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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"
  1. GRB 250225B: INTEGRAL SPI-ACS detection
  2. EP250225a: NOT optical candidate counterpart
  3. EP250226a/GRB 250226A:Xinglong optical follow-up observations
  4. EP250226a / GRB 250226A: SVOM/VT optical observations
  5. EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
  6. EP250225a: TRT optical upper limits
  7. EP250226a/GRB 250226A: 1.6m Mephisto observations
  8. LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
  9. EP250226a/GRB 250226A: Kinder optical follow-up observations
  10. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  11. LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate
  12. LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
  13. Fermi GRB 250226B: Global MASTER-Net observations report
  14. LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
  15. GRB 250226B: Fermi GBM Final Real-time Localization
  16. GRB 250225B: Fermi GBM Observation
  17. GRB 250221A: ATCA Detections and Upper Limits
  18. GRB 250225B: REM NIR upper limits
  19. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  20. Konus-Wind detection of GRB 250225B
  21. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  22. EP250223a: CrAO ZTSH optical observation
  23. GRB 250225B: VLT optical and near-infrared candidate counterpart
  24. GRB 250225B: VLT/FORS2 candidate optical afterglow
  25. GRB 250225B: SVOM/GRM observation of a long burst
  26. GRB 250226A: GECAM-B detection
  27. GRB 250221A: EP-FXT detection of the X-ray afterglow
  28. GRB 250214A: SVOM/GRM observation
  29. EP250226a/GRB 250226A: GSP detects optical counterpart
  30. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  31. EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
  32. EP250226a / GRB 250226A: TRT optical counterpart observation
  33. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  34. EP250226a: Global MASTER-Net observations report
  35. Swift GRB 250225B: Global MASTER-Net observations report
  36. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  37. Fermi GRB 250226A: Global MASTER-Net observations report
  38. Fermi trigger No 762205158: Global MASTER-Net observations report
  39. GRB 250226A: Fermi GBM Final Real-time Localization
  40. EP250225a: Global MASTER-Net observations report
  41. EP250225a: GSP optical upper limit
  42. EP250223a: GMG Optical Observation
  43. EP250225a: Einstein Probe detected of a fast X-ray transient
  44. Fermi GRB 250225A: Global MASTER-Net observations report
  45. GRB 250225B: Swift detection of a burst
  46. EP250223a: GROWTH-India Telescope optical observations
  47. GRB 250221A: Swift-BAT refined analysis
  48. GRB 250223C: SVOM/GRM observation of a long burst
  49. EP250215A: J band upper limit by SYSU 80cm telescope
  50. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  51. GRB 250225A: Fermi GBM Final Real-time Localization
  52. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  53. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  54. EP250223a: Kinder optical follow-up observations
  55. GRB 250207a: ATCA Radio Upper Limits
  56. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  57. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  58. GRB 250119B: VZLUSAT-2 detection
  59. GRB 250223C: Fermi GBM Final Real-time Localization
  60. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  61. GRB 250202B: VZLUSAT-2 detection
  62. GRB 250219A: EP-FXT afterglow detection
  63. EP250223a: GOTO optical afterglow detections
  64. GRB 250222A: SVOM/GRM observation of a burst
  65. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  66. GRB 250210A: VZLUSAT-2 detection
  67. GRB 250206A: VZLUSAT-2 detection
  68. EP250223a: REM NIR upper limit
  69. EP250223a: TRT optical afterglow observation
  70. EP250223a: refined analysis of the EP-WXT and FXT observations
  71. EP250223a: 1.6m Mephisto and 50cm array observations
  72. GRB 250221A: TNOT detection of the optical counterpart
  73. EP250223a: SVOM/VT optical observation
  74. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  75. 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
  76. The EP-WXT trigger 01709131882 is likely a flaring star
  77. EP250223a: OASDG optical observations
  78. EP250223a: LCO detection of the afterglow
  79. EP250223a: early optical detection by BOOTES-4
  80. EP250223a: NOT redshift z = 2.756
  81. EP250223a: Swift/XRT localization
  82. EP250223a: NOT optical afterglow candidate
  83. GRB 250223B: Fermi GBM Final Localization
  84. EP250223a: Global MASTER-Net observations report
  85. GRB 250221A: VLA radio detection
  86. Fermi GRB 250223A: Global MASTER-Net observations report
  87. Fermi trigger No 762020305: Global MASTER-Net observations report
  88. GRB 250223A: Fermi GBM Final Real-time Localization
  89. EP250223a: Einstein Probe detection of an X-ray transient
  90. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  91. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  92. GRB 250221A: continued Mondy optical observations, brightening afterglow
  93. GRB 250221A: Optical counterpart detection by LCO.
  94. GRB 250221A: Mondy optical observations
  95. Konus-Wind detection of GRB 250221A
  96. GRB 250221A: Assy optical observations
  97. EP250220a: FTW optical and NIR observations and upper limits
  98. EP250220a: EP-FXT follow-up observations
  99. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  100. GRB 250221A: VLT/X-shooter redshift z = 0.768

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