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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel  17417, 17418
Message-Id: <20250925071206.53EA028808E6@server.astronomerstelegram.org>
Date: Thu, 25 Sep 2025 03:12:06 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17417							     ATEL #17417

Title:	Fermi-LAT detection of enhanced gamma-ray activity from the
		FSRQ CGRaBS J1848+3219
Author:	A. Holzmann Airasca (University of Trento &amp; INFN Bari)
		and G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf
		of the Fermi Large Area Telescope Collaboration
Queries:	a.holzmannairasca@unitn.it
Posted:	24 Sep 2025; 18:34 UT
Subjects:Gamma Ray, >GeV, 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 CGRaBS
J1848+3219, also known as B2 1846+32A and 4FGL J1848.4+3217 (Abdollahi
et al. 2020, ApJS, 247, 33), with coordinates R.A. = 282.09204 deg, Decl.
= +32.31739 deg (J2000, Le Bail et al., 2016, AJ, 151, 79), and redshift
z=0.798 (Sowards-Emmerd et al. 2005, ApJ, 626, 95).

Preliminary analysis indicates that this source was in an elevated gamma-ray
emission state on September 23, 2025, with a daily averaged gamma-ray flux
(E>100MeV) of (0.4+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty
only). This corresponds to a flux increase of a factor of 20 relative to
the average flux reported in the fourth data release of the fourth Fermi-LAT
catalog (4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546). The corresponding
photon index is 2.0+/-0.2 indicating a significantly harder spectral state
than the one inferred from the average power-law spectral index of 2.42
+/- 0.03 reported in 4FGL-DR4. The Fermi LAT Collaboration has previously
reported flaring activity from this source in ATel #2954.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray
monitoring of this source will continue. This source is part of the Fermi-LAT
daily Monitored source list, so its daily light curve is available <a href="https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/CGRaBS_J1849p6705">here</a>.
A preliminary light curve can also 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_J1848.4+3217">4FGL
J1848.4+3217</a>. We encourage multifrequency observations of this source.
For this source, the Fermi-LAT contact person is Aldana Holzmann Airasca
(a.holzmannairasca@unitn.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: Giovanni La Mura (giovanni.lamura@inaf.it)
https://www.astronomerstelegram.org/?read=17417
==============================================================================
ATEL #17418							     ATEL #17418

Title:	Early Swift-XRT detection of heavily-absorbed shock-powered
		X-rays from nova V1935 Cen = PNV J14372177-5847400
Author:	Kirill Sokolovsky (UIUC), Kim Page (U. Leicester), Elias Aydi
		(TTU), Laura Chomiuk, Peter Craig, Isabella Molina (MSU), Jennifer
		Sokoloski (Columbia), Justin Linford (NRAO), Koji Mukai (NASA/GSFC)
Queries:	kirx@kirx.net
Posted:	24 Sep 2025; 21:42 UT
Subjects:X-ray, Nova

Nova Centauri 2025, also known as V1935 Cen and  
PNV J14372177-5847400 was discovered by John Seach at magnitude 6.2  
using DSLR camera images obtained on 2025-09-22.396 UT with  
a 40-mm-f.l. f/1.4 lens. Nothing brighter than magnitude 11.0 was  
visible at the nova position in images obtained the previous night  
on 2025-09-21.366 with the same setup. A low-resolution optical  
spectrum obtained by Rob Kaufman on 2025-09-23.383 was interpreted  
as that of a classical nova (CBET #5611). The nova was detected as  
a bright GeV source by Fermi-LAT with the first detection in  
a 6-hr bin starting on 2025-09-21.50, prior to the optical discovery  
(ATel #17414).

V1935 Cen was observed with Swift for 3.4ks split in two visits  
centered on 2025-09-23.64 (1.2 days after the optical discovery,  
2.3 days after the latest optical non-detection). Swift-XRT was  
operating in Windowed Timing mode to minimize optical loading.  
A bright and hard X-ray source was detected at the position  
of the nova having the grade 0-2 count rate of 0.20 +/-0.01 cts/s  
with all the source counts being above 1.5 keV. The spectrum is  
consistent with that of a thermal plasma with kT= 15 keV absorbed  
by an equivalent hydrogen column of N_H= 1.1x10^23 cm^-2, an order  
of magnitude above the Galactic value in this direction  
(8.6x10^21 cm^-2; Kalberla et al. 2005 A&A, 440, 775).  
The unabsorbed flux extrapolated to the full Swift-XRT band  
of 0.3-10 keV is 4.7x10^-11 ergs/cm^2/s.

Most classical novae remain undetected by Swift-XRT at the time  
when they emit gamma-rays (Gordon et al. 2021, ApJ, 910, 134),  
while novae embedded in red giant wind tend to show early  
detections (e.g., RS Oph; Cheung et al. 2022, ApJ, 935, 44).  
The early Swift-XRT detection of V1935 Cen may indicate a symbiotic  
nature of the host binary system. Alternatively, this nova may be  
unusually fast in clearing up its ejecta sufficiently to enable  
Swift-XRT detection two days after the eruption.

We thank the Neil Gehrels Swift Observatory team and PI, Brad Cenko,  
for rapid execution this ToO observation.

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Password Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
https://www.astronomerstelegram.org/?read=17418
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