Study of spectral and temporal behaviour of AXP 1E 1048.1-5937 using AstroSat

Anirban Chakraborty

Hansraj College, University of Delhi, Mahatma Hansraj Marg, Delhi 110007

Dr. Manoneeta Chakraborty

Centre of Astronomy, Indian Institute of Technology Indore, Khandwa Road, Simrol, Indore 453552

Abstract

Anomalous X-Ray Pulsars (AXP) are a class of celestial enigmas characterized by slow spin periods ( P ~ 5 – 12 s), high spin-down rates ( ~ 10 ^{– 10} – 10 ^{– 13} s s ^{– 1} ) and typically persistent X-ray luminosities ( L ~ 10 ³³ – 10 ³⁶ ergs s ^{– 1} ). These X-ray bright objects were theorized to be young isolated neutron stars having ultra-strong magnetic fields ( > 10 ¹⁴ G, as inferred from their spin and spin down rates) and are identified as “Magnetars". They are entirely powered by the decay of this intense internal magnetic field.

In this project, we present a study of the temporal and spectral properties of persistent emission from the Anomalous X-Ray Pulsar AXP 1E 1048.1−5937 located in the Carina constellation, using the ~40 ks exposure time data recorded over 11^th and 12^th January 2017 by the Large Area X Ray Proportional Counter (LAXPC) instruments aboard AstroSat – India’s first dedicated multi-wavelength astronomy satellite.

We studied the source spectrum in soft and intermediate X-ray bands (~4 − 25 KeV) to understand the possible emission behaviour, and its mechanisms and emission regions. Through short-term timing studies, we determined the spin period of the source and studied the pulse profile and pulse fraction evolution in order to probe the magnetic field of this source and its complex morphologies. We discuss our temporal and spectral results in the context of the radiative behaviour of the magnetar and also with respect to the long-term evolution of this source and address its implications.

Keywords: Magnetars, Anomalous X-Ray Pulsars, Neutron Stars, Timing, Spectrum, LAXPC