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Sabyasachi Pal

Publications and source records attributed to Sabyasachi Pal.

At least 55 records · Page 3Linked to original sources
arXiv2023

Evidence for low power radio jet-ISM interaction at 10 parsec in the dwarf AGN host NGC 4395

Black hole driven outflows in galaxies hosting active galactic nuclei (AGN) may interact with their interstellar medium (ISM) affecting star formation. Such feedback processes, reminiscent of those seen in massive galaxies, have been reported recently in some dwarf galaxies. However, such studies have usually been on kiloparsec and larger scales and our knowledge on the smallest spatial scales to which these feedback processes can operate is unclear. Here we demonstrate radio jet$-$ISM interaction on the scale of an asymmetric triple radio structure of $\sim$ 10 parsec size in NGC 4395. This triple radio structure is seen in the 15 GHz continuum image and the two asymmetric jet-like structures are situated on either side of the radio core that coincides with the optical {\it Gaia} position. The high resolution radio image and the extended [OIII]$λ$5007 emission, indicative of an outflow, are spatially coincident and are consistent with the interpretation of a low power radio jet interacting with the ISM. Modelling of the spectral lines using {\tt MAPPINGS}, and estimation of temperature using optical integral field spectroscopic data suggest shock ionization of the gas. The continuum emission at 237 GHz, though weak, was found to spatially coincide with the AGN. However, the CO(2$-$1) line emission was found to be displaced by around 20 parsec northward of the AGN core. The spatial coincidence of molecular H$_2$$λ$2.4085 along the jet direction, the morphology of ionised [OIII]$λ$5007 and displacement of the CO(2$-$1) emission argues for conditions less favourable for star formation in the central $\sim$ 10 parsec region.

astro-ph.GA↗
arXiv2023

Probing spectral and timing properties of the X-ray pulsar RX J0440.9+4431 in the giant outburst of 2022-2023

The X-ray pulsar RX J0440.9+4431 went through a giant outburst in 2022 and reached a record-high flux of 2.3 Crab, as observed by Swift/BAT. We study the evolution of different spectral and timing properties of the source using NICER observations. The pulse period is found to decrease from 208 s to 205 s, and the pulse profile evolves significantly with energy and luminosity. The hardness ratio and hardness intensity diagram (HID) show remarkable evolution during the outburst. The HID turns towards the diagonal branch from the horizontal branch above a transition (critical) luminosity, suggesting the presence of two accretion modes. Each NICER spectrum can be described using a cutoff power law with a blackbody component and a Gaussian at 6.4 keV. At higher luminosities, an additional Gaussian at 6.67 keV is used. The observed photon index shows negative and positive correlations with X-ray flux below and above the critical luminosity, respectively. The evolution of spectral and timing parameters suggests a possible change in the emission mechanism and beaming pattern of the pulsar depending on the spectral transition to sub- and super-critical accretion regimes. Based on the critical luminosity, the magnetic field of the neutron star can be estimated in the order of 10$^{12}$ or 10$^{13}$ G, assuming different theoretical models. Moreover, the observed iron emission line evolves from a narrow to a broad feature with luminosity. Two emission lines originating from neutral and highly ionized Fe atoms were evident in the spectra around 6.4 keV and 6.67 keV (higher luminosities).

astro-ph.HE↗
arXiv2023

Identification of the simplest sugar-like molecule glycolaldehyde towards the hot molecular core G358.93-0.03 MM1

Glycolaldehyde (CH$_{2}$OHCHO) is the simplest monosaccharide sugar in the interstellar medium, and it is directly involved in the origin of life via the 'RNA world' hypothesis. We present the first detection of glycolaldehyde (CH$_{2}$OHCHO) towards the hot molecular core G358.93-0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array (ALMA). The calculated column density of CH$_{2}$OHCHO towards G358.93-0.03 MM1 is (1.52$\pm$0.9)$\times$10$^{16}$ cm$^{-2}$ with an excitation temperature of 300$\pm$68.5 K. The derived fractional abundance of CH$_{2}$OHCHO with respect to H$_{2}$ is (4.90$\pm$2.92)$\times$10$^{-9}$, which is consistent with that estimated by existing two-phase warm-up chemical models. We discuss the possible formation pathways of CH$_{2}$OHCHO within the context of hot molecular cores and hot corinos and find that CH$_{2}$OHCHO is likely formed via the reactions of radical HCO and radical CH$_{2}$OH on the grain surface of G358.93-0.03 MM1.

astro-ph.GA↗
arXiv2023

Multi-frequency study of large size radio galaxies 3C 35 and 3C 284

We report multi-frequency observations of large radio galaxies 3C 35 and 3C 284. The low-frequency observations were done with Giant Metrewave Radio Telescope starting from $\sim150$ MHz, and the high-frequency observations were done with the Very Large Array. We have studied the radio morphology of these two sources at different frequencies. We present the spectral ageing map using two of the most widely used models, the Kardashev-Pacholczyk and Jaffe-Perola models. Another more realistic and complex Tribble model is also used. We also calculate the jet-power and the speed of the radio lobes of these galaxies. We check whether any episodic jet activity is present in these galaxies and found no sign of such activity.

astro-ph.GA↗
arXiv2023

Detection of complex nitrogen-bearing molecule ethyl cyanide towards the hot molecular core G10.47+0.03

The studies of the complex organic molecular lines towards the hot molecular cores at millimeter and submillimeter wavelengths provide instructive knowledge about the chemical complexity in the interstellar medium (ISM). We present the detection of the rotational emission lines of the complex nitrogen-bearing molecule ethyl cyanide (C$_{2}$H$_{5}$CN) towards the chemically rich hot molecular core G10.47+0.03 using the Atacama Large Millimeter/Submillimeter Array (ALMA) band 4 observations. The estimated column density of C$_{2}$H$_{5}$CN towards the G10.47+0.03 is (7.7$\pm$0.5)$\times$10$^{16}$ cm$^{-2}$ with the high rotational temperature of 352.9$\pm$66.8 K. The estimated fractional abundance of C$_{2}$H$_{5}$CN with respect to H$_{2}$ towards the G10.47+0.03 is 5.70$\times$10$^{-9}$. We observe that the estimated fractional abundance of C$_{2}$H$_{5}$CN is similar to the existing three-phase warm-up chemical modelling abundance of C$_{2}$H$_{5}$CN. We also discuss the possible formation mechanism of C$_{2}$H$_{5}$CN towards the hot molecular cores, and we claim the barrierless and exothermic radical-radical reaction between CH$_{2}$ and CH$_{2}$CN is responsible for the production of low abundant of C$_{2}$H$_{5}$CN ($\sim$10$^{-9}$) in the grain surface of G10.47+0.03.

astro-ph.GA↗
arXiv2023

Detection of monothioformic acid towards the solar-type protostar IRAS 16293-2422

In the interstellar medium (ISM), the complex organic molecules that contain the thiol group ($-$SH) play an important role in the polymerization of amino acids. We look for SH-bearing molecules in the chemically rich solar-type protostar IRAS 16293-2422. After the extensive spectral analysis using the local thermodynamic equilibrium (LTE) model, we have detected the rotational emission lines of trans-isomer monothioformic acid (t-HC(O)SH) towards the IRAS 16293 B using the Atacama Large Millimeter/Submillimeter Array (ALMA). We did not observe any evidence of cis-isomer monothioformic acid (c-HC(O)SH) towards the IRAS 16293 B. The column density of t-HC(O)SH towards the IRAS 16293 B was (1.02$\pm$0.6)$\times$10$^{15}$ cm$^{-2}$ with an excitation temperature of 125$\pm$15 K. The fractional abundance of t-HC(O)SH with respect to H$_{2}$ towards the IRAS 16293 B is 8.50$\times$10$^{-11}$. The column density ratio of t-HC(O)SH/CH$_{3}$SH towards the IRAS 16293 B is 0.185. We compare our estimated abundance of t-HC(O)SH towards the IRAS 16293 B with the abundance of t-HC(O)SH towards the galactic center quiescent cloud G+0.693-0.027 and hot molecular core G31.41+0.31. After the comparison, we found that the abundance of t-HC(O)SH towards the IRAS 16293 B is several times of magnitude lower than G+0.693-0.027 and G31.41+0.31. We also discuss the possible formation mechanism of t-HC(O)SH in the ISM.

