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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

24881 results found.

  1. EP250302a: Nanshan/HMT optical counterpart detection
  2. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  3. GRB 250225B: VLT near-infrared afterglow confirmation
  4. EP250228a: Optical observations with Kinder and Swift/UVOT
  5. Konus-Wind detection of GRB 250226A
  6. GRB 250225B: EIRSAT-1 GMOD Detection
  7. GRB 250226A: KAO Optical Upper Limit
  8. GRB 250226A: AbAO AS-32 Optical Upper Limit
  9. EP250227a: Global MASTER-Net observations report
  10. EP250223A: Upper limits from Fermi-GBM Observations
  11. EP250227a: TRT optical upper limit
  12. GRB 250225B: VLT/HAWKI near-infrared observations
  13. EP250227a: Optical upper limits with Kinder observations
  14. EP250227a: NOT optical observations
  15. EP250227a: Einstein Probe detected of a fast X-ray transient
  16. EP250228a: updates on the EP observations
  17. GRB 250226A: Fermi GBM Observation
  18. EP250223a: J band upper limit by SYSU 80cm telescope
  19. EP250228a: Swift/XRT localisation
  20. EP250228a: Einstein Probe detection of an X-ray transient
  21. GRB 250226A / EP250226a: LCO detection of the afterglow
  22. LIGO/Virgo/KAGRA S250227e: Updated Sky localization
  23. LIGO/Virgo/KAGRA S250226dl: Updated Sky localization
  24. GRB 250225B: VLT/Xshooter imaging
  25. GRB 250205A / EP250205A: further radio observations with the VLA
  26. EP250225a: NOT optical candidate counterpart
  27. EP250226a/GRB 250226A:Xinglong optical follow-up observations
  28. EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
  29. EP250225a: TRT optical upper limits
  30. EP250226a/GRB 250226A: 1.6m Mephisto observations
  31. LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
  32. EP250226a/GRB 250226A: Kinder optical follow-up observations
  33. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  34. LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
  35. LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
  36. GRB 250225B: Fermi GBM Observation
  37. GRB 250225B: REM NIR upper limits
  38. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  39. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  40. EP250223a: CrAO ZTSH optical observation
  41. GRB 250225B: VLT optical and near-infrared candidate counterpart
  42. GRB 250225B: SVOM/GRM observation of a long burst
  43. EP250226a/GRB 250226A: GSP detects optical counterpart
  44. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  45. EP250226a / GRB 250226A: TRT optical counterpart observation
  46. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  47. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  48. EP250225a: GSP optical upper limit
  49. EP250223a: GMG Optical Observation
  50. EP250225a: Einstein Probe detected of a fast X-ray transient
  51. GRB 250225B: Swift detection of a burst
  52. EP250223a: GROWTH-India Telescope optical observations
  53. GRB 250221A: Swift-BAT refined analysis
  54. EP250215A: J band upper limit by SYSU 80cm telescope
  55. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  56. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  57. EP250223a: Kinder optical follow-up observations
  58. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  59. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  60. GRB 250119B: VZLUSAT-2 detection
  61. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  62. GRB 250202B: VZLUSAT-2 detection
  63. GRB 250222A: SVOM/GRM observation of a burst
  64. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  65. GRB 250206A: VZLUSAT-2 detection
  66. EP250223a: REM NIR upper limit
  67. EP250223a: TRT optical afterglow observation
  68. EP250223a: refined analysis of the EP-WXT and FXT observations
  69. EP250223a: 1.6m Mephisto and 50cm array observations
  70. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  71. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
  72. EP250223a: OASDG optical observations
  73. EP250223a: LCO detection of the afterglow
  74. EP250223a: Swift/XRT localization
  75. EP250223a: NOT optical afterglow candidate
  76. EP250223a: Einstein Probe detection of an X-ray transient
  77. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  78. GRB 250221A: Optical counterpart detection by LCO.
  79. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  80. GRB 250221A: GRANDMA/TAROT Detection
  81. GRB 250221A: Swift-XRT refined Analysis
  82. GRB 250221A: NOT optical observations
  83. GRB 250221A: 1.6m Mephisto optical detection
  84. GRB 250221A: AKO Optical Upper Limit
  85. GRB 250221A: Swift/UVOT Detection
  86. EP250220a: Liverpool Telescope upper limits
  87. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  88. GRB 250221A: REM optical/NIR afterglow detection
  89. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  90. GRB 250221A: Enhanced Swift-XRT position
  91. EP250220a: 1.6m Mephisto observations
  92. EP250220a: Liverpool Telescope optical upper limits
  93. EP250220a: Optical upper limit with Kinder observations
  94. SVOM trigger sb25022102 is not an astrophysical event
  95. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  96. GRB 250221A: Swift detection of a burst with an optical counterpart
  97. Swift GRB250221.15: Global MASTER-Net OT detection
  98. EP250220a: Xinglong optical upper limit
  99. GRB 250219A: Swift/UVOT Upper Limits
  100. GRB 250219A: OHP/T193 optical upper limit

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