arXiv subjects

Sabyasachi Pal

Publications and source records attributed to Sabyasachi Pal.

At least 73 records · Page 4Linked to original sources

arXiv2021

Detection of continuum emission and atomic hydrogen (HI) from comet C/2020 F3 NEOWISE using GMRT

Comets are the most primordial objects in our solar system. Comets are icy bodies that release gas and dust when they move close to the Sun. The C/2020 F3 (NEOWISE) was a nearly isotropic comet that was moving in a near-parabolic orbit. The comet C/2020 F3 (NEOWISE) was the brightest comet in the northern hemisphere after comet Hale-Bopp in 1997 and comet McNaught in 2006. In this article, we reported the first interferometric high-resolution detection of the comet C/2020 F3 (NEOWISE) using the Giant Metrewave Radio Telescope (GMRT). We detected the radio continuum emission from comet C/2020 F3 (NEOWISE) with flux density level 2.84($\pm$0.56)$-$3.89($\pm$0.57) mJy in the frequency range 1050$-$1450 MHz. We also detected the absorption line of atomic HI with Signal to Noise Ratio (SNR) $\sim$5.7. The statistical column density of the detected HI absorption line was $N_{HI} = (3.46\pm0.60)\times(T_{s}/100)\times10^{21}$ cm$^{-2}$ where we assumed spin temperature $T_{s}$ = 100 K and filling factor $f$ = 1. The significant detection of continuum emission from the comet C/2020 F3 (NEOWISE) in $\sim$21 cm wavelength indicated that it arose from the large Icy Grains Halo (IGH) region.

astro-ph.EP↗

arXiv2021

ALMA detection of water vapour in the low mass protostar IRAS 16293$-$2422

The low mass protostar IRAS 16293$-$2422 is a well-known young stellar system that is observed in the L1689N molecular cloud in the constellation of Ophiuchus. In the interstellar medium and solar system bodies, water is a necessary species for the formation of life. We present the spectroscopic detection of the rotational emission line of water (H$_{2}$O) vapour from the low mass protostar IRAS 16293$-$2422 using the Atacama Large Millimeter/submillimeter Array (ALMA) band 5 observation. The emission line of H$_{2}$O is detected at frequency $ν$ = 183.310 GHz with transition J=3$_{1,3}$$-$2$_{2,2}$. The statistical column density of the emission line of water vapour is $N$(H$_{2}$O) = 4.2$\times$10$^{16}$ cm$^{-2}$ with excitation temperature ($T_{ex}$) = 124$\pm$10 K. The fractional abundance of H$_{2}$O with respect to H$_{2}$ is 1.44$\times$10$^{-7}$ where $N$(H$_{2}$) = 2.9$\times$10$^{23}$ cm$^{-2}$.

astro-ph.GA↗

arXiv2021

ALMA detection of sulfur dioxide and carbon monoxide in the atmosphere of Neptune

The space and ground-based observations have shown a lot of activities and instabilities in the atmosphere of the giant ice planet Neptune. Using the archival data of high resolution Atacama Large Millimeter/Submillimeter Array (ALMA) with band 7 observation, we present the spectroscopic detection of the rotational emission line of sulfur dioxide (SO$_{2}$) at frequency $ν$ = 343.476 GHz with transition J=57$_{15,43}$$-$58$_{14,44}$. We also re-detect the emission line of carbon monoxide (CO) at frequency $ν$ = 345.795 GHz with transition J=3$-$2. The molecular lines of SO$_{2}$ and CO in the atmosphere of Nepure are detected with the $\geq$4$σ$ statistical significance. The statistical column density of SO$_{2}$ is N(SO$_{2}$) = 2.61$\times$10$^{15}$ cm$^{-2}$ with rotational temperature $T_{SO_{2}}$ = 50 K and the statistical column density CO is N(CO) = 1.86$\times$10$^{19}$ cm$^{-2}$ with $T_{CO}$ = 29 K. The typical mixing ratio in the atmosphere of Neptune for SO$_{2}$ is 1.24$\times$10$^{-10}$ and CO is 0.88$\times$10$^{-6}$. The SO$_{2}$ and CO gas in the atmosphere of Neptune may create due to Shoemaker-Levy 9 impacts in Jovian planets since 1994.

astro-ph.EP↗

arXiv2021

ALMA detection of acetone, disulfur monoxide, and carbon monoxide in the Jupiter volcanic moon Io

