TY - ICOMM
T1 - Brightening of MAXI J0903-531 Seen with Fermi GBM and Swift BAT, and a Candidate Orbital Period
AU - Corbet , R. H. D.
AU - Jenke, P.
AU - Ballhausen, R.
AU - Becker , P. A.
AU - Coley, J. B.
AU - Fuerst, F.
AU - Islam , N.
AU - Jaisawal, G. K.
AU - Kretschmar, P.
AU - Malacaria, C.
AU - Pottschmidt, K.
AU - Rothschild, R. E.
AU - Thalhammer , P.
AU - Wilms, J.
AU - Wilson-Hodge, C. A.
AU - Wolff, M. T.
PY - 2021/6/21
Y1 - 2021/6/21
N2 - The transient X-ray binary system MAXI J0903-531 (ATel #14555) contains an X-ray pulsar with a period of
approximately 14 s (ATel #14559, #14604).
It has an optical counterpart (ATel #14557) that has been classified as a Be star (ATel #14564).
Optical photometry has revealed periods of 3.84 days (ATel #14564) and 0.79 days (ATel #14568, #14569).
Hard X-ray light curves are presently available from the Swift/BAT
transient monitor (15 - 50 keV;
https://swift.gsfc.nasa.gov/results/transients/index.html) with
measurements currently provided since
MJD 59,323 (2021-04-19), and measurements of the pulsed flux are
provided by the Fermi GBM (12 - 50 keV;
https://gammaray.nsstc.nasa.gov/gbm/science/pulsars.html) for times
since MJD 58,850 (2020-01-02).
Both the BAT and the GBM indicate that MAXI J0903-531 has recently
experienced another outburst.
The GBM has detected pulsed emission starting approximately MJD 59,375
(2021-06-10) at a pulsed
flux level of ~0.1 keV cm^-2 s^-1. The determination of the time of an
increase in the flux in the BAT
is hampered by the large error bars, but the daily average shows an
increase after about this time
reaching ~40 mCrab, which may now be returning to a lower level.
Although the MAXI 2 - 20 keV light curves of this source
(http://maxi.riken.jp/star_data/J0905-535/J0905-535.html) do not clearly
show a strong recent brightening, this may be due to different
instrument sensitivities.
The Fermi GBM pulsed flux light curve also shows detections between time ranges of MJD 59,204.5 - 59,207.6,
59,255.6 - 59,261.5, and 59,318.4 - 59,324.4. Large frequency changes are observed during some outbursts but
with a possible longer term spin-down trend. We note that the intervals between the central times of these detections
are ~53, 63, and 57 days. This may indicate that the activity is connected to periastron passage
in an eccentric system. If MAXI J0903-531 has an orbital period of ~57 days, then the source's location
in the pulse period/orbital period diagram (e.g. Corbet 1986, MNRAS, 220, 1047) would be typical
for a Be star HMXB, while a 3.84 or 0.79 day period would be exceptionally short. In this case
the shorter period could, as noted in ATel #14568, be a pulsation or rotation period of the Be star.
With this ephemeris, another outburst would be expected around August 6, although with several days uncertainty.
AB - The transient X-ray binary system MAXI J0903-531 (ATel #14555) contains an X-ray pulsar with a period of
approximately 14 s (ATel #14559, #14604).
It has an optical counterpart (ATel #14557) that has been classified as a Be star (ATel #14564).
Optical photometry has revealed periods of 3.84 days (ATel #14564) and 0.79 days (ATel #14568, #14569).
Hard X-ray light curves are presently available from the Swift/BAT
transient monitor (15 - 50 keV;
https://swift.gsfc.nasa.gov/results/transients/index.html) with
measurements currently provided since
MJD 59,323 (2021-04-19), and measurements of the pulsed flux are
provided by the Fermi GBM (12 - 50 keV;
https://gammaray.nsstc.nasa.gov/gbm/science/pulsars.html) for times
since MJD 58,850 (2020-01-02).
Both the BAT and the GBM indicate that MAXI J0903-531 has recently
experienced another outburst.
The GBM has detected pulsed emission starting approximately MJD 59,375
(2021-06-10) at a pulsed
flux level of ~0.1 keV cm^-2 s^-1. The determination of the time of an
increase in the flux in the BAT
is hampered by the large error bars, but the daily average shows an
increase after about this time
reaching ~40 mCrab, which may now be returning to a lower level.
Although the MAXI 2 - 20 keV light curves of this source
(http://maxi.riken.jp/star_data/J0905-535/J0905-535.html) do not clearly
show a strong recent brightening, this may be due to different
instrument sensitivities.
The Fermi GBM pulsed flux light curve also shows detections between time ranges of MJD 59,204.5 - 59,207.6,
59,255.6 - 59,261.5, and 59,318.4 - 59,324.4. Large frequency changes are observed during some outbursts but
with a possible longer term spin-down trend. We note that the intervals between the central times of these detections
are ~53, 63, and 57 days. This may indicate that the activity is connected to periastron passage
in an eccentric system. If MAXI J0903-531 has an orbital period of ~57 days, then the source's location
in the pulse period/orbital period diagram (e.g. Corbet 1986, MNRAS, 220, 1047) would be typical
for a Be star HMXB, while a 3.84 or 0.79 day period would be exceptionally short. In this case
the shorter period could, as noted in ATel #14568, be a pulsation or rotation period of the Be star.
With this ephemeris, another outburst would be expected around August 6, although with several days uncertainty.
KW - X-ray
KW - Binary
KW - Neutron Star
KW - Transient
KW - Pulsar
M3 - Net publication - Internet publication
T3 - The Astronomer's telegram
ER -