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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17142, 17143
Message-Id: <20250413071205.C24C3288082E@server.astronomerstelegram.org>
Date: Sun, 13 Apr 2025 03:12:05 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17142							     ATEL #17142

Title:	Swift XRT follow-up observations of 3C138
Author:	Federica Giacchino (INFN Roma Tor Vergata &amp; SSDC ASI),
		 Pietro Monti-Guarnieri (University of Trieste and INFN Trieste),
		Giovanni La Mura (INAF-OAC) on behalf of the Fermi Large Area Telescope
		Collaboration
Queries:	federica.giacchino@roma2.infn.it
Posted:	12 Apr 2025; 20:14 UT
Subjects:Optical, Ultra-Violet, X-ray, AGN, Blazar, Quasar

Following the flaring activity observed (ATel #17107) from a gamma-ray
source positionally consistent with the compact steep spectrum quasar 3C
138 also known as 4FGL J0521.2+1637 (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546),
with radio coordinates R.A. = 80.29119 deg, Decl. = +16.63946 deg (J2000;
Truebenbach and Darling 2017, ApJS, 233, 3), and redshift z= 0.759 (Lynds
et al. 1966, ApJ, 144, 1244), we requested a medium-urgency Swift target
of opportunity multiple observation.

Swift XRT data were taken in photon counting mode for a total net exposure
of approximately 3.2 ksec split in three observations performed on March
27, 2025 (three days after the Fermi LAT flare announced in ATel#17107)
for 1.8 ksec exposure, on March 29, 2024 for 1.38 ksec and on March 31,
2024 for 0.2 ksec. For these three single observations the XRT X-ray spectrum
of 3C 138 can be fitted by an absorbed single power law with the HI column
density fixed to the Galactic value of N_HI = 10^22 cm^-2 (Dickey & Lockman
1990) and a power-law variable photon spectral index respectively of 1.77+/-0.40
for March 27 and 1.68+/-0.37 for March 29. The 0.2ks XRT exposure on March
31 did not yield enough counts to estimate the spectral properties.

The unabsorbed X-ray fluxes in the 0.4-10 keV energy band respectively
are (3.1+/-0.1)x10^-12 erg cm^-2s^-1 for March 27 and (3.9+/-0.2)x10^-12
erg cm^-2s^-1 for March 29 observations. The flux level of both observations
is larger than previous X-ray detected by Chandra for the source and reported
in Wang et al. (2016, ApJS, 224, 40W).

Simultaneous Swift-UVOT observations have been performed. The observed
magnitude on March 27 is: UVW2=18.20+/- 0.07; on March 29 UVW1=17.52+/-0.05.
No previous observations in these bands have been found.

In consideration of the ongoing activity of this source, confirmed also
by the Swift observations and radio observations ATel #17077 and #17104,
we encourage further multiwavelength observations. For this source, the
Fermi-LAT contact persons are Ettore Bronzini (ettore.bronzini@inaf.it)
and C.C. Cheung (Teddy.Cheung@nrl.navy.mil).

We would like to thank the Swift Team for making these observations possible,
in particular J. J. DeLaunay as the Swift Observatory Duty Scientist

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Password Certification: Federica Giacchino (federica.giacchino@roma2.infn.it)
https://www.astronomerstelegram.org/?read=17142
==============================================================================
ATEL #17143							     ATEL #17143

Title:	Long-Term X-Ray Flaring in the TeV-Decected Blazar 1ES 1101-232
Author:	Bidzina Kapanadze (Ilia State University, Tbilisi, Georgia;
		National Astrophysical Observatory, Abastumani, Georgia)
Queries:	bidzina_kapanadze@iliauni.edu.ge
Posted:	13 Apr 2025; 06:17 UT
Subjects:X-ray, Blazar

The southern TeV-detected ultra-high-frequency peaked BL Lac object (UHBL)
1ES 1101-232 (z=0.186) has been observed 83 times with the X-Ray Telescope
(XRT) onboard onboard the Neil Gehrels Swift Observatory since 2005 June
30. These observations showed a strong flaring activity several times,
with the highest-amplitude flare and  the highest historical XRT-band state
during 2023 November--2024 January (recorded during the Swift-TOO observations
triggered by us; see Kapanadze B., ATels #16322 and #16396). Since 2024
March 5, the source was visited six times by Swift-XRT (in the framework
of our TOO Request Number 22119 and 22371)  and this monitoring revealed
an onset of another long-term X-ray flare: the last observation (performed
on April 11) was characterized  by the 0.3-10 keV count rate of 2.19+/-0.08
cts/s (after the gradual brightening during the monitoring), which is ~20%
higher than the mean rate from all XRT observations of 1ES 1101-232. Since
the source is in X-ray flaring state and a further brightening may occur,
as well as enhanced multiwavelength (MWL) activity is predicted also in
other spectral ranges in the framework of one-zone SSC scenario, we strongly
encourage intense MWL observations with the space and ground-based instruments.

XRT is one of the Swift instruments along with Burst Alert Telescope (BAT)
and UV/Optical Telescope (UVOT). It is a JET-X Wolter I type telescope,
developed jointly by Pennsylvania State University, Brera Astronomical
Observatory (OAB) and University of Leicester. Thanks to the unique characteristics,
good photon statistics and low background counts of this instrument (in
combination with EEV CCD2 detector), we can investigate a flux variability
on different time-scales from minutes to years, obtain high-quality spectra
for the majority of the observations, derive different spectral parameters,
and study their timing behaviour in the 0.3-10 keV range of the electromagnetic
spectrum. The Swift Satellite is operated by Pennsylvania State University.

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Password Certification: Bidzina  Kapanadze (bidzina_kapanadze@iliauni.edu.ge)
https://www.astronomerstelegram.org/?read=17143
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