The extremely thin atmosphere of Jupiter's volcanic moon Io primarily consists of sulfur (S), sodium (Na), and oxygen (O) molecules that are controlled by the combination of the sublimation and volcanic outgasses. We present the first spectroscopic detection of the two rotational emission lines of acetone (CH$_{3}$COCH$_{3}$) and a single emission line of disulfur monoxide (S$_{2}$O), and carbon monoxide (CO) at frequency $ν$ = 346.539, 346.667, 346.543, and 345.795 GHz respectively using the archival data of high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) interferometer with band 7 observation. All molecular species are detected with $\ge$5$σ$ statistical significance. Jupiter's moon Io is the most volcanically active body in the solar system with a very thin and spatially variable atmosphere. The volcanic gas CH$_{3}$COCH$_{3}$, S$_{2}$O, and CO are mainly coming from volcanic plumes. The statistical column density of CH$_{3}$COCH$_{3}$ line is N(CH$_{3}$COCH$_{3}$) = 3.18$\times$10$^{15}$ cm$^{-2}$ but for the cases of S$_{2}$O and CO, the column densities are N(S$_{2}$O) = 2.63$\times$10$^{16}$ cm$^{-2}$ and N(CO) = 5.27$\times$10$^{15}$ cm$^{-2}$ respectively. The carbon monoxide gas is mainly formed by the photolysis of the volcanic gas acetone.

astro-ph.EP↗

arXiv2021

Detection of simplest amino acid glycine in the atmosphere of Venus

Amino acids are considered to be prime ingredients in chemistry, leading to life. Glycine is the simplest amino acid and most commonly found in animal proteins. It is a glucogenic and non-essential amino acid that is produced naturally by living bodies and plays a key role in the creation of several other important bio-compounds and proteins. We report the first spectroscopic detection of the rotational absorption lines of the simplest amino acid glycine (NH$_{2}$CH$_{2}$COOH) with confirmer I and II in the atmosphere of Venus using the archival data from the Atacama Large Millimeter/Submillimeter Array (ALMA). We detect the eleven rotational absorption lines of NH$_{2}$CH$_{2}$COOH between the frequency range of $ν$ = 245$-$262 GHz with $\geq$3$σ$ statistical significance. We calculate the total column density of glycine in the atmosphere of Venus is $N$(NH$_{2}$CH$_{2}$COOH) $\sim$ 5$\times$10$^{14}$ cm$^{-2}$. Using the column density information of glycine, we calculate the abundance of glycine is $\sim$ 1.6$\times$10$^{-9}$ in the atmosphere of Venus. The detection of glycine in the atmosphere of Venus might be one of the keys to an understanding of the formation mechanisms of prebiotic molecules in the atmosphere of Venus. The detection of glycine indicates that the upper atmosphere of Venus may be going through nearly the same biological method as Earth billions of years ago.

astro-ph.EP↗

arXiv2021

ALMA spectroscopic detection of water vapour in the atmosphere of the giant gas planet Jupiter

In the Jovian atmosphere, the trace species are detected for the first time after the collision of comet Shoemaker-Levy 9 near 44$^\circ$S in July 1994. Most of these trace species are detected with spectroscopic millimeter/submillimeter observation. In the atmosphere of Jupiter, trace gases play an important role in atmospheric chemistry with heterogeneous and homogeneous chemical reactions, interaction with radiation, and phase transition. Here we present the first spectroscopic detection of the rotational emission line of water (H$_{2}$O) in the atmosphere of Jupiter at frequency $ν$ = 183.310 GHz with molecular transition J = 3$_{1,3}$$-$2$_{2,2}$ using Atacama Large Millimeter/Submillimeter Array (ALMA). The statistical column density of water emission line is N(H$_{2}$O)$\sim$4$\times$10$^{15}$ cm$^{-2}$. The rotational emission line of H$_{2}$O is found in the stratosphere of Jupiter with $\geq$3$σ$ statistical significance. The column density of H$_{2}$O corresponds to the fractional abundance relative to H$_{2}$ is f(H$_{2}$O)$\sim$ 4$\times$10$^{-9}$.

astro-ph.EP↗

arXiv2021

Winged Radio Sources from LOFAR Two-metre Sky Survey First Data Release (LoTSS DR1)

