13-18 December 2015
International Conference Centre Geneva
Europe/Zurich timezone

Spectral Analysis of ULXs in Pairs of Interacting Galaxies M51 and NGC 4485/90 Using Swift-XRT

17 Dec 2015, 18:42
Level 0, Room 23 (International Conference Centre Geneva)

Level 0, Room 23

International Conference Centre Geneva

17 Rue de Varembé, 1211 Geneva


Ms Lis Sulistiyowati (Institut Teknologi Bandung)


In this study, we report the examinations of the spectra of ULXs in two nearby (< 10 Mpc) pairs of interacting galaxies M51 and NGC 4485/90 collected by Swift-XRT observations from 2005 to 2014 and 2008 to 2015 for each target, respectively. We consider 9 ULXs in M51 and 5 ULXs in NGC 4485/90. We obtain 116 ObsIDs of M51 and 37 ObsIDs of NGC 4485/90. For each pair of interacting galaxy, there are about 10% data that do not meet our criteria for further analysis. The count rate of individual observation ranges from 0.00003 to 0.05 counts/s in 0.3 - 10 keV band with typical errorbar ~ 30%. Some ULXs in M51 exhibit a considerable fluctuation of intensity, up to three times, from 0.01 counts/s to 0.03 counts/s. ULXs in NGC 4485/90 show more stable light curves with no significant changes in intensity. For every source, we divide the data into two categories, e.g. hard-state (those with hardness ratio ≥ 1) and soft-state (those with hardness ratio < 1). Due to the short exposure time during the observation, we got low S/N data with wide errorbar. Therefore, we combine spectrum from many observations with similar spectral characteristics for fitting purpose. We fit the co-added spectra with commonly used models: disk blackbody, power law, and the combination of several models.

Primary author

Ms Lis Sulistiyowati (Institut Teknologi Bandung)


Mr Febrie Azizi (Institut Teknologi Bandung) Dr Hesti Wulandari (Institut Teknologi Bandung) Dr Kiki Vierdayanti (Institut Teknologi Bandung) Mr Mahadipa Priajana (Institut Teknologi Bandung) Dr Premana Premadi (Institut Teknologi Bandung)

Presentation Materials