arXiv subjects

Santanu Mondal

Publications and source records attributed to Santanu Mondal.

At least 37 records · Page 2Linked to original sources

arXiv2024

The first detection of X-ray polarization in a newly discovered Galactic transient Swift\,J151857.0-572147

We study the spectro-polarimetric properties of a newly discovered black hole X-ray binary Swift\,J151857.0-572147 jointly using {\it IXPE} and {\it NuSTAR} observations during March 2024. The analysis of {\it IXPE} data reports the first detection of X-ray polarization with degree (PD) $1.34\pm0.27$ and polarization angle (PA) $-13.69^\circ\pm5.85^\circ$ using model-independent approach, while the model-dependent analysis gives PD $1.18\pm0.23$ and PA $-14.01^\circ\pm5.80^\circ$. The joint spectral analysis of the broadband data and {\it NuSTAR} analysis in isolation constrain the mass of the central black hole between $\sim 9.2\pm1.6-10.1\pm1.7 M_\odot$ and a moderate spin parameter of $\sim0.6\pm0.1-0.7\pm0.2$ with disk inclination $\sim 35^\circ\pm7^\circ-46^\circ\pm15^\circ$. The power-law photon index and cutoff energy are $2.19\pm0.03-2.47\pm0.06$ and $\sim 36\pm4-78\pm10$ keV, suggesting a transition to the soft spectral state (SS). Additionally, a relatively lower corona size of $6\pm1-9\pm2$ $r_S$, a low mass outflow rate ($<3$\% $\dot M_{\rm Edd}$), and the best-fitted halo accretion is less compared to the disk accretion rate further confirms the same state. The low PD detected in the SS can be due to repeated scattering inside the dense corona and the dominant emission from the disk, agrees with the low spin and low disk inclination. The hydrogen column density obtained from the fit is relatively high $\sim 4-5\times 10^{22}$ cm$^{-2}$.

astro-ph.HE↗

arXiv2024

Detection of the Fe K lines from the binary AGN in 4C+37.11

We report the discovery of the Fe K line emission at $\sim6.62^{+0.06}_{-0.06}$ keV with a width of $\sim0.19^{+0.05}_{-0.05}$ keV using two epochs of {\it Chandra} archival data from the nucleus of the galaxy 4C+37.11, which is known to host a binary supermassive black hole (BSMBH) system where the SMBHs are separated by $\sim7$ mas or $\sim$ 7pc. Our study reports the first detection of the Fe K line from a known binary AGN, and has an F-statistic value of 20.98 and probability $2.47\times 10^{-12}$. Stacking of two spectra reveals another Fe K line component at $\sim7.87^{+0.19}_{-0.09}$ keV. Different model scenarios indicate that the lines originate from the combined effects of accretion disk emission and circumnuclear collisionally ionized medium. The observed low column density favors the gas-poor merger scenario, where the high temperature of the hot ionized medium may be associated with the shocked gas in the binary merger and not with star formation activity. The estimated total BSMBH mass and disk inclination are $\sim1.5\times10^{10}$ M$_\odot$ and $\gtrsim75^\circ$, indicating that the BSMBH is probably a high inclination system. The spin parameter could not be tightly constrained from the present data sets. Our results draw attention to the fact that detecting the Fe K line emissions from BSMBHs is important for estimating the individual SMBH masses, and the spins of the binary SMBHs, as well as exploring their emission regions.

astro-ph.HE↗

arXiv2024

Spectro-polarimetric study to constrain accretion-ejection properties of MCG-5-23-16 using IXPE and NuSTAR observations

We conducted a study on the X-ray polarization properties of MCG-5-23-16 by analyzing long-term monitoring data from {\it NuSTAR} jointly with {\it IXPE} observations made in May and November 2022. The re-analysis of {\it IXPE} data gives model-dependent polarization degree, PD (\%) = $1.08\pm0.66$ in the energy band $2-8$ keV. The model-independent analysis of PD poses an upper limit of $\leq3.8$ ($1σ$ level) for the same energy band. The observed upper limit of PD, along with broadband spectral analysis ($2-79$ keV) using an accretion-ejection based model, allowed us to derive the corona geometry (i.e. radius and height) and the accretion disk inclination ($\sim 33^\circ$). Additional {\it NuSTAR} observations were also analyzed to gain insights into the accretion flow properties of the source and to estimate the expected polarization during those epochs with PD $\sim 4.3\%$. The radius and height of the corona varies between $28.2\pm3.1 - 39.8\pm4.6$ r$_s$ and $14.3\pm1.7-21.4\pm1.9$ r$_s$ respectively, with a mass outflow rate from the corona measuring $0.14\pm0.03-0.2\pm0.03$ Eddington rate ($\dot m_{\rm Edd}$). The spectral analysis further provided an estimate for the mass of the central black hole $\sim 2\times 10^7$ M$_\odot$ and the velocity of the outflowing gas $\sim 0.16-0.19c$. A comparative broadband spectral study using reflection-based models estimates the disk inclination between $\sim 31^\circ\pm8^\circ-45^\circ\pm7^\circ$, and yields an expected PD of 3.4-6.0\%. The expected PD measured using accretion-ejection and reflection models is less compared to the expected PD measured for a given disk inclination of $45^\circ$. Our modeling of the disk-corona-outflows and polarization connection can be extended and validated with data from the recently launched \textit{XPoSat}, India's first X-ray Polarimeter Satellite, offering potential applications to other sources.

astro-ph.HE↗

arXiv2024

Update on flavor diagonal nucleon charges from clover fermions

We present a summary of the full calculation of the axial, scalar and tensor flavor diagonal charges of the nucleon carried out using Wilson-clover fermions on eight ensembles generated using 2+1+1-flavors of highly improved staggered quarks (HISQ) by the MILC collaboration. We also give results for the $3\times 3$ matrix of renormalization factors between the RI-sMOM and $\overline{\rm MS}$ scheme for the 2+1 flavor theory that include flavor mixing. Preliminary results for $g_{A,S,T}^{u,d,s}$ are presented in the $\overline{\rm MS}$ scheme at scale 2 GeV.

hep-lat↗

arXiv2023

Spectral Properties of GX~339--4 in the Intermediate State Using AstroSat Observation

We present the results obtained from the spectral studies of black hole X-ray binary GX~339--4 using \astrosat~ observations during its 2021 outburst. \astrosat~ observed the source in the intermediate state for $\sim600$ ks. The combined spectra of SXT and LAXPC in the $0.7-25$ keV energy range are studied with phenomenological and physical models. The spectral study reveals a receding disc and a contracting corona during the observation period. The outflow rate is found to be increased though the accretion rates did not vary during the observation period. The X-ray flux decreases as the disc recedes and the spectrum becomes hard. At the same time, the Comptonized flux decreases with increasing fraction of thermal emission. This could be plausible that episodic jet ejection modified the corona and reduced Comptonized flux. An iron emission line at 6.4 keV is observed in the spectra of all the orbits of observation. We find that the equivalent width of the iron emission line correlates with the photon index, indicating a decrease in the reflection strength as the spectrum becomes hard. We observe that the disc flux does not follow $F_{\rm DBB}-T^{4}$ relation.

astro-ph.HE↗

arXiv2023

Evolution of low frequency quasi-periodic oscillations in GX 339-4 during its 2021 outburst using AstroSat data

The black hole X-ray binary GX\,339-4 showed an X-ray outburst during 2021. The {\it AstroSat} captured this outburst when the source entered into the intermediate flux state while the count rate was declining. The source showed an alternating flux profile in a timescale of $\lesssim$100 ks, where the hard energy band was more variable than the soft band. The energy-dependent timing study showed that the observed quasi-periodic oscillation (QPO) was prominent in the low energy bands, with its nearly sub-harmonic and harmonic components. These components appear and disappear with time, as observed in the orbit-wise QPO study. The Q-value, fractional rms, and 4.8-5.6 Hz frequency infer the QPOs as type-B and the spectral state as soft intermediate. The rms spectra of all orbits exhibiting QPOs show an increase in amplitude till $\sim$ 10 keV, beyond which it starts decreasing. This may indicate that $\sim$ 10 keV photons contributed relatively more in QPOs than other energy band photons. The Lorentzian normalization of the type-B QPO in different energy bands is consistent with the 10 keV peak. The energy-dependent time lag is complex and could be associated with the Comptonizing corona or jet. Finally, we discuss possible reasons behind the origin of different timing properties observed.

astro-ph.HE↗

arXiv2023

Electroweak box diagram contribution for pion and kaon decay from lattice QCD

One of the sensitive probes of physics beyond the standard model is the test of the unitarity of the Cabbibo-Kobyashi-Maskawa (CKM) matrix. Current analysis of the first row is based on $|V_{ud}|$ from fourteen superallowed $0^+ \to 0^+$ nuclear $β$ decays and $|V_{ud}|$ from the kaon semileptonic decay, $K \to π\ell ν_\ell$. Modeling the nuclear effects in the $0^+ \to 0^+$ decays is a major source of uncertainty, which would be absent in neutron decays. To make neutron decay competitive requires improving the measurement of neutron lifetime and the axial charge, as well as the calculation of the radiative corrections (RC) to the decay. The largest uncertainty in these RCs, which comes from the non-perturbative part of the $γW$-box diagram and its evaluation using lattice QCD, is still not under control. Here, we show that the analogous calculations for the pion and kaon decays are robust and give $\square_{γW}^{VA}|_π = 2.810 (26) \times 10^{-3}$ and $\square_{γW}^{VA}|_{K^{0, S U(3)}} = 2.389 (17) \times 10^{-3}$ in agreement with the previous analysis carried out by Feng et al. using a different discretization of the fermion action.

hep-lat↗

arXiv2023

Broadband X-ray spectral analysis of the ULX NGC 1313\,X-1 using JeTCAF: Origin of the ULX bubble

NGC 1313\,X-1 is a mysterious Ultra-luminous X-ray (ULX) source whose X-ray powering mechanism and a bubble-like structure surrounding the source are topics of intense study. Here, we perform the X-ray spectroscopic study of the source using a joint {\it XMM-Newton} and {\it NuSTAR} observations taken during 2012 $-$ 2017. The combined spectra cover the energy band 0.3 $-$ 20 keV. We use the accretion-ejection-based JeTCAF model for spectral analysis. The model fitted disc mass accretion rate varies from 4.6 to 9.6 $\dot M_{\rm Edd}$ and the halo mass accretion rate varies from 4.0 to 6.1 $\dot M_{\rm Edd}$ with a dynamic Comptonizing corona of average size of $\sim 15$ $r_g$. The data fitting is carried out for different black hole (BH) mass values. The goodness of the fit and uncertainties in model parameters improve while using higher BH mass with most probable mass of the compact object to be $133\pm33$ M$_\odot$. We have estimated the mass outflow rate, its velocity and power, and the age of the inflated bubble surrounding the source. Our estimated bubble morphology is in accord with the observed optical bubble and winds found through high-resolution X-ray spectroscopy, suggesting that the bubble expanded by the outflows originating from the central source. Finally, we conclude that the super-Eddington accretion onto a nearly intermediate mass BH may power a ULX when the accretion efficiency is low, though their efficiency increases when jet/outflow is taken into account, in agreement with numerical simulations in the literature.

astro-ph.HE↗

arXiv2023

Spectral and Temporal Studies of Swift\,J1658.2--4242 using {\it AstroSat} Observations with {\tt JeTCAF} Model

We present the X-ray spectral and temporal analysis of the black hole X-ray transient Swift J1658.2--4242 observed by {\it AstroSat}. Three epochs of data have been analysed using the JeTCAF model to estimate the mass accretion rates and to understand the geometry of the flow. The best-fit disc mass accretion rate ($\dot m_d$) varies between $0.90^{+0.02}_{-0.01}$ to $1.09^{+0.04}_{-0.03}$ $\dot M_{\rm Edd}$ in these observations, while the halo mass accretion rate changes from $0.15^{+0.01}_{-0.01}$ to $0.25^{+0.02}_{-0.01}$ $\dot M_{\rm Edd}$. We estimate the size of the dynamic corona, that varies substantially from $64.9^{+3.9}_{-3.1}$ to $34.5^{+2.0}_{-1.5}$ $r_g$ and a moderately high jet/outflow collimation factor stipulates isotropic outflow. The inferred high disc mass accretion rate and bigger corona size indicate that the source might be in the intermediate to soft spectral state of black hole X-ray binaries. The mass of the black hole estimated from different model combinations is $\sim 14 M_\odot$. In addition, we compute the quasi-periodic oscillation (QPO) frequencies from the model-fitted parameters, which match the observed QPOs. We further calculate the binary parameters of the system from the decay profile of the light curve and the spectral parameters. The estimated orbital period of the system is $4.0\pm0.4$ hr by assuming the companion as a mid or late K-type star. Our analysis using the JeTCAF model sheds light on the physical origin of the spectro-temporal behaviour of the source, and the observed properties are mainly due to the change in both the mass accretion rates and absorbing column density.