Winged radio sources are a small sub-class of extragalactic radio sources which display a pair of low surface brightness radio lobes, known as `wings' aligned at a certain angle with the primary jets. Depending on the location of wings, these galaxies look like X or Z and are known as X-shaped Radio Galaxy (XRG) or Z-shaped Radio Galaxy (ZRG). We report the identification of 33 winged radio sources from the LOFAR Two-metre Sky Survey First Data Release (LoTSS DR1) out of which 21 sources are identified as X-shaped radio galaxies and 12 as Z-shaped radio galaxies. Optical counterparts are identified for 14 XRGs (67 per cent) and 12 ZRGs (100 per cent). We studied various physical parameters of these sources like spectral index, radio luminosity, and power. The radio spectrum of the majority of XRGs and ZRGs is steep ($α_{1400}^{144}>0.5$), which is typical of lobe dominated radio galaxies. The statistical studies are done on the relative size of the major and minor axes and the angle between the major axis and minor axis for XRGs.

astro-ph.GA↗

arXiv2021

Head Tail Radio Sources from VLA FIRST Survey

The study of Head Tail (HT) radio galaxies track the information of associated galaxy clusters. With the help of the VLA FIRST survey at 1.4 GHz, we detected 607 new HT radio sources, among them, 398 are Wide Angle Tail (WAT) and 216 are Narrow-Angle Tail (NAT) sources. NAT sources generally have `V' shaped structure with an opening angle less than ninety degrees and for WAT sources opening angle between the jets is more than ninety degrees. We found that almost 80 per cent of our sources are associated with a known galaxy cluster. We mentioned various useful physical properties of these HT sources. Taking advantage of a large sample of newly discovered HT sources, various statistical studies have been done. The luminosity range of sources presented in the current paper is $10^{39}$ $\leq$ $L_{1.4GHz}$ $\leq$ $10^{43}$ erg sec$^{-1}$. We identified optical counterparts for 193 WAT and 104 NAT sources. The sources are found up to redshift 2.08.

astro-ph.HE↗

arXiv2021

Detection of Low-Frequency QPO From X-ray Pulsar XTE J1858+034 During Outburst in 2019 with NuSTAR

We study the timing properties of XTE J1858+034 using the Nuclear Spectroscopic Telescope Array (NuSTAR) and Burst Alert Telescope onboard Swift during the outburst in October--November 2019. We have investigated for Quasi-Periodic Oscillation (QPO) during the outburst and detected a low-frequency QPO at $\sim$196 mHz with $\sim$6% RMS variability from the NuSTAR observation. The QPO is fitted and explained with the model - power law and a Lorentzian component. We have also studied the variation of QPO frequency with energy. The beat frequency model and Keplerian frequency model both are suitable to explain the origin of the QPOs for the source. Regular pulsations and QPOs are found to be stronger in high energy which suits the beat frequency model. The variation of the hardness ratio is studied over the outburst which does not show any significant variation.

astro-ph.HE↗

arXiv2020

FIRST winged radio galaxies with X and Z symmetry

X-shaped radio galaxies are a subclass of radio sources that exhibit a pair of secondary low surface brightness radio lobes oriented at an angle to the primary high surface brightness lobes. Sometimes, the secondary low brightened lobes emerge from the edges of the primary high brightened lobes and form a Z-symmetric morphology. We present a systematical search result for X-shaped radio galaxies (XRGs) and Z-shaped radio galaxies (ZRGs) from the VLA Faint Images of the Radio Sky at Twenty-Centimeters (VLA FIRST) Survey at 1.4 GHz. Our search yields a total of 296 number of radio sources, out of which 161 are XRGs and 135 are ZRGs. We have also made optical identification of these sources from the different available literature. J1124+4325 and J1319+0502 are the farthest known XRG and ZRG, respectively. We have estimated spectral index and radio luminosity of these radio sources and made a comparative study with previously detected XRGs and ZRGs. The average value of luminosities for XRGs is higher than that of ZRGs. With the help of a large sample size of the newly discovered XRGs and ZRGs, various statistical properties of these sources are studied. Out of 161 XRGs presented in the current paper, 70% (113) are FR II radio galaxies and 13% (20) are FR I radio galaxies. For 28 XRGs, the morphology is complex and could not be classified. For XRGs, the statistical studies are done on the angle between the major axis and minor axis and the relative size of the major and minor axes. For the ZRGs a statistical study is done on the angular size.

