Discovery of powerful millisecond flares from Cyg X-1 Marek Gierliński University of Durham, England Andrzej Zdziarski N. Copernicus Astronomical Center, Warsaw, Poland

Cyg X-1 variability from years to milliseconds

Powerful millisecond flares from Cyg X-1 28 October Cyg X-1: a tame source Persistent source Spectral states: hard and soft Variability nothing like as dramatic as in transients Cyg X-1 is a well-behaved black hole PCA+HEXTE

Powerful millisecond flares from Cyg X-1 28 October Seven years of Cyg X /2002 soft state (400 days) ASM BATSE

Powerful millisecond flares from Cyg X-1 28 October Spectral transitions – days to weeks Typical transition between states takes about a week There are faster events with timescales of a day Cui, Feng & Ertmer 2002

Powerful millisecond flares from Cyg X-1 28 October Kilosecond outbursts Stern, Beloborodov & Poutanen keV

Powerful millisecond flares from Cyg X-1 28 October Power spectrum of Cyg X-1 Revnivtsev, Gilfanov & Churazov 2000 Not much variability above 100 Hz

Powerful millisecond flares from Cyg X-1 28 October Other black holes too Sunyaev & Revnivtsev 2000

Powerful millisecond flares from Cyg X-1 28 October Cyg X-1 high-frequency PDS Revnivtsev, Gilfanov & Churazov 2000

Very short events from Cyg X-1

Powerful millisecond flares from Cyg X-1 28 October X-ray archaeology: 1973 Rothschild et al. 1974

Powerful millisecond flares from Cyg X-1 28 October Shots Flares or ‘shots’ are weak, each of them 2–3 times brighter than the continuum Superposition of hundreds of ‘shots’ Timescales of ~10 and ~100 ms (sum of two exponentials) Feng, Li & Chen 1999

So, you don’t expect sudden dramatic events from Cyg X-1…

Powerful millisecond flares from Cyg X-1 28 October …until this happened Enormous flare on 31 July 2002 (during extended soft state) PCA count rate increased by factor 20 in 100 ms  20 PCA 2–60 keV (4 PCUs)

Powerful millisecond flares from Cyg X-1 28 October Is it real? An external event not from Cyg X-1? Perhaps an energetic particle hit the PCA detector? Or is it a solar flare? Or is it a gamma-ray burst? 27 August 1998: SGR flare recorded by PCA looking somewhere else

Powerful millisecond flares from Cyg X-1 28 October Multiple detection The flare was detected by four units of PCA (PCU1 was switched off) and one HEXTE cluster

Powerful millisecond flares from Cyg X-1 28 October Even BATSE can see it! PCA BATSE

Powerful millisecond flares from Cyg X-1 28 October It really comes from Cyg X-1 HEXTE (15–150 keV) contains two detector clusters switching between the source and background 1.5 deg away When cluster B detected the flare, cluster A looked at background and did not see anything The flare comes from Cyg X-1 source background

Flare properties

Powerful millisecond flares from Cyg X-1 28 October More flares We’ve scanned all the PCA data from Cyg X-1 Found 13 strong flares with c peak -  c  > 10  12 flares in the hard state, 1 in the soft state

Powerful millisecond flares from Cyg X-1 28 October Flare profile (soft state)   20 ms   0.7 PCA 20  HEXTE exp(-|t/  |  )

Powerful millisecond flares from Cyg X-1 28 October Very short precursor Increase  10 in 2 ms 2 ms ~ 40GM/c 3

Powerful millisecond flares from Cyg X-1 28 October Flare anatomy (soft state) Flux (3–30 keV)  (2–15 keV)  (6–60 keV) Spectral hardening  ~ 1.8 Spectral hardening  ~ 1.3  30 flux increase L peak ~ 1.4  erg/s

Powerful millisecond flares from Cyg X-1 28 October Flare anatomy (hard state) Flux (3–30 keV)  (2–15 keV)  (6–60 keV)  10 flux increase L peak ~ 0.9  erg/s Spectral softening  ~ 0.3

Powerful millisecond flares from Cyg X-1 28 October Flare spectrum (soft state) SAX/OSSE soft state PCA/HEXTE continuum around flare Flare spectrum Model luminosity L bol ~ 0.3L Edd

Powerful millisecond flares from Cyg X-1 28 October Flare spectrum (hard state) SAX/OSSE hard state PCA/HEXTE continuum around flare Flare spectrum Model luminosity L bol ~ 0.25L Edd

Powerful millisecond flares from Cyg X-1 28 October Not only Cyg X-1 XTE J

Powerful millisecond flares from Cyg X-1 28 October Not only Cyg X-1 GX 339–4

Powerful millisecond flares from Cyg X-1 28 October Rapid flare in Sgr A* Baganoff et al Shortest timescale ~30GM/c 3

Powerful millisecond flares from Cyg X-1 28 October Conclusions We have discovered several strong millisecond X-ray flares from Cyg X-1 and other black holes Shortest observed timescales correspond to ~40GM/c 3 or half of the Keplerian period on the marginally stable orbit The flares must be due to a sudden release of accretion energy in the inner region of the disc Magnetic flares? e.g. Beloborodov 1999; Poutanen & Fabian 1999; Machida & Matsumoto 2003 Challenge for theorists!

Powerful millisecond flares from Cyg X-1 28 October Magnetic flares in plunging region Machida & Matsumoto 2003