo-u.ac.jp)
https://www.astronomerstelegram.org/?read=17136
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