astro-ph.GA↗

arXiv2017

Transient nature of J195754+353513

We have searched for transient and/or variable radio sources in the field of Galactic micro-quasar Cygnus X-1 in 1.4 GHz (L band) using data from the Karl G. Jansky Very Large Array (JVLA). We used twenty years of data between 1983 and 2003. We found a source J195754+353513 showing transient behavior. The source was also mentioned earlier in NVSS and WENSS catalog but its transient nature was not reported earlier. The source is located 23.8 arcminutes far from Cygnus X-1. It is detected many times during the span of our study and it varied between less than 0.3 mJy to 201 mJy. J195754+353513 also showed high intra-day variability. In one occasion, the source rose from ~20 mJy to ~180 mJy 700 second. For limited number of cases circularly polarized emission could be detected from the source with V/I vary between 0.15 to 0.25. 2MASS J19575420+3535152 may be the near-infrared counterpart of the source. We compared the properties of the source with other Galactic transient sources having similar properties. The nature of the source is still unknown. We speculate on its possible nature.

astro-ph.HE↗

arXiv2013

Discovery of a small diameter young supernova remnant G354.4+0.0

We report discovery of a shell like structure G354.4+0.0 of size 1.6' that shows morphology of a shell supernova remnant. Part of the structure show polarized emission in NRAO VLA sky survey (NVSS) map. Based on 330 MHz, 1.4 GHz Giant Metrewave Radio Telescope (GMRT) observations and existing observations at higher frequencies, we conclude the partial shell structure showing synchrotron emission is embedded in an extended HII region of size ~4'. The spectrum of the diffuse HII region turns over between 1.4 GHz and 330 MHz. HI absorption spectrum shows it to be located more than 5 kpc away from Sun. Based on morphology, non-thermal polarized emission and size, this object is one of the youngest supernova remnants discovered in the Galaxy with an estimated age of about 100-500 years.

astro-ph.GA↗

arXiv2010

The AKARI Deep Fields: Early Results from Multi-wavelength Follow-up Campaigns

We present early results from our multi-wavelength follow-up campaigns of the AKARI Deep Fields at the North and South Ecliptic Poles. We summarize our campaigns in this poster paper, and present three early outcomes. (a) Our AAOmega optical spectroscopy of the Deep Field South at the AAT has observed over 550 different targets, and our preliminary local luminosity function at 90 microns from the first four hours of data is in good agreement with the predictions from Serjeant & Harrison 2005. (b) Our GMRT 610 MHz imaging in the Deep Field North has reached ~30 microJy RMS, making this among the deepest images at this frequency. Our 610 MHz source counts at >200 microJy are the deepest ever derived at this frequency. (c) Comparing our GMRT data with our 1.4 GHz WSRT data, we have found two examples of radio-loud AGN that may have more than one epoch of activity.

astro-ph.CO↗

arXiv2010

Circularly polarized emission from the transient bursting radio source GCRT J1745-3009

We report detection of strong circularly polarized emission from the transient bursting source GCRT J1745-3009 based on new analysis of 325 MHz GMRT observations conducted on 28 September 2003. We place 8 Solar radius as the upper limit on the size of the emission region. The implied high brightness temperature required for an object beyond 1 pc and the high fraction of circular polarization firmly establish the emission as coherent. Electron cyclotron or plasma emission from a highly subsolar magnetically dominated dwarf located less than 4 kpc away could have given rise to the GCRT radio emission.

astro-ph.GA↗

arXiv2009

Discovery of one new class in the light curve of GRS 1915+105

From the study of X-ray light curve and color-color diagram of the low mass X-ray binary GRS 1915+105, observed by on board proportional counter array (PCA) of Rossi X-ray Timing Explorer (RXTE), we discover a new class of variability, which we name $ε$ class. We have studied observations between MJD 51200 and 51450. The class shows unusual periodic-like variation in count rate during rise time of two x-ray bursts. The class take place when the source is in radio quiet state. The huge expansion in color-intensity diagram indicates the class to be an adjusting stage of increasing accretion rate. Spectral analysis shows that during lower count rate, the spectrum is hard power-law dominating, indicating similarity towards hard intermediate state, and during higher count rate, the spectrum is thermal disk blackbody component dominating, indicating similarity towards high soft state. Hence, this class is important in understanding the way of state transition leads to change in accretion rate. No signature of any low frequency quasi periodic oscillation was seen in this class. We also find that when the class was showing higher counts, the average RMS amplitude is significantly high for high energy band (14-60 keV) compared to low energy band (2-8 keV).

