73 research outputs found
Testing the Blazar Sequence with Spectra of Recently Discovered Dim Blazars from the Fermi Unassociated Catalog
Recent works have developed samples of blazars from among the Fermi-LAT
unassociated sources via machine learning comparisons with known blazar
samples. Continued analysis of these new blazars tests the predictions of the
blazar sequence and enables more flux-complete samples of blazars as a
population. Using Fermi, Swift, WISE, and archival radio data, we construct
broadband spectral energy distributions for 106 recently identified blazars.
Drawn from the unassociated 4FGL source sample, this new sample has a lower
median flux than the overall sample of gamma-ray blazars. By measuring the
synchrotron peak frequency, we compare our sample of new blazars with known
blazars from the 4LAC catalog. We find that the bulk of the new blazars are
similar to High-Synchrotron Peak (HSP) BL Lac objects, with a higher median
synchrotron peak; the sample has a median via
BLaST peak estimation, compared to for the
4LAC BL Lacs. Finally, we conduct synchrotron self-Compton (SSC) leptonic
modeling, comparing fitted physical and phenomenological properties to brighter
blazars. We find that the new blazars have smaller characteristic Lorentz
factors and fitted magnetic fields , in agreement with
blazar sequence predictions. The new blazars have slightly higher Compton
dominance ratios than expected, which may point to alternative emission models
for these dim blazars. Our results extend the predictions of the blazar
sequence to a sample of dimmer blazars, confirming the broad predictions of
that theory.Comment: 13 pages main body with 10 figures. 8 pages of data table
Using Neural Networks to Differentiate Newly Discovered BL Lacs and FSRQs among the 4FGL Unassociated Sources Employing Gamma-ray, X-ray, UV/Optical and IR Data
Among the ~2157 unassociated sources in the third data release (DR3) of the
fourth Fermi catalog, ~1200 were observed with the Neil Gehrels Swift
Observatory pointed instruments. These observations yielded 238 high S/N X-ray
sources within the 95% Fermi uncertainty regions. Recently, Kerby et al.
employed neural networks to find blazar candidates among these 238 X-ray
counterparts to the 4FGL unassociated sources and found 112 likely blazar
counterpart sources. A complete sample of blazars, along with their
sub-classification, is a necessary step to help understand the puzzle of the
blazar sequence and for the overall completeness of the gamma-ray emitting
blazar class in the Fermi catalog. We employed a multi-perceptron neural
network classifier to identify FSRQs and BL Lacs among these 112 blazar
candidates using the gamma-ray, X-ray, UV/optical, and IR properties. This
classifier provided probability estimates for each source to be associated with
one or the other category, such that P_fsrq represents the probability for a
source to be associated with the FSRQ subclass. Using this approach, 4 FSRQs
and 50 BL Lacs are classified as such with >99% confidence, while the remaining
58 blazars could not be unambiguously classified as either BL Lac or FSRQ.Comment: Accepted for publication in A
Swift Follow-Up of Reported Radio Pulsars at Fermi 4FGL Unassociated Sources
Following the discovery of radio pulsars at the position of Fermi-LAT
unassociated sources by the TRAPUM group, we conduct Swift-XRT observations of
six of those 4FGL sources to determine if any pulsar-like X-ray sources are
present and to confirm the reported detection of an X-ray counterpart via
eROSITA at 4FGL J1803.1-6708. At two of the six targets, we detect no X-ray
sources at the TRAPUM radio position, placing an upper limit on the 0.3-10.0
keV flux. At 4FGL J1803.1-6708 we find an X-ray source at the TRAPUM and
eROSITA position. At 4FGL J1858.3-5424 we find a new X-ray counterpart at the
TRAPUM position with S/N=4.17, but also detect a distinct and separate X-ray
source. At 4FGL J1823.8-3544 and 4FGL J1906.4-1757 we detect no X-ray flux at
the TRAPUM positions, but we do detect separate X-ray sources elsewhere in the
Fermi error ellipse. At these last two targets, our newly detected Swift
sources are possible alternatives to the radio pulsar associations proposed by
TRAPUM. Our findings confirm several of the discoveries reported by the TRAPUM
group but suggest that further observations and investigations are necessary to
confirm the low-energy counterpart of several unassociated sources.Comment: 10 pages main text, 6 figures, 2 table
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