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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"

6405 results found.

  1. GRB 250329B: Swift-XRT afterglow detection
  2. GRB 250329B: 1.6m Mephisto Optical Upper Limits
  3. GRB 250329A: Swift-XRT afterglow detection
  4. GRB 250329A: Fading optical counterpart detection by LCO.
  5. GRB 250327B: LCO optical counterpart detection
  6. GRB 250327B: CrAO and SAO RAS Optical Observations
  7. GRB 250327B: further optical observations by LCOGT
  8. GRB 250327A: SVOM/VT upper limits on the XRT position
  9. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  10. GRB 250327A: Swift-XRT refined Analysis
  11. GRB 250327B: SVOM detection of a burst
  12. GRB 250327A: Fermi GBM observation
  13. Konus-Wind detection of GRB 250322A (short)
  14. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  15. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  16. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  17. GRB 250321B: Swift-XRT observations
  18. GRB 250322A: Swift-XRT refined Analysis
  19. GRB 250322A: NOT optical upper limits
  20. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  21. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  22. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  23. GRB 250320B: Fermi GBM Observation
  24. GRB 250321A: Swift-XRT refined Analysis
  25. GRB 250320B: Fermi-LAT detection
  26. EP250321a: Kinder optical follow-up observations
  27. EP250321a: Swift-XRT detection of an X-ray source
  28. EP250321a: TRT optical counterpart detection
  29. GRB 250321A: Swift-XRT localisation
  30. GRB 250321A: Fermi GBM Observation
  31. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  32. GRB 250317B: NOT optical observations suggest an optical plateau phase
  33. GRB 250317B: Swift-XRT observations
  34. GRB 250316A: Swift/UVOT Upper Limits
  35. EP 250317B: Fading optical counterpart detection by LCO
  36. GRB 250316A: Swift-XRT afterglow detection
  37. GRB 250317B: LCO detection of the fading optical afterglow
  38. GRB 250316A: Fermi GBM Observation
  39. GRB 250316A: Swift-XRT observations
  40. GRB 250314A: Swift/UVOT Upper Limits
  41. GRB 250314A: SVOM/VT upper limit
  42. GRB 250313A: Fermi GBM Detection
  43. GRB 250312B: Fermi GBM Observation
  44. GRB 250313A: Swift-XRT observations
  45. GRB 250313A: Fermi-LAT detection
  46. EP250302a: Chandra X-ray Detection
  47. GRB 250312A: Swift-XRT refined Analysis
  48. GRB 250226B: Fermi GBM Observation
  49. GRB 250302A: Fermi GBM Observation
  50. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  51. GRB 250223B: Fermi GBM Observation
  52. GRB 250311A: Swift-XRT observations
  53. GRB 250228A: Fermi GBM Observation
  54. GRB 250309B / AT2025dws: further SAO RAS optical observations
  55. Konus-Wind detection of GRB 250309B
  56. GRB 250309B: Swift-XRT refined Analysis
  57. GRB 250309B / IceCube-250309A: GECAM-B observations
  58. GRB 250309B / AT2025dws: SAO RAS optical observations
  59. GRB 250309B: Fermi GBM Observation
  60. Fermi GRB 250309A: Global MASTER-Net observations report
  61. Fermi-LAT gamma-ray observations of IceCube-250309A
  62. EP250308a: Einstein Probe detection of an X-ray transient
  63. EP250308a: NOT optical upper limit
  64. Fermi trigger No 762963055: Global MASTER-Net observations report
  65. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  66. EP250302a: Optical Observations at CrAO and SAO RAS
  67. EP250302A: 1.3m DFOT optical afterglow detection
  68. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  69. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  70. EP250304a: Swift-XRT detection of a fading X-ray source
  71. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  72. EP250302a: SAO RAS optical observations
  73. EP250302a: Kinder optical follow-up observations
  74. EP250302a: NUTTelA-TAO Early Measurments
  75. EP250302a: Swift-XRT observations of a fading X-ray source
  76. EP250228a: Optical observations with Kinder and Swift/UVOT
  77. Konus-Wind detection of GRB 250226A
  78. EP250227a: TRT optical upper limit
  79. GRB 250225B: VLT/HAWKI near-infrared observations
  80. EP250227a: Optical upper limits with Kinder observations
  81. GRB 250226A: Fermi GBM Observation
  82. EP250225a: EP-FXT follow-up observation
  83. GRB 250226A / EP250226a: LCO detection of the afterglow
  84. EP250225a: TRT optical upper limits
  85. EP250226a/GRB 250226A: 1.6m Mephisto observations
  86. EP250226a/GRB 250226A: Kinder optical follow-up observations
  87. GRB 250221A: EP-FXT detection of the X-ray afterglow
  88. EP250226a / GRB 250226A: TRT optical counterpart observation
  89. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  90. Fermi GRB 250226A: Global MASTER-Net observations report
  91. EP250223a: Kinder optical follow-up observations
  92. EP250223a: 1.6m Mephisto and 50cm array observations
  93. EP250223a: LCO detection of the afterglow
  94. EP250223a: NOT optical afterglow candidate
  95. Konus-Wind detection of GRB 250221A
  96. EP250220a: EP-FXT follow-up observations
  97. GRB 250221A: Swift-XRT refined Analysis
  98. GRB 250221A: 1.6m Mephisto optical detection
  99. EP250220a: 1.6m Mephisto observations
  100. EP250220a: Optical upper limit with Kinder observations

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