Abstract
Modelling of thermonuclear X-ray bursts on accreting neutron stars has to date focused on stable accretion rates. However, bursts are also observed during episodes of transient accretion. During such events, the accretion rate can evolve significantly between bursts, and this regime provides a unique test for burst models. The accretion-powered millisecond pulsar SAX J1808.4-3658 exhibits accretion outbursts every 2-3 yr. During the well-sampled month-long outburst of 2002 October, four helium-rich X-ray bursts were observed. Using this event as a test case, we present the first multizone simulations of X-ray bursts under a timedependent accretion rate.We investigate the effect of using a time-dependent accretion rate in comparison to constant, averaged rates. Initial results suggest that using a constant, average accretion rate between bursts may underestimate the recurrence time when the accretion rate is decreasing, and overestimate it when the accretion rate is increasing. Our model, with an accreted hydrogen fraction of X = 0.44 and a CNO metallicity of ZCNO = 0.02, reproduces the observed burst arrival times and fluences with root mean square (rms) errors of 2.8 h, and 0.11 × 10-6 erg cm-2, respectively. Our results support previous modelling that predicted two unobserved bursts and indicate that additional bursts were also missed by observations.
| Original language | English |
|---|---|
| Pages (from-to) | 2112-2118 |
| Number of pages | 7 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 477 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 21 Jun 2018 |
Keywords
- Methods: Numerical
- Pulsars: Individual: (SAX J1808.4-3658)
- Stars: Neutron
- X-rays: Bursts
Cite this
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Simulating X-ray bursts during a transient accretion event. / Johnston, Zac; Heger, Alexander; Galloway, Duncan K.
In: Monthly Notices of the Royal Astronomical Society, Vol. 477, No. 2, 21.06.2018, p. 2112-2118.Research output: Contribution to journal › Article › Research › peer-review
TY - JOUR
T1 - Simulating X-ray bursts during a transient accretion event
AU - Johnston, Zac
AU - Heger, Alexander
AU - Galloway, Duncan K.
PY - 2018/6/21
Y1 - 2018/6/21
N2 - Modelling of thermonuclear X-ray bursts on accreting neutron stars has to date focused on stable accretion rates. However, bursts are also observed during episodes of transient accretion. During such events, the accretion rate can evolve significantly between bursts, and this regime provides a unique test for burst models. The accretion-powered millisecond pulsar SAX J1808.4-3658 exhibits accretion outbursts every 2-3 yr. During the well-sampled month-long outburst of 2002 October, four helium-rich X-ray bursts were observed. Using this event as a test case, we present the first multizone simulations of X-ray bursts under a timedependent accretion rate.We investigate the effect of using a time-dependent accretion rate in comparison to constant, averaged rates. Initial results suggest that using a constant, average accretion rate between bursts may underestimate the recurrence time when the accretion rate is decreasing, and overestimate it when the accretion rate is increasing. Our model, with an accreted hydrogen fraction of X = 0.44 and a CNO metallicity of ZCNO = 0.02, reproduces the observed burst arrival times and fluences with root mean square (rms) errors of 2.8 h, and 0.11 × 10-6 erg cm-2, respectively. Our results support previous modelling that predicted two unobserved bursts and indicate that additional bursts were also missed by observations.
AB - Modelling of thermonuclear X-ray bursts on accreting neutron stars has to date focused on stable accretion rates. However, bursts are also observed during episodes of transient accretion. During such events, the accretion rate can evolve significantly between bursts, and this regime provides a unique test for burst models. The accretion-powered millisecond pulsar SAX J1808.4-3658 exhibits accretion outbursts every 2-3 yr. During the well-sampled month-long outburst of 2002 October, four helium-rich X-ray bursts were observed. Using this event as a test case, we present the first multizone simulations of X-ray bursts under a timedependent accretion rate.We investigate the effect of using a time-dependent accretion rate in comparison to constant, averaged rates. Initial results suggest that using a constant, average accretion rate between bursts may underestimate the recurrence time when the accretion rate is decreasing, and overestimate it when the accretion rate is increasing. Our model, with an accreted hydrogen fraction of X = 0.44 and a CNO metallicity of ZCNO = 0.02, reproduces the observed burst arrival times and fluences with root mean square (rms) errors of 2.8 h, and 0.11 × 10-6 erg cm-2, respectively. Our results support previous modelling that predicted two unobserved bursts and indicate that additional bursts were also missed by observations.
KW - Methods: Numerical
KW - Pulsars: Individual: (SAX J1808.4-3658)
KW - Stars: Neutron
KW - X-rays: Bursts
UR - http://www.scopus.com/inward/record.url?scp=85047144794&partnerID=8YFLogxK
U2 - 10.1093/mnras/sty757
DO - 10.1093/mnras/sty757
M3 - Article
VL - 477
SP - 2112
EP - 2118
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -