Venkatessh Ramakrishnan
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View article: Search for Lorentz Invariance Violation with spectral lags of GRB 190114C using profile likelihood
Search for Lorentz Invariance Violation with spectral lags of GRB 190114C using profile likelihood Open
We search for Lorentz invariance violation (LIV) by re-analyzing the spectral lag data for GRB 190114C from Fermi-GBM using frequentist analysis, where we deal with the astrophysical nuisance parameters using profile likelihood. For this u…
View article: Shared-optical-path VLBI frequency phase transfer from 86 to 258 GHz on an 8600km baseline
Shared-optical-path VLBI frequency phase transfer from 86 to 258 GHz on an 8600km baseline Open
Context . The receiver N3AR operating at a frequency range between 67 and 116 GHz was commissioned at the APEX telescope in October 2024. It adds a new low-frequency band for APEX, with the capability of simultaneous dual-frequency observa…
View article: NGC 6860, Mrk 915, and MCG -01-24-012
NGC 6860, Mrk 915, and MCG -01-24-012 Open
We present a study of the cold molecular versus ionized gas distribution in three nearby Seyfert galaxies: NGC 6860, Mrk 915, and MCG -01-24-012. To constrain the cold molecular flux distribution at ∼0.5−0.8″ (∼150−400 pc) scales, we used …
View article: Accessing a New Population of Supermassive Black Holes with Extensions to the Event Horizon Telescope
Accessing a New Population of Supermassive Black Holes with Extensions to the Event Horizon Telescope Open
The Event Horizon Telescope (EHT) has produced resolved images of the supermassive black holes (SMBHs) Sgr A* and M87*, which present the largest shadows on the sky. In the next decade, technological improvements and extensions to the arra…
View article: Tracking X-Ray Variability in Next-generation EHT Low-luminosity Active Galactic Nucleus Targets
Tracking X-Ray Variability in Next-generation EHT Low-luminosity Active Galactic Nucleus Targets Open
We present a 5 month NICER X-ray monitoring campaign for two low-luminosity active galactic nuclei (LLAGNs)—NGC 4594 and IC 1459—with complementary Swift and NuSTAR observations. Utilizing an absorbed power-law and thermal source model com…
View article: Determination of Hubble constant from Megamaser Cosmology Project using Profile Likelihood
Determination of Hubble constant from Megamaser Cosmology Project using Profile Likelihood Open
The Megamaser Cosmology Project inferred a value for the Hubble constant given by $H_0=73.9 \pm 3.0 $ km/sec/Mpc. This value was obtained using Bayesian inference by marginalizing over six nuisance parameters, corresponding to the velociti…
View article: Keplerian molecular gas disk and black hole mass of NGC 4751
Keplerian molecular gas disk and black hole mass of NGC 4751 Open
Aims. We aim to measure the mass of the supermassive black hole (SMBH) in the S0 galaxy NGC 4751 using CO J:3−2 emission from the 5″-scale nuclear rotating molecular disk. Methods. We imaged the kpc-scale molecular gas disk in NGC 4751 at …
View article: Constraints on Lorentz Invariance Violation from Gamma-ray Burst rest-frame spectral lags using Profile Likelihood
Constraints on Lorentz Invariance Violation from Gamma-ray Burst rest-frame spectral lags using Profile Likelihood Open
We reanalyze the spectral lag data for 56 Gamma-Ray Bursts (GRBs) in the cosmological rest frame to search for Lorentz Invariance Violation (LIV) using frequentist inference. For this purpose, we use the technique of profile likelihood to …
View article: Gamma-ray flares from the jet of the blazar CTA 102 in 2016–2018
Gamma-ray flares from the jet of the blazar CTA 102 in 2016–2018 Open
CTA 102 is a γ -ray bright blazar that exhibited multiple flares in observations by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope during the period of 2016–2018. We present results from the analysis of multi-wavelen…
View article: Tracking X-ray Variability in Next Generation EHT LLAGN Targets
Tracking X-ray Variability in Next Generation EHT LLAGN Targets Open
We present a 5 month NICER X-ray monitoring campaign for two low luminosity active galactic nuclei (LLAGNs) -- NGC 4594 and IC 1459 -- with complementary Swift and NuSTAR observations. Utilizing an absorbed power law and thermal source mod…
View article: Gamma-ray flares from the jet of the blazar CTA 102 in 2016-2018
Gamma-ray flares from the jet of the blazar CTA 102 in 2016-2018 Open
CTA 102 is a $γ$-ray bright blazar that exhibited multiple flares in observations by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope during the period of 2016-2018. We present results from the analysis of multi-wavele…
View article: Demographics of black holes at $<$100 R$_{\rm g}$ scales: accretion flows, jets, and shadows
Demographics of black holes at $<$100 R$_{\rm g}$ scales: accretion flows, jets, and shadows Open
Using the Event Horizon Telescope (EHT), the gravitationally lensed rings around the supermassive black holes (SMBHs) in Messier 87 (M87) and Sagittarius A* (Sgr A*) have now been successfully imaged at a resolution under 10 gravitational …
View article: Search for transient gamma-ray emission from magnetar flares using Fermi-LAT
Search for transient gamma-ray emission from magnetar flares using Fermi-LAT Open
We search for transient gamma-ray emission in the energy range from 0.1-10 GeV using data from the Fermi-LAT telescope in coincidence with magnetar flares. For our analysis, we look for coincidence with 15 distinct flares from 11 magnetars…
View article: Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episode
Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episode Open
