Evidence for Enhanced Formation Rate of Black Hole LMXBs in the Galaxy from Historical Outbursts from DASCH
Abstract
Using the data releases DR1 and DR2 as well as from the "Development Fields" from DASCH (Digital Access to a Sky Century @ Harvard), we have searched for historical optical outbursts of black hole low mass X-ray binaries (BH-LMXBs). With now 4 systems (XTEJ1118+480, GROJ1655-40, V4641Sgr and V404 Cyg) at least partially covered by the ongoing production DASCH plate scanning of the ~500,000 plates in the Harvard archives, we have discovered single or single + "echo" historical outbursts from each of these 4 BH-LMXBs over the past century of coverage available from DASCH. This provides the first confirmation of what was suspected from the single historical outbursts previously reported for outbursts from A0620-00 (from the Harvard plates) and the "hiistorical nova" V404 Cyg and greatly strengthens the case that these systems have much lower duty cycles than the otherwise similar "X-ray novae" from NS-LMXBs. This, in turn, suggests that their total population or rate of formation may exceed that for NS-LMXBs, when allowing for a Kroupa IMF for BH vs. NS production and plausible differences in outburst peak luminosity that impose selection effects in their discovery wihch until now has been with wide-field X-ray (or hard X-ray) surveys such as BATSE, RXTE/ASM, Swift/BAT and MAXI. By the time of this presentation, more confirmed BH-LMXBs may have been scanned in the ongoing DASCH scanning that will provide an even larger sample (which will extend ultimately to the full sample of ~25 BH-LMXBs now dynamically confirmed). Comparisons will be made with the known NS-LMXB X-ray transient sample and their duty cycle for comoparison with the the BH-LMXBs to derive new constraints on total populations for each and the implications for both their formation mechanisms in the Galaxy.The (rare) optical "transients" produced by BH-LMXB outbursts due to the accretion disk instability model may be be searched for independently (of known BH-LMXBs) in the DASCH data, which will provide a new way of constraining the stellar mass black hole population in the Galaxy. DASCH development, and now production scanning has been supported by the NSF (currently AST-1313370), for which we are grateful
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22340606G