astro-ph.HE↗

arXiv2023

On unit-weighted zero-sum constants of $\mathbb Z_n$

Given $A\subseteq\mathbb Z_n$, the constant $C_A(n)$ is defined to be the smallest natural number $k$ such that any sequence of $k$ elements in $\mathbb Z_n$ has an $A$-weighted zero-sum subsequence having consecutive terms. The value of $C_{U(n)}(n)$ is known when $n$ is odd. We give a different argument to determine the value of $C_{U(n)}(n)$ for any $n$. A $C$-extremal sequence for $U(n)$ is a sequence in $\mathbb Z_n$ whose length is $C_{U(n)}(n)-1$ and which does not have any $U(n)$-weighted zero-sum subsequence having consecutive terms. We characterize the $C$-extremal sequences for $U(n)$ when $n$ is a power of 2. For any $n$, we determine the value of $C_A(n)$ where $A$ is the set of all odd (or all even) elements of $\mathbb Z_n$ and also when $A=\{1,2,\ldots,r\}$ where $r<n$.

math.NT↗

arXiv2023

Zero-sum constants related to the Jacobi symbol

For $A\subseteq\mathbb Z_n$, the $A$-weighted Gao constant $E_A(n)$ is defined to be the smallest natural number $k$ such that any sequence of $k$ elements in $\mathbb Z_n$ has a subsequence of length $n$ whose $A$-weighted sum is zero. When $A$ is the set of all units in $\mathbb Z_n$, we determine the value of $E_A(n)$ and values of two related constants $C_A(n)$ and $D_A(n)$. We also characterize all sequences of length $E_A(n)-1$ in $\mathbb Z_n$ which do not have any $A$-weighted zero-sum subsequence of length $n$ when $n$ is a power of 2.

math.NT↗

arXiv2023

On a different weighted zero-sum constant

For a finite abelian group $(G,+)$, the constant $C(G)$ is defined to be the smallest natural number $k$ such that any sequence in $G$ having length $k$ will have a subsequence of consecutive terms whose sum is zero. For a subset $A\subseteq\mathbb Z_n$, the constant $C_A(n)$ is the smallest natural number $k$ such that any sequence in $G$ having length $k$ has an $A$-weighted zero-sum subsequence of consecutive terms. We determine the value of $C_A(n)$ for some particular weight-sets $A$.

math.NT↗

arXiv2023

Nucleon form factors and the pion-nucleon sigma term

This talk summarizes the progress made since Lattice 2021 in understanding and controlling the contributions of towers of multihadron excited states with mass gaps starting lower than of radial excitations, and in increasing our confidence in the extraction of ground state nucleon matrix elements. The most clear evidence for multihadron excited state contributions (ESC) is in axial/pseudoscalar form factors that are required to satisfy the PCAC relation between them. The talk examines the broader question--which and how many of the theoretically allowed positive parity states $N(\textbf p)π(-\textbf p)$, $N(\textbf 0)π(\textbf 0)π(\textbf 0)$, $N(\textbf p)π(\textbf 0)$, $N(\textbf 0)π(\textbf p),\ \ldots$ make significant contributions to a given nucleon matrix element? New data for the axial, electric and magnetic form factors are presented. They continue to show trends observed in Ref[1]. The N${}^2$LO $χ$PT analysis of the ESC to the pion-nucleon sigma term, $σ_{πN}$, has been extended to include the $Δ$ as an explicit degree of freedom [2]. The conclusion reached in Ref [3] that $N π$ and $N ππ$ states each contribute about 10 MeV to $σ_{πN}$, and the consistency between the lattice result with $N π$ state included and the phenomenological estimate is not changed by this improvement.

hep-lat↗

arXiv2023

Update on Flavor Diagonal Nucleon Charges

This talk provides an update on the calculation of matrix elements of flavor diagonal axial, scalar and tensor quark bilinear operators between the nucleon ground state. The simulations are done using Wilson-clover fermions on a sea of eight 2+1+1-flavor HISQ ensembles generated by the MILC collaboration. We discuss the signal in the sum of the connected and disconnected contributions for the up, down and strange quarks, control over fits to remove excited state contamination, and the simultaneous chiral-continuum fit used to extract the charges.

hep-lat↗

arXiv2022

Electroweak box diagrams on the lattice for pion and neutron decay

CKM matrix is unitary by construction in the standard model(SM). The recent analyses on the first row of CKM matrix show $ \approx 3σ$ tension with unitarity. Nonperturbative calculations of the radiative corrections can reduce the theory uncertainty in CKM matrix elements. Here we compute the electroweak box contribution to the pion and kaon $β$ decays using seven $N_f=2+1+1$ HISQ-Clover lattice with various pion mass and lattice spacing. The continuum and chiral limit is taken using the leading dependence on $M_π$ and $a$, where $M_π$ extrapolation is taken to the physical pion mass and $SU(3)$ symmetric mass for pion and kaon box contribution, respectively. Our results are $ \square_{γW}^{VA} |_π = 2.820 (28) \times 10^{-3} $ and $ \square_{γW}^{VA} |_{K} = 2.384 (17) \times 10^{-3} $.

hep-lat↗

arXiv2022

Extremal sequences related to the Jacobi symbol

For a weight-set $A\subseteq \mathbb Z_n$, the $A$-weighted zero-sum constant $C_A(n)$ is defined to be the smallest natural number $k$, such that any sequence of $k$ elements in $\mathbb Z_n$ has an $A$-weighted zero-sum subsequence of consecutive terms. A sequence of length $C_A(n)-1$ in $\mathbb Z_n$ which does not have any $A$-weighted zero-sum subsequence of consecutive terms will be called a $C$-extremal sequence for $A$. Let $\big(\frac{x}{n}\big)$ denote the Jacobi symbol of $x\in\mathbb Z_n$. We characterize the $C$-extremal sequences for the weight-set $S(n)=\big\{\,x\in U(n):\big(\frac{x}{n}\big)=1\,\big\}$ and for the weight-set $L(n;p)=\big\{\,x\in U(n):\big(\frac{x}{n}\big)=\big(\frac{x}{p}\big)\,\big\}$ where $p$ is a prime divisor of $n$. We can define $D$-extremal sequences for these weight-sets in a way analogous to the definition of $C$-extremal sequences. We also characterize these sequences.

math.NT↗

arXiv2022

Misaligned jets from Sgr A$^*$ and the origin of Fermi/eROSITA bubbles

One of the leading explanations for the origin of Fermi Bubbles is a past jet activity in the Galactic center supermassive black hole Sgr A$^*$. The claimed jets are often assumed to be perpendicular to the Galactic plane. Motivated by the orientation of pc-scale nuclear stellar disk and gas streams, and a low inclination of the accretion disk around Sgr A$^*$ inferred by the Event Horizon Telescope, we perform hydrodynamical simulations of nuclear jets significantly tilted relative to the Galactic rotation axis. The observed axisymmetry and hemisymmetry (north-south symmetry) of Fermi/eROSITA bubbles (FEBs) due to quasi-steady jets in Sgr A$^*$ can be produced if the jet had a super-Eddington power ($\gtrsim 5\times 10^{44}$ erg s$^{-1}$) for a short time (jet active period $\lesssim 6$ kyr) for a reasonable jet opening angle ($\lesssim 10^\circ$). Such powerful explosions are, however, incompatible with the observed O VIII/O VII line ratio towards the bubbles, even after considering electron-proton temperature non-equilibrium. We argue that the only remaining options for producing FEBs are i) a low-luminosity ($\approx 10^{40.5-41}$ erg s$^{-1}$)) magnetically dominated jet or accretion wind from the Sgr A$^*$, and ii) a SNe or TDE driven wind of a similar luminosity from the Galactic center.

astro-ph.HE↗

arXiv2022

Extremal sequences for a weighted zero-sum constant

The constant $C_A(n)$ is defined to be the smallest natural number $k$ such that any sequence of $k$ elements in $\mathbb Z_n$ has a subsequence of consecutive terms whose $A$-weighted sum is zero, where the weight set $A\subseteq \mathbb Z_n\setminus \{0\}$. If $C_A(n)=k$, then a sequence in $\mathbb Z_n$ of length $k-1$ which has no $A$-weighted zero-sum subsequence of consecutive terms is called an $A$-extremal sequence. We characterize these sequences for some particular weight sets.

math.NT↗