Context. The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (M…
View article: First Very Long Baseline Interferometry Detections at 870 μm
First Very Long Baseline Interferometry Detections at 870 μm Open
The first very long baseline interferometry (VLBI) detections at 870 μ m wavelength (345 GHz frequency) are reported, achieving the highest diffraction-limited angular resolution yet obtained from the surface of the Earth and the highest-f…
View article: Accessing a New Population of Supermassive Black Holes with Extensions to the Event Horizon Telescope
Accessing a New Population of Supermassive Black Holes with Extensions to the Event Horizon Telescope Open
The Event Horizon Telescope has produced resolved images of the supermassive black holes Sgr A* and M87*, which present the largest shadows on the sky. In the next decade, technological improvements and extensions to the array will enable …
View article: Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode
Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode Open
The nearby elliptical galaxy M87 contains one of the only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) f…
View article: Metadata for the Flux Density Calibration of the April 2018 Event Horizon Telescope Data
Metadata for the Flux Density Calibration of the April 2018 Event Horizon Telescope Data Open
The Event Horizon Telescope (EHT) observations carried out in 2018 April at 1.3 mm wavelengths included 9 stations in the array, comprising 7 single-dish telescopes and 2 phased arrays. The metadata package for the 2018 EHT observing campa…
View article: A Near Magnetic-to-kinetic Energy Equipartition Flare from the Relativistic Jet in AO 0235+164 during 2013-2019
A Near Magnetic-to-kinetic Energy Equipartition Flare from the Relativistic Jet in AO 0235+164 during 2013-2019 Open
We present the multiwavelength flaring activity of the blazar AO 0235+164 during its recent active period from 2013 to 2019. From a discrete correlation function (DCF) analysis, we find a significant (>95%) correlation between radio and $γ…
View article: A near magnetic-to-kinetic energy equipartition flare from the relativistic jet in AO 0235 + 164 during 2013–2019
A near magnetic-to-kinetic energy equipartition flare from the relativistic jet in AO 0235 + 164 during 2013–2019 Open
We present the multiwavelength flaring activity of the blazar AO 0235 + 164 during its recent active period from 2013 to 2019. From a discrete correlation function analysis, we find a significant ($\gt 95~{{\ \rm per\ cent}}$) correlation …
View article: Multiwavelength Temporal Variability of the Blazar PKS 1510–089
Multiwavelength Temporal Variability of the Blazar PKS 1510–089 Open
We perform correlation and periodicity search analyses on long-term multiband light curves of the flat-spectrum radio quasar PKS 1510−089 observed by the space-based Fermi-Large Area Telescope in γ -rays, the SMARTS and Steward Observatory…
View article: Multi-wavelength temporal variability of the blazar PKS 1510-089
Multi-wavelength temporal variability of the blazar PKS 1510-089 Open
We perform correlation and periodicity search analyses on long-term multi-band light curves of the FSRQ 1510-089 observed by the space-based Fermi--Large Area Telescope in gamma-rays, the SMARTS and Steward Observatory telescopes in optica…
View article: Cold molecular gas outflow encasing the ionized one in the Seyfert galaxy NGC 3281
Cold molecular gas outflow encasing the ionized one in the Seyfert galaxy NGC 3281 Open
We present ALMA CO (2-1) observations of the Seyfert 2 galaxy NGC 3281 at ∼100 pc spatial resolution. This galaxy was previously known to present a bi-conical ionized gas outflow extending to 2 kpc from the nucleus. The analysis of the CO …
View article: Cold molecular gas outflow encasing the ionised one in the Seyfert galaxy NGC 3281
Cold molecular gas outflow encasing the ionised one in the Seyfert galaxy NGC 3281 Open
We present ALMA CO(2-1) observations of the Seyfert 2 galaxy NGC 3281 at $\sim$ 100 pc spatial resolution. This galaxy was previously known to present a bi-conical ionised gas outflow extending to 2 kpc from the nucleus. The analysis of th…
View article: The Event Horizon Telescope Image of the Quasar NRAO 530
The Event Horizon Telescope Image of the Quasar NRAO 530 Open
We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5−7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object…
View article: Event Horizon and Environs (ETHER): A Curated Database for EHT and ngEHT Targets and Science
Event Horizon and Environs (ETHER): A Curated Database for EHT and ngEHT Targets and Science Open
The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility…
View article: Resolving the Inner Parsec of the Blazar J1924–2914 with the Event Horizon Telescope
Resolving the Inner Parsec of the Blazar J1924–2914 with the Event Horizon Telescope Open
The blazar J1924–2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center’s black hole Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with the unpre…
View article: Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign
Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign Open
The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5–11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Mill…
View article: Radio and γ-Ray Activity in the Jet of the Blazar S5 0716+714
Radio and γ-Ray Activity in the Jet of the Blazar S5 0716+714 Open
We explore the connection between the γ -ray and radio emission in the jet of the blazar 0716+714 by using 15, 37, and 230 GHz radio and 0.1–200 GeV γ -ray light curves spanning 10.5 yr (2008–2019). We find significant positive and negativ…