Determination of K4000 of potential blazar candidates among EGRET unidentified gamma-ray sources. (arXiv:2004.03154v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Uwitonze_E/0/1/0/all/0/1">Emmanuel Uwitonze</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nkundabakura_P/0/1/0/all/0/1">Pheneas Nkundabakura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mutabazi_T/0/1/0/all/0/1">Tom Mutabazi</a>
Blazars are radio-loud Active Galactic Nuclei (AGN) with relativistic jets
oriented towards the observer’s line-of-sight. Based on their optical spectra,
blazars may be classified as flat-spectrum radio quasars (FSRQs) or BL Lacs.
FSRQs are more luminous blazars with both narrow and broad emission and
absorption lines, while BL Lacs are less luminous and featureless. Recent
studies show that blazars dominate (93%) the already-identified EGRET sources
(142), suggesting that among the unidentified sources (129) there could still
be faint blazars. Due to the presence of a strong non-thermal component inside
their jets, blazars are found to display a weaker depression at 4000 {AA}
(K4000<0.4). In this study, we aimed at determining the K4000 break for a
selected sample among the potential blazar candidates from unidentified EGRET
sources to confirm their blazar nature. We used two blazar candidates,
3EGJ1800-0146 and 3EGJ1709-0817 associated with radio counterparts, J1802-0207
and J1713-0817, respectively. Their optical counterparts were obtained through
spectroscopic observations using Robert Stobie spectrograph (RSS) at the
Southern African Large Telescope (SALT) in South Africa. The observed Ca II H &
K lines depression at 4000 {AA} in spectra of these sources show a shallow
depression, K4000=0.35+-0.02 and 0.24+-0.01, respectively, suggesting that
these sources are blazar candidates. Moreover, the redshifts z=0.165 and 0.26
measured in their spectra confirm the extragalactic nature of these sources.
Keywords: line: identification, radiation mechanisms: non-thermal,
techniques: spectroscopic, galaxies: active, galaxies: jets, galaxies: BL
Lacertae objects
Blazars are radio-loud Active Galactic Nuclei (AGN) with relativistic jets
oriented towards the observer’s line-of-sight. Based on their optical spectra,
blazars may be classified as flat-spectrum radio quasars (FSRQs) or BL Lacs.
FSRQs are more luminous blazars with both narrow and broad emission and
absorption lines, while BL Lacs are less luminous and featureless. Recent
studies show that blazars dominate (93%) the already-identified EGRET sources
(142), suggesting that among the unidentified sources (129) there could still
be faint blazars. Due to the presence of a strong non-thermal component inside
their jets, blazars are found to display a weaker depression at 4000 {AA}
(K4000<0.4). In this study, we aimed at determining the K4000 break for a
selected sample among the potential blazar candidates from unidentified EGRET
sources to confirm their blazar nature. We used two blazar candidates,
3EGJ1800-0146 and 3EGJ1709-0817 associated with radio counterparts, J1802-0207
and J1713-0817, respectively. Their optical counterparts were obtained through
spectroscopic observations using Robert Stobie spectrograph (RSS) at the
Southern African Large Telescope (SALT) in South Africa. The observed Ca II H &
K lines depression at 4000 {AA} in spectra of these sources show a shallow
depression, K4000=0.35+-0.02 and 0.24+-0.01, respectively, suggesting that
these sources are blazar candidates. Moreover, the redshifts z=0.165 and 0.26
measured in their spectra confirm the extragalactic nature of these sources.
Keywords: line: identification, radiation mechanisms: non-thermal,
techniques: spectroscopic, galaxies: active, galaxies: jets, galaxies: BL
Lacertae objects
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