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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"

25095 results found.

  1. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  2. GRB 250327A: DDOTI Optical Observations
  3. GRB 250327A: COLIBRÍ optical upper limit
  4. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  5. IPN triangulation of GRB 250322B
  6. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  7. EP250321a: Mondy AZT-33IK Continued Optical Observations
  8. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  9. GRB 250322A: third epoch of NOT optical observations
  10. GRB 250322A: Swift-BAT refined analysis
  11. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  12. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  13. GRB 250322A: further NOT optical observations
  14. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  15. GRB 250322A: Swift/UVOT Upper Limits
  16. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  17. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  18. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  19. GRB 250321B: Swift-XRT observations
  20. GRB 250322A: Swift-XRT refined Analysis
  21. EP250321a: TNOT Observation of Optical Counterpart
  22. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  23. SVOM/sb25032302: SVOM detection of a long X-ray transient
  24. GRB 250322B: AstroSat CZTI detection of a bright long burst
  25. GRB 250322A: VLT optical observations
  26. GRB 250322A: VLT near-infrared observations
  27. FRB 250316A: DDOTI Continued Optical Observations
  28. GRB 250322A: NOT optical upper limits
  29. GRB 250322A: Enhanced Swift-XRT position
  30. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  31. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  32. EP250321a: Liverpool Telescope optical follow-up
  33. EP250321a: Mondy AZT-33IK Optical Observations
  34. GRB 250322A: Swift detection of a short burst
  35. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  36. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  37. EP250321A: COLIBRÍ Continuing Optical Observations
  38. EP250321a: WFST optical observations
  39. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  40. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  41. GRB 250320B: Fermi GBM Observation
  42. EP250321a: Xinglong 216 decaying optical observations
  43. GRB 250321A: Swift-BAT refined analysis
  44. GRB 250321A: Swift-XRT refined Analysis
  45. EP 250321A: Optical counterpart detection by LCO.
  46. EP250321a: Kinder optical follow-up observations
  47. GRB 250321A: Swift/UVOT Upper Limits
  48. GRB 250320B: SVOM/GRM observation of a long burst
  49. EP250321a: LCO optical counterpart detection
  50. EP250321a: Swift-XRT detection of an X-ray source
  51. EP250321A: COLIBRÍ Optical Observations
  52. GRB 250320B: AstroSat CZTI detection
  53. EP250321a: REM optical/NIR afterglow detection
  54. EP250321a: TRT optical counterpart detection
  55. Swift GRB 250321A: Global MASTER-Net observations report
  56. EP250321a: Einstein Probe detection of an X-ray transient
  57. GRB 250321A: GOTO optical upper limits
  58. GRB 250314A: Keck/NIRC2 J-band upper limit
  59. EP250226a/GRB 250226A: KAIT optical observations
  60. GRB 250321A: Fermi GBM Observation
  61. GRB 250321A: Swift detection of a burst
  62. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  63. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  64. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  65. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  66. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  67. GRB 250317D: EIRSAT-1 GMOD Detection
  68. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  69. GRB 250314A: ATCA radio upper limits
  70. GRB 250317B: OHP/T193 continued follow-up
  71. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  72. GRB 250317C: SVOM/GRM observation of a long burst
  73. GRB 250317B: Leavitt Observatory optical upper limit
  74. GRB 250317B: Mondy AZT-33IK Optical Observations
  75. GRB 250317B: NOT optical observations suggest an optical plateau phase
  76. GRB 250317C: GECAM-B detection
  77. GRB 250317B: OHP/T193 optical observations
  78. GRB250312A: Swift/UVOT Upper Limits
  79. GRB 250317B: REM optical/NIR observations
  80. GRB 250317B: Swift-XRT observations
  81. GRB 250316A: Swift/UVOT Upper Limits
  82. GRB 250314A: REM optical/NIR upper limits
  83. GRB 250316A: AbAO AS-32 Optical Upper Limit
  84. EP 250317B: Fading optical counterpart detection by LCO
  85. GRB 250316A: Swift-XRT afterglow detection
  86. GRB 250317B: LCO detection of the fading optical afterglow
  87. GRB250317B: SVOM/VT detection of an optical candidate from VHF data
  88. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  89. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  90. GRB 250317B: SVOM detection of a burst
  91. GRB 250316A: Fermi GBM Observation
  92. GRB 250316A: Swift-XRT observations
  93. GRB 250314A: SVOM/GRM analysis
  94. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  95. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  96. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  97. GRB 250314A: EP-FXT afterglow detection
  98. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  99. GRB 250314A: Swift/UVOT Upper Limits
  100. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection

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