V4641 Sgr: 2002 Active State

Outburst in May 2002

On May 19, R. Stubbings reported that the microquasar (galactic jet source) V4641 Sgr was brightening up to 11.5mag (vsnet-campaign-xray 140). The object underwent a giant outburst in 1999 September, preceded by optical brightening (vsnet-campaign-xray 141, vsnet-campaign-news 152, vsnet-campaign-v4641sgr 1). The object then quickly faded to 12th mag on May 20 (vsnet-campaign-v4641sgr 2, 4, 5, 7). M. Linnolt reported on May 21 that the object varied chaotically from mag 12.5 to 12.8 with a timescale of just a few seconds (vsnet-campaign-v4641sgr 8). This short-term modulations were supported by other observations on May 20-21 (vsnet-campaign-v4641sgr 9, 10). The object was active also in the X-ray range as detected by RXTE/PCA on May 17 and 20 (vsnet-campaign-v4641sgr 11). The object then started fading. It experienced a deep fading between May 22.0 and 22.1 UT (vsnet-campaign-v4641sgr 20, 21, 22, 23, 25). On late May 22, it again brightened. And short-term variations also became prominent (vsnet-campaign-v4641sgr 13, 14, 15, 16, 17, 29, 30). On May 23, the short-term oscillations were still strong and some deep dip-like features appeared (vsnet-campaign-v4641sgr 31, 33, 35). M. Linnolt reported a momentary flash to mag 10.7 (vsnet-campaign-v4641sgr 26, 38, 42, 63, 64). M. Rupen reported that radio observations on May 23 showed no evidence for extremely rapid fluctuations, or for any dramatic extension to the source (vsnet-campaign-v4641sgr 36). On May 24, the object reached the maximum of the outburst about 10.2mag, as reported by B. Monard (vsnet-campaign-v4641sgr 59). Short-term variations were still detected, but hump-like features were dominate rather than the dips (vsnet-campaign-v4641sgr 39). The simultaneous observation at Ouda and Kyoto revealed that the color became bluer during the large humps (vsnet-campaign-v4641sgr 53). C. Markwardt reported the detection of large amplitude X-ray fluctuations, similar to those in the optical flux (vsnet-campaign-v4641sgr 41). On May 25, the outburst was suddenly terminated by a rapid fading to a near quiescent level (vsnet-campaign-v4641sgr 47, 48, 49, 52).

Very Active: Post-outburst state in May

Although the outburst state was terminated, short-term modulations, particularly 1-mag humps, were still seen in the May 25 light curves (vsnet-campaign-v4641sgr 50). Observations by R. Santallo on May 25 detected steadily increasing activity, which smoothly evolved into the violent state later on May 25 (vsnet-campaign-v4641sgr 67). The object became bluer than that on May 24 (vsnet-campaign-v4641sgr 55). B. Sault reported an inverted spectrum in radio observation (vsnet-campaign-v4641sgr 51). T. Kato commented that the rise of the radio flux on May 24 seems to be associated with the optical "flare" following this rapid rise in the radio (vsnet-campaign-v4641sgr 56). On May 26, the object further faded to the quiescent level, however still showed 1-mag humps (vsnet-campaign-v4641sgr 57, 58, 60). The object then suddenly switched from the violently variable state to a calm state (vsnet-campaign-v4641sgr 61). The "violently variable" segment of the light curve lasted only for ~hours, which indicates rapid state transitions in V4641 Sgr (vsnet-campaign-v4641sgr 62). C. Markwardt reported that the majority of the X-ray violent flaring activity was on May 24-25, but that there was one large (May 26.65 UT) and several small X-ray flares on May 26 (vsnet-campaign-v4641sgr 69). Short-term fluctuations weakened, or disappeared on May 27 (vsnet-campaign-v4641sgr 65, 66).

Activity weakened?: Post-outburst state in June

G. Masi reported that observations by F. Mallia on May 31-June 1 showed an evident modulation, with a full amplitude around 0.1 mag (vsnet-campaign 1316, vsnet-campaign-v4641sgr 80). M. Uemura reported a 0.4mag-hump around June 2.66 (vsnet-campaign-v4641sgr 73, 74). The short-term modulations became more prominent on June 3, while the average magnitude has been at the quiescent level (vsnet-campaign-v4641sgr 75, 76, 77). A large hump to Rc=12.6 was reported on June 4 (vsnet-campaign-v4641sgr 78). The small flares (0.2mag) were also observed around the hump. They have a weak, but characteristic periodicity (50-100s) (vsnet-campaign-v4641sgr 79, 84). The ~0.1mag modulations still appeared on May 5, and the object was relatively calm on June 6 (vsnet-campaign-v4641sgr 88, 91). The activity was also reported on June 9 (vsnet-campaign-v4641sgr 92). M. Rupen reported that V4641 Sgr became active again in the radio range since June 24 (vsnet-campaign 1323, 1324, vsnet-campaign-v4641sgr 99, 100, 102). In the optical range, it was relatively calm on June 27 (vsnet-campaign-v4641sgr 101, 103). M. Rupen reported on June 29 that the radio observations by VLA revealed that the object was still active with mini-flares every few days (vsnet-campaign 1326, vsnet-campaign-v4641sgr 104). The time-series observation by Y. Sano on June 30 showed moderate rather irregular variations (amplitude up to 0.2 mag) (vsnet-campaign-v4641sgr 105).

Rapid, large optical flare on July 7

T. Scarmato reported a brightening to 12.0mag on July 5 (vsnet-campaign-v4641sgr 107, 108, 109). The light curve obtained by R. Santallo on July 7 showed dramatic repeated flare-like brightenings by 0.5 mag. T. Kato reported that the typical e-folding decay time of the flares was only a few minutes and the rise usually took 30 s to 2 min (vsnet-campaign-v4641sgr 110). The strong activity was confirmed in time-series observations by K. Torii, K. Tanabe, R. Santallo, and the Kyoto team on July 7 (vsnet-campaign-v4641sgr 112, 113, 115). During this active state, the object experienced an unmistakable 1 mag short flare. The 1 mag rise took only 30s, and the actual maximum may have been even brighter. There were also multiple smaller flares (0.3 mag) with typical durations less than 1 min (vsnet-campaign-v4641sgr 119, 121). R. Santallo detected some flares up to 10.5v mag with time-scales of seconds on July 8 (vsnet-campaign-v4641sgr 114). T. Scarmato reported second-order flares on July 9 (vsnet-campaign-v4641sgr 116, 117). V. Goranskij reported they detected no flares between June 28 and July 8 (vsnet-campaign-v4641sgr 118). Time-series observations by B. Monard on July 8-9 showed some modulations, but no sharp flares (vsnet-campaign-v4641sgr 126). The light curves on July 11 showed the object entered a relatively calm state, except for a ~0.15mag short flare detected by K. Torii (vsnet-campaign-v4641sgr 125, 127, 141).

Return to the quiescent state

While possible moderate variations was present, no short "flash"-like flare was observed until July 18 when M. Linnolt reported a small flare to 12.7mag (vsnet-campaign-v4641sgr 146, 148, 149, 150, 151, 152). The light curves on July 16 obtained by S. Kiyota and K. Torii also showed a number of sudden brightenings by ~0.5 mag, which look like real as compared with error statistics (vsnet-campaign-v4641sgr 153, 154). No major short-term variation has been reported after these observations (vsnet-campaign-v4641sgr 155, 156). M. Uemura reported a minor outburst occurred on August 5. During the outburst, the object reached 13.1mag with rapid brightening and fading. The light curve showed some hints of short-term (a few minutes) modulations with amplitudes of 0.1-0.2 mag (vsnet-campaign-v4641sgr 164).

Other articles:
vsnet-campaign-v4641sgr 6, 12, 19, 27, 28, 32, 43, 44, 45, 54, 68, 70, 71, 72, 81, 82, 85, 87, 89, 90, 93, 94, 95, 96, 97, 98, 106, 111, 128, 137, 130, 131, 132, 138, 139, 142, 124, 129, 140, 143, 144, 145, 157, 158, 159, 160, 161, 162, 163

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