arXiv subjects

Sakshi Maurya

Publications and source records attributed to Sakshi Maurya.

5 recordsLinked to original sources

arXiv2026

Importance and Science Outcomes from the first XSPECT/XPoSat Workshop

This paper summarizes the science outcomes of the first Workshop on Data Analysis using observations from the XSPECT payload onboard the XPoSat, which brought together early-career researchers and experts to explore the instrument's scientific capabilities through lectures and hands-on analyses. Participants performed end-to-end data analysis, including calibration, spectral modeling, and timing studies, on seven sources comprising Neutron Star Low-Mass X-ray Binaries, pulsars, and Black Hole X-ray Binaries, demonstrating the instrument's scientific potential. The observations, obtained during the first year of XSPECT operations, together with in-house developed software, were provided to the participants, making them the first users outside the instrument team to analyze XSPECT data. For NS-LMXBs, Aql X-1 exhibited a classical Type-I X-ray burst, enabling constraints on the stellar radius through spectral fitting. Sco X-1, observed across its complete Z-track, revealed systematic spectral evolution driven by accretion-rate fluctuations and disk-corona coupling, while Cir X-1 displayed orbital phase-dependent transitions between hard and soft states, reflecting changes in accretion geometry. Among accretion-powered pulsars, GX 301-2 showed a double-peaked, energy-dependent pulse profile and strong iron fluorescence lines due to stellar wind reprocessing, whereas Vela X-1 exhibited orbital phase-dependent absorption and steady coronal temperatures. Among BH-XRBs, Cyg X-1 transitioned from a hard to soft-intermediate state with increasing disk contribution and spectral softening, while Cyg X-3 remained in the intermediate state with multiple emission lines originating from a clumpy stellar wind. The workshop outcomes highlight the scientific promise of XSPECT and the importance of collaborative training in maximizing the science from XSPECT and future Indian space astronomy missions.

astro-ph.HE↗

arXiv2025

BL Lacertae under the Flare of 2024: Probing Temporal and Spectral Dynamics

In October 2024, the object BL Lacertae experienced the brightest flaring event in gamma-ray ($>$100 MeV) with a historically bright $γ$-ray flux of $\sim$2.59 $\times 10^{-5}$ erg cm$^{-2}$ s$^{-1}$ with a detection of a 175.7 GeV photon with Fermi-LAT. This event was also followed by very high-energy $γ$-ray detection with LHAASO, VERITAS, and MAGIC. Soon after, Swift-XRT and Swift-UVOT follow-up confirmed the concurrent flare in X-ray, UV, and optical bands. A minimum flux doubling/halving time of 1.06 $\pm$ 0.26 hour with 4$σ$ significance has been observed with the Fermi-LAT orbit binned light curve. No compelling correlation has been found between $γ$-ray spectral indices and fluxes. The log-normal $γ$-ray flux distribution during the flare confirms the multiplicative nature of the non-linear perturbation causing the flare. We applied a one-zone leptohadronic model to fit the broadband SED during the flaring period. The broadband SED modeling reveals that the sudden enhancement of the magnetic field and bulk factor might promote the flare. The SED modeling also suggested a more compact emission region, which may be described by a shorter variability time than the observed one. The hadronic part best fitted the high energy part of the spectrum, suggesting the jets of BL Lac could provide a promising environment to accelerate the cosmic ray particles, such as protons. The jets of BL Lacertae could also be the possible source of astrophysical neutrinos, as an upper limit on neutrinos has already been reported from IceCube.