astro-ph.HE↗

arXiv2009

The origin of the diffuse non-thermal X-ray and radio emission in the Ophiuchus cluster of galaxies

We present high resolution 240 and 607 MHz GMRT radio observations, complemented with 74 MHz archival VLA radio observations of the Ophiuchus cluster of galaxies, whose radio mini-halo has been recently detected at 1400 MHz. We also present archival Chandra and XMM-Newton data of the Ophiuchus cluster. Our observations do not show significant radio emission from the mini-halo, hence we present upper limits to the integrated, diffuse non-thermal radio emission of the core of the Ophiuchus cluster. The XMM-Newton observations can be well explained by a two-temperature thermal model with temperatures of ~=1.8 keV and ~=9.0 keV, respectively, which confirms previous results that suggest that the innermost central region of the Ophiuchus cluster is a cooling core. We also used the XMM-Newton data to set up an upper limit to the (non-thermal) X-ray emission from the cluster. The combination of available radio and X-ray data has strong implications for the currently proposed models of the spectral energy distribution (SED) from the Ophiuchus cluster. In particular, a synchrotron+IC model is in agreement with the currently available data, if the average magnetic field is in the range (0.02-0.3) microG. A pure WIMP annihilation scenario can in principle reproduce both radio and X-ray emission, but at the expense of postulating very large boost factors from dark matter substructures, jointly with extremely low values of the average magnetic field. Finally, a scenario where synchrotron and inverse Compton emission arise from PeV electron-positron pairs (via interactions with the CMB), can be ruled out, as it predicts a non-thermal soft X-ray emission that largely exceeds the thermal Bremsstrahlung measured by INTEGRAL.

astro-ph↗

arXiv2008

GCRT J1742-3001: A New Radio Transient Towards the Galactic Center

We report the detection of a new transient radio source, GCRT J1742-3001, located ~1 degree from the Galactic center. The source was detected ten times from late 2006 to 2007 May in our 235 MHz transient monitoring program with the Giant Metrewave Radio Telescope (GMRT). The radio emission brightened in about one month, reaching a peak observed flux density of ~100 mJy on 2007 January 28, and decaying to ~50 mJy by 2007 May when our last monitoring observation was made. Two additional faint, isolated 235 MHz detections were made in mid-2006, also with the GMRT. GCRT J1742-3001 is unresolved at each epoch, with typical resolutions of ~20 arcsec x 10 arcsec. No polarization information is available from the observations. Based on nondetections in observations obtained simultaneously at 610 MHz, we deduce that the spectrum of GCRT J1742-3001 is very steep, with a spectral index less than about -2. Follow-up radio observations in 2007 September at 330 MHz and 1.4 GHz, and in 2008 February at 235 MHz yielded no detections. No X-ray counterpart is detected in a serendipitous observation obtained with the X-ray telescope aboard the Swift satellite during the peak of the radio emission in early 2007. We consider the possibilities that GCRT J1742-3001 is either a new member of an existing class of radio transients, or is representative of a new class having no associated X-ray emission.

astro-ph↗

arXiv2007

The Local Group dwarf Leo T: HI on the brink of star formation

We present Giant Meterwave Radio Telescope (GMRT) and Westerbork ynthesis Radio Telescope (WSRT) observations of the recently discovered Local Group dwarf galaxy, Leo T. The peak HI column density is measured to be 7x10^20 cm^-2, and the total HI mass is 2.8Xx10^5 Msun, based on a distance of 420 kpc. Leo T has both cold (~ 500 K) and warm (~ 6000 K) HI at its core, with a global velocity dispersion of 6.9 km/s, from which we derive a dynamical mass within the HI radius of 3.3x10^6 Msun, and a mass-to-light ratio of greater than 50. We calculate the Jeans mass from the radial profiles of the HI column density and velocity dispersion, and predict that the gas should be globally stable against star formation. This finding is inconsistent with the half light radius of Leo T, which extends to 170 pc, and indicates that local conditions must determine where star formation takes place. Leo T is not only the lowest luminosity galaxy with on-going star formation discovered to date, it is also the most dark matter dominated, gas-rich dwarf in the Local Group.

astro-ph↗