astro-ph.GA↗
arXiv2023

Identification of interstellar cyanamide towards the hot molecular core G358.93-0.03 MM1

The amide-related molecules are essential for the formation of the other complex bio-molecules and an understanding of the prebiotic chemistry in the interstellar medium (ISM). We presented the first detection of the rotational emission lines of the amide-like molecule cyanamide (NH$_{2}$CN) towards the hot molecular core G358.93$-$0.03 MM1 using the Atacama Large Millimeter/Submillimeter Array (ALMA). Using the rotational diagram model, the derived column density of NH$_{2}$CN towards the G358.93$-$0.03 MM1 was (5.9$\pm$2.5)$\times$10$^{14}$ cm$^{-2}$ with a rotational temperature of 100.6$\pm$30.4 K. The derived fractional abundance of NH$_{2}$CN towards the G358.93$-$0.03 MM1 with respect to H$_{2}$ was (4.72$\pm$2.0)$\times$10$^{-10}$, which is very similar to the existent three-phase warm-up chemical model abundances of NH$_{2}$CN. We compare the estimated abundance of NH$_{2}$CN towards G358.93$-$0.03 MM1 with other sources, and we observe the abundance of NH$_{2}$CN towards G358.93$-$0.03 MM1 is nearly similar to that of the sculptor galaxy NGC 253 and the low-mass protostars IRAS 16293-2422 B and NGC 1333 IRAS4A2. We also discussed the possible formation mechanisms of NH$_{2}$CN towards the hot molecular cores and hot corinos, and we find that the NH$_{2}$CN molecule was created in the grain-surfaces of G358.93-0.03 MM1 via the neutral-neutral reaction between NH$_{2}$ and CN.

astro-ph.GA↗
arXiv2023

Temporal and spectral study of the X-ray pulsar 2S 1553-542 during the 2021 outburst

We study the timing and spectral properties of the X-ray pulsar 2S 1553--542 using the NuSTAR, and NICER during the outburst in January--February 2021. During the outburst, the spin period of the neutron star was 9.2822 s based on NuSTAR data. The pulse profiles are studied using different NICER observations, which implies that the profile is more or less sinusoidal with a single peak and the beaming patterns are mostly dominated by the pencil beam. The NICER spectra of the source are studied for different days of the outburst and can be well described by a model consisting of a blackbody emission and power law along with a photoelectric absorption component. The variation of spectral parameters with luminosity is studied over the outburst. The photon index shows anti-correlation with luminosity below the critical luminosity, which implies that the source was accreting in the sub-critical accretion regime during the NICER observations. We also report the anti-correlation between pulsed fraction (PF) and luminosity of the 2S 1553--542 using NICER observations. The evolution of spin-up rate with luminosity is studied during the outburst, which implies that both are strongly correlated. The torque-luminosity model is applied to estimate the magnetic field at different spin-up rates. The magnetic field is estimated to be 2.56 $\times 10^{12}$ G from the torque-luminosity model using the source distance of 20 kpc. The magnetic field is also estimated using the critical luminosity, which is also consistent with our findings.

astro-ph.GA↗
arXiv2023

A new catalogue of head-tail radio galaxies from LoTSS DR1

The unique morphology of head-tail (HT) radio galaxies suggests that radio jets and their intra-cluster medium interact strongly. We conducted a systematic search for HT radio galaxies using the LOFAR Two-metre Sky Survey first data release (LoTSS DR1) at 144 MHz. In this paper, a catalogue of fifty-five new HT radio galaxies is presented, ten of which are narrow-angle tailed sources (NATs) and forty-five of which are wide-angle tailed sources (WATs). NATs are characterised by tails that are bent like a narrow `V' shape with a less than 90 degree opening angle. The opening angle between jets in WAT radio galaxies is greater than ninety degrees, exhibiting wide `C'-like morphologies. We found that thirty out of fifty-five HT radio galaxies reported in this article are associated with known galaxy clusters. Most of the sources presented in the current paper have redshifts $<$ 0.5. The various physical properties and statistical studies of these HT radio galaxies are presented.

astro-ph.GA↗
arXiv2023

The study of thermonuclear X-ray bursts in accreting millisecond pulsar MAXI J1816-195 with NuSTAR and NICER

The millisecond pulsar MAXI J1816-195 was recently discovered in an outburst by MAXI in 2022 May. We study different properties of the pulsar using data from NuSTAR and NICER observations. The unstable burning of accreted material on the surface of neutron stars induces thermonuclear (Type-I) bursts. Several such thermonuclear bursts have been detected by MAXI J1816-195 during its outburst. We investigate the evolution of the burst profile with flux and energy using NuSTAR and NICER observations. During the NuSTAR observation, a total of four bursts were detected from the source. The duration of each burst is around $\sim$ 30 s and the ratio of peak to persistent count rate is $\sim$ 26 as seen from the NuSTAR data. The burst profiles are modelled using a sharp linear rise and exponential decay function to determine the burst timing parameters. The burst profiles show a relatively long tail at lower energies. The broadband time-resolved spectra during the burst periods are successfully modelled with a combination of an absorbed blackbody along with a non-thermal component to account for the persistent emission. From our modelling results, we are able to estimate the maximum apparent emitting area of the blackbody of the neutron star to be $\sim$12.5 km during the peak of the outburst and the maximum distance to the object to be 8.7 kpc. Our findings for the mass accretion rate and the alpha factor indicate the stable burning of hydrogen via a hot CNO cycle during the bursts.

astro-ph.HE↗
arXiv2022

Timing and Spectral Studies of the X-ray Pulsar 2S 1417$-$624 During the Outburst in 2021

We study the timing and spectral properties of the X-ray pulsar 2S 1417--624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observation. We also used some early data from the 2018 outburst to compare different temporal and spectral properties. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate is found to be varied between $\simeq(0.8-1.8)\times 10^{-11}$ Hz s$^{-1}$. The pulse profile shows energy dependence and variability. The pulse profile shows multiple peaks and dips which evolve with energy. The evolution of the spectral state of this source is also studied using the hardness intensity diagram (HID). The HID shows a transition from the horizontal to the diagonal branch, which implies the source went through a state transition from the subcritical to supercritical accretion regime. The NICER energy spectrum is well described by a composite model of a power-law with a higher cut-off energy and blackbody components along with a photo-electric absorption component. An iron emission line is detected near 6.4 keV in the NICER spectrum with an equivalent width of $\sim$0.05 keV. The photon index shows an anti-correlation with flux below the critical flux. The mass accretion rate is estimated to be $\simeq1.3\times10^{17}$ g s$^{-1}$ near the peak of the outburst. We have found a positive correlation between the pulse frequency derivatives and luminosity. The Ghosh and Lamb model is applied to estimate the magnetic field at different spin-up rates, which is compared to the earlier estimated magnetic field at a relatively high mass accretion rate. The magnetic field is estimated to be $\simeq10^{14}$ G from the torque-luminosity model using the distance estimated by Gaia, which is comparatively higher than most of the other Be/XBPs.

astro-ph.HE↗
arXiv2022

First detection of methyl formate in the hot molecular core IRAS 18566+0408

The studies of the complex molecular emission lines in millimeter and submillimeter wavelengths towards the hot molecular cores demonstrate valuable details about the chemical complexity in the interstellar medium (ISM). We presented the first detection of the rotational emission lines of the complex organic molecule methyl formate (CH$_{3}$OCHO) towards the hot molecular core region IRAS 18566+0408 using the high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) band 3 observation. The estimated column density of CH$_{3}$OCHO using the rotational diagram analysis was (4.1$\pm$0.1)$\times$10$^{15}$ cm$^{-2}$ with rotational temperature 102.8$\pm$1.2 K. The estimated fractional abundance of CH$_{3}$OCHO towards the IRAS 18566+0408 relative to hydrogen (H$_{2}$) was 3.90$\times$10$^{-9}$. We noted that the estimated fractional abundance of CH$_{3}$OCHO is fairly consistent with the simulation value predicted by the three-phase warm-up model from Garrod (2013). We also discussed the possible formation mechanism of CH$_{3}$OCHO towards the hot molecular cores.

astro-ph.GA↗
arXiv2022

Detection of interstellar cyanamide (NH$_{2}$CN) towards the hot molecular core G10.47+0.03

In the interstellar medium, the amide-type molecules play an important role in the formation of the prebiotic molecules in the hot molecular cores or high-mass star formation regions. The complex amide-related molecule cyanamide (NH$_{2}$CN) is known as one of the rare interstellar molecule which has played a major role in the formation of urea (NH$_{2}$CONH$_{2}$). In this article, we presented the detection of the emission lines of cyanamide (NH$_{2}$CN) towards the hot molecular core G10.47+0.03 between the frequency range 158.49$-$160.11 GHz using the Atacama Large Millimeter/submillimeter Array (ALMA) interferometric radio telescope. The estimated column density of the emission lines of NH$_{2}$CN using the rotational diagram model was $N$(NH$_{2}$CN) = (6.60$\pm$0.1)$\times$10$^{15}$ cm$^{-2}$ with rotational temperature ($T_{rot}$) = 201.2$\pm$3.3 K. The fractional abundance of NH$_{2}$CN with respect to H$_{2}$ towards G10.47+0.03 was $f$(NH$_{2}$CN) = 5.076$\times$10$^{-8}$. Additionally, we estimated the NH$_{2}$CN/NH$_{2}$CHO abundance ratio towards the G10.47+0.03 was 0.170, which was nearly similar with NH$_{2}$CN/NH$_{2}$CHO abundance ratio towards IRAS 16293$-$2422 B and Sgr B2 (M). We found that the observed abundance of NH$_{2}$CN with respect to H$_{2}$ towards G10.47+0.03 fairly agrees with the theoretical value predicted by Garrod (2013). We also discussed the possible formation and destruction pathways of NH$_{2}$CN.

astro-ph.GA↗
arXiv2022

Swift J1728.9-3613 is a black hole X-ray binary: spectral and timing study using NICER

We study different timing and spectral properties of the new Galactic X-ray transient Swift J1728.9-3613 using NICER and Swift, discovered by the Burst Alert Telescope (BAT) on the Neil Gehrels Swift Observatory. The source went through multiple transitions to different spectral states during the outburst, and the complete evolution created a q-shaped track in the hardness intensity diagram. A partial hysteresis is also observed in the RMS-intensity diagram, which is another well-defined phenomenon of black hole transients. In SIMS, power density spectra were dominated by broadband noise components, and two type B QPOs were detected. We have fitted 1-10 keV energy spectra obtained from NICER observations that were performed during the outburst, and the temporal evolution of spectral parameters were studied. On MJD 58584.69, a small-scale reflare happened, and we observed that the spectral index decreased to a much lower value associated with finite changes in other spectral parameters also, and the 1-10 keV averaged flux also increased. We observed that the innermost radius of the accretion disc was almost constant during the soft state, which corresponds to the Innermost Stable Circular Orbit (ISCO). We have measured the lower limit of mass of the compact object to be approximately 4.6 M, considering a non-spinning black hole binary system, by fitting 1-10 keV NICER spectra with the diskbb component. The soft-to-hard transition occurred when the bolometric luminosity was 0.01 times the Eddington luminosity. Based on our combined study of the evolution of the timing and spectral properties, we conclude that the new source Swift J1728.9-3613 is a black hole X-ray binary.

astro-ph.HE↗
arXiv2022

RAD@home citizen science discovery of an AGN spewing a large unipolar radio bubble onto its merging companion galaxy

AGN feedback during galaxy merger has been the most favoured model to explain black hole-galaxy co-evolution. However, how the AGN-driven jet/wind/radiation is coupled with the gas of the merging galaxies, which leads to positive feedback, momentarily enhanced star formation, and subsequently negative feedback, a decline in star formation, is poorly understood. Only a few cases are known where the jet and companion galaxy interaction leads to minor off-axis distortions in the jets and enhanced star formation in the gas-rich minor companions. Here, we briefly report one extraordinary case, RAD12, discovered by RAD@home citizen science collaboratory, where for the first time a radio jet-driven bubble ~137 kpc is showing a symmetric reflection after hitting the incoming galaxy which is not a gas-rich minor but a gas-poor early-type galaxy in a major merger. Surprisingly, neither positive feedback nor any radio lobe on the counter jet side, if any, is detected. It is puzzling if RAD12 is a genuine one-sided jet or a case of radio lobe trapped, compressed and re-accelerated by shocks during the merger. This is the first imaging study of RAD12 presenting follow-up with the GMRT, archival MeerKAT radio data and CFHT optical data.

astro-ph.GA↗
arXiv2022

Search for hybrid morphology radio galaxies from FIRST survey at 1400 MHz

Hybrid Morphology Radio Sources (HyMoRS) are a very rare subclass of radio galaxies with apparent mixed FR morphology, i.e. these galaxies seem to have an FR-I structure on one side of the core and an FR-II structure on the other side of the core. We systematically searched for HyMoRS using Very Large Array (VLA) Faint Images of the Radio Sky at Twenty-cm (FIRST) survey with 1400 MHz frequency and identified 33 candidate HyMoRS. Our finding significantly increased the known sample size of HyMoRS. HyMoRS may play an essential role in understanding the interaction of jets with the interstellar medium and the much-debated topic of the FR dichotomy. We identified optical counterparts for 29 sources in our catalogue. In our sample of sources, one source (J1106+1355) had quasar-like behaviour. Four sources were BRCLG (Brightest Cluster Galaxies) and six were LRG (Luminous Red Galaxies). We have estimated the spectral index and radio luminosity of HyMoRS in our catalogue, when possible. We found that J1136--0328 was the most luminous source in our sample ($\log L = 27.01$ W Hz$^{-1}$sr$^{-1}$). It was also the farthest HyMoRS (with a redshift $z$ = 0.82) in our sample. With the help of a large sample size of discovered sources, various statistical properties of detected galaxies were studied.

astro-ph.GA↗
arXiv2022

Identification of interstellar amino acetonitrile in the hot molecular core G10.47+0.03: Possible glycine survey candidate for the future

Amino acids are the essential keys that contribute to the study of the formation of life. The simplest amino acid, glycine (NH$_{2}$CH$_{2}$COOH), has been searched for a long time in the interstellar medium, but all surveys of glycine have failed. Since the detection of glycine in the interstellar medium was extremely difficult, we aimed to search for the precursor of glycine. After detailed searches of the individual prebiotic molecular species, we successfully identified the emission lines of possible glycine precursor molecule amino acetonitrile (NH$_{2}$CH$_{2}$CN) towards the hot molecular core G10.47+0.03 using the Atacama Large Millimeter/Submillimeter Array. We estimated the statistical column density of amino acetonitrile was (9.10$\pm$0.7)$\times$10$^{15}$ cm$^{-2}$ with rotational temperature ($T_{rot}$) 122$\pm$8.8 K. The estimated fractional abundance of amino acetonitrile was 7.01$\times$10$^{-8}$. We found that the estimated fractional abundance of NH$_{2}$CH$_{2}$CN fairly agrees with the theoretical value predicted by the three-phase warm-up model from Garrod (2013).

astro-ph.GA↗
arXiv2022

Study of timing and spectral properties of the X-ray pulsar 1A 0535+262 during the giant outburst in 2020 November-December

We made a detailed study of the timing and spectral properties of the X-ray pulsar 1A 0535+262 during the recent giant outburst in 2020 November and December. The flux of the pulsar reached a record value of $\sim$12.5 Crab as observed by Swift/BAT (15--50 keV) and the corresponding mass accretion rate was $\sim6.67\times10^{17}$ g s$^{-1}$ near the peak of the outburst. There was a transition from the subcritical to the supercritical accretion regime which allows exploring different properties of the source in the supercritical regime. A q-like feature was detected in the hardness-intensity diagram during the outburst. We observed high variability and strong energy dependence of pulse profiles during the outburst. Cyclotron Resonant Scattering Feature (CRSF) was detected at $\sim44$ keV from the NuSTAR energy spectrum in the subcritical regime and the corresponding magnetic field was $B\simeq4.9\times10^{12}$ G. The energy of the CRSF was shifted towards lower energy in the supercritical regime. The luminosity dependence of the CRSF was studied and during the supercritical regime, a negative correlation was observed between the line energy and luminosity. The critical luminosity was $\sim6\times10^{37}$ erg s$^{-1}$ above which a state transition occurred. A reversal of correlation between the photon index and luminosity was observed near the critical luminosity. The NuSTAR spectra can be described by a composite model with two continuum components, a blackbody emission, cut-off power law, and a discrete component to account for the iron emission line at 6.4 keV. An additional cyclotron absorption feature was included in the model.

astro-ph.HE↗