astro-ph.HE↗

arXiv2025

Minute time scale variability in $γ$-ray flare of BL Lacertae

In October 2024, The object BL Lac experienced a brightest flaring event in gamma-ray ($>$100 MeV) with a historical $γ$-ray flux of $\sim$10$^{-5}$ erg cm$^{-2}$ s$^{-1}$. Soon after the event was followed across the waveband and in X-ray (0.3-10 keV) it was also found to be flaring with the maximum flux achieved during this event as 8.30$\times$10$^{-11}$ erg cm$^{-2}$ s$^{-1}$. The high gamma-ray significance enables us to probe the shortest time scale variability possible and for that, we produced the orbital binned light curve, 5 minutes binned light curve, and the 2 minutes binned light curve. A clear variation is seen in the 5-minute light curve and is fitted with the sum of exponentials to derive the rise and decay time scale which ranges between 3 to 12 minutes. The fastest variability time is also estimated to be an order of 1 minute from 2 minute. The estimated size of the emission region is very small (10$^{13}$ cm) compared to the size of the black hole event horizon. The location of the emission region is estimated to be very close to the supermassive black hole (10$^{14}$ cm) and much inside the BLR (0.1 pc). We discussed the possible way to explain this fast-flux variability in BL Lac.

astro-ph.HE↗

arXiv2025

Flare genesis in relativistic jet: Disentangling the drivers of variability in the blazar 4C +27.50

Recently, blazar 4C +27.50 was found to be flaring in gamma-rays since its detection with Fermi-LAT in 2008. For the first time, a dedicated temporal and spectral study of the blazar 4C +27.50 has been performed in this work to understand the nature of this object. We used the Bayesian block algorithm to identify four flaring states and one quiet state in the 2-year-long Fermi-LAT light curve. Simultaneous broadband flaring episodes have been observed, and a significant correlation is seen between optical and $γ$-ray emission, suggesting the co-spatial origin of the broadband emission. The variation of fractional variability amplitude with respect to frequency shows a nearly double hump structure similar to broadband SED. The fastest flux doubling time in the 1-day binned $γ$-ray light curve is found to be about 7.8 hours. A curvature in $γ$-ray spectra has been observed, possibly caused by a stochastic particle acceleration process rather than radiative cooling. No evident correlation was found in the $γ$-ray flux-index plot, but a clear harder-when-brighter trend is observed in the X-ray flux-index plot. A one-zone leptonic model has been implemented to understand broadband emission during the quiet and flaring states, and the variation of the jet parameters is been investigated. A gradual increment in BLR and Disk energy density has been observed from a quiet to the flaring state. Broadband SED modeling suggested that an enhancement in the magnetic field, particle energy, and bulk Lorentz factor might have caused the flaring events.

astro-ph.HE↗

arXiv2025

On the origin of multifrequency temporal and spectral variability in Ton 599

In this work, we studied the broadband temporal and spectral properties of the flat-spectrum radio quasar (FSRQ) Ton 599. We collected the long-term data from Jan 2019 to August 2024 when the source was in a long flaring episode. We used the Bayesian block methodology to identify the various flux states, including three flares. The broadband fractional variability is estimated during two flaring states. The Fvar variation with respect to frequency shows a nearly double hump structure similar to broadband SED. The Power spectral density (PSD) shows a pink-noise kind of stochastic variability in the light curve and we do not see any break in the power spectrum, suggesting a much longer characteristic time scale is involved in gamma-ray variability. The flux distribution is well-fitted with a double log-normal flux distribution, suggesting the variability of non-linear in nature. The gamma-ray, optical, and X-ray emissions were found to be highly correlated with a zero time lag, suggesting a co-spatial origin of their emissions. We used the one-zone leptonic model to reproduce the broad-band spectrum in the energy range from IR to very high-energy gamma-ray. The increase in the magnetic field and the Doppler factor were found to be the main cause for high flux states. The XMM-Newton spectra taken during one of the flaring durations exhibit a signature of thermal black body emission from the accretion disk, suggesting a possible disk-jet coupling. This has also been indicated by the gamma-ray flux distribution, which shows the distribution as non-linear in nature, which is mostly seen in galactic X-ray binaries or AGN where the accretion disk dominates the emission.

astro-ph.HE↗