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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. LIGO/Virgo/KAGRA S250206dm: early X-ray upper limits from Einstein Probe WXT and preliminary results of FXT observations
  2. GRB 250225B: VLT near-infrared afterglow confirmation
  3. EP250228a: Optical observations with Kinder and Swift/UVOT
  4. Konus-Wind detection of GRB 250226A
  5. GRB 250225B: EIRSAT-1 GMOD Detection
  6. GRB 250226A: KAO Optical Upper Limit
  7. GRB 250226A: AbAO AS-32 Optical Upper Limit
  8. EP250227a: Global MASTER-Net observations report
  9. EP250223A: Upper limits from Fermi-GBM Observations
  10. EP250227a: TRT optical upper limit
  11. GRB 250225B: VLT/HAWKI near-infrared observations
  12. EP250227a: Optical upper limits with Kinder observations
  13. EP250227a: NOT optical observations
  14. EP250227a: Einstein Probe detected of a fast X-ray transient
  15. EP250228a: updates on the EP observations
  16. GRB 250226A: Fermi GBM Observation
  17. EP250225a: EP-FXT follow-up observation
  18. EP250223a: J band upper limit by SYSU 80cm telescope
  19. EP250228a: Swift/XRT localisation
  20. EP250228a: Global MASTER-Net observations report
  21. EP250228a: Einstein Probe detection of an X-ray transient
  22. GRB 250226A / EP250226a: LCO detection of the afterglow
  23. LIGO/Virgo/KAGRA S250227e: Updated Sky localization
  24. LIGO/Virgo/KAGRA S250226dl: Updated Sky localization
  25. GRB 250225B: VLT/Xshooter imaging
  26. GRB 250205A / EP250205A: further radio observations with the VLA
  27. GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection
  28. EP250226a/GRB 250226A: INTEGRAL SPI-ACS and PICsIT detection
  29. GRB 250225B: INTEGRAL SPI-ACS detection
  30. EP250225a: NOT optical candidate counterpart
  31. EP250226a/GRB 250226A:Xinglong optical follow-up observations
  32. EP250226a / GRB 250226A: SVOM/VT optical observations
  33. EP250226a/GRB 250226A: refined analysis of the EP-WXT and FXT observations
  34. EP250225a: TRT optical upper limits
  35. EP250226a/GRB 250226A: 1.6m Mephisto observations
  36. LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
  37. EP250226a/GRB 250226A: Kinder optical follow-up observations
  38. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  39. LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate
  40. LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
  41. Fermi GRB 250226B: Global MASTER-Net observations report
  42. LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
  43. GRB 250226B: Fermi GBM Final Real-time Localization
  44. GRB 250225B: Fermi GBM Observation
  45. GRB 250221A: ATCA Detections and Upper Limits
  46. GRB 250225B: REM NIR upper limits
  47. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  48. Konus-Wind detection of GRB 250225B
  49. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  50. EP250223a: CrAO ZTSH optical observation
  51. GRB 250225B: VLT optical and near-infrared candidate counterpart
  52. GRB 250225B: VLT/FORS2 candidate optical afterglow
  53. GRB 250225B: SVOM/GRM observation of a long burst
  54. GRB 250226A: GECAM-B detection
  55. GRB 250221A: EP-FXT detection of the X-ray afterglow
  56. GRB 250214A: SVOM/GRM observation
  57. EP250226a/GRB 250226A: GSP detects optical counterpart
  58. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  59. EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
  60. EP250226a / GRB 250226A: TRT optical counterpart observation
  61. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  62. EP250226a: Global MASTER-Net observations report
  63. Swift GRB 250225B: Global MASTER-Net observations report
  64. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  65. Fermi GRB 250226A: Global MASTER-Net observations report
  66. Fermi trigger No 762205158: Global MASTER-Net observations report
  67. GRB 250226A: Fermi GBM Final Real-time Localization
  68. EP250225a: Global MASTER-Net observations report
  69. EP250225a: GSP optical upper limit
  70. EP250223a: GMG Optical Observation
  71. EP250225a: Einstein Probe detected of a fast X-ray transient
  72. Fermi GRB 250225A: Global MASTER-Net observations report
  73. GRB 250225B: Swift detection of a burst
  74. EP250223a: GROWTH-India Telescope optical observations
  75. GRB 250221A: Swift-BAT refined analysis
  76. GRB 250223C: SVOM/GRM observation of a long burst
  77. EP250215A: J band upper limit by SYSU 80cm telescope
  78. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  79. GRB 250225A: Fermi GBM Final Real-time Localization
  80. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  81. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  82. EP250223a: Kinder optical follow-up observations
  83. GRB 250207a: ATCA Radio Upper Limits
  84. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  85. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  86. GRB 250119B: VZLUSAT-2 detection
  87. GRB 250223C: Fermi GBM Final Real-time Localization
  88. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  89. GRB 250202B: VZLUSAT-2 detection
  90. GRB 250219A: EP-FXT afterglow detection
  91. EP250223a: GOTO optical afterglow detections
  92. GRB 250222A: SVOM/GRM observation of a burst
  93. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  94. GRB 250210A: VZLUSAT-2 detection
  95. GRB 250206A: VZLUSAT-2 detection
  96. EP250223a: REM NIR upper limit
  97. EP250223a: TRT optical afterglow observation
  98. EP250223a: refined analysis of the EP-WXT and FXT observations
  99. EP250223a: 1.6m Mephisto and 50cm array observations
  100. GRB 250221A: TNOT detection of the optical counterpart

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