AstroSat observations of the Be/X-ray binary XTE J1946+274 during 2018 and 2021 outbursts

Abstract

We present the timing and spectral studies of the Be/X-ray binary XTE J1946+274 during its 2018 and 2021 giant outbursts using observations with the SXT and the LAXPC instruments on the AstroSat satellite. Unlike the 1998 and 2010 outbursts, where a giant outburst was followed by several low intensity periodic outbursts, the 2018 and 2021 outbursts were single outbursts. The X-ray pulsations are detected over a broad energy band covering 0.5-80 keV from the compact object. We construct the spin evolution history of the pulsar over two decades and find that the pulsar spins-up during the outbursts but switches to spin-down state in the quiescent periods between the outbursts. Energy resolved pulse profiles generated in several bands in 0.5-80 keV show that the pulse shape varies with the energy. The energy spectrum of the pulsar is determined for the 2018 and 2021 outbursts. The best fit spectral models require presence of Cyclotron Resonant Scattering Feature (CRSF) at about 43 keV in the energy spectra of both the outbursts. We find indication of possible reversal in the correlation between the cyclotron line energy and luminosity which needs to be ascertained from future observations. Using the best fit spectra the X-ray luminosity of XTE J1946+274 is inferred to be $2.7\times 10^{37}$ erg s${}^{-1}$ for the 2018 observations and $2.3\times 10^{37}$ erg s${}^{-1}$ for the 2021 observations. We discuss possible mechanisms which can drive outbursts in this transient Be X-ray binary.

arXiv commentAccepted for publication in Research in Astronomy and Astrophysics

References in corpus (51)

• On the Absorption of X-rays in the Interstellar Medium
• The Fermi Gamma-Ray Burst Monitor
• Be/X-ray binaries
• A natural explanation for periodic X-ray outbursts in Be/X-ray binaries
• Thermal and Bulk Comptonization in Accretion-Powered X-Ray Pulsars
• Spectral Formation in Accreting X-Ray Pulsars: Bimodal Variation of the Cyclotron Energy with Luminosity
• The critical accretion luminosity for magnetized neutron stars
• Calibration of the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat
• V0332+53 in the outburst of 2004--2005: luminosity dependence of the cyclotron line and pulse profile
• NuSTAR discovery of a luminosity dependent cyclotron line energy in Vela X-1
• The Be/X-ray transient 4U 0115+63/V635 Cas: II. Outburst mechanisms
• Giant Outbursts in Be/X-ray Binaries
• Timing Characteristics of the Hard X-ray Emission from Bright X-ray Pulsars Based on INTEGRAL Data
• Large Area X-ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its performance in the orbit
• Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53
• The Ups & Downs of Accreting X-Ray Pulsars: Decade-long observations with the Fermi Gamma-Ray Burst Monitor
• Pulse-amplitude-resolved spectroscopy of bright accreting pulsars: indication of two accretion regimes
• Hard Spectra of X-Ray Pulsars from INTEGRAL Data
• Study of Recent outburst in the Be/X-ray binary RX J0209.6-7427 with AstroSat: A new ultraluminous X-ray pulsar in the Magellanic Bridge?
• The X-ray properties of Be/X-ray pulsars in quiescence
• Distances to Galactic X-ray Binaries with Gaia DR2
• Luminosity-dependent changes of the cyclotron line energy and spectral hardness in Cep X-4
• Discovery of a Cyclotron Resonance Feature in the X-ray Spectrum of GX 304-1 with RXTE and Suzaku during Outbursts Detected by MAXI in 2010
• XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-ray Binary
• GRO J1008-57: an (almost) predictable transient X-ray binary
• Hydrodynamic Interaction between the Be Star and the Pulsar in the TeV Binary PSR B1259-63/LS 2883
• The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. III. Quasi-cyclic variability
• Precessing Warped Be Disk Triggering the Giant Outbursts in 2009 and 2011 in A 0535+262/V725 Tau
• Discovery and Modeling of a Flattening of the Positive Cyclotron Line/Luminosity Relation in GX 304-1 with RXTE
• Luminosity-dependent spectral and timing properties of the accreting pulsar GX 304-1 measured with INTEGRAL
• Detection of Cyclotron Resonance Scattering Feature in High Mass X-ray Binary Pulsar SMC X-2
• On the Spin Period Distribution in Be/X-ray Binaries
• The Be/X-ray Binary Swift J1626.6-5156 as a Variable Cyclotron Line Source
• The Swift-BAT monitoring reveals a long term decay of the cyclotron line energy in Vela X-1
• Kozai-Lidov Disc Instability
• Discovery of a Cyclotron Resonance Scattering Feature in the X-ray Spectrum of XTE J1946+274
• Changes in the cyclotron line energy on short and long timescales in V 0332+53
• Pulse phase dependent variations of the cyclotron absorption features of the accreting pulsars A 0535+26, XTE J1946+274 and 4U 1907+09 with Suzaku
• The identification of the optical/IR counterpart of the 15.8-s transient X-ray pulsar XTE J1946+274
• The Orbital Period of Swift J1626.6-5156
• The reawakening of the sleeping X-ray pulsar XTE J1946+274
• The Transient Accereting X-Ray Pulsar XTE J1946+274: Stability of the X-Ray Properties at Low Flux and Updated Orbital Solution
• Warped disks during type II outbursts in Be/X-ray binaries: evidence from optical polarimetry
• Eccentric neutron star disk driven type II outburst pairs in Be/X-ray binaries
• Detection of nearly periodic spin period reversals in Vela X-1 on long time-scales: inkling of solar-like cycle in the donor star?
• BeppoSAX observations of XTE J1946+274
• Performance of Large Area X-ray Proportional Counters in a Balloon Experiment
• Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+274
• Improved background model for the Large Area X-ray Proportional Counter (LAXPC) instrument on-board AstroSat
• Study of the X-ray Pulsar XTE J1946+274 with NuSTAR
• X-ray and optical monitoring of the December 2017 outburst of the Be/X-ray binary AX J0049.4-7323

Cited by in corpus (4)

• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
• Study on the magnetic field of the ultraluminous X-ray pulsar RX J0209.6-7427
• Search for neutrino signals correlated with LHAASO diffuse Galactic emission
• Long-term spin-down and low luminosity regime in the Be/X-ray binary pulsar GX 304-1