TIMING AND SPECTRAL PROPERTIES OF Be/X-RAY PULSAR EXO 2030+375 DURING A TYPE I OUTBURST

Abstract

We present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy dependent pulse profiles were clearly detected up to 100 keV. Narrow dips are seen in the profiles up to ∼70 keV. Presence of prominent dips at several phases in the profiles up to such high energy ranges were not seen before. At higher energies, these dips gradually disappeared and the profile appeared singlepeaked. The 1.0-200.0 keV broad-band spectrum is found to be well described by a partial covering high energy cut-off power-law model. Several low energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with above continuum model yielding similar parameter values. The partial covering with partially ionized absorber resulted into marginally better fit. The spectral fitting did not require any cyclotron feature in the best fit model. To investigate the changes in spectral parameters at dips, we carried out pulsephase-resolved spectroscopy. During the dips, the value of additional column density was estimated to be high compared to other pulse phases. While using partially ionized absorber, the value of ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar.

Suzakuview of the Be/X-ray binary pulsar GX 304-1 during Type I X-ray outbursts

“…This confirms that the amount of mass accreted by the neutron star from the Be circumstellar disk during 2010 August outburst was significantly more than that during 2012 January outburst. Similar findings have also been reported for EXO 2030+275 during its Type I outbursts with significantly different luminosities (Naik et al 2013;. High value of NH 2 during more luminous Type I outbursts in Be/X-ray binary pulsars can be explained as due to significant amount of mass accreted by the neutron star from the circumstellar disk of the Be companion star.…”

“…The pulse profiles of EXO 2030+375 during these two outbursts were significantly different (Naik et al 2013;. During the luminous outburst in 2007 May, the pulse profile of EXO 2030+375 consisted of several absorption dips as seen in the pulse profiles of GX 304-1 during 2012 January outburst.…”

“…4U 0115+63, X0331+53, Cep X-4; Makishima et al 1999) continuum models. However, recently it has been found that while performing phase-resolved spectroscopy on data taken during X-ray outbursts of these pulsars, above models do not yield acceptable fit at all phase bins, specifically at phases of prominent and narrow absorption dips in the pulse profiles Naik et al 2013 and references therein). To investigate the changes in spectral parameters at all phase bins (dip and non-dip phases of the pulse profiles), a partial covering absorption component has been added to above standard continuum models.…”

“…However, there are a few Be/X-ray pulsar in which the absorption dips are seen at same phase in the pulse profiles up to higher energy (∼70 keV) e.g. EXO 2030+375 (Naik et al 2013). This is interpreted as due to the presence of dense additional absorbers at various narrow pulse phase bins of the pulsar.…”

Suzakuobservations of the 2013 outburst of KS 1947+300

“…Many neutron star binaries show the opposite behavior with peaks vanishing at high energies, e.g., 4U 0115+634 (Müller et al 2010), 4U 1909+07 (Fürst et al 2011), Vela X-1 (Kreykenbohm et al 2002), GX 304−1 (Devasia et al 2011), 1A 1118−61 Maitra et al 2012), GRO J1008−57 (Naik et al 2011b), or EXO 2030+375 (Naik et al 2013). We note, however, that IGR J16393−4643 shows an evolution with energy that is similar to that in KS 1947+300 (Islam et al 2015).…”