CI Camelopardalis: The first sgB[e]-High Mass X-ray Binary Twenty Years on, a Supernova Imposter in our own Galaxy?. (arXiv:1812.08170v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bartlett_E/0/1/0/all/0/1">E. S. Bartlett</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clark_J/0/1/0/all/0/1">J. S. Clark</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Negueruela_I/0/1/0/all/0/1">I. Negueruela</a>
The Galactic supergiant B[e] star CI Camelopardalis (CI Cam) was the first
sgB[e] star detected during an X-ray outburst. The star brightened to $sim$2
Crab in the X-ray regime within hours before decaying to a quiescent level in
less than 2 weeks, clearly indicative of binarity. Since the outburst of CI
Cam, a number of sgB[e] stars have been identified as X-ray overluminous for a
single star (i.e. $L_X > 10^{-7}~L_{bol}$). This small population has recently
expanded to include two Ultra Luminous X-ray sources (ULX), Holmberg II X-1 and
NGC300 ULX-1/supernova imposter SN2010da. We revisit CI Cam to investigate its
behaviour over several timescales and shed further light on the nature of the
compact object in the system, its X-ray outburst in 1998 and the binary system
parameters. We analyse archival XMM-Newton EPIC-pn spectra and light curves
along with new data from Swift and NuSTAR. We also present high-resolution
MERCATOR/HERMES optical spectra, including a spectrum taken 1.02 days after our
NuSTAR observation. Despite being in quiescence, CI Cam is highly X-ray
variable on timescales of days, both in terms of total integrated flux and
spectral shape. We interpret these variations by invoking the presence of an
accreting compact companion immersed in a dense, highly structured, aspherical
circumstellar envelope. The differences in the accretion flux and circumstellar
extinction represent either changes in this environment, triggered by variable
mass loss from the star, or the local conditions to the accretor due to its
orbital motion. We find no evidence for pulsations in the X-ray light curve. CI
Cam has many similarities with SN2010da across mid-IR, optical and X-ray
wavelengths suggesting that, subject to distance determination for CI Cam, if
CI Cam was located in an external galaxy its 1998 outburst would have led to a
classification as a supernova imposter.
The Galactic supergiant B[e] star CI Camelopardalis (CI Cam) was the first
sgB[e] star detected during an X-ray outburst. The star brightened to $sim$2
Crab in the X-ray regime within hours before decaying to a quiescent level in
less than 2 weeks, clearly indicative of binarity. Since the outburst of CI
Cam, a number of sgB[e] stars have been identified as X-ray overluminous for a
single star (i.e. $L_X > 10^{-7}~L_{bol}$). This small population has recently
expanded to include two Ultra Luminous X-ray sources (ULX), Holmberg II X-1 and
NGC300 ULX-1/supernova imposter SN2010da. We revisit CI Cam to investigate its
behaviour over several timescales and shed further light on the nature of the
compact object in the system, its X-ray outburst in 1998 and the binary system
parameters. We analyse archival XMM-Newton EPIC-pn spectra and light curves
along with new data from Swift and NuSTAR. We also present high-resolution
MERCATOR/HERMES optical spectra, including a spectrum taken 1.02 days after our
NuSTAR observation. Despite being in quiescence, CI Cam is highly X-ray
variable on timescales of days, both in terms of total integrated flux and
spectral shape. We interpret these variations by invoking the presence of an
accreting compact companion immersed in a dense, highly structured, aspherical
circumstellar envelope. The differences in the accretion flux and circumstellar
extinction represent either changes in this environment, triggered by variable
mass loss from the star, or the local conditions to the accretor due to its
orbital motion. We find no evidence for pulsations in the X-ray light curve. CI
Cam has many similarities with SN2010da across mid-IR, optical and X-ray
wavelengths suggesting that, subject to distance determination for CI Cam, if
CI Cam was located in an external galaxy its 1998 outburst would have led to a
classification as a supernova